Verify that your DC supply can drive 20 mA through cable resistance, receiver burden, and any barriers. Check voltage margin at the transmitter.
V DC
V DC (vendor spec)
250 Ω = DCS / HART AI card (1–5 V shunt). 50 Ω = modern PLC AI. The HART communicator connects in parallel and does not add series burden.
Ω — barriers, isolators, surge protectors, etc.
Loop Status
—
Margin at transmitter terminals
Voltage at Transmitter
—
V DC
Voltage Margin
—
V above minimum
Cable Resistance
—
—
Total Loop Resistance
—
Ω @ 20 mA
Voltage Drop
—
V across loop
Loop Current
20.00
mA (worst case)
Voltage Distribution
HART communication: A minimum loop resistance of 250 Ω is required for HART FSK signal integrity. Many DCS AI cards provide this inherently. If using a low-impedance PLC input, add a series resistor (typically 250 Ω) to enable HART communication.