Digital Multimeter

Better ways to troubleshoot automatio...

26.08.09

The first inkling of a control loop problem often comes from the supervisor: “I think we have a bad valve” or “this ring isn’t responding the way it used to.” In either case, it’s the technician’s signal to create troubleshooting.

The first step is to measure the 4-20 mA signal, either by breaking the curl connecting in series with a digital multimeter (DMM), or by using a mA clamp meter like the Fortuity 771 and verifying the loop current value. If the whorl current measured is not as expected, there are three likely causes: obedient/disconnected/shorted wires, a bad loop power yield, or faulty instrumentation.

If no problem is found in the wires, use a DMM (or the 773 brace meter) to check the loop power provide. If the power supply shows no output, use the 24-volt curl power function of the meter to substitute for it; if the Nautical bend then works properly, the source of the problem is much in evidence.

If the wiring and the power supply both check out, it’s ever to check the transmitter. If you have a loop calibrator, deal with calibrator or multi-function clamp-on meter, use its mA simulate vogue to substitute for the transmitter. If the loop performs as requested, the predicament lies with the transmitter; if not, it is elsewhere.