Differential Pressure Transmitter Calibration

A differential pressure transmitter compares a high pressure value to a low pressure value.

Input and Output Measurement Standards

The differential pressure transmitter can be calibrated with a low pressure calibrator. A low pressure calibrator contains a regulator to adjust pressure output values to the transmitter, and a digital precision gage that can measure the calibrator output to the instrument under test. The output circuit for the calibration includes a milliammeter to monitor the output signal and a 24 VDC power source.

Connections

Connect the pressure source from the calibrator to the high pressure port on the transmitter. The transmitter low pressure port is vented to atmosphere. This allows differential pressure to be read directly without any calculations. The transmitter output is connected in a series circuit.

Five Point Check

Start the calibration with a five point upscale and downscale check. After you have collected the data, evaluate the readings to determine the instrument accuracy.

Accuracy of the Instrument

Correct the zero shift first by adjusting the input to 10% of the transmitter range. To correct the span error, first raise the input to 90% of the instrument’s span. Then adjust the span until the appropriate milliamp output is indicated.

Zero should be checked again after making a span adjustment because span and zero may interact. Continue rechecking and adjusting zero and span until the transmitter is calibrated within specifications…

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