Differential pressure transmitters measure the difference in pressure between two different environments. Two level transmitters are connected to two columns and are used to measure the pressure of one column with respect to the other column. For example, the pressure from one water column will be subtracted from the pressure of the other water column to measure the differential pressure. An important step in using these instruments is calibration, as an improperly calibrated differential pressure transmitter will not provide accurate measurements. Calibrating this device can be done in a few short steps.

- Skill level:
- Moderate

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## Instructions

- 1
Fill two columns of the pressure transmitter with liquid. Both columns will be connected and will have a level transmitter located on the column.

- 2
Calibrate the level transmitters by setting one column to be at 0 per cent level--that is, the level of the liquid is even with the level transmitter, so the transmitter measures 0 per cent pressure--and one column to be at 100 per cent. The choice of level for this column is arbitrary as the transmitter only measures the change of one column relative to the other. However, choose a round number, such as 1,000 millimetres of water column (mmWC).

- 3
Multiply the liquid height by the specific gravity of the liquid and recalibrate the transmitter to the new liquid column height to measure the pressure in one of the specific columns. For example, if a liquid has a specific gravity of 1.2, then multiplying this number by the water column height (1,000 mmWC) gives 1,200 mmWC. Therefore, the level transmitter must be recalibrated to 1,200 mmWC. The differential pressure transmitter should now be ready to take measurements.