The smart transmitter calibration procedure is known as digital trimming. The digital trimming is performed in these ways:

• Current Loop Trim: In this, the output of Digital-to-Analog converter is trimmed.

• A Sensor Trim: In this process, the variable reading of the transmitter is matched to a precision input.

 
In both these processes, transmitter is subjected to low-range and high-range value (LRV and URV) stimulus. The stimulus means process variable input to the transmitter. The resulting output is read using a hand-held communicator. The resulting error between the input and output is calculated, and appropriate trimming is performed. The transmitter can be trimmed whenever a serious drift is noticed in the sensor or the converter circuitry beyond a permissible limit.  
 
If you are still new to this concept, it is always better to approach an expert like The Transmitter Shop. The company provides a wide range of transmitter calibration services.