AThe most common cause for a process monitor not responding to changes in the loop current occurrs when a single-ended transmitter is driving two single-ended input process monitors. The second process monitor's grounded negative (-) input effectively shunts the transmitter's output current around the first monitor, that is, no loop current passes through the DMS-30PC-4/20s-24RL's input circuit. The solution is to either power the second process monitor from an isolated dc power supply or use one of DATEL's "-I" isolated-power process monitors.