The speed of a production line dropped considerably. The responding maintenance technician is an electronics guy. He checked everything in the programmable logic controller (PLC), and found no problems. All settings match the spec sheet, and the system isn’t showing any errors. Using a digital multimeter (DMM), he verified the desired 11.8mA on the output module terminals. Just as a test, he raised the setting on the line speed and the line was able to get up to the desired speed. He then put the setting back where it was and called you. The production supervisor wants to know why the line is back to running slowly.
What are your first steps in solving this problem?
It was good to check the PLC, but the technician erred in using up production time doing that. The PLC is rarely the problem in a PLC-controlled system. He should have contacted you first, and then checked the PLC in parallel with your troubleshooting.
First, listen to the gearbox. One technique is to put your largest screwdriver against the case with the handle to your ear. If you hear anything other than smooth gear meshing, contact the mechanics right away. Then turn to the motor supply; take voltage and current measurements. Use a vibration tester at the motor. Based on the “As Found” data you just collected, you know which path to go down next.
