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
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 Mesh Networks
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.
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