Regarding differential pressure transmitters
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In the field installation of differential pressure transmitters, pressure tubes for positive and negative pressures are generally used. Is there any type of differential pressure transmitter that uses only a pressure tube on the positive pressure side, with no pressure tube on the negative pressure side, allowing that side to be directly connected to the atmosphere?
Yes, micro-pressure measurements, which involve very low pressures, are installed in this way, for example for measuring the pressure in boiler furnaces or the liquid level in open containers.
The negative pressure side is connected to the atmosphere, so it measures absolute pressure. Both gauge pressure transmitters and differential pressure transmitters can be used.
It is used in many situations, especially when measuring micro-pressure; since the range of conventional pressure transmitters is not small enough, differential pressure transmitters have to be used.
As long as the reference pressure is the atmospheric pressure, the device to be measured can be connected to either the high-pressure side or the low-pressure side, with the other side being directly connected to the atmosphere. There are many such occasions.
Connecting to the atmosphere isn’t very accurate; we usually use a gas seal tank.