You're likely to come across the term Modbus when you're searching for industrial control modules. Various sensors use Modbus, VFD, actuator control, and PLC, particularly in the oil & gas and agricultural industry.

If you're not familiar with Modbus, choosing industrial modules and setting them up can be challenging. You could be overwhelmed by the various registers and struggle to communicate with a Modbus device.

Modbus is, thankfully, relatively simple technology, and we've put together everything you should know about Modbus in this comprehensive guide.

What Is Modbus?

Let’s start with a simple Modbus definition.

Modbus is what you’ll call a communication protocol built for industrial controllers. It enables industrial controllers or PLCs to communicate with sensors, actuators, HMIs, and other modules used in instrumentation and control. Almost every integrable industrial device supports Modbus.

Modbus is a half-duplex, serial digital communication protocol. It works perfectly with the popular communication medium for industrial controllers, which is RS485. RS485 enables Modbus communication over long distances. Modbus is also compatible with other serial communication interfaces, such as RS232 and RS422.

Here's how the Modbus story started.

It all began in 1979 when Modicon, now Schneider Electric, built a protocol to make communication easier for its range of PLCs. Modbus is an application layer protocol, which means that it’s independent of the electrical medium of transfer. The Modbus standard covers the format, fields, and transmission sequence of the Modbus frame.

Today, the Modbus Organization manages the protocol. The de-facto industrial protocol has evolved throughout the decades. Initially, there were two types of Modbus protocol — Modbus RTU and Modbus ASCII. With the emergence of ethernet networking, Modbus TCP was introduced to leverage the connection-based nature of TCP protocol.

Why Is Modbus Popular?

You would have thought a protocol that spans over 40 years would have been rendered obsolete. Not with Modbus. It remains the most common protocol used by modern industrial systems. Modbus is such a hit with industrial engineers, equipment manufacturers, and PC programmers for a few reasons.


Modbus is an open-source protocol. Thus, manufacturers can incorporate the protocol into their industrial products without paying royalty fees. Incorporating Modbus into a controller is also reasonably straightforward. It’s a matter of adding the Modbus driver into the controller’s firmware.

Modbus has an advantage over the direct connection of switches (input) and solenoids (output) in terms of wiring. Modbus only takes a pair of twisted cables for an RS485 connection, while a direct link will require as many wiring connections for the individual I/O.

Given that cabling cost is always on the rise, it makes sense to opt for Modbus.


You’ll never get a more straightforward protocol than Modbus. It provides read/write operation on an industrial device’s coil, status, input registers, and holding registers, mapped to a range of addresses.

Programming skills are not needed to operate a Modbus-featured controller. The concept of writing and reading from coils and registers is easy to comprehend. With the aid of a visual interface, system engineers can set up and control Modbus-operated devices without any programming skills.

A Mature Ecosystem

Over the decades, Modbus has matured into a large ecosystem of industrial control products. As a result, PLC programmers and system engineers are accustomed to working with Modbus.

There isn’t a growing need for a different form of protocol. Unlike consumer applications, industrial controls do not need streaming megabytes of data in real-time. Existing Modbus infrastructures are unlikely to undergo drastic changes even with technology upgrades.

How Does Modbus Work?

Modbus simplifies data acquisition and output control for an industrial controller. A Modbus connection requires a master controller and at least one slave device. The master controller sends Modbus commands, and slave devices respond with data or acknowledgment.

Modbus can’t have more than one master controller. Doing so will result in corrupted data packets when multiple controllers try to send commands simultaneously on the Modbus network.

Modbus replaces individual connections to I/O modules. As such, it retains familiar terms like coils and inputs in its data representation. All Modbus protocols share the same data types, which are allocated to specific addresses.

Modbus Data Type

Here’s how Modbus data types are represented:

Modbus Data Type Read/Write Format Address Range (Dec)
Coil R/W 1 bit 00001-09999
Discrete Input Read-only 1 bit 10001-19999
Input Register Read-only 16 bit 30001-39999
Holding Register R/W 16 bit 40001-49999

Fig 1 - Modbus Data Type

The coil data type will be typically associated with a solenoid output or solid-state relays. Discrete inputs are often flow switches, limit switches, or other single-bit digital inputs. Input registers are similar to discrete inputs, except that it returns a 16-bit data.

The holding register is a read/write storage that can be used for various purposes—for example, writing and reading parameter configuration on a Modbus actuator. In addition, the holding register can be used to set parameters like maximum torque, alarms, relay contact, fail-safe measures by writing the appropriate 16-bit data variable.

Modbus Message Frame

The next question lies in how a Modbus data packet is transferred between master and slave devices. The following diagram of a typical Modbus message frame gives a clearer picture.

Modbus message frame
Device ID
Function Code
Register Address
Register Count

Fig 2 - Modbus Message Frame

The above message frame is valid for Modbus RTU and Modbus ASCII. In Modbus TCP, the Checksum and End fields are removed, and the Start field is replaced with a 6- byte overhead. We’ll explain the differences between these protocols in the next section.

Each Modbus message frame is wrapped by a start and end field. It allows the receiving unit to segregate different data packets.

The Device ID indicates the recipient of the Modbus message. The device ID ranges from 1 to 247, but the limit differs based on the transmission medium. Most industrial systems run on RS485, which allows up to 32 connected devices. If you’re using RS232, you’ll have a maximum of 2 devices. Running Modbus on TCP will expand the device count, subjected to the network switches and gateways.

Modbus Function Code

The core of Modbus lies in the Function Code, Register Address, and Data. They are also known as the Protocol Data Unit (PDU). These fields provide specific instruction to Modbus slaves on what information needs to be retrieved, written, and where they are located.

These are standard function codes supported by industrial Modbus devices.

Function Code (Dec) Function


Read Coil


Read Discrete Input


Read Holding Registers


Read Input Registers


Write Single Coil


Write Single Holding Register


Write Multiple Coils


Write Multiple Holding Registers

Fig 3 - Modbus Function Codes

Modbus Communication Flow

So, how does data get moved around in a Modbus connection?

Modbus communication always starts with a master controller sending a request to a slave device. It can be a write or read request, depending on the function code selected in the message frame.

The controller specifies the register address, register count, and data written on the Modbus PDU for a written request. A read request has a similar format, minus the data field.

When a slave device successfully processes a request, it’ll return an acknowledgment Modbus frame to the master controller. The acknowledgment frame contains the functioned code that was executed and data if it’s a read request. If a Modbus slave fails to process the request, it’ll respond with an exception code.

Modbus Exception Code

There are instances where a master controller sends a request that is not supported by a slave device, or the latter experiences technical issues. In such cases, the slave device will respond with a Modbus exception code.

Exception Code Name


Illegal Function


Illegal Data Address


Illegal Data Value


Slave Device Failure

Modbus Data Integrity

Industrial automation and instrumentation rely on data integrity. Measured value from the sensor must be received without alteration by the controller. The same goes from configurations sent by a controller to a Modbus device.

It will be disastrous for the data to be corrupted during transmission and processed by the devices. For example, a temperature sensor measured 24 degrees C but returned 18 degrees C because some bits got flipped during transmission.

Therefore, the Checksum in the Modbus frame is vital to ensure the data integrity of Modbus transmission.

The 2-bytes Checksum is calculated from each byte of the Device ID and PDU. It is then appended on the Modbus message. Upon receiving a Modbus frame, the recipient will compare the checksum value against the calculated Checksum based on the received packet. If there’s a mismatch between the checksum values, the device discards the Modbus data packet.

Modbus Distance and Speed

You can run it over RS232, RS485, or an ethernet cable. Each transmission medium allows different distances and speed limits. For example, you can’t go further than 50 ft. on a 9600 baud rate with RS232.

Most installations are on RS485, which works up to 4,000 feet and a speed limit of 115,200 baud. Ethernet cable provides a distance of 100 meters and the speed of the network switches.

Theoretically, Modbus RS-485 has an upper limit of 115,200 baud rate, but real-life applications rarely go beyond 19,200. Often, there isn’t a need for such a high data transfer rate, and most slave devices aren’t built to handle such a high baud rate.

Common Modbus Protocols

Not all Modbus devices are built equal. When you’re setting up a Modbus system, you’ll need to ensure that all devices can communicate on the same protocol. Modbus RTU is the most popular protocol, but if you’re choosing a Modbus ASCII or Modbus TCP sensor, you’ll need to ensure that the master controller supports both protocols.

The protocols differ in formatting and size. So let’s take a deeper look at each protocol.

What Is Modbus RTU

Modbus RTU Frame Length (bits)
Start (silence)


Device ID


Function Code



n x 8



End (silence)


Fig 5- Modbus RTU Frame

The Modbus RTU protocol transmits data in 8-bits (byte) binary format. For example, the function code of 16 is represented by a single byte 0x10 hexadecimal value. Using the Modbus RTU format allows you to send or receive data with the smallest bandwidth.

It’s interesting to point out how Modbus RTU uses a period of science to indicate the start and end of a message. Timing is crucial for a Modbus RTU device as it needs to time the silence interval to mark the end of a message frame.

