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Can someone explain why Net 4 in the attached image doesn't work as expected?

On power up MB2 and MB5 are both set.

When Input 41 goes HI should not Output 57 and Output 59 both turn on?   They don't.

MB9 - MB12 are buttons on the HMI and they turn on the respective outputs so I know the outputs are functioning correctly.

Running on a V570 with addon modules etc...




Contact Contact Coil.jpg

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  • MVP 2023

You have O57 and O59 assigned to duplicate coils.  This is very bad programming practice.  Unlike Set, Reset, and Toggle, you should only use a regular coil once in your program for a given output or bit.

When the ladder scans, EVERY rung is evaluated.  The last coil assigned to a particular memory location wins.  While O57 and O59 may be ON in Net 4, In Nets 9 and 10 they will be turned OFF if MB 9 and/or MB10 are not on.

Put an intermediate MB in place of O57 and O59 in Net 4.  Then OR your intermediate MB with MB 9 and MB 10 in Nets 9 and 10 to turn the output on.

Joe T.

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