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M91 2T1 output problem

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i am using this PLC in my hydraulic machine since the last 3-4 yrs.

recently, since the last 8-10 days i m facing this problem that one particular output doesnt fire at times ( machine is in a closed loop system)

i changed the relay that fires the hydraulic solenoid, SMPS that fires hydraulic solenoid, solenoid valve but cant figure out the problem.

can somebody advise me whether there is a problem with the PLC ?

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You did not give very much inoformation, but given what you said it is probably not a programing or processor problem of the PLC. If the relay is question fires correctly sometimes and not other times then I would be suspecting wiring has come loose somewhere in the system or a solder joint or connector has developed a vibration related failure (check that all terminals and wires are tight throughout the entire panel). There is a lot that can happen over several years. It is also possible that over time there has been a solder joint inside the PLC that has developed a crack and would cause an intermittend firing of the relay, if so you will have to go inside the PLC and re-solder the connections (check them all under a magnifying glass). If you are unable to check this or perform the re-solder of affected connections then you possibly would need to install a replacement PLC.


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  • MVP 2023

It is very possible that the contacts of the PLC's relay have become pitted and intermittent, especially if you have an inductive load such as a solenoid connected without an RC snubber across it to absorb the electrical spike that is created when the solenoid is released. If you have a spare output try changing your program to use it and move the wire to the solenoid.

Joe T.

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