What Is Modbus ASCII

Modbus ASCII Frame Length (byte)


Device ID


Function Code



n x 2

Checksum (LRC)




Fig 6- Modbus RTU Frame

The Modbus ASCII shares the same field types with Modbus RTU, but that's where the similarity ends. Instead of binary formatting, Modbus ASCII uses ASCII characters to encode the data into the message frame. For example, function code 16 is represented by two characters of 0x31, 0x36.

ASCII formatting also limits the device limit to 247 (0xF7). Thus, the most significant device ID on a Modbus ASCII frame is 0x46, 0x37, the ASCII values for 'F' and '7'. The same applies to the register address and data that are passed in the message body.

A 2-byte LRC checksum is calculated for error-checking and appended to the message.

Unlike Modbus RTU, Modbus ASCII uses characters to indicate the starting and ending of a message. It uses 0x3A (:) as a start character and CRLF (0x0D, 0x0A) to terminate the transmission.

The payload uses only alphanumeric characters, which means that it produces intelligible text string when monitored on a Modbus sniffer software. It's also less sensitive to timing requirements as the message starts and ends with characters.

The downside of Modbus ASCII is that it takes at least twice the size of Modbus RTU. For example, it takes 2 bytes to transfer 0x5469 in Modbus RTU, but it'll take 4 bytes to convert the value to ASCII representations of 0x35, 0x34, 0x36, 0x39.

What Is Modbus TCP

Modbus TCP Frame Length (byte)
Transaction Identifier


Protocol Identifier


Length Field


Unit Identifier


Function Code


Data Bytes


Fig 7- Modbus TCP Frame

The 1990s saw the introduction of the 10-Base-T ethernet standard and the internet going mainstream. In 1999, Modbus TCP was introduced to leverage ethernet connectivity.

TCP is a connection-based transport layer protocol on the OSI stack. It automates connection synchronization, handshaking, error checking, and packet handling. With TCP taking care of the data transfer mechanism, some of the fields in the original Modbus frame become redundant.

The Start and End bits are no longer needed, and the same goes for the checksum. Therefore, the Modbus TCP saw a revision in its data frame. The Start, Stop, and checksum were removed. They are replaced by a 6-bytes header.

What’s new in the Modbus TCP is the Transaction Identifier, which is used to determine that a request is followed by a matching response. In addition, the Protocol Identifier is set to 0, indicating TCP protocol, while the Length Field indicates the remaining byte in the data packet.

What about Modbus Plus?

Despite sounding similar, Modbus Plus is not Modbus. Instead, it is a high-speed peer-to-peer communication protocol developed by Schneider that allows data transfer at 1 Mbps.

Modbus Plus specification includes protocol and hardware layers such as cabling and terminating connector. It involves token-passing in a flat network hierarchy, which differs from Modbus’s master-slave configuration.

Understanding Modbus Addressing And Messaging

We’re about to dive deeper into the workings of Modbus. Understanding how Modbus addressing and messaging works helps when you’re configuring and troubleshooting a Modbus network.

Device ID

A single byte can hold up to 255 possible Device IDs. However, Modbus specifications limit the valid IDs from 1 to 247. So, if you’re sending address 0x00 or 0xF8-0xFF on a Modbus RTU frame, the data frame will be ignored.

Relative Addressing

The standard Modbus specification allocates 9,999 memory points for different data types ( coil, discrete input, input register, holding register). On a Modbus device, these data are stored in volatile and non-volatile memories.

For example, configuration values for a Modbus transducer are stored on a non-volatile memory like an EEPROM. Meanwhile, sensor values are stored and updated on an SRAM. Of course, the physical storage is abstracted for a PLC programmer. A programmer needs to know how to access the data with the address allocation of each data type.

Here’s where it gets tricky.

Modbus data frame takes in relative addresses and not absolute addresses. The absolute and relative address for the data types are as follow:

Modbus Data Type Absolute Address (Dec) Relative Address Data Frame (Hex)
Coil 00001-09999 0001-9999 0x0000-0x270E
Discrete Input 10001-19999 0001-9999 0x0000-0x270E
Input Register 30001-39999 0001-9999 0x0000-0x270E
Holding Register 40001-49999 0001-9999 0x0000-0x270E

Fig 8- Modbus Addressing

The relative address is the result of discarding the tenth-thousandth decimal from the address. For example, an input register at an absolute address at 35,468 has a relative address of 5,468.

A device receiving the Modbus frame will determine the data type from the relative address by inspecting the function code. For example, a Read Holding Register request has a function code of 04, and the device automatically translates the relative address to 35,468.

It gets trickier.

The register address sent in a Modbus frame is deducted by one from the corresponding relative address. To read a coil at an absolute address at 00100, you’ll need to send a command request with an address of 0x63 (00099) in the data frame.

Extended Addressing

Each of the data types is allocated 9,999 memory spaces. Often, they will be sufficient for most applications. However, some devices require registries exceeding the standard allocation, and that's where extended addressing comes in.

Extended addressing stretches the address limits to 65,535 (0xFFFF), which is the maximum address possible with 2-byte addressing. The Modbus protocol remains the same in fields and syntax with extended addressing. However, devices that don't support extended addressing will respond with an exception when responding to a request with a vast address range.

How To Interpret Modbus Values

We wouldn’t call this a Bible of Modbus without showing what Modbus data packets look like when observed on a protocol sniffer software. Here, you’ll start piecing together what you’ve learned about Modbus and gain clarity.

Modbus Transmission Example 1 - Read Input Register

Let’s consider an example where a PLC reads 1 input register 30100 from a device (ID 2)

The PLC will transmit the following sequence in Modbus RTU (Hex).

02 04 00 63 00 01 C1 E7

Request frame breakdown.

The slave device responds with the next data frame.

02 04 01 5F 27 74 DA

Response frame breakdown

The above protocol sequence is similar when you’re performing a Read Holding Register request.

Modbus Transmission Example 2 - Write Holding Register

Write holding register is usually used for setting configuration parameters on a Modbus device.

For example, a PLC writing 0x782A and 0xB7C3 into register 40078 and 40079 on a device (ID 3)

The request sequence will be as follow:

03 10 00 4C 00 02 78 2A B7 C3 B7 05

Request frame breakdown

When successfully executed, the device will respond with:

03 10 00 4C 00 02 81 FD

Response frame breakdown

Modbus Transmission Example 3 - Read Multiple Coil

Understanding the data frame for reading coils (and discrete inputs) is more challenging, as each of the addresses holds only 1 bit. When retrieving multiple coil values, interpreting the value requires bit-wise identification.

A PLC reading 10 coils from an address 00500 from a Device ID 4 has the following request sequence.

04 01 01 F3 00 0A 4F 97

Request frame breakdown

Assuming that coils 501 and 508 are set, the response will be as follow:

04 01 02 01 02 F5 AD

Response frame breakdown

The value of the coils returns as 0x01, 0x02. How does this correspond to the 10 coil addresses?

Modbus is a Big-Endian protocol. It means that the most significant bytes are transmitted first. Within a byte, the value starts with the most significant bit from left to right.

Basics of Tank Level Indication

To know how to measure oil in industrial tanks best, we need to go over how to achieve tank level indication. The measurement of the position of an interface between two media is known as level measurement. These media are usually a liquid and a gas, but they could even be two liquids.

A comprehensive kind of physical principle applied to measurements of liquids, solids, and slurries levels such as pressure, level-sight, radiation, sonic principles, electrical properties, etc. Different regulations govern the operation of level devices. The three major categories include:



  1. measuring the position (height) of the surface
  2. the head pressure
  3. the weight of the material through load cells

Based on the above categories, various technologies are available to measure liquid levels. They include:

Relying on the type of level measurement chosen, consider many parameters when using level-measuring devices. Ignoring such parameters may result in an outsized margin of error or measurement with a short lifetime. In addition, level-measuring devices, like all other pieces of instrumentation and control, should be installed in a location that allows for simple inspection and maintenance.

Answer the following questions to determine which type of level sensor to use for an application:

  1. What is the material to measure: liquid or solid?
  2. Can the sensor be placed within the chamber, or should it be external?
  3. Would you like contact or non-contact level measurement?
  4. What’s the acceptable degree of accuracy?
  5. What are the application's temperature and pressure ranges?
  6. Is the density of the liquid changing with time?
  7. Is point level or continuous measurement required?
  8. What level measurement range do I require?
  9. Is the measured material electrically conductive?
  10. Will the material coat or build around surfaces?
  11. Does foam, vapor, or turbulence occur at the surface of the liquid?
  12. What about output? Do I need: analog, relay, digital display, etc.?

Construction materials of the sensor are essential and can not affect the material within the tank. A tank level detector can be customized for a selected application. In that case, the user should research what method to use in their industry before purchasing the instrument.

Floating System As A Level Indicator

In this system, a float movement depends on the liquid surface. The results of this vertical movement of the float are shown to the observer. Actuating a float switch alongside or creating a quantitative analog signal in its route supported the variation of the resistance placed inside the stem of the instrument because the magnetic float moves.

