32.What is zero check in the case of pressure and differential pressure transmitters?

In certain plants, it is practiced to check the transmitter zero between certain period.

Pressure transmitter and DP transmitters will be isolated from process. The drain will be opened for PTs. The equalizing valve will be opened for DPTs. The output shall be 4 mA. Otherwise the zero will be adjusted to get 4 mA..

This is similar to one point calibration for zero. The above is known as zero check