Strange situation in PLC Q02

[drozdu 0]

Hello, Recently I came across a strange problem, in attachment file I enclose the screenshot from GX Developer. Does anyone have any idea why B980 is turned on and M5162 is not ?? M2500 and M2501 are turned on and off by SET/RESET commands. Perhaps this might be the reason of the problem, but I'm not sure. Best regards, Drozdu Edited 13 Feb 2009 by drozdu

[Gambit 326]

M1 (Running) isn't ON!!!! When I look at your program only B980 or M5162 can be on. For the first network M1 is normally open in the second normally closed Edited 13 Feb 2009 by Gambit

[drozdu 0]

M1 is for some kind of use/pass operation. When M1 is off machine is in the pass mode. M5162 is required in both kinds of operation, that's why in the first line M1 is normally open and in the last line it is normally closed. Condition for turning on M5162 (in pass mode) are like this: (B981 is on) AND (M1 is off) AND (L1071 is on) AND ((M2500 is off) OR (T205 is on) OR (M2501 is off)) According to the device state displayed in GX Developer, all conditions are met, but M5162 is still off

[Gambit 326]

Sorry Didn't see the Line between the networks before!!!! One thing to rememeber is that What you see when you monitor the PLC is that the status of the devices displayed are status of the devices at the end of the SCAN not at the ladder code. Most likely M5162 is reset somewhere. Have you made a cross reference to check all the places M5162 is used in the program?

[funfrok 0]

You can put another coil to M5162 in parallel to check if M5162's coil is activated in this rung. Use another M that you are sure that it is not used. I usually use data registers with INC command like INC D0, to check if some part of the ladder is working or not.

[panic mode 246]

exactly, check if the code is scanned, or if something else writes to it (double coil, move etc.)

[drozdu 0]

Ok, problem was solved :) Set and reset instruction was executed at the same time for M2500 and that was the cause the problem. Thanks for help!! Regards, Bartek