Magnetic floats shouldn't be used for liquids containing iron particles or other strongly magnetic materials. Magnetic Float Type Level Switches could also be available both as horizontal and vertical versions. The horizontal type is used on the sidewall of tanks. Its operating principle is that the rising liquid level tilts the float upward, the magnet attached to the highest of the body actuates the switch.

The vertical type is installed on the very best of the tank. Thus, the floats are made from stainless steel or other materials like plastic, Teflon, etc., suitable for liquids with a density above the precise gravity of the float.

If the instrument should be connected to the side of the tank, a selection of chambers could even be used for side connection. Moreover, the device can have multiple floats and switches to manage and notify the operator of the numerous liquid levels within the tank.

When using magnetic floats in level indication, they use the magnetostrictive principle to provide continuous level data without direct contact between the indicator and thus the fluid within the system. The float inside the hermetically sealed tube moves with the changing liquid level, and since it travels, the colored wafers (flag display). Sincere magnetically coupled to the float, rotate, and color changes. The wafers should be visible within the dark without light. A ruler is mounted along the wafer column to the distance unit or a percentage of the total height.

A transmitter or magnetic switches are often installed along the tube on these floating systems to act as an indicating level.

The Magnetic Level Gauge (by-pass) is an improved alternative to sight gauges (glass tubes) to visually monitor liquid levels in boilers, storage tanks, etc. Replacing the sight gauges with magnetic level gauges results in improved safety, increased visibility (10 times), reduced maintenance, and lower overall operating cost throughout the life cycle.

Dial Liquid Level indicators are for level measurement of bunker-c, water, diesel fuel, etc. Easy installation of these transmitters makes them the right choice for several level measurement and control applications. The operating principle is premised on the buoyancy of float and spring force. As the float rises and falls, the spring displays the extent on the front scale and produces an analog signal. This system is also available with switching contacts or analog (4...20 mA) output.

Pressure Type Measurements

The pressure at a given depth for a static liquid is the load of the liquid working on a unit area at that depth plus any force acting on the surface of the liquid. Thus, level measurement predicated the pressure measurement is also called hydrostatic tank gauging.

To determine the hydrostatic pressure of a column of liquid, multiply the density of the liquid by the height of the liquid column. Therefore, if we all know the hydrostatic pressure measured by the pressure sensor and the density of the fluid therein specific temperature, we will calculate the height of the liquid column.

Use pressure measuring elements to infer that the liquid level has been achieved successfully in both open tanks (the top of the liquid column is open to the atmosphere) and closed tanks (liquid is in a pressurized tank).

When measuring a level in an open tank, the effect of atmospheric pressure is compensated by utilizing a gauge pressure device. Thus, the pressure reading is directly proportional to its specific gravity and the height of the liquid. While in closed tanks, the effect of the pressurized air above the liquid column must inherit consideration and be deducted from the measured value of the pressure at the bottom of the fluid column. Therefore, differential pressure cells (DP cells) are mandatory for closed tanks by measuring two forces.

Capillary tubes of the diaphragm seals must be as short as possible and shielded from the radiation heat and ambient temperature.

Radar Level Measurement

Radar level measurement is based on the principle of measuring the time required for the microwave pulse and its reflected echo to form an entire return trip between the non-contacting transducer and thus the sensed material level. Then, the transceiver converts this signal electronically into level/distance and depicts it as an analog and/or digital signal. The transducer’s output often selected by the user is directly or inversely proportional to the span.

Pulse radar takes many 'shots' every second. The return echoes from the merchandise surface are sampled and averaged, which is especially important in challenging applications where small amounts of energy are being received from low dielectric and agitated product surfaces. The averaging of the center beat technique reduces the noise curve to permit smaller echoes to be detected.

The achievable accuracy of a current radar level meter depends heavily on the following:

  1. antenna design
  2. mechanical installation
  3. state and quality of the electronics
  4. echo processing software employed

The accuracy of an existing instrument is additionally dependent upon signal-to-noise ratio and interference.

Level Measurement With Radar Instrument For Agitated Liquid

High-frequency radar transmitters are prone to signal to scatter from agitated surfaces. The high-frequency radar will receive considerably less signal than an equivalent 5.8 GHz radar when agitated liquid surface. Installing the radar using a stilling well/ bypass tube ensures a calm surface with no scattering of the echo signal.

Condensation And Build-Up Effects On Radar Instruments

High-frequency radar level transmitters are more inclined to condensation and product build-up on the antenna. However, a 6" horn antenna with a 5.8 or 6.3 GHz frequency is unaffected by condensation and build-up.

Ultrasonic Level instruments

Ultrasonic level instruments operate on the basic principle of using sound waves to determine liquid/solid/slurries. In addition to standard level or volume measurement, they can monitor open channel flow, determine the actual volumetric throughput in lift stations, measure differential level and control the pumps.

Ultrasonic Level Transmitters consist of two elements, a high-efficiency transducer and) an associated electronic transceiver. Together, they operate to determine the time for a transmitted ultrasonic pulse and its reflected echo to make a complete return trip between the non-contacting transducer and the sensed liquid level. A piezoelectric crystal inside a top-of-tank mounted transducer converts electrical pulses into sound energy that travels in the form of a wave at the established frequency and at a constant speed downward onto the surface of the material whose level is to be measured. Echoes of these waves return to the transducer, which performs calculations to convert wave travel distance into a measure of level in the tank. The time-lapse between firing the sound burst and receiving the return echo is directly proportional to the distance between the transducer and the material in the vessel. The medium is usually air over the material’s surface, but it could be a blanket of other gases or vapors. The instrument measures the time for the bursts to travel down to the reflecting surface and return. This time will be proportional to the distance from the transducer to the surface and can determine the level of fluid in the tank. This fundamental principle lies at the heart of the ultrasonic measurement technology and is illustrated in the equation:

Distance = (Velocity of Sound x Time)/2.

These non-contact devices are available in models that convert readings into 4–20 mA outputs to DCSs, PLCs, or other remote controls.

The frequency range for ultrasonic methods is in the range of 15...200 kHz.Several factors must be considered for practical applications of ultrasonic measurement. A few key points are:

Capacitance Level Instruments

Capacitance level instruments operate on the basic principle of the variation of the electrical capacity of a capacitor formed by the sensor, the vessel wall, and the dielectric material. A capacitor is made of two conductive plates which are isolated from each other by a dielectric.

The storage capability of a capacitor is directly dependent on the plate's areas (A), their distance (d), and the dielectric constant of the material between the plates (ε).

C = kεA/d

Where C is the value of capacitance, expressed in Farad.

k is a constant with a value of 0.225 or 0.0885 depending on the units used.

The dielectric constant of the process material is the most critical consideration of this level measurement application. The higher the dielectric of the process material, the easier and more reliable would be the level measurement. Temperature, moisture content, humidity, and density can change the dielectric constant of the process materials must be taken into account.

Moreover, it is essential that the probe’s tip instead of the entire probe be covered with the process material—typical insertion probe lengths ranging from 20 to 40 cm.

Wet and sticky materials cause permanent coating and build-up to the probe and introduce errors in the level measurements. Therefore, it is recommended to use a Teflon insulator on the conductive probe when the dielectric constant of the process material is high.

Installation of the probe must be such that it does not contact the vessel wall or any structural element of the vessel.

This type of level sensor is suitable for interface measurement.

Conductivity Level Measurement

Conductivity level measurement is similar to the capacitance technique. However, conductivity level sensors detect the medium’s resistance while the process material covers its electrodes.

This method is usually used for water vessels and in processes like water & wastewater treatments, chemical, pulp & paper, food, wine, biological, etc. They’re mounted multi-point sensors with up to four probes or three probes and one reference electrode.

They can be mounted on various open or closed vessels (suitable for pressurized tanks) or ordered because of the submersible version for level detection in wells or deep tanks. They’re going to control the differential of minimum and the maximum level, with an adjustment for sensitivity.

Vibrating Fork Level Measurement

Vibration Fork Level Switches are designed considering vibration at its frequency by a pair of piezo-ceramic discs. The frequency and amplitude of vibration change when coming into contact with the medium. This change is detected, processed, and converted into a switch signal.

They can be used for liquids with a density of more than 0.7 and on free-flowing granules and powders of light and medium density. In addition, they cover an outsized variety of applications such as overfill or rehearsal protection, pump controls, high/low fail-safe limit switch, dry/wet indication in pipes.

High excitation frequency in a sound vibration sensor ensures interference-free operation and enables high vibrating fewer and turbulent liquid surfaces. This measurement technique is exceptionally well suitable for top viscosity liquids (response time will be longer). Thus, the operation won't be affected by the foam and gas content of the material. Vibration forks are often utilized in liquid, solid, and slurry level detection.

Thermal Dispersion Level Measurement

The principle of thermal level sensors is to differentiate between the temperatures of the vapor above the liquid. The fluid itself or, more commonly, the rise in thermal conductivity as an inquiry becomes submerged within the tactic liquid. One of the only thermal level switch designs consists of a temperature sensor heated with an unbroken warmth input. While the probe is within the vapor space, the temperature remains the same. This is because the low-conductivity vapors don't carry much heat far away from the probe. When the probe is submerged, the liquid absorbs more heat dropping the probe temperature. The switch is actuated when this alteration in temperature occurs.

