Need help for Ladder Logic

[riouxhugo]

Ok,

I have tried several logic now including Robert's suggestion with your precisions. Thanks.
First pass work perfectly.
When I first hit PB work perfectly.
But, when I 2nd, 3rd, 4th and etc. hit the PB, B59:0/1 stay ON.

I am lost...

Still need help to get out of this (suppose) simple flip/flop circuit.

Hugo

First pass and first hit PB works perfectly. Same results if I toggle the bit N51:50/1 from RSLogix.

 

[robertmee]

First pass and first hit PB works perfectly. Same results if I toggle the bit N51:50/1 from RSLogix.

Check the state of N51:50/1 after the first pass or first PB when it works. Is it still ON or OFF at that point?

Here's what could be happening:

You press the button on the HMI which sets N51:50/1.
For the time of one scan (miliseconds), N51:50/1 is unlatched.

However, depending on how the HMI is set up, if the operator is still holding the button down (longer than a few milliseconds), N51:50/1 could be back ON when the scan reaches the rung again. At this point, both OSR memory bits are still set high and they won't fire again because they never saw a TRUE to FALSE transistion of N51:50/1. When you release the button, there's nothing to now unlatch it and N51:50/1 continues to stay high.

It would seem to me that it's unlikely, but at this point, something else to check. But it does make sense considering your symptoms that it works the first time and then no time after. That's likely because the first time N51:50/1 is OFF and everytime after it is ON and still ON.

 

[kamenges]

As a purely logical matter, the oneshots are not necessary. You are resetting the input bit as soon as one of the two rungs detects the input bit is true. So the input bit will be on for less than one scan in any case.

From a functional standpoint you are doing something I have never done. I have never had a case where I knowingly used a oneshot after a condition I knew wouldn't be high for a full scan. You may have found an 'undocumented feature' in the plc where it doesn't correctly handle that case (input condition to a oneshot not true for greater than one scan).

Keith

 

[OkiePC]

Try this version. It has only one OSR and unlatches the HMI bit in one place.

 

[xcode]

S:1 is a word ( 16 bits) for processor mode and control status. Each bit means something different. See pdf's below for SLC and PLC5 status

Thank you . I appreciate the help.

 

[SCADA_Dude]

Some advice:
1. Add descriptions to your LL variables, it makes it easier to spot errors.
2. Try to avoid the use of ONS/OSR unless they absolutely necessary.
3. Avoid toggles they can be a real pain - its easier to handle this in the HMI using multiple discrete if needed.