If tank level measurement is crucial to your business, sooner or later you may need to monitor tank level activity at a remote location. This will require two pieces of technology: a sensor to do the monitoring, and communication equipment to give you remote access to the sensor data.
For many remote monitoring situations, fully wired scenarios are difficult or impractical at best. Cellular modems, wireless mesh networks, and wireless serial radios are popular technology choices for transmitting data where cabling is physically impossible or cost prohibitive.
Let’s look at how each one works.
Serial wireless adapter radios are great for simple tank level applications. As the name indicates, serial wireless radios use serial communication (often, but not exclusively, RS232) over radio frequencies. The radios are generally transceivers, capable of both transmitting and receiving communication, and depending on configuration, can either operate as one-to-one or many-to-one.
The challenges are relatively simple: your sensor needs to have an output compatible with the radios (4-20 mA or RS485 usually work, 0-5 VDC in some cases), your control network needs to be compatible with the radios, and you need to be able to power remote radios and the sensors connected to them.
A serial adapter located near a sensor on a tank can be line powered, or, if no power is at the tank site, a battery that can be charged by a solar panel will work fine. The second serial adapter near the computer/control system can be powered by the USB connector or by an external AC adapter.
Set up of the wireless serial adapters is easy and takes only a few minutes. When the installation is complete, the liquid level measurement data from the tank(s) can be transmitted 3 miles or more (depending on the frequency of the radios) line of sight to the office computer.
Wireless Ethernet routers work well for multi-device networks, as many homes, offices, and public spaces demonstrate. However, a tank level network using wireless Ethernet routers (e.g., multiple routers, each with multiple tanks/sensors connected) would require each sensor to be wireless Ethernet compatible, which can be expensive.
A Mesh Network can be a cost effective method to transmit tank data from several tanks using only one wired internet access point. While the tank network is wireless, only the internet gateway node needs to be TCP/IP compatible, allowing you to choose wireless technologies that make the most sense for the size and scope of your tank monitoring operations. This separation of communication technologies allows many Mesh Radio Nodes to communicate over a larger area without all the pieces being tied to wireless Ethernet adapters.
There are two ways to structure a mesh network: unstructured (omni-directional) and structured. Unstructured mesh networks are just that: unstructured. Each node is allowed to communicate with any other node, with no particular hierarchy or transmission order. Structured mesh networks, on the other hand, have specified connections between nodes, establishing specific communication paths.
Each tank in your network would have one wireless node radio that sends and receives information via the wireless mesh network. Depending on the mesh configuration, the data travels from the sensor node to the node that serves as the Ethernet gateway. This would in turn allow all tank data to be transmitted via Internet for display and monitoring.
This, then, is the difference between wireless serial radios and mesh networks: whether one to one, or many to one, wireless serial radio networks are governed by the one transceiver. Each and every sensor transceiver communicates only with the one transceiver connected to the control system. In a mesh network, even if there is only one Ethernet or control network connection point, communication can, and generally will, pass through multiple nodes between a sensor and the network connection point.
Mesh network nodes are available with many ranges. Basic models can have ranges of 1-2 miles between nodes and the internet gateway. They are easy to install and uninstall thus making a tank network more adaptable to changes in coverage in its network connection.
Cellular technology is common in Supervisory Control and Data Acquisition (SCADA) applications. The key device in this technology is a cellular modem. Cellular modems can be used for data communication and for text messaging, which allows for sending alarm messages directly to cell phones.
Setting up a cellular modem is a fairly straight forward process. Cellular modems use the same networks that cell phones use, so you will need a SIM card for the network you plan to use. Programming is done with included software.
There are two types of cellular modems: isolated cellular modems are separate component from the sensor, while embedded cellular modems are integrated into the sensor.
Tank level sensors with embedded cellular modems are generally very expensive because of the licensing approvals needed to manufacture and to keep them in service year after year. Also, each sensor needs its own SIM card, which means cellular reception would be at the mercy of exactly where each sensor is mounted.
Isolated cellular modems can be mounted away from the tank level sensor in order to receive the best cellular reception. An isolated cellular modem allows you to use the sensor you really want and need for your application. A single isolated cellular modem can also be used with multiple sensors which is a great money is saving advantage.
As technology evolves, effective, cost-saving wireless solutions for tank level monitoring applications are available which can replace cabled networks, both existing and new construction, no matter how many tanks you are monitoring or how remote they are.