Thermal level switches are set to detect the presence or absence of any fluid as all process materials have a characteristic heat transfer coefficient. Therefore, these switches are often utilized under challenging services, like interfaces, sludge, and slurry applications. They might detect thermally conductive foams if spray-cleaned after each operation.

Thermal level and interface switches haven't any mechanical moving parts and are rated for top pressure. Therefore, they work best with non-coating liquids and a slurry with 0.4-1.2 density and low to medium viscosity.

Optical Level Measurement

In level measurements, the optical sensors depend on the sunshine transmitting, reflecting, or refracting properties of the method material. A refracting sensor relies on the principle that light or infrared changes direction (refracts) during passing through the interface between two media.

When the sensor is within the vapor phase, most of the sunshine from the LED reflects within a prism. When the prism is submerged, most of the sunshine refracts into the liquid, and therefore the amount of reflected light that reaches the receiver drops substantially. Thus, a drop by the reflected light signal indicates contact with the method liquid.

One sort of transmission sensor relies on ​the refraction principle utilizing an unclad, U-shaped fiber optic cable. A light source transmits a pulsed beam through the fiber cable, and therefore the sensor measures the quantity of sunshine that returns. The utilization of fiber-optics makes the system impervious to electrical interference, and a few designs also are intrinsically safe., A level switch that combines an optical with a conductivity-type level sensor to determine the presence of both water (conductive) and hydrocarbons (non-conductive).

Finding The Right Tank Level Indication Tool

There are many options for measuring your various liquids including oil. Knowing which one to choose is no small feat, but the experts at APG sensors are here to help you along your way.

Feel free to give us a call and we can find the right one for you.


Drilling in agricultural areas requires a strong blend of safe and efficient operations. The right tools and materials go a long way toward your success. Mud tanks are an essential part of any large drilling project, and equally important is the condition of the mud.

In this article, we will talk about mud tanks, drilling mud, and how float level transmitters ensure the right consistency for the job.

What is a Mud Tank?

A mud tank is a large, rectangular container made of square-shaped steel tubing and plates that holds drilling mud (also called drilling fluid) on drilling platforms. In addition to storing mud, the tank is used for mixing and treating the mud and removing rocks and other unwanted materials from a drilling platform.

The tank is often open-topped with walkways for workers to inspect the mixture and operate other drilling platform equipment. Inside, the tank is composed of sections to help separate rocks and sediment and aid with agitation.

A mud tank can be a portable or permanent installation on or near a drilling platform. The quantity and size will depend on the drilling depth, the application, and the drilling method.

There are two basic types of tanks on a job: an active tank and a reserve tank. The active tank holds the mud used for most drilling while aiding with mixing chemicals or additives before usage. The reserve tank is set aside to store excess mud or other types of mud to aid with the project.

What is Drilling Mud?

oil rig worker covered in drilling mud

Drilling mud is a mud-like mixture pumped down the drilling pipe and through the drill bit to help lubricate and cool the bit. The mud also rises back up the same drilling pipe, bringing with it loose rock cuttings from the drilling pipe.

The drilling mud comes in three versions: water-based, oil-based, or synthetic-based:

Water-based drilling mud is made from either freshwater or seawater and often contains clay (bentonite) for ideal viscosity. It is also composed of special minerals like barite to make the column heavier for added borehole stability. Water-based muds are often used for less strenuous or less demanding drilling.

Oil-based mud often uses diesel oil or mineral oil, bentonite, brine, and barite to aid with viscosity and weight and other agents for lubricating properties. This mud is used for drilling work that puts more stress on the drill, such as deep drilling, horizontal drilling, and directional drilling.

Synthetic-based mud is an environmental alternative to oil. It uses highly refined compounds blended with similar additives as oil-based mud.

How Mud Tanks Interact with Drilling Platforms

Unless the tanks are already installed or you use holes in the ground as mud tanks (called mud pits), the active and reserve tanks are transported from an outside location to your drilling platform. Bulk tanks may also be used to assist in pouring additives into the mud. In large jobs, these bulk tanks may have the additives already in them; otherwise, the additives come as dry sacks and stored in a safe house to be mixed in at the appropriate time.

The process starts by preparing the mud in the active tank with the needed ingredients. Then one or more mud pumps move the mud from the tank through pipes and into the interior of the drill bit, pushing cuttings away while you drill. The mud then travels up the pipe's interior sides and back to the surface into the original mud tank, carrying loose cuttings with it.

The returning mud is filtered using a desander and distiller or settling tanks to remove rocks and sediment. The mud is tested for volume to spot any inconsistencies. If any are found, more ingredients are added to retain previous levels. Then the entire process starts again.

How Float Level Transmitters Aid with Understanding Volume

drilling rig with mud tank for oil

Safe and economical drilling requires the right quantity and consistency of mud, so catching any volume changes is of paramount importance. Volume increases indicate changes in the ingredients such as water and oil levels. Volume decreases indicate loss of mud into the drilling pipe. Issues like these can damage your drill, rig, and the surrounding land area.

Level transmitters provide real-time readings of changes in volume. Today's transmitters come with varying technology for the job. Automation Products Group (APG) is a leader in the sensor market and offers a range of transmitter styles. One style of APG sensor called a float level transmitter has been a leader in the market for drilling platforms across North America, and it is a good example of how level transmitters work.

The continuous float level transmitter is used to measure a wide variety of liquids. In the case of drilling, it provides changes in volume to spot any loss of mud or increase in chemicals that can become hazardous during a drill.

There are two options of float level transmitters:

Magnetostrictive Level Measurement Sensor

This option consists of a magnetic float that travels up and down a rod with a wire waveguide that aligns itself to surrounding magnetic fields. An electrical pulse aligns molecules in one direction. When the pulse meets the competing magnetic field from the float, the molecules shift into a different direction that causes a vibration back to the sensor called a strain pulse. By measuring the time delay of the first electrical pulse and the strain pulse, the float's position can be determined with high accuracy.

This type of transmitter can also house multiple floats to measure more than one ingredient, such as oil and water – a rather unique feature for a level transmitter.

Resistive Level Measurement Technology

This type of transmitter consists of a float with a magnet attached to a stem with a sensing rod. The rod contains closely spaced switches and sensors that are triggered as the float moves up and down the rod, charting divisions in the original voltage sent for an easy and reliable read on the foam's position.

Transmitters used for mud tanks must withstand significant pressures from rushing mud and internal turbulence in the tank. This is no place for the weak. APG sensors are no exception to this rule. The company's products are known for their durability, accuracy, and longevity, making them helpful in hazardous drilling locations.

Other Tools for the Job

To learn more about these sensors, other APG sensors, and what industrial automation tools are available today, visit the APG website at

As you may already know, agriculture relies on two things: speed and efficiency. No matter how hard you work, it seems like there’s always more to do, and delays can quickly add up—and that can cost you money.

To meet the demands of the modern farm, you need to be able to get the most out of your equipment, which means you’ll often push your equipment hard, day in and day out.

Whether you’re threshing, fertilizing, or baling, you need your machinery to work as efficiently as possible, running at the highest speed and power imaginable.

Of course, this puts a lot of stress on your equipment, which can, in turn, put you at risk of breakdowns that will cost you time or lead to wasted crops. However, modern farm machinery has many sensors built into them to help monitor your equipment’s condition to prevent breakdowns. These sensors provide you with instant feedback so that you can avoid costly damage.

One of the most valuable—and overlooked—sensors on your agricultural equipment is the torque sensor. This device measures the amount of force occurring to make something turn or spin.

These sensors prevent overdriving your equipment by constantly monitoring torque, saving you from expensive repairs and unnecessary delays. But, first, let’s take a deeper look at how torque sensors work.

What is Torque?

Before we start looking at torque sensors, it’s helpful to take a moment and talk about what precisely “torque” means. Torque has to do with forces that twist an object, but it’s worth knowing how torque relates to other forces present in your machinery.

At a basic level, torque is a force that propels an object to spin or rotate around a central axis. Take a nut threaded onto a bolt, for example. The force that moves the nut up and down the bolt is torque, and the more torque you apply to a nut, the tighter the connection will be once that nut is driven home.

In terms of your equipment, though, it helps think of torque with two other values: revolutions per minute (RPM) and horsepower. The first is pretty straightforward: RPM is simply the number of times a motor’s shaft rotates every minute. The higher the RPM, the faster the engine is running.

Horsepower, on the other hand, describes the amount of power an engine produces. When you’re calculating horsepower, you multiply the amount of force your engine is making by the distance that force propels an object, then divide that number by the time it takes to perform the work. One unit of horsepower is equal to 550 foot-pounds per second.

If you’re looking to improve the power output of your equipment, you should avoid trying to increase the RPM. Instead of raising power output, you’ll decrease your engine’s torque while consuming more energy. Instead, increasing torque is the best way to expand your equipment’s horsepower.

For many of your applications, it’s torque that’s doing the work. Efficient torque usage helps spread fertilizer evenly, break up difficult soil, and move through your fields without getting bogged down.

