Basics of Smart Pressure Transmitter Calibration:

Calibration is the process of optimizing transmitter accuracy over a specific range by adjusting the factory sensor characterization curve located in the microprocessor. Calibrating a smart transmitter is different from calibrating an analog transmitter. The one-step calibration process of an analog transmitter is done in several steps with a smart transmitter. These calibration steps involved are:

(a) Re-ranging - Re-ranging involves setting the lower and upper range points (4 and 20 mA) points at required pressures. Re-ranging does not change the factory sensor characterization curve.

(b) Analog Output Trim - This process adjusts the transmitter’s analog  characterization curve to match the plant standard of the control loop.

(c) Sensor Trim - This process adjusts the position of the factory characterization curve to optimize the transmitter performance over a specified pressure range or to adjust for mounting effects. Trimming has two steps, zero and sensor trims.

Factory Characterization Curve of Pressure Transmitter.

The characterization of a smart transmitter allows for permanent storage of reference information. In the factory setup, known pressures are applied and the transmitter stores information about these pressures and how the pressure sensor reacts to these pressure changes. This creates a transfer function of applied pressures versus output shown below:

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