ControlLogix FOR Instruction with Timer

ohnedich6 · Jun 24, 2017

Good day all,

I was hoping the forum could help me with something I've been wondering (I looked through the Forum's Search function but did not find anything).

If I am running a FOR instruction in ControlLogix's Ladder logic, Version >= 20, and I have a timer in the Routine that the FOR instruction is calling how does it react? If the Timer is Enabled does it finish timing before the FOR instruction will continue on to the next Index in the array? I want to say the answer is "Yes", but wanted to hear it from the "horses mouth" so to say.

Thank you.

-Nathan

ControlLogix FOR Instruction with Timer.jpg

GaryS · Jun 24, 2017

your answer is NO
The timer ACC will update with each loop the timer itself will continue to run in the background The loop will not be held up whit the timer runs

labeledas · Jun 24, 2017

What are you trying to do. And do you need it to hold before proceeding

ohnedich6 · Jun 25, 2017

labeledas,

I was trying to use index arraying to have, let's say, PbAuto as a Bool[32] & AutoTmr as a Timer[32] that I could write one line, or two, of logic and just index through it depending on Task scan rate to UnLatch the tag that was set by an HMI. I would not need the Scan to hold while the Timer times before it proceeds onward.

This is just a "what-if" situation for me that I was curious if/how it would work.

Thanks all.

-Nathan

OkiePC · Jun 25, 2017

Looping in a PLC is rarely a good idea. The PLC runs in a loop by design. It is better to enter a thousand lines of straightforward code than to try to be slick and save yourself some keyboard time...at the expense of simplicity and ability to understand and make changes in the future.

daba · Jun 25, 2017

I *believe* what you are attempting to achieve is to ensure you "see" all the HMI pushbuttons.

A sure-fire way to do this is to have your HMI buttons configured as "Set ON", and just leave it to the PLC to see it as and when, fire an internal bit ON (this bit will be true for one complete scan after this), then unlatch the HMI bit. See the picture...

daba · Jun 25, 2017

FYI the above FOR loops through 128 buttons, and execution time is approximately 1mS

ohnedich6 · Jun 25, 2017

daba said:
I *believe* what you are attempting to achieve is to ensure you "see" all the HMI pushbuttons.

A sure-fire way to do this is to have your HMI buttons configured as "Set ON", and just leave it to the PLC to see it as and when, fire an internal bit ON (this bit will be true for one complete scan after this), then unlatch the HMI bit. See the picture...

Daba,

I would be using a "Set On" button on the HMI but I was curious as to how a FOR loop would act if I had an array of Auto Pushbuttons that Unlatched themselves after so long via a Timer in the PLC.

This is just a what-if situation that I've been wondering about for a while now and just thought I'd ask the collective here on the forum for input.

-Nathan

daba · Jun 25, 2017

ohnedich6 said:
Daba,

I would be using a "Set On" button on the HMI but I was curious as to how a FOR loop would act if I had an array of Auto Pushbuttons that Unlatched themselves after so long via a Timer in the PLC.

This is just a what-if situation that I've been wondering about for a while now and just thought I'd ask the collective here on the forum for input.

-Nathan

I think you are thinking too deep - an HMI button will act as you configure it, and why would it unlatch itself via any timer, HMI or PLC ????

A button has been pushed, it's up to the PLC to deal with it. I don't think any "time" is involved, so why the need for a "timer".

A button push is an asynchronous "event" that can occur in real-time, the PLC code has to decide whether to act on that event according to the specification.

GaryS · Jun 25, 2017

what HMI are you using
Set the HMI button to monetary when the button is pushed the bit in the PLC is when the button in the HIMI is released the bit n the PLC is cleared
no scan in the PLC is required
you can also set the HMI button to maintained push on push off simple

ControlLogix FOR Instruction with Timer

ohnedich6

Member

GaryS

Member

labeledas

Member

ohnedich6

Member

OkiePC

Lifetime Supporting Member

daba

Lifetime Supporting Member

daba

Lifetime Supporting Member

ohnedich6

Member

daba

Lifetime Supporting Member

GaryS

Member

Similar Topics