Torque is the driving force behind most of your equipment, and that makes torque measurement incredibly important.

Torque Measurements

The question, then, becomes how to measure torque. That’s where an accurate, reliable torque sensor comes into play.

Torque sensors provide instant feedback for equipment operators, allowing them to monitor power output and machine strain to adjust machinery for optimal efficiency.

A torque sensor is a kind of transducer, which measures torque forces and changes them into an electrical signal that an electric receiver can interpret. A torque transducer allows you to constantly monitor torque as your equipment operates since the electrical signal transmitted from your sensor increases in proportion to the amount of torque detected.

All torque sensors use the same basic principle: the strain gauge. For example, a torsion sensor involves a metal body bonded to a neutral polyimide film, with strain gauges made of foil attached. As these strain gauges stretch or compress, the current passing through changes as the torque creates pressure, adjusting the resistance.

As torque applies to a shaft, it introduces a twisting force, and this twist causes the strain gauges to stretch or deform. As the gauges deform and the current changes, the difference is recorded using a Wheatstone bridge, a type of circuit that compares a constant flow of electricity against an unknown current.

This difference in current is what a torque sensor uses to measure the amount of torque a shaft is experiencing. That reading is sent electronically to the output panel, which converts the readings into usable information, which you can use to adjust power, speed, and other factors to improve efficiency while preserving your equipment.

Types of Torque Sensors

In general, there are two types of torque sensors: static torque sensors and rotary torque sensors. While there are countless variations of models and applications for each of these types of torque sensors, it’s essential to understand the underlying properties of how each model works.

Here are some of the key differences between these two sensor types.

Static Torque Sensors

Also known as a reaction torque transducer, static torque sensors measure torque at the point where it meets the ground. These sensors usually involve two flanges, one attached to a sturdy, fixed element and the other with the rotating part. The gauge then measures the shearing force between the two flanges.

These sensors are usually less complex than rotary torque sensors, which gives them several advantages. Although they still rely on wires or cables to transmit signals, they tend to be less expensive, require less maintenance, and outlast the rotating elements they’re measuring.

However, static torque sensors also have limited uses, especially in the agricultural field. Instead, they are used primarily for testing and tool calibration, like calibrating torque wrenches.

While these sensors have some utility for agriculture, most farmers will use rotary torque sensors much more frequently.

Rotary Torque Sensors

Unlike a static sensor, rotary torque sensors must rotate with the shaft itself, operating in line with the rotation. Because of this, the sensor can’t have any attached wires, as they would quickly become bound up in the shaft and rendered useless.

Instead, rotary torque sensors transmit data wirelessly to a receiver, where it is interpreted and read.

A rotary torque sensor is typically attached to the shaft itself, located between the motor driving the rotation and the load connected at the other end. This attachment allows the sensor to measure the torque being applied along the shaft, helping to calculate both power and stress forces acting on the shaft.

Because the sensor is on the shaft, it has to transmit the forces to the sensor itself. The transmission can be achieved either through a keyed shaft (where the sensor is attached to the shaft with a piece of metal, or key, inserted into a slot cut into the shaft) or slip rings, which sit between two bearings in the sensor housing.

To get the most accurate torque measurements possible, it must account for any deflections across the shaft resulting from side loads, usually due to a heavy load at the far end of the shaft. Therefore, the only measurements a rotary torque sensor should be taking are those occurring in a clockwise or counterclockwise pattern around the shaft.

While these sensors are usually more expensive, they provide invaluable real-time data, especially in agriculture.

Let’s take a look at some of the many ways farmers can benefit from torque sensors.

How a Torque Sensor Helps the Agriculture Industry

combine harvester equipped with a torque sensor

When it comes to agricultural machinery, you’re probably looking for a few key characteristics. Everything on your farm needs to be durable to stand up to the long hours and hard work you need your equipment to perform. Your machinery needs to be efficient to get as much work done as quickly as you can.

Lastly, your farm equipment needs to be reliable. You need to trust that your machines are going to work every time you turn them on.

Torque sensors play a huge role in all three of these major needs, and companies like APG do everything they can to make sure you get your money’s worth from your sensors.

Agricultural torque sensors need to withstand the punishment of the daily work farmers need to accomplish, and part of that is ensuring that they provide you reliable, accurate information every time.

Consider a combine harvester, which requires several different torque sensors working together. Starting from the front end, the reel and the platform auger rely on torque to accomplish their work.

During harvests, any variations can lead to overdriving the torque, whether they stem from the uneven ground or particularly dense growth areas. A torque sensor can detect this imbalance, adjusting the drive to keep the combine working without damaging the machinery or the crops.

Next, the conveyors and the auger screws move the harvest through the combine. Both rely on torque sensors to keep material moving smoothly. Unfortunately, these areas are susceptible to jams. While the high torque power of the auger usually overcomes any obstacles, the sensor can detect when more power is needed, saving you time and fuel.

Finally, once your combine is full, the unloader mechanism relies on another auger to move harvested material up into the unloading pipe. An additional torque sensor regulates the speed and volume of grain passing through this pipe, ensuring you get all of the material out of your combine.

Of course, harvesting isn’t the only place where torque sensors are valuable. For example, fertilizer spreaders and similar tools are much more efficient when used in conjunction with torque sensors.

In fertilizer spreaders, for instance, a torque sensor can be used to adjust several aspects of fertilizer distribution. Constantly monitoring torque in your spreading equipment allows you to ensure that you’re spreading your fertilizer as evenly and efficiently as possible. In addition, sensors can detect differences in material, adjusting hydraulics, power, and other factors to ensure you aren’t wasting fertilizer or fuel.

There are many other instances in which you’ll come across torque sensors, from poultry feeding machines to other applications. These functions use paddle wheel switches, which distribute small particles from bins and hoppers using specific torque settings, which allows you to adjust the distribution width of the bits.

Another practical application is monitoring the motors that power your farm equipment. Keeping everything running can be difficult between the challenging environmental factors and the heavy wear and tear these machines endure throughout the year. With effective torque sensors, you can continually monitor your engine performance.

Not only can you prevent breakdowns by tackling minor problems before they get bigger, but you can also reduce excess wear by integrating these sensors into the operation of your equipment. In addition, these sensors allow you to keep your equipment running at peak efficiency, driving your machine hard without running the risk of overdoing it.

Finding the Right Torque Sensors for You

As you can see, torque sensors offer several advantages to those working in agriculture. From increasing efficiency to reducing the number of hours (and potentially crops) lost from breakdowns and other delays, top-notch torque sensors can quickly pay for themselves.

If you’re interested in learning more about how you can get the most out of your torque sensors, contact the team at APG. We’ll use our expertise to give you all of the information you need about sensor technology and help you get started on adding the latest, most sophisticated sensors to your equipment.

Often abbreviated as DAQ, data acquisition refers to collecting sample signals allowing the measurement of physical phenomena in the real world. These signals convert into a digital medium that a computer can calculate when equipped with data acquisition software.

DAQ is the modern variation of past measurement practices that relied on paper charts or tape-recording devices. However, in those methods, the signals remained in analog form.

In contrast, data acquisition involves converting analog measurements into the digital domain. The DAQ system will record the data on a digital device, like a hard disk drive (HDD), solid-state drive (SSD), or flash media.

Below, we’ll outline the critical components of DAQ. We’ll also discuss the capabilities and features of a data acquisition system so that you can understand how DAQ software is in use today and its overall importance within various industries.

Data Acquisition System: What You Need

What is DAQ? Regardless of its purpose, every DAQ system must offer four essential components. These include:


A sensor or transducer is responsible for interacting with the measured phenomena. Depending on the analyzed event, the interaction may occur either indirectly or directly.

The sensor is responsible for converting the physical values of the measurable event into electric signals. The exact type of sensor used on a project will depend on the application of the DAQ system.

For instance, measuring light requires a photovoltaic sensor. Conversely, if your goal is to obtain exact temperature measurements, you will need a temperature sensor.

The standard function of all types of sensors is to convert analog signals relating to things like speed, light, or temperature into digital signals. Then, the computer can interpret the converted signals by the computer’s data acquisition software.

Signal Conditioning Equipment

Often, incoming signals from DAQ sensors cannot convert without modification. In addition, these signals are so weak that the data acquisition software cannot measure them.

DAQ systems include transmission or signal conditioning equipment to resolve conversion issues. This additional circuitry is responsible for optimizing the signals to be used by the data acquisition system.

The signal conditioner filters out irrelevant noise from the true signal and amplifies this feedback. In addition, some signal conditioners can perform additional tasks, such as calibrating the DAQ sensor.

DAQ Hardware

What is DAQ hardware? Data acquisition hardware is the entity that bridges the gap between the sensors and the computer software.

DAQ hardware can be connected to your computer in one of two ways: It can be plugged into the USB ports or tied directly to one of the PCI-Express slots on the motherboard.

The chief function of DAQ hardware is to take analog signals from the sensors and convert them into digital signals that the computer software can read.

Additional functions of data acquisition hardware may include:


Analog-to-digital conversion (ADC) is the most basic function of DAQ hardware. Without this conversion process, the data collected by the sensors would not be usable.

