In modern process automation, over 80% of field instruments communicate via 4-20 mA current loops. Multi-function process calibrators are essential for validating sensors, transmitters, and DCS/PLC analog input cards.

1. 4-20 mA Loop Sourcing vs. Simulating vs. Measuring

Understanding the distinction between loop modes prevents blown fuses and device damage:

  • Source Mode: The calibrator powers the loop (delivering 24V DC) and regulates the 4-20 mA current.
  • Simulate Mode: The calibrator modulates current within an externally powered loop.
  • Measure Mode: The calibrator acts as a precision multi-meter measuring loop current.

2. Calibrating Temperature Transmitters

When calibrating a 2-wire temperature transmitter, use a multi-channel calibrator like the DB Thermet Series to simulate the sensor signal (RTD PT100 or TC Type K) on the input while simultaneously measuring the 4-20 mA loop current output. Perform 5-point calibration (0%, 25%, 50%, 75%, 100% span) to verify linearity and span accuracy.