For the measurement of liquid level, most of the liquid level transmitters are used, but the types of liquid level transmitters are also diverse, today we will learn about the difference between the choice of liquid level measuring instruments in open containers and closed containers. In the selection of liquid level measuring instruments, it is necessary to confirm whether the site is open or closed, and different forms of field conditions are completely different for the selection of instruments and meters. The level measuring instrument generally used in open containers is a submersible level transmitter. The working principle of the submersible liquid level transmitter is that when the liquid 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 surface is connected with the negative pressure cavity of the sensor through the cable air guide pipe to offset the Po on the front of the sensor, so that the pressure measured by the sensor is: ρgh, obviously, the liquid level depth can be obtained by measuring the pressure P. Submersible level transmitters are generally used in drinking water systems, water level overflow weirs, pumping stations, water treatment plants, water circulation and other working environments. The submersible level transmitter is cabled and can be used directly in the field for easy installation. The figure below shows the level measurement of the solar return water of the submersible level transmitter in the water circulation system.

Closed containers are generally used to measure the liquid level using differential pressure transmitters. In the case of closed containers, the container containing the liquid often works under pressure. In this case, it is necessary to reflect the level of the liquid by means of a gauge pressure signal. In general, the density and gravitational acceleration of the medium to be measured are known, so the differential pressure measured by the differential pressure transmitter is proportional to the height H of the liquid, thus turning the problem of measuring the height of the liquid into a problem of measuring the differential pressure. Differential pressure transmitters are commonly used in the pharmaceutical, food, and chemical industries for level measurement. The figure below shows the differential pressure transmitter measuring the liquid level of the medium in a closed container in the chemical industry.

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