Digital to Analog Conversions

DAQ hardware can also support digital-to-analog conversions, which allows the output of binary signals back to the sensors.


Data acquisition hardware can even facilitate communication between supplemental devices, including handheld equipment that allows you to operate the DAQ system remotely.

Standalone Functionality

As technology continues to advance, standalone DAQ hardware has become more prevalent. This equipment can operate without a connection to a computer because it has its processor and CPU.

Standalone equipment gives users access to real-time data. Some examples of these types of DAQ hardware include data loggers and standalone oscilloscopes.


The final piece of the data acquisition puzzle is the computer. The computer is responsible for gathering all of the transmitted data from the DAQ hardware. However, you can’t simply connect data acquisition hardware to any computer. The computer must install the requisite software.

DAQ software leverages the data from the hardware and converts it into readable forms. The data acquisition software links the user to the newly digitized data. Computers with the proper software allow users to perform advanced computations to use the data meaningfully.

What Measurements Can a DAQ System Provide?

The primary purpose of data acquisition systems is to allow for the measurement of physical occurrences and attributes, such as:

man using ruler to measure water level as precursor of DAQ

While these are the primary data types collected with DAQ systems, signals can also measure sounds, mass, speed, and light. If you need to measure and track natural phenomena precisely, data acquisition equipment is the best way to accomplish this mission.

Purpose of DAQ

Generally speaking, the purpose of DAQ is to obtain and store data about physical phenomena. However, these systems also provide users with real-time capabilities for visualization and data analysis. Furthermore, since the systems record the data, users can also review the data after the measurement process has concluded.

Most DAQ systems have built-in report generation and analytics capabilities. In addition, modern data acquisition equipment usually pairs with a precision control system, which allows you to measure physical occurrences and actively alter specific attributes in real-world scenarios.

While engineers in different industries have varying needs, the following are capabilities that are present in almost every data acquisition system:

While DAQ instruments’ primary design is for data collection, they are also for monitoring purposes. A few examples include:

Data acquisition equipment and its associated software are essential to the success of hundreds of industries. Through the power of DAQ, organizations can improve the efficiency of their processes and maintain a safe working environment for all.

Why Data Acquisition Systems Are Important

Data acquisition systems are essential for a variety of reasons. Perhaps most significant is that DAQ is used to test virtually every kind of electromechanical equipment, including medical devices and industrial machinery.

Before the rise of data acquisition software, these products were tested using highly questionable and subjective methods. For instance, vehicles were tested by gathering user feedback on how it felt to drive them. As you might imagine, this left a lot of room for error and user bias.

Fortunately, the implementation of DAQ has allowed manufacturers to replace these unreliable testing methods with real-world data. As a result, they can objectively measure products for reliability, safety, and performance.

Data acquisition has become the industry standard for testing and refining aircraft, medical equipment, vehicles, and machinery.

The Process

Now that we have outlined what DAQ is and when to utilize this equipment let’s break down the actual measurement process.

The first stage of data acquisition is to measure analog signals in the physical world, which occurs through transducers and sensors.

One of the most common examples of a sensor is a digital thermometer. It collects analog data (temperature), converts the information into a digital format, and displays the reading on a small screen.

The second stage of DAQ is signal conditioning. This circuitry prepares the analog data and sends it in a digital format. It isolates and amplifies the analog signals so that the DAQ hardware can sufficiently measure them.

The third phase involves ADC or analog-to-digital conversion. The DAQ hardware performs ADC. The data acquisition equipment will convert the signals to a digital format and relay them to the computer software or built-in CPU.

During the final stage of DAQ, the computer records and displays the real-time data. Again, the information displays in such a manner that it is easy to interpret.

The data from the digital thermometer example displays as a series of numbers that indicate the user’s temperature.

More advanced DAQ systems will display the data and store it, allowing for the review of the information later.

Common Types of DAQ Systems

When you’re designing a data acquisition system, there are many different possible configurations. First, you must choose the type of sensors, signal conditioning equipment, and hardware that will be the most suitable for your intended purposes.

Second, DAQ systems typically have two main categories, which are:

DIY Platforms

A DIY platform involves the use of modular components. With this approach, you must select each piece of your DAQ system individually and assemble it, including the software package, sensors, hardware, and signal conditioners.

DIY platforms offer superior customization, but they also require an advanced understanding of data measurement principles.

The primary benefit of a DIY platform is that it offers superior flexibility. You can create a DAQ system to meet the unique demands of your organization. However, building out and programming your system can be incredibly time-consuming. That is why many users opt for a turn-key system.

Turn-Key DAQ System

More commonly referred to as an integrated DAQ system, turn-key equipment is ready to use right out of the box. The wholly integrated hardware and software require virtually no setup or programming.

Integrated systems do not offer as much flexibility as DIY setups, but they are great for data logging applications.

Data loggers are to record environmental information over an extended period. They allow you to measure, analyze, and validate the data by transferring it to a computer equipped with the required software.

Typical DAQ Configurations

man on computer as part of DAQ system of sensors

Every DAQ system must include sensors, signal conditioners, hardware, and a computer equipped with data acquisition software. However, DAQ systems can be configured in a wide variety of ways.

Below, we’ve identified two of the most common physical configurations that are popular in many industries.

Modular Systems

In a modular DAQ system, all core components are separate entities. First, they must connect via USB or other types of cables. Next, the sensors are connected directly to the DAQ hardware. Then, the data acquisition hardware finally links to the computer, responsible for storage, data processing, and display.

Most of the time, the signal conditioner and DAQ hardware are together in a single piece of equipment connected to the computer, as described above. However, some modular DAQ systems have to be installed into the computer using a PCI or other standardized format. Installing data acquisition hardware using this method requires a little more technical knowledge.

If you need data acquisition solutions in a fixed location, such as in a manufacturing facility, then modular equipment is an excellent option.

Integrated DAQ Systems

Integrated data acquisition systems are a much more convenient solution. The single piece of equipment contains all vital components, including A/D converters, signal conditioners, storage hardware, data display equipment, and data processing capabilities.

Integrated DAQ systems offer many benefits over modular packages. The most apparent is that they are immediately ready for use as soon as the equipment arrives.

In addition, integrated systems are the superior choice for mobile applications and fieldwork. You can rapidly deploy the integrated data acquisition equipment without having to hassle with cords or cables.

Integrated systems do have two drawbacks. The first is that these data acquisition solutions are a bit more expensive than modular systems. Secondly, integrated systems do not offer as much room for customization.

However, DAQ technology continues to advance year after year. These advancements have created integrated systems that are much more robust than they were in the past.

Unless you have highly strenuous data acquisition needs, integrated DAQ equipment is likely the most practical solution for your organization.

Sensor Solutions from APG

If you are looking for high-quality measurement devices like transmitters, sensors, and transducers, reach out to Automation Products Group, Inc. We offer cutting-edge solutions for your DAQ system needs.

Contact us today to find out more on how to get started.


A tank cloud sensor by APG Sensors leverages technology and Internet connectivity to provide excellent local and a wide range of remote tank level monitoring. Our cloud sensors enable you to monitor liquid levels with various monitoring technologies, including ultrasonic, float, and pressure sensors. Also, our tank cloud sensors can monitor liquid levels in different types of tanks, including chemical injection, IBC, and oil tanks. APG Sensors has the perfect local and remote monitoring sensor for you regardless of your application. Pair your level sensor with our controller to manage a whole host of functions, including liquid levels, control pumps and valves, and log files.

Level Monitoring Definition

Level monitoring refers to the process of observing liquid and solid volumes in industrial, residential, or commercial tanks using technology. Typically, it involves installing a level sensor in a tank or container and transmitting measurement data from the sensor to a monitoring device.

This is essential for measuring fuel, oil, and chemicals in various tanks. Checking such elements manually or by using traditional methods can be unsafe or difficult. Installation is a one-time activity that enables you to monitor tank contents locally on a display or remotely via a cloud service or browser.

How Oil Tank Cloud Sensors Work

Tank cloud gauges work through wireless sensor network controllers that interpret measurement data from the level sensor near the fill pipe and make the data available to users via an Internet or network connection. You can configure your sensor data to be accessed locally or remotely, depending on preference. In many cases, tank cloud sensors require a cloud service subscription to work. Fortunately, our controllers allow direct access over a network, which means you do not necessarily need a cloud service subscription for the level monitoring system to work.

Tips for Choosing a Tank Cloud Sensor

Tank cloud monitoring systems use three main types of sensors:

Consider several factors when choosing a level sensor for your tank monitoring system.

First, know the media you will be measuring. Most level switches are designed to work with clean liquids. Therefore, consider using a float switch or pressure transducer sensors if you intend to measure dirty or corrosive liquids.

Second, know where the access point for installing the level sensor is. Level switches are easy to install on a tank with an access point at the top. However, if the tank top is inaccessible, consider installing a pressure transducer.

Third, think about the tank size. Level sensor types have a range of measurements that need to be considered. Talk to one of our representatives to determine the best level switch for your tank cloud system.

