output flickering problem

[nileshsurya 0]

hi thr u all plc experts recently i came across a machine which is used to make paper cups for beverages now listen carefully the machine is controlled by a slc-5/03 processor interfaced with a PV600 as an MMI, the problem is that one output on a PLC o/p card (which is an OA16 110V ac o/p card) flickers(that is the o/p chatters and does not remain steady, the indicator LED on the module also flickers same) i tried following steps to eliminate the problem:- 1)changed the o/p card (thinkin the module has some problem), but it didnt work 2)changed the module slot (thinkin thr must be some problem in the backplane), but it didnt work there is another machine which is an exact clone of this machine(ie: the PLC program is exactly same in both the machines), that machine is working perfectly fine. so i also replaced the PLC program in the machine with the program which was in perfectly working fine machine (but this also didnt work) this flickering problem comes only with that one specific o/p this output is energized with a rotary encoder(ie when the degree is between 0-40 degrees) so i replaced the encoder,but this is also not working will any PLC expert plz tell me whr the exact problem must be. i have really tried all these things but the problem is still not solved waiting for reply from all u guys eagerly reply ASAP regards NileshSURYA

[navillusi 2]

Can you post the code and identify exactly which output you are having probelms with?

[Guest trn_psycho]

Just curious, but have you disconnected the output wire from the module to see if it’s your load that’s causing the problem? If you get the same result without the wire attached, then I’d start looking into hardware or software issues at the PLC end. (You may also try and force the output to see if it stays steady or continues to flicker. –Only do this last step if you’re sure that it will not cause damage or harm to anything/anyone.)

[brucechase 1]

I'm with trn_psycho on this. Assuming what you say is true (the programs are exactly the same), the next logical place to look is in the field wiring. I did have something very similar to this happen to me during a machine modification. The program was the same before and after but one relay would chatter whenver the output came on. It was a loose jumper pin in the terminal block. Took 2 days to find it since it wasn't in the wiring at all. If you are using a wiring arm, verify that there is no insulation under the terminal screw. Good luck and let us know what (if anything) you find. BGC

[Guest]

this points toward the problem NOT being associated with the output field wiring ... if you've changed all of the things that you say you have, and the problem remains, then I'd take a good look at things OUTSIDE the PLC ... have you checked the MMI to make sure that it is not sending an intermittent signal to the PLC over its communication link? ... I've seen a typographical error in an MMI tag address cause problems like this ... for troubleshooting try disconnecting the MMI communications and see if the problem goes away ... note that the MMI does not have to write specifically to the exact output address to cause a problem ... if it "flickers" a bit somewhere in the output's control logic, then the output might be erratic as a result ... best regards, Ron

[b_carlton 61]

If the encoder is an absolute encoder see if you can stop the machine, rotate the encoder very slowly, and watch for all codes to come up. I would guess a broken or intermittent wire in the cable or connectors, probably with an intermediate bit. The could lead to the count jumping into then out of the 0-40 range very quickly.

[alleprocessing 0]

Dear Sir: I've had some problem like this and I've realized that it has to be the encoder cable or the HSCE card. Let me know if it works out for you. PINNY

[TechJunki 0]

Sounds like this is most likely a Hardware issue, especially if you have done as trn_psycho advised. I too would look into the encoder and all associated wiring. JJ Edited 9 Mar 2005 by TechJunki