A variable that must be taken into account for using a pressure transmitter to measure level within a tank is whether the tank is sealed or open/vented. Depending on what gas occupies the space above the water level within the tank, extra pressure may be exerted by whatever gas occupies that space (which is common in any sealed tank).
Any extra pressure created within that head space exerts additional pressure on the liquid below and also increases the total pressure on the pressure sensor. If that pressure is subject to change, based on environmental conditions, then using another level reading technology type is advisable.
If a pressure sensor method is really desired, a bypass/capillary tube can be installed on the outside of the tank. The high side of the bypass tube must be high enough that it is always exposed to the “empty” head space and not any liquid. The lower end should be installed at the lowest point of measurement possible.
The pressure sensor in this instance must be a differential pressure sensor, like our PAD Differential Pressure Transmitter, that will measure the pressure difference between the head space area and the pressure at the bottom of the tank where liquid is exerting pressure. To use this type of system, environmental conditions should not vary much in temperature because that could throw off the readings. You must also make sure that the differential pressure transmitter can withstand any environmental challenges like exposure to elements if outside the tank.
Vented or open tanks generally are not subject to any additional pressure besides the liquid and using a pressure transmitter is a good choice for many applications where the tank allows for exposure to normal atmospheric pressure.