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  • Calling Electrical Gurus And Practitioners Of PLC Magics...

    This is a post in several parts.

    First is a description of the problem:

    "The tester started the morning fine, we ran a bunch of parts. Then it stopped functioning... the motor turned off and the machine refused to cycle.

    We powered it down, let it sit figuring it was too hot in here. Turned it back on and got a couple of cycles out of it before it quit again.

    We opened up the back to check the PLC, the POWER GOOD light is on but the normal PLC blinkenlightz are not blinken nor are they light'n. We can get the motor to cycle if we hold the breaker button in the power cabinet, but as soon as we let go it trips again.

    We don't have anyone to troubleshoot this, so we are asking you via Brian ("Liger Zero")."


    ---

    Liger talking now:

    The machine is a test rig that pull on a finished product... 20,000 pounds delivered by a hydro-cylinder, other end is a load cell.

    All this is coordinated via a PLC, several position sensors, a bank of switches and an activation trigger.

    I was off today so I didn't see what happened, but based on the symptoms I'm leaning twords a cooked power-supply that erased/smoked the PLC.


    Attached are some pictures. Tomorrow I'll attempt to reload the PLC from my laptop but I want to eliminate other issues first.
    This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
    Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
    Plastic Operators Dot Com

  • #2
    MODICON MICRO
    110 CPU 311 03


    Allen Bradly Automatic Switch


    Controls For Automatic Switch


    Power Supply For PLC
    This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
    Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
    Plastic Operators Dot Com

    Comment


    • #3
      Ok Liger talking again:

      I had this issue on another test rig at another job... Those silver thingies with three legs on the top of the power supply were at fault. I had similar symptoms in that case.

      On this particular machine, the Automatic Switch failed recently, it was Quite Burnt. There is a possibility that the switch is failed again, but if I recall the PLC stayed lit.

      I'll know more when I hook the PC up to the PLC tomorrow, just looking for advice and other possible causes.
      This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
      Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
      Plastic Operators Dot Com

      Comment


      • #4
        plc's

        Let's start with this. A plc does not usually loose it's mind. First rule. no input no output.. Are any of the inputs led's on? Does the power supply have an output? Most plc's are powered with 24 V DC. Most machine builders use that 24 V DC to provide power to the various sensors, limit switches, &c As the unit resumed working after a cool down, I would be very suspect of the power supply. The 3 leg thingies are usually pass transistors. they are sourced <> 30 volts then other circuits adjust the output voltage to the required 24 volts. If you have a volt ohm meter with diode test it should be easy to t'shoot the electrics. By the way the panel builder didn't do a very neat job of layout/wiring. Does the machine have an E stop? Guarding interlock? HTH John from Dayton

        Comment


        • #5
          There are two position sensors. Both position sensors are lit when I power on the machine.

          The diagnostic for the load-cell shows no faults there.

          The switch that acts as the trigger is also lit.

          The PLC however only has ONE light lit and that is "power ok" everything else is dark, and the hydro-pack motor won't start.

          In normal operation the PLC is a riot of blinking lights, and the hydro motor makes it's normal "motor sound."

          To start the machine, you pull out the Red Button and the PLC lights up and the motor kicks in when it gets the signal from the PLC to start.

          Today, you pull the Red Button and Nothing Happens. At all. No motor no PLC light no pull in of the Automatic Switch.


          Gut tells me it's the power supply and the PLC is dormant, nothing more. I hope the heck it's not a "dead" PLC as this would be a "major hardship" for the customer.
          This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
          Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
          Plastic Operators Dot Com

          Comment


          • #6
            How old is that PLC? john hawkins is right that PLC's don't usually loose their mind. But it has been known to happen. Usual cause is the end of life of the memory battery if the PLC is so equipped. Next is a power surge - scrambles the program memory - not generally likely with the PLC insulated from the lines by a good DC power supply - but again, it does happen. Then, there is just plain old natural death. Rare, but it still happens. I've seen all three in 35 years in the trade.

