Process control loop current verification

A method in a process device for verifying loop current in a two wire process control loop comprising:

• sensing a process variable;
• changing a digital measured value from a first value to a second value as a function of the sensed process variable;
• converting the digital measured value to an analog measured value using a first low pass filter;
• adjusting a loop current in the two wire process control loop as a function of the analog measured value wherein the first low pass filter introduces a first error in loop current in response to a step change in the sensed process variable;
• sensing the loop current in the two wire process control loop;
• converting the sensed loop current to a measured loop current value using a second low pass filter wherein the second low pass filter introduces a second error in the measured loop current value in response to the step change in the sensed process variable;
• compensating for the first and second errors based upon the measured loop current value and properties of the first and second low pass filters and generating for the first and second errors;
• and
• generating a diagnostic signal based on a comparison of the approximated loop current value to the measured loop current value.