Simulated signals

I like NO DIs to be tested by shorting across the switch/contact in the field and NC DIs to be tested by lifting a lead at the switch/contact in the field. I like to use a process calibrator that can source an appropriate current, voltage, or resistance signal connected at the field instrument to test AIs. I test at the field device instead of at the PLC panel because that checks the wiring. For I/O checks during panel shop testing before the shop ships to the field, I always test from the location where the field wiring will terminate to include any interconnecting wiring within the panel.

I test DOs and AOs using forces in the PLC and observing operation of the actuated device and measuring the signal at the device. A meter with a clamp-on current sensor for 4-20 mA circuits is nice to have for current loops, and any DMM works for voltage sensing. I've also seen ice cube relays with the appropriate coil voltage used for DO checks and jumper wires with clamp-on current metering used for AO checks during factory panel testing as dummy loads.

xnuke
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