Benefits of Oil Tank Cloud Sensors

hands on computer using cloud to monitor oil tanks

Storage tanks can be used in many locations and environments, including indoors, outdoors, below, and above ground. Tank cloud sensors enable users to monitor media levels in tanks to boost productivity, efficiency, and profitability.

Saves on Installation Costs and Time

Compared to wired systems, tank cloud sensors are far more affordable and easier to install. Minimal infrastructure changes are required to implement. It involves connecting a wireless node to a level switch such as a wireless ultrasonic sensor and installing it in a container. You could install single or multiple wireless nodes, depending on your preference. The wireless nodes bound to wireless gateways or controllers form a network. Once the connections have been made, our technicians will survey the location to ensure the deployed nodes and the gateway are properly connected.

Then, our technicians configure the system and set inspection parameters and alarm thresholds. One great feature is that our tank cloud sensors can monitor multiple containers. We can set up this system at a much shorter time and lower cost than other level measurement systems.

Boosts Efficiency

Tank cloud sensors provide real-time monitoring and alerts, which boosts efficiency. For instance, they provide real-time monitoring of remote containers, which means you do not have to send staff to a site based on forecasted expectations of media levels inside the containers. Instead, you can plan site visits strategically based on actual needs. Tank cloud sensors save time and costs and ensure your tanks are full and processes run seamlessly.

man in suit boosting efficiency in oil tank monitoring

APG Sensors technicians can set up automated alerts to notify your staff of potential problems and minimize emergencies. We understand the effects of emergencies on tank fill levels. For instance, dry oil tanks can draw processes to an unexpected halt. On the other hand, overfills can be extremely wasteful and may have considerable effects on the environment. The real-time monitoring alerts when your tanks do not meet a specific threshold preventing accidents.

oil tank cloud software on computer and phone

In addition, sensor cloud systems provide data that can be analyzed and used by management in decision-making regarding assets, utilization of the assets, tank servicing, and the resources required for the servicing.

Increased Versatility

Tank cloud sensors enable businesses and industrial ventures to adapt to changing business needs which are highly dynamic due to changing environments and client requirements. Fortunately, APG tank cloud sensors are scalable and highly adaptable to changing needs and requirements.

  1. You can move your containers as often as you want without affecting the tank cloud sensors.
  2. You do not even need to disconnect the measuring device when transporting your containers, which means you can continue monitoring your containers even in transit.
  3. Our technicians can integrate new nodes in new containers into your existing network.

You could even deploy a new network to new tanks because tank cloud sensors do not have the time and labor requirements of wired level monitoring systems.

How To Order Your Oil Tank Sensor

There are many advantages of tank cloud sensors. This level monitoring system is easy to install, affordable, and does not have significant time and labor commitments. Also, we can monitor multiple containers and are scalable to accommodate new containers. We could even configure the system to send automated alerts to prevent accidents and emergencies.

Let APG Sensors find the best tank cloud sensor for you. Call us today to learn more about our industrial automation tools.


A lease tank for oil waiting to be picked up by a truckThere are some places where level and pressure measurement is easier than others. A rainwater collection tank for a garden, for instance. Anything associated with oil and gas exploration? No, that's not easy. From detailed regulations to keep people and the environment safe, to the various hazardous, poisonous, or corrosive chemicals involved, to the remote places where most drilling occurs, oil and gas exploration is a tough industry for level and pressure sensors. APG's new MPXI-F explosion proof, flexible stem, magnetostrictive probe is made to excel in these specific harsh conditions.

The MPXI-F Meets API 18.2 Requirements

Standards issued by the American Petroleum Institute--including Chapter 18.2, Custody Transfer of Crude Oil from Lease Tanks Using Alternative Measurement Methods, of the Manual of Petroleum Measurement Standards (API 18.2)--have been adopted as regulations or best practices by oil-producing countries around the world (pdf). For a level sensor without API 18.2 compliance, many oil and gas exploration applications are a no-go. Like the API 18.2 MPX-R and MPX-T before it, the MPXI-F meets the measurement accuracy requirements and provides the necessary the temperature reporting to be API 18.2 compliant.

The MPXI-F’s PVDF Stem is H2S Compatible

Many of the chemicals involved in oil and gas exploration do not "Play Well with Others," to put it mildly. But the toughest one to deal with might be hydrogen sulfide, or H2S. Hydrogen sulfide will eat stainless steel for breakfast and considers many plastics a lite snack. Knowing that hydrogen sulfide is an aggressive yet inescapable part of oil and gas exploration, APG created the particular blend of PVDF plastic used for the stem of the MPXI-F to withstand the nastiness that H2S can dish out. H2S may corrode many level measurement sensors, but it can't hurt the proprietary-PVDF-blend stem of the MPXI-F.

The MPXI-F’s PVDF Stem is Flexible

A PVDF-stem MPXI-F with curled stemNot only will the PVDF stem of the MPXI-F stand up to hydrogen sulfide, it bends and curls easily, simplifying and reducing the costs of shipping and installation. APG designed special shipping boxes that can hold two MPXI-F probes, each up to 25' long, or one MPXI-F probe up to 50' long. This means no more special, 50' boxes that require long flatbed trailers for delivery, and no cranes that have to be taller than the tank and probe together. That's a lot of cost savings.

MPXI-F is Designed For Remote Operation

Most lease tanks and other storage vessels associated with oil and gas exploration are in remote places where the supply of electrical power is limited. Whether these systems run on batteries, generators, or are dependent on solar cells, power consumption of every device is managed carefully so that critical equipment has enough power at all times. This is no place for a power-hungry level sensor. The MPXI-F has three key design features to maximize its utility in limited-power situations. First, it is designed for ultra-low power consumption. In an always-on scenario, both the 4-20 mA and Modbus outputs have been designed to be fully functional with the lowest power. Second, for power up-measurement-power down scenarios, the MPXI-F has a power up time of less than 5 seconds. That's a fully accurate, temperature-compensated measurement in less than 5 seconds, and at the low power consumption rate. Third, the MPXI-F PVDF-stem has an optional, independently wired, high-level switch. So even while the MPXI-F probe is powered down, the high-level switch can provide an overfill or overflow alarm.

The MPXI-F is Built For Your Success

From top to bottom and inside to out, the explosion proof, flexible stem MPXI-F is built for use in demanding environments of oil and gas exploration. It can handle the aggressive chemicals, carries world-wide hazardous location certifications, and reduces critical shipping, installation, and operational costs. Whether it's in lease tanks or any other oil storage tanks, the MPXI-F is built for success. Your success.

Have questions about how the MPXI-F can provide dependable, highly accurate, liquid level measurements to your operation? Give our Measurement Experts a call, send them an email, or live chat with them here on our website. They specialize in helping you get the right level and pressure measurement technology for your specific needs.

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top photo credit: Roy Luck via cc by 2.0 cropped, edited



What is a Pressure Transducer?


A pressure transducer is a type of sensor used to measure pressure and then convert that pressure reading into a continuous voltage output. Depending on where you put it and how you connect it, a pressure transducer can tell you the pressure in a pipe or tank, the weight of an object, or even the depth of fluid above it. Most industrial pressure transducers are made of two technical parts, a transducer and a transmitter, inside a third, equally important part, the housing.

APG's PT-L1 Industrial Pressure TransducerAPG's PT-500 Submersible Pressure TransducerAPG's PT-400 Heavy Duty Pressure Transducer


What is a transducer?


A transducer converts a physical action--often a vibration--into an electrical signal. Microphones and the pickups on an electric guitar, which both convert sound waves into electrical signals, are transducers. Pressure transducers, then, convert pressure--air pressure, fluid pressure, oil pressure, etc.--into electrical signals.


Types of Pressure Transducers



Piezoelectric Pressure Transducers


Piezoelectric pressure transducers or piezoelectric sensors are devices that use the piezoelectric effect to measure any changes in acceleration, pressure, strain, temperature or force. This type of pressure transducer sensor works by converting the energy they are measuring into an electric charge.

A notable characteristic of a piezoelectric pressure transducer sensor is when they flex. When this type of pressure transducer flexes, it produces a voltage. The voltage generated by a piezoelectric pressure transducer can even be used to power the “deflection detection” circuit (the circuit the transducer is a part of).


Piezoresistive Pressure Transducer


Piezoresistive pressure transducer sensors are one of the most common types of pressure transducer sensors. This kind of pressure transducer uses the change in electrical resistance of a material when that particular material is being stretched.

The main difference between piezoresistive and piezoelectric is that piezoresistive pressure transducers change the resistance of a circuit as they are flexed, whereas piezoelectric pressure transducers produce a voltage. Another big difference between piezoelectric and piezoresistive pressure transducers is that piezoresistive transducers need power supplied to them.

Wheatstone bridge circuit with shunt It's easy to mix the two up. A quick internet search will turn up plenty of conflicting uses and descriptions, sometimes even within a single site. Throw in more general terms, like "strain gauge," or specific configurations, such as "Wheatstone bridge," and it looks like chaos reigns. But remember, that's the internet. (Also, "Hello," from the internet!) Some careful consideration helps solve most confusion. (I did say _most_.) Strain gauge really is a more general term than either piezoelectric or piezoresistive, but is usually used as shorthand only for piezoresistive transducers. For example, some people use piezoelectric for piezoelectric transducers, and strain gauge for all others, including piezoresistive ones. A Wheatstone bridge is a specific configuration of the bridge electric circuit that is usually used on pressure transducers.


