For level measurement, most of the use of level transmitters, but the types of level transmitters are also diverse, today we will understand together what is the difference between the choice of level measurement instruments in open containers and closed containers.

In the selection of liquid level measuring instruments, it is necessary to first confirm whether the site used is open or closed, and different forms of on-site working conditions are completely different for the selection of instrumentation.

The level measuring instrument generally used in open containers is a submersible level transmitter. The working principle of the submersible level transmitter is that when the level transmitter is put into a certain depth in the measured liquid, the pressure of the measured medium is introduced into the positive pressure cavity of the sensor, and the atmospheric pressure Po on the liquid level is connected to the negative pressure cavity of the sensor through the cable air tube to offset the Po on the front of the sensor, so that the sensor measures the pressure as: ρgh, obviously, by measuring the pressure P, the level depth can be obtained. Submersible level transmitters are generally used in drinking water systems, water level overflow weirs, pumping stations, water treatment plants, water circulation and other working conditions. The submersible level transmitter adopts a cable connection, which can be directly put into the field for use, and is easy to install.

The figure below shows the level measurement of solar return water in the water circulation system of the submersible level transmitter.

Closed vessels generally use differential pressure transmitters to measure liquid level. For closed containers, containers containing liquids often work under pressure. In this case, the level height needs to be reflected by the gauge signal. In general, the density and gravitational acceleration of the measured medium are known, so the differential pressure measured by the differential pressure transmitter is proportional to the height H of the liquid, which turns the problem of measuring the height of the liquid into the problem of measuring the differential pressure. In the pharmaceutical, food and chemical industries, differential pressure transmitters are commonly used for liquid level measurement.

The figure below shows the level measurement of the medium in a closed container by a differential pressure transmitter in the chemical industry.

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