            Hopefully, it is a recoverable failure and there is a backup disk of the program. You do have a backup disk, don't you?
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

            Comment


            • #7
              Originally posted by Weston Bye

              Hopefully, it is a recoverable failure and there is a backup disk of the program. You do have a backup disk, don't you?
              FIRST thing I do when I get a PLC driven fixture or begin work on anyone's PLC equipment: I backup the program myself. Have quite the assortment of interconnects AND software thanks to my step-father... who is out of town at the moment.
              This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
              Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
              Plastic Operators Dot Com

              Comment


              • #8
                Just some thoughts...

                You pull the red button and the PLC starts flashing. Possibly no power to the I/O rack. Meaning you have lost a fuse to the I/O power supply, or you have lost the I/O power supply itself. You also might have lost the Power OK input and the PLC is not executing its program because of that.

                First thing to look at is power supply and proper voltages. Can you disconnect the output of the I/O power supply and see if it works?

                Could also be a bad Master Control Relay not pulling in and nothing powering up.


                Got any schematics? It is always a lot easier to troubleshoot with the schematic because without it no-one is going to have much clue what is supposed to be happening on the outside of the PLC. Once you have that you can then try to find out what inputs should be active and also see if they have any power.

                Comment


                • #9
                  &quot; pull out the red button &quot;

                  The red button is the E stop. It seems from your description the E stop interupts power to the PLC which is common practice. I would jump out the E stop button. This is a normmaly closed switch. When you press the E stop it removes power to the PLC. The machine will do nothing in this state. Remove one wire from the E stop and put BOTH wires under one screw. This will jump the E stop, and maybe power the PLC. E stops are noted for failure, as any dirt will hold the contacts open. at least in the failed state the machine will remain stoped. Be sure that you lock out tag out the main power before you do any of this. Also have a helper stand by to turn the power off, as there will be now way to stop the machine when you test the results.

                  Comment


                  • #10
                    I will recheck the fuses tomorrow, my meter was giving me "funny" readings because... well I dropped it.

                    ...that's why I called it a day and came home and logged on here... after buying a new one.
                    This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                    Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                    Plastic Operators Dot Com

                    Comment


                    • #11
                      I should have said the E stop removes power to all input devices and also to the output relays in the PLC. The PLC is still thinking. But has no input therefore no output. If it were to output there is no power to output.

                      Comment


                      • #12
                        Tomorrow I will do the following:

                        1) Pull all the fuses and check them with the meter. Eliminate the obvious.

                        2) Check the voltages at the power supply.

                        3) Check the relays, there are six of them that I know of.

                        4) Put the PC on it and see what the software has to say about the PLC.

                        I got off the phone with my Step Father his opinion is the PLC is either DOA or not getting the right kind of power, that it is getting SOME power but not enough to "engage..." sort of a low-voltage condition. He says the POWER OK LIGHT is nothing more than a pilot light that comes on when voltage is present and has little to no diagnostic function on this unit.
                        This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                        Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                        Plastic Operators Dot Com

                        Comment


                        • #13
                          I'm not seeing any attention being given to the issue of the breaker opening...... but the folks with the problem say they can't get it to stay in.

                          To me, that is the immediate issue.

                          See what it supplies power to, and disconnect them one at a time until the breaker does NOT open..... at which point you MAY have found the problem.

                          And make sure that you are not fooled by taking power off something that merely activates the bad item....... if the contactor for the shorted motor never closes, you don't get an open breaker..... but you have not disconnected the real problem yet.

                          Once you KNOW what is causing the breaker to open, you can evaluate what otehr things may have happened.

                          First rule of complex systems is NOT TO GUESS.

                          Second rule is to FIX WHAT YOU KNOW IS WRONG
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            Good advice.

                            This is the startup sequence:

                            Pull the red button. PLC comes on, goes through a diagnostic routine then it signals the automatic switch and the motor comes on.

                            Problem is no sign of life from the PLC. PLC isn't waking up therefore the motor isn't starting.

                            Pushing the black thing on the automatic switch does no good as the PLC isn't awake and talking to the rest of the machine.

                            As far as I have been told that auto-switch is JUST for the motor circuit.

                            However, I will check it tomorrow.
                            This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                            Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                            Plastic Operators Dot Com

                            Comment


                            • #15
                              Used many types of PLC's, but not Modicon, but I would say if the power light is on but the run light is not, it is not going to be external power supplies.
                              The program sounds like it is in Halt, whether the program is still there is another matter.
                              Max.

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