Industrial Tank Level Monitoring

The monitoring is required for two purposes. One purpose is to make sure the liquid does not run out / the tank does not run dry. Another purpose is to ensure the liquid is being drawn from the tank in line with the expected usage, which is another indicator that the process using the liquid is operating correctly, and is a derived measure of the flow from the tank.

Application Detail

For this application, it would be appropriate to use a pressure sensor, and use the pressure from that sensor to determine the level in the tank. The sensor would be most likely strain gauge technology, sometimes called a hydrostatic sensor.

These sensors can be either vented or non-vented. Vented sensors have one side of the sensor exposed to the liquid being measured and the other side of the sensor open to the air, either directly exposed, or exposed by using a small vent tube inside the cable with a vent to the atmosphere at the termination end of the cable. Non vented sensors need a barometric pressure sensor at the location of the measurement to provide the current atmospheric pressure, which is then used in a calculation to compensate / normalize the pressure reading based on the current atmospheric pressure at that location and at that time.

The casing for such sensors can be either stainless steel or titanium. Titanium is chosen for more corrosive environments. The output of such sensors is usually either 0 to 5 volts or 4 – 20 mA however there are some with SDI 12 or Modbus interfaces.

The diagram shows two methods of connecting the sensor. The first method is to immerse the sensor in the liquid and the cable exits from the top of the tank. The second method is to add a T piece to the output pipe, and the pressure sensor then is attached to that T piece to measure the pressure exhibited at the T piece and this pressure is directly related to the level in the tank.

Some form of communication is required for the telemetry function, either cell phone or satellite. For areas covered by cell phone, this is the most economical choice, and the Neon field units which use cell phone technology is appropriate, either the Neon Metering Module or the Neon Remote Terminal.

If there is no cell phone coverage the Neon Remote Terminal Satellite is another option. As this is a low volume application a small low earth orbit satellite service is sufficient, or perhaps the Neon Remote Terminal Lite which uses the regional beam of the Inmarsat equatorial satellite service could be chosen.