Have questions about remote tank monitoring, or wireless technology, or both? Give our Measurement Experts a call, or drop them a line. They would love to help you find the solution that fits your needs.
The best maintenance for mission-critical equipment is preventative maintenance. You know what needs to be done, when it needs to be done, and there’s no emergency scrambling. The necessary system downtime pays for itself in on-going system reliability.
But hands down, the best preventative maintenance isn’t done during scheduled down time, or any time after installation. It’s done when you buy your equipment.
Getting the best match between your equipment and your application is, without a doubt, the best preventative maintenance you can do. It works for motors, drives, and pumps, and it works sensors and switches, too.
Float switches for water tanks are no exception. Yes, “float switches for water tanks” does sound like one of the most straight-forward application scenarios out there. If you allow yourself to cut corners when choosing the easy stuff, it’s easier to miss the details necessary for getting the more difficult applications right. So let’s walk through the application questions for float switch connections on water tanks, looking particularly at APG’s FL series of float switches. We’ll look at three criteria:
Most stem-mounted float switches use a magnetic reed switch to open or close an electrical circuit. A reed switch consists of two ferromagnetic contact tips (reeds) encased in a glass tube which is secured on a plastic, brass or stainless steel stem with epoxy. A permanent magnet in the float is the most common means of actuating a reed switch on a stem-mounted float switch.
Float switches are usually built to operate as Normally Open or Normally Closed switches. (Other possibilities include SPDT switches, but that is more common for cable suspended, rather stem-mounted, switches.) The float of a normally open switch rises with the liquid level toward the reed switch, and the permanent magnet actuates the switch contacts, closing the electrical circuit. When the liquid and float descend, the reed switch contacts will open again, de-energizing the electrical circuit. This is a common configuration for a High Level alarm.
For a normally closed float switch connection, it’s just the opposite. When the float falls toward the reed switch, the switch contacts will close the electrical circuit. When the float rises with the liquid, the reed switch contacts will open de-energizing the electrical circuit. This is an ideal set up for a Low Level alarm.
Dealing with tough or harsh environments is a basic piece of many instrumentation applications. While they may not pertain to the water in your water tank, some of these may apply to the environment around your tank. So it’s better to be in the habit of asking these environmental questions than to hope you remember to ask them when your application does call for them.
So, consider the following float switch environment factors:
The two main physical factors to consider in selecting a float switch are mounting options and float specifications.
The float switch you choose must be mountable on your water tank. Some the most common mounting options are:
Note: If the only mounting option available is near an inlet, or surface wave action is an anticipated source of erroneous switching, a stilling tube or time-delay relay are highly recommended for providing physical or electronic (respectively) error control.
To optimize float sensor accuracy, it is important to know the specific gravity of the liquid (across all temperature ranges) to be measured, and choose a float with a specific gravity that is less than that of the liquid. A float with a specific gravity equal to the liquid it sits in won’t necessarily float on top of the liquid, and a float with a greater specific gravity will sink in the liquid.
Also be aware that any sand or sediment within the measurement environment (i.e, your water tank) can eventually collect on top of the float, causing the float to sink. If such sediment could be an issue in your environment, the sloped sides of a spherical float will allow the sediment to slide off, preventing buildup.
Each FL series of float switch can be fitted with one of two sets of float types. The floats are spherical or cylindrical in shape, are made from stainless steel, and are 1 to 2 inches in diameter.
Do I want a Normally Open (High Level Alarm) switch or a Normally Closed (Low Level Alarm) switch?
Are there NEMA or IP ratings necessary for protecting the circuitry of my switch? Does my switch need hazardous location approvals to prevent incendiary or explosive accidents?
How will the switch be mounted to the tank or vessel? Is the specific gravity of the float(s) less than the specific gravity of the liquid being monitored?
Answering the questions we’ve looked at will help ensure years of reliable service for your FL level switch. Knowing the performance you expect from your instrument, based on the physical environment it will be functioning in, before you purchase and install it, puts you in position to get the best match of instrument capabilities to application demands.
One last important (post-installation) recommendation for your stem-mounted switch’s health: un-install your FL float switch every so often (yearly at least, more often if necessary) and give it a good cleaning. This will extend the life of your probe.
Still have questions? Drop our Measurement Experts a line today. They would love to help you get the most out of every switch, gauge, sensor, and transducer you use.
