Calibration of a DP cell

DP stands for? ... yes, Differential Pressure! Think about it.

Yes, If you are troubleshooting one, maybe there is a screen filter on the low side protecting the instrument from dirt, and it could be dirty, making your measurment reading off. So to testing the low side, this is what you would look for.

You would apply calibration pressure to the L side anytime you felt the urge to apply vacuum to the H side, as in a dp level system with a wet reference leg. Sometimes this pressure is notated as a negative dp.

It depends. If you are referring to a differential pressure cell, the higher pessure should be applied to the H-pressure side. If the pressure you are measuring is below atmosphere, you apply it to the L-press side. If you are talking about a dew-point cell, the sample gas inlet will be on the H-Pressure side. If you are referring to a dope-pipe, always suck on the L-pressure side.

The Low pressure side of any differential pressure measuring device is simply your reference pressure. For instants, if you evacuate the low side to as good of a vacuum as you can get, you have turned your differential measuring device into a barometer measuring absolute pressure (vacuum reference). On the other hand you may have a pressurized tank and want to know the difference between the pressure at the top and bottom of the tank (tank level). The reference pressure is the tank pressure. Usually instruments will not shift with reference pressures other than atmosphere, but for the most precise calibration, I would use the reference pressure you anticipate during use.

Slightly disagree- if you hold a reference pressure during calibration, now you have the instrument error of your second gauge potentially causing calibration error.

Example: it would be extremely difficult to hold 1000 psi on the LP and vary the HP from 1000 psi + 30" water column for a 0-30 " dp instrument.

If static pressure is a concern, you can perform your calibration with a single gauge and the other port vented. At the conclusion of the calibration, then apply your static pressure of concern simultaneously to the HP and LP ports. The transmitter should not drift off of zero dp indication. Some older Rosemount 115x transmitters were notorious for this years ago, and even had prescribed a static zero/span shift procedure due to this issue.