Differential pressure transmitters and pressure transmitters
Thread Content
I’ve seen that some level gauges use differential pressure transmitters, which measure the pressure of the liquid phase as well as that of the gas phase; while others have only one pressure sensing wire that is connected directly to the transmitter. What is the difference between these two types? After all, they are both differential pressure devices!
For differential pressure vessels, the key factor is whether they are sealed containers; if they are sealed, two pressure guide tubes are used to balance the static pressure above the liquid surface. If it is an open container, then it is in direct contact with the atmosphere, and a pressure guide tube is sufficient.
But with a pressure tapping tube, what you measure is the atmospheric pressure plus the pressure of the liquid column
The negative pressure side of the differential pressure transmitter is connected directly to the atmosphere, and the pressure of the liquid column is equal to the difference between the positive pressure side and the negative pressure side.
To measure the liquid level in a sealed container, a differential pressure transmitter is required; for an open-container, only a pressure transmitter is needed, with the height equal to pressure divided by density. With differential pressure transmitters, the nature of the medium also needs to be taken into account to determine whether calibration is necessary.
With one tube, you are measuring gauge pressure, while with two tubes, you are measuring the pressure of the medium
The situation described by the poster is as follows: 1. When measuring a sealed container, a differential pressure transmitter is used, with one sensor measuring the pressure in the liquid phase and another measuring the pressure in the gas phase. 2. For the measurement of open containers, there is only one pressure tapping tube; a pressure transmitter or a differential pressure transmitter can be used~~~
I’ve learned it.* Thank you! Who can introduce me to the knowledge of these instruments?