Controlling pumps with your standard cable suspended float switch is honestly a pain in the neck. You’ll need at least two of them to get the job done, with a controller that handles all the logic. You have to tie them to some conduit to keep them from getting tangled. And the failure rate isn’t that great either.
Most maintenance technicians expect them to fail two or three years into service.
That’s why the Kari Float Switch is so awesome. It can have up to four switch points in a single float, built-in hysteresis to handle the logic, and doesn’t need to be secured to conduit since you usually only need one.
And they last a very long time. Some Kari Float Switches have been in service for over 20 years.
They’re also easy to use. A simple weight acts as the anchor point and can be adjusted to lengthen the distance between switch points. There’s not a lot more to it than that.
However, there are some nuances that are good to know about and will help you get the job done faster. Here are step by step instructions for float switch installation– for empty control and for fill control.
Let’s assume you have a KA-3H. This model has built-in hysteresis to control the emptying of a well or tank, with a high alarm – all in one float.
You should start with the lowest point because you never want the level to go below the required Net Positive Suction Head (NPSH) for your pump. Essentially, the NPSH is the suction pressure your pumps need to avoid cavitation and other problems.
In tanks and wells, liquid level equals pressure, so find that level and make sure you don’t go below it – for your pump’s sake.
Hint: Call us about NPSH if you have questions. We can help you calculate how much liquid level you’ll need to satisfy your pump’s requirements.
Float switch installation requires you to mount the device with some way of fixing the cable above the tank or well. There is a mounting bracket available for the Kari Float Switch that uses a snug wedge to fix the cable into place. This bracket can be attached to a wall or a rail using a simple bolt or screw.
The lowest allowable point is a good place to hang the bottom of your float when it’s vertical. We’ll refer to this point as ground zero. From here, the lowest switch for the KA-3H model will activate 9 inches above ground zero. This will happen at the “low” level.
If you choose a model with a low alarm (at the “low low” level), this switch point will activate at 5 inches above ground zero. The next lowest point (the “low” level) would activate at 9 inches above ground zero, or 4 inches above the low alarm.
The weight position determines how much space there is between the two higher points. The KA-3H, for example, uses both of these switch points to activate the pump at the “high” level and to activate a high alarm at the “high high” level.
The space between the “low” level and the “high” level is called the switching differential. Standard Kari switch points have a minimum differential of 10 inches, and maximum of 50 inches.
Moving the weight up and down on the cable will affect both the distance between the two high switches and the switching differential.
To give you a quick idea, the bottom of the weight will be about 6 inches or so from the bottom of the float, or ground zero, when the switching differential is 10 inches. At this weight position, the space between the two high switch points will be about 4 inches.
By contrast, the weight must be 35 inches from ground zero to get the maximum 50-inch switching differential. That would result in about 8 inches between the “high” and “high high” levels.
Once you’ve figured out the weight position and your switching levels, you’ll need to install float switch wiring to your waterproof enclosure. Make sure you seal the cable entrance with a cable gland.
For wiring instructions, refer to the user manual, or our new float switch wiring guide.
Each Kari Float Switch model will have a different number of conductors that need to be wired into different places. Typically, they share a common wire to complete the circuit. However, some of the models have isolated switch points that you can wire to a lower voltage alarm circuit, for example.
You’ll follow the same basic steps you did for empty control, but you have to reverse the way you determine your levels. Let’s use a KA-4L5E, which will control duplex pumps with a low alarm. It also has built-in hysteresis to control the on/off logic.
You need to prevent over-filling your tank, so start by choosing when you want the pump to turn off. For the KA-4L5E, this is the “high high” level.
The position of the weight will determine the distance of your highest point from ground zero, or the position of the bottom of the Kari Float Switch when it is hanging vertically.
So we’ll adjust our weight first, using the same method we learned in Step 3 for Empty Control. You’ll have to think backwards though:
How much space do you want between the switch points? How far does this push the float down?
Once you have figured out your switch points, use a clip or a mounting bracket to secure the cable above the well or tank, with the bottom of the float hanging at the exact position needed (ground zero).
Depending on your Kari model, wire up the cable to the appropriate terminals in your control panel box. Refer to our float switch wiring guide as mentioned above for additional help.
You won’t need to worry about hanging multiple float switches in the same well or tank, or about tying everything down so it doesn’t tangle. You can even skip the controller in backup pump control applications because of the built-in hysteresis.
There is nothing else like it on the market. Let us know how we can help with your float switch installation or selecting the correct device.
