Process variable transmitter with two-wire process control loop diagnostics

A method of performing diagnostics in a two-wire process variable transmitter of an industrial process, comprising:

• coupling terminals of the two-wire process variable transmitter to a two-wire process control loop;
• sensing a process variable of a process fluid of the industrial process;
• providing an output on the two-wire process control loop which is related to the sensed process variable;
• coupling current measurement circuitry to the two-wire process control loop, the current measurement circuitry configured to measure a loop readback current flowing through the terminals of the two-wire process variable transmitter and a shunt current;
• coupling terminal voltage measurement circuitry to the terminals of the two-wire process variable transmitter, the terminal voltage measurement circuitry configured to measure a terminal voltage across the terminals of the two-wire process variable transmitter;
• and
• performing diagnostics on the two-wire process control loop, the diagnostics performed using the measured loop readback current, the measured shunt current, and the measured terminal voltage, the diagnostics including calculating a loop resistance based upon a difference in the measured terminal voltage measured with two different current levels flowing through the two-wire process control loop and a different in the measured loop readback current with the two different current levels flowing through the two-wire process control loop.