2-Wire vs 4-Wire Transmitter Loop Power & Troubleshooting Ground Loops in Industrial Plants

Ground loops and insufficient loop power supply voltage cause mysterious reading offsets in DCS and SCADA monitoring networks.

1. Calculating Maximum Loop Impedance

R_max = (V_supply - V_min_transmitter) / 0.022 A. Ensure the 24V DC internal supply of the DB Thermet Series provides adequate compliance voltage across 250-ohm HART dropping resistors.

2. Identifying Earth Ground Faults

Measure mA current at the field transmitter and compare against control room analog input card readings. A deviation indicates leakage current to earth.