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  • P2-HSI Counting Issues

    I have a P2000 PLC controlling 5 conveyors operated by drives. Each of the conveyors has a quadrature shaft encoder on the conveyor which I am hoping to use for keeping the conveyors in sequence. The problem I have is that if I run anyone of the motors all the counters change in value. To help fault find I removed all the field wiring from the cards and then run one of the motors. They stayed at zero which seem to indicate an issue with the wiring picking up noise. However after a few minutes one of the counters jumped to a very large number, 536870912, while all the other counters stayed at zero. Reset the counters a few times and only one of them changes to that number. If I wait a few more minutes that number will double, 1073741824, and then it doubles again to 2147483647. It has now appeared to stop increasing and all my other cards are still at zero. Have I got a wiring issue or a software issue or a hardware issue?

  • #2
    Show picture of how you got the system wired. What drives?

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    • #3
      Just to confirm, you are using a separate inpuit channel for each quadrature encoder right? Which should mean you have 3 HSI cards for the 5 encoders?

      Since this should mean you have a spare channel open, could you try switching the wiring from the "bad channel" onto the spare and see if the behavior is the same?

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      • #4
        What I have just done is set the spare channel with some parameters for Count, Velocity and Reset. Since doing that all the counters keep their zero value. This has run for an hour with no issues. Rewired the encoders back into the 5 channels and now they are all counting again. Will order some new cable for the encoders as this is an old panel which is being upgraded to the new PLC.

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        • #5
          Originally posted by robertkeenan View Post
          What I have just done is set the spare channel with some parameters for Count, Velocity and Reset. Since doing that all the counters keep their zero value. This has run for an hour with no issues. Rewired the encoders back into the 5 channels and now they are all counting again. Will order some new cable for the encoders as this is an old panel which is being upgraded to the new PLC.
          Was the channel that was acting funny on the same module as the spare that wasnt set up for anything before?

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          • #6
            The funny channel is on a different card from the spare one. Should unused channels be connected to ground.

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            • #7
              I dont think so. I have never connected them to ground before.

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              • #8
                I have now found some good screened cable and wired up the first two encoders on card one. They appear to be working and counting proper values. Still concerned about why the other encoder positions which have no field wires in them yet are still counting. Maybe once I get more cable and wire them up this problem will be fixed but in the future how will I know it is a count and not a random number.

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                • #9
                  Eventually the cable arrived and I now have wired up all 5 encoders with screened encoder cable and it is earthed at the encoder end. When I run one of the motors all the other encoders will produce random counts. It is most noticeable when the motor is stopped. The counting will accelerate while the drive is slowing down and produce some extremely large numbers. The PLC is controlling the drives over the network so it does not have any direct connection to the drive. The drives are at least a meter from the PLC and the cabling is going out on different sides of the panel. I am starting to think that these P2-HSI cards are very sensitive to noise and was thinking of wiring the encoders to ordinary PLC inputs. This will give me a counter but I might have to live with the fact that it is not a directional counter. Has anyone written a bit of ladder logic which would allow the encoders to count along with being directional. The speed it counts at will not be an issue.

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                  • #10
                    I suggest you go online with the cpu and create a system report so we can see how you have the system configured. In addition, please provide pics of your wiring from the HSI to ZL-RTB40, encoder wiring and cabinet.

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                    • #11
                      What are the specific encoders you are using and how did you wire them up with new wire? Take pictures of your installation of the encoders themselves, the wiring on them, show us how the cables are run to the PLC and pictures of the PLC installation itself and closeups of the ziplink wiring.


                      and how long are the wire runs from each encoder back to the PLC?

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                      • #12
                        Update, without changing any wiring I have taken the programmed inputs for the cards, Ch1 A, Ch1 B and Ch1 Z to my own bit of ladder logic and created an up/down counter. It has now worked all day without fail and i cannot create any false readings by turning the drives off.

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                        • #13
                          I dont think that is a real solution and you may develop problems down the road at some point. Best to find the actual cause of your noise issue.

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                          • #14
                            If I remove the high speed cards and just wire into normal inputs this will allow the conveyors to run. What would the maximum count rate be with normal inputs and counters. As for understanding electrical noise I wish there was a tool which could measure it and give a green or red light. The only problem I see with the motor wiring is the cable is glanded where it enters the panel but then there is a length of exposed cable which is not screened. Is this enough to cause issues, but then why does my encoder inputs count with normal counters but not with the high speed counters. SystemReport.11.2.2019_0.55.56.zip

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                            • #15
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