How Does A Pressure Transducer Work?


We touched on part of how a pressure transducer works above: an electrical circuit (usually a bridge) is attached to the backside of a diaphragm, a small piece of flexible material. As the pressure that the diaphragm is exposed to changes, the diaphragm flexes, changing the characteristics of the circuit. That's the transducing part of a pressure transducer. However, in order for the measurement to be of much use, it has to be transmitted somewhere: to a display, or a control system, etc. So a transmitter converts the measurement into a standardized signal--4-20 mA, Modbus, mV/V, etc.--and communicates it to whatever control or display system it is connected to.

There are some instances when it is advantageous to denote a pressure transducer as separate from a pressure transmitter, i.e., differentiating between the physical measurement and the electronic signal. In reality, neither can be used without the other. A pressure transducer sensor without a pressure transmitter generates a signal far too weak to be communicated to a controller, and a transmitter without a transducer has no message to communicate.

An integral part of how a pressure transducer works is how it is built to measure pressure. There are five main types of pressure measurement:

  1. Gauge Pressure: Reads “0” when measured pressure is equal to local atmospheric pressure (i.e., same pressure inside and outside the tank/vessel/pipe, etc.). Registers pressures higher than atmospheric pressure. The body of the transducer is vented to accommodate changing atmospheric pressure.
  2. Vacuum Pressure: Also reads “0” when measured pressure is equal to atmospheric pressure, but only registers when measured pressure is less than atmospheric (negative pressure). Vented.
  3. Compound Pressure (or Compound Gauge Pressure): Combines gauge and vacuum in a single sensor: Reads "0" when monitored pressure is equal to atmospheric pressure, registers both lower and higher pressures than atmospheric, and is vented.
  4. Sealed Pressure (or Sealed Gauge Pressure): Transducer body is sealed to protect the electronics from moisture, dust, or other environmental hazards. Because the body is sealed, the pressure measurement will reflect the changes in atmospheric pressure (i.e., a storm blowing in will cause readings to increase because atmospheric pressure is decreasing), so sealed pressure is generally reserved for high pressure measurements that are impervious to atmospheric pressure changes.
  5. Absolute Pressure: Transducer body is sealed under vacuum conditions (absolute 0 pressure). Used for relatively low pressure ranges so that atmospheric changes can be observed.


Pressure Transducer Type Reference


wheatstone bridge circuit

Some pressure transducers are used for single-point-pressure detection, i.e. as pressure switches. But most are used for continuous pressure readings, with the analog or digital output signal always indicating the current pressure reading. In fact, it's often easy to configure a control system for individual, pressure-based outputs, thus allowing a continuous output pressure transducer to generate single-point actions.


Choosing A Pressure Transducer


APG's PG7 - pressures transducer and display, all in oneWhat a pressure transducer is needed to measure, and where, and the required output will do most of the determining when choosing between pressure transducers. Is a local readout for the pressure reading all that's necessary? Then a pressure gauge--a transducer and display combined into a single unit--will do the job nicely. On the other hand, line pressure on fracking rigs can only be measured safely by pressure transducers with hammer union process connections. So, as we say quite frequently around here, the application will largely determine what kind of pressure transducer one chooses. Some of the questions that need to be answered to ensure a good technology fit are:

Application Questions

Environmental Questions

Output Questions

Pressure Transducer Applications


APG's Recalibratable Hammer Union Pressure TransducerThere are so many ways and places a pressure transducer can be used. Any kind of commercial or industrial system that uses pumps needs to be able to monitor line pressure before and after those pumps; pressure transducers can do that. Pressure transducer sensors can be used to monitor the weight applied by a hydraulic ram, or even a fighter jet! The output of a pressure transducer at the bottom of a liquid-containing-vessel can be used to calculate the level of the liquid above it. Thus, submersible pressure transducers can measure the level of water in a deep well, sewage at a lift station, or even refined diesel fuel in a storage tank. Need to make sure that a pressurized system has the appropriate pressure in multiple places? Pressure transducers are the way to go. From fracking rigs to industrial process systems to water system pressure relief valves, pressure transducers provide important pressure readings to keep people and equipment safe.


Best Practices for Pressure Transducers


Don't use tools to clean your transducer faceBest practices for pressure transducers are going to vary a bit, depending on what kind of pressure transducer is being used in what sort of environment. Pressure transducers built for light-duty applications (i.e., indoors, low vibration, low moisture and dust) are going to need different care than hammer union transducers in an oil field. That said, installing any threaded pressure transducer is fairly easy if you follow the right procedure. And while this video is specifically for cleaning submersible pressure transducers, we hope it's obvious that touching the diaphragm on any pressure transducer is just asking for trouble. In general, the Measurement Experts here at APG suggest the following:

If you have further questions about pressure transducers, including how a pressure transducer can help your system operate more safely, let us know. Our Measurement Experts can help you find the right technology to fit your application like a glove. Give them a call or drop them an email today.

Explore Pressure Transducers

Map showing the extent of drought in the continental United States as of 27 October 2020At the time of this writing, the American Intermountain/Southwest is in the grip of an extensive drought. 100% of the population of the Four-Corners states (Utah, Colorado, New Mexico, and Arizona) and Nevada are experiencing D1 or worse drought, which makes what little water there is that much more precious. And while use of the water in rivers, reservoirs, and aquifers is subject to highly negotiated rights, and the use of wells is dependent on the location of the wells, there is a source of water that is gaining in popularity, despite its irregularity: rainwater.

Rainwater Harvesting Restrictions in the U.S.

Catching, harvesting, or collecting rainwater is legal in all 50 states. Several states have adopted restrictions on how much rainwater can be collected (Colorado and Utah), where or what kind of water can be collected (Colorado, Idaho, Oregon, Texas), or how it can be used (Arkansas, California, Colorado [anyone else see a theme here?], Georgia, Kansas, Nevada, Ohio), as shown in this graphic. Colorado (pdf) and Utah (pdf) currently have the most stringent restrictions on rainwater collection and storage (maximum of 110 gallons total capacity; and maximum of two barrels up to 100 gallons each for unregistered catchment, maximum 2,500 gallons registered, respectively). The most common usage restrictions limit collected rainwater to non-potable or outdoor uses.

Rainwater Harvesting Apparatus

Opps. Too much rain for this tank.How, then, does one go about collecting rainwater? The most basic setup, it would seem, would be a bucket set under the eaves or downspout of one's dwelling. It certainly would be catching or harvesting rainwater. But storing? Not so much. So, rather than a bucket, upgrade to a barrel with a lid. Excellent! But what size barrel to get? A quick check with a precipitation history map will help determine what size barrel (or even cistern!) make the most sense for the yearly precipitation in one's area. But then how to get the water out? Gravity-fed spigot; pour spout on top (smaller barrels only); pump handle; fractional horsepower electric pump? All of these are feasible and available solutions. Again, determining which solution fits any specific situation depends the amount of precipitation and how much of that precipitation is intended to be stored and dispensed.

Collected Rainwater Level Indicators

The final question to be answered before purchasing a collection system is a variation of the one that will have to be answered continuously after installation: how will I know how much water is in the barrel? Some collection containers will come with float level indicators installed. But those only work when you are looking at them. If you want any kind of remote indication (i.e., a low- or high-level indicator light inside the dwelling where the collection system is installed), an electronic level indicator will be necessary. Simple float switches can provide 'Yes' or 'No' indications at specific levels, while more complicated float switches or combinations can indicate multiple levels. For the rare situations where a continuous level indication is needed on a rainwater collection system, an ultrasonic level sensor, submersible pressure transducer, or a pressure transducer mounted near the bottom of the tank on the outside can provide the necessary measurement.

Rainwater Harvesting: One Size Does Not Fit All

One of our favorite sayings here at APG applies to rainwater harvesting as much as it does to the rest of our level and pressure business: the application determines everything. There are no one-size-fits-all answers. Where one is looking to set up for rainwater harvesting will determine what, if any, permits or licenses are necessary, the ways that the collected water can be used, and how much water will be available to collect. Once the basics are settled, the fun begins: how many barrels are needed? What size barrels? What kind of feeding system from downspouts to the collection barrels makes the most sense? What kind of level indicators should be used? See? The fun questions!

If you have more questions about rainwater harvesting, check out the American Rainwater Catchment Systems Association. Their mission is "[t]o provide resources and information on rainwater and stormwater collection to promote the advancement of rainwater conservation and to work with government at all levels in promoting rainwater and stormwater management." In Canada, the Canadian Association for Rainwater Management performs much the same function.

If you have questions about level measurement, in rainwater or any other liquid or even some solids, our Measurement Experts can give you expert guidance, based on your particular application. We promise no 'pat answers.' You can call them, send them an email, or even live chat with them here on this page.


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top photo credit: The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. Map courtesy of NDMC. and NIDIS

bottom photo credit: Jan Smith via Creative Commons 2.0

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