How to Measure the Pressure in the underground cooling water pipeline by using Pressure Transmitter? what about the tapping position?
If the transmitter is not directly mounted on the underground pipe, which is not unusual unless there is vault access, then an impulse tube/pipe has to come up out of the ground.
The pressure measurement will be in error, low, by the difference in elevation between the pipe’s elevation and the pressure transmitter’s elevation.
Suppose the pipe is 2.1m below the grade level and the pressure transmitter is 1.6m above grade. The elevation difference is 3.7m. The measurement is 3.7m or 0.362 bar low. It is not unusual to have water supplied at a pressure between at 4-8 bar.
At 4 bar pressure, an error of 0.36m water column is a 9% error, a very large value for an instrument capable of 0.25% or better accuracy.
The commissioning of the unit should include the appropriate zero correction to compensate for such a large error.
Credits: Carl Ellis