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Old March 12th, 2018, 09:10 PM   #16
rupej
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I may be misunderstanding, but I don't see how my method makes that any more likely. The PB bit is only cleared if it is held for 2 seconds (or whatever time is programmed). The HMI clears the bit any time someone releases it, which would also happen if someone else was using a 2nd HMI somewhere.
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Old March 13th, 2018, 12:12 AM   #17
Geoff White
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The issue is if the communications is interrupted before the bit is cleared. You then have a button stuck on.
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Old March 13th, 2018, 06:13 AM   #18
rupej
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But that's the whole point of the PLC logic- if the comms fail and the PB bit gets stuck on a 1, it will automatically be reset to a 0 after a set time.

Not trying to go super nerd about this- just trying to make sure I understand any concerns because if there's something I'm not seeing, I'd like to know!

Last edited by rupej; March 13th, 2018 at 06:15 AM.
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Old March 13th, 2018, 11:55 AM   #19
arlenjacobs
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Quote:
Originally Posted by rupej View Post
I may be misunderstanding, but I don't see how my method makes that any more likely. The PB bit is only cleared if it is held for 2 seconds (or whatever time is programmed). The HMI clears the bit any time someone releases it, which would also happen if someone else was using a 2nd HMI somewhere.
Rupej your idea is clean, efficient and is easy when you have a lot of push buttons to manage. It can work well in a project, but I've come across a few that didn't.

It matters what you are doing with the input PB bit (trigger or hold an action), and where that is in your ladder code (before or after the clear, in the scan).


Scenario A:
PB #1 is pressed, then just before two seconds is up PB #2 is pressed.
PB #2 will be immediately cleared, being held high for a very short period of time.

That has a few outcomes:
1) Any ladder code for PB #2 after the PB clear will not run. Obvious yes, but when there are more than 1 PLC programmers you can't control everything.
So, I assume that this issue won't occur because it's easy to find in a code review.

2) There is no feedback to the HMI that the PB press was valid. The HMI uses the PB tag as a feedback. With a short time of PB #2 being held high there is no feedback that the PB press was valid.


3) The parallel PB input can work for push buttons that trigger an action in the PLC. But it cannot work for push buttons that hold an action.
Both cases are a Momentary PB in the HMI (set 1 on press, clear 0 on release).
It's the hold action of an HMI momentary PB that would cause a problem; with multiple HMIs.
PB #1 would cause the hold action of PB#2 to be very short.


Scenario #2
4) If PB #1 is pressed for 1 second, then before that is released you have PB #2 pressed for 1 second. The timer would never stop and ends up clearing all PB bits 1 second into the PB #2 press. That is an issue for push buttons with a hold action.


You could increase the timer to 5 or 10 seconds, and reduce the chance of problems. That can work for a lot of projects, as long as you are mindful of the issues.
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Old March 13th, 2018, 12:40 PM   #20
Geospark
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Quote:
Originally Posted by arlenjacobs
FYI: The button issues that ASF is talking about exists in every HMI.
Something to think about.

There is one HMI that I know of which uses class 1 comms (like an Ethernet I/O module). But that's a limited scope and a different topic.
I'm not sure if you mean the following HMI, but if you don't mind me mentioning it (I'm so exited by it!) - I've used the HMIBC instruction (introduced at v27) with the new PanelView 5500 terminals and it's a brilliant feature. The terminal is added to the I/O Configuration to utilize a fast Class 1 connection at 100ms which is monitored under the watchdog timer. Once the connection is maintained, the controller tag assigned to the instruction is reset automatically each and every time. No need for catch & release logic. If the HMI loses comms the instruction resets the tag value automatically. It is very responsive, especially for quick touch jogging.

1046714 - Using HMI Button Control (HMIBC) instruction with a PanelView 5500
Access Level: TechConnect

For the age old issue of "stuck bits" - Yes, the catch & release method, as I call it, and however you achieve it, is a must in your logic to prevent undesirable retention of HMI button actions.

I would also add that the use of the mentioned popup confirmation window is also best practice for the prevention of unintended HMI button actions.

Good stuff all round.

Regards,
George
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Old March 14th, 2018, 06:34 PM   #21
arlenjacobs
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Quote:
Originally Posted by Geospark View Post
I'm not sure if you mean the following HMI, but if you don't mind me mentioning it (I'm so exited by it!) - I've used the HMIBC instruction (introduced at v27) with the new PanelView 5500 terminals and it's a brilliant feature.
Yep, the same one.

You need both the PV5000 terminal and a Logix controller.
It solves all the problems you didn't know existed in an HMI push button.
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Old March 15th, 2018, 07:57 AM   #22
rupej
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Quote:
Originally Posted by arlenjacobs View Post
Rupej your idea is clean, efficient and is easy when you have a lot of push buttons to manage. It can work well in a project, but I've come across a few that didn't.

It matters what you are doing with the input PB bit (trigger or hold an action), and where that is in your ladder code (before or after the clear, in the scan).


Scenario A:
PB #1 is pressed, then just before two seconds is up PB #2 is pressed.
PB #2 will be immediately cleared, being held high for a very short period of time.

That has a few outcomes:
1) Any ladder code for PB #2 after the PB clear will not run. Obvious yes, but when there are more than 1 PLC programmers you can't control everything.
So, I assume that this issue won't occur because it's easy to find in a code review.

2) There is no feedback to the HMI that the PB press was valid. The HMI uses the PB tag as a feedback. With a short time of PB #2 being held high there is no feedback that the PB press was valid.


3) The parallel PB input can work for push buttons that trigger an action in the PLC. But it cannot work for push buttons that hold an action.
Both cases are a Momentary PB in the HMI (set 1 on press, clear 0 on release).
It's the hold action of an HMI momentary PB that would cause a problem; with multiple HMIs.
PB #1 would cause the hold action of PB#2 to be very short.


Scenario #2
4) If PB #1 is pressed for 1 second, then before that is released you have PB #2 pressed for 1 second. The timer would never stop and ends up clearing all PB bits 1 second into the PB #2 press. That is an issue for push buttons with a hold action.


You could increase the timer to 5 or 10 seconds, and reduce the chance of problems. That can work for a lot of projects, as long as you are mindful of the issues.
Thanks for taking the time to respond, that's interesting to think about. So yeah this certainly doesn't work for buttons that need to be held, like jog buttons. But thinking about it, the classic catch and release doesn't work for jogs either . How do y'all deal with that situation?

Just a side note, at least for PanelViews, I don't think scenario #2 would happen. When PB#1 is released, the bit would clear. And it wouldn't go high again unless PB#2 released and pressed a second time.
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Old March 15th, 2018, 11:37 AM   #23
arlenjacobs
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Quote:
Originally Posted by rupej View Post
Thanks for taking the time to respond, that's interesting to think about. So yeah this certainly doesn't work for buttons that need to be held, like jog buttons. But thinking about it, the classic catch and release doesn't work for jogs either . How do y'all deal with that situation?
That is a good question; PLC code to handle HMI jog push buttons.
I'm guessing most don't use any code. Just let the HMI handle it.


Quote:
Originally Posted by rupej View Post
Just a side note, at least for PanelViews, I don't think scenario #2 would happen. When PB#1 is released, the bit would clear. And it wouldn't go high again unless PB#2 released and pressed a second time.
Maybe. You'd have to try it.
If all the PB inputs are in parallel, then overlapping PB presses (of 1 second) would run out the timer.
Post up your ladder for the PB timer. It'd be a lot easier when we could see it.
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