panelviw 550 control tags

I have a panelview 550 being used in conjunction with a micrologix 1500 to determine alarm conditions and display alarm messages.

At the end of the main program ladder I have a line of code:

IF N12:0 <Panelview page monitor tag> EQU N12:1 <Panelview page control tag> THEN MOV 0 INTO N12:1

I imagined that this would return the panelview page control to the panelview at the end of each program scan, which it does most of the time.

Every few days i get an error message on the panelview "Remote device has screen control", and when I check the code it N12:0 is not holding the actual page number, and therefore the processor does not return screen control.

Can anyone explain why this might be? Doesn't the panelview update this monitor tag every scan? Is there any way I can prompt it to update?

Thanks

It's a question of timing

The simple answer - sometimes you push the buttons on the panelview too fast.

What happens is this:

The PLC executes a "screen change command" by moving a non-zero number into the <Panelview page control tag>.

"Eventually" (depending on network traffic, panelview scan rates, and other factors) the panelview gets around to reading this command.

In the meanwhile, the PLC may have gone through many, many scans. At the end of each scan, the PLC sees that the Panelview has not told it about accenpting any screen change data, so the data is not cleared.

The panelview, having now seen the screen change command, goes to that screen, reads all the tags from the PLC, and writes a new value to ITS INTERNAL <Panelview page monitor tag>.

"Eventually" (depending on network traffic, panelview scan rates, and other factors) the panelview gets around to sending this tag's value to the PLC.

The PLC then writes a zero to the <Panelview page control tag>.

"Eventually" (depending on network traffic, panelview scan rates, and other factors) the panelview gets around to reading the zero and knowing that the operator has screen control.

If between the last two "eventually"s, you were to try to change screens, yoo will get the error message that you see.

I've seen "eventually" take up to 5 seconds, so you have an "error" window of up to 10 seconds - an eternity.

Allen, thanks for your quick response.

I don't think this is a comms problem.

The fault gets reported, I eventually get around to looking at it, go and get the laptop, plug in, turn on, sometimes up to 3 hrs later! The problem is still there.

The program works 99% of the time, just every now and then i get this glitch.

N12:0 is definately not being written to anywhere else, I am stuck!

Hi
Just an idea...
If N12:0 is 10, requesting screen 10, but the current screen is on a 'system' screen i.e. the alarm pop up or the config screen then the requested will not match the actual. The system screens are number in the 32000's I think. Maybe this is confusing the PV.
Once you leave the system screen though, your code should remove the force though.
Welcome to the forum, btw.

pp

Ok, a bit more information.

If the processor detects an alarm, an alarm page is displayed, this page can be cleared by an operator, or will be automatically cleared if the alarm is no longer active.

The panelview can also display various pages of data (driven by user menu). If no activity is detected (page changes) and no alarm is active for 10 minutes the panelview reverts to screen 1 (main menu screen), The panelview always makes it back to this main menu but this is where it "locks up" (remote device has control).

Perhaps I'll change the panelview, just to rule it out...

Paraffin Power, thanks for the welcome, have posted a couple of questions (and answers) as a guest, but thought i'd better register and show my support...

Is it possible to post the PLC code and the Panelview program? It's difficult to get a handle on what exactly is going on and the programs may help others to find something.

lc03

Check out this thread. I posted the same logic as you but with a one shot before moving the 0 to the control register.

http://www.plctalk.net/qanda/showthread.php?s=&threadid=1721

This is what I did

I set up a remote I/O PV-550 and wrote the ladder such that whenever a value was written to the screen tag a timer is started. When the timer is done a zero is written to the screen tag. This way the processor can change screens but it doesn't retain control indefinitely.

Thanks for all your replys,

GRS - I am not in a position to post all of the code, however, I can post the subroutine that controls the panelview.
This is at the very end of the program scan, and other than alarms,nothing else in the program has any other control over the panelview.

Ndzied1 - The logic is very similar, where do you see the advantage in adding the oneshot, my thinking was that if the panelview missed the command on that scan (if this is possible) you would be stuffed!

Doug-P - I can see your point, how long is your timer? I want the program to appear "flawless" to the operator (ie no warning messages about processor having control), but i also want the processor to be able to control the panelview when necessary even with heavy network traffic as mentioned by allen nelson.

Thanks again

I guess all I can say is that I never experienced the lock up you are getting when I use the 1-shot. I beileve, on occasion, and for the reasons Allen stated, the screen control message would appear but it would not lock up. I never experienced the 5 sec. delay he mentioned but then again I always was working on systems with at most 5 DH+ nodes.

You could try it and report back the results...???

Timer is set at .50 sec. Remember, it's on RIO and it's the only remote rack so the traffic situation is different from DH+.

lc03:

If I've read your post correctly, you are saying that the Panelveiw is on screen 1 (just like the PLC told it to go to), but N12:0 (where the Panelview is supposed to write it's current screen number) does not contain a "1". Is that what's happening? If not '1', what screen number DOES the panelview report that it is on?

One more question: Do you have security enabled on your Panelview, and is the auto-logout ("Secure On Idle") enabled? What's the time duration (screen saver time)?

Allen,

Yes this is correct,

The panelview is still reporting that it is on whatever screen it came from, (this could be whatever the operator was viewing). This is why I wondered if the panelview status tag updates continuously or if it only happesns once on a screen change.

I only have security enabled for the configuration screen.

The auto logout is not enabled.

As far as i was aware the Panelview 550 does not have a screensaver (but I may be wrong!)

From the "If I had it to do over" department.

I've done screens both ways--go to screen buttons and PLC controlled screens---and like both to some extent. What works best for me is to let the PV control it's own screen navigation, for the most part. The other part is when some event or alarm occurs and the PLC wants the PV to go to some specific screen automatically. Then damn the handshaking and screen checking and put the darn screen number in the goto tag for 2 or 3 seconds, then clear it. Lots less headaches and it works.