What procedure is done to check the zero and span of a dP cell?

To effectively check the zero and span of a differential pressure (dP) cell, various procedures are employed that involve manipulating pressure inputs and ensuring the device responds correctly.

Closing the high and low pressure tap block valves is a necessary step because it isolates the dP cell from the process, preventing any unintended influences from the system. This isolation allows for a controlled environment where the testing can be accurately performed.

Venting the low side to the atmosphere is also a crucial part of the procedure. By venting the low side, you establish a reference point for zero pressure, which is essential for confirming the zero reading of the dP cell. This allows you to ensure that the device is calibrated correctly when no pressure differential is present.

Connecting and applying a known calibration pressure to the high side is essential for checking the span of the dP cell. By applying a known pressure, you can determine how the dP cell responds and whether its output corresponds correctly to the input pressure. This step ensures that the device gives an accurate reading over its operational range.

Each of these actions plays a vital role in the overall calibration process, confirming the functionality and accuracy of the dP cell across its operational range. Therefore, incorporating all these steps represents a comprehensive procedure to