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Old March 9th, 2015, 07:34 AM   #16
Bering C Sparky
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I got schooled a bit on this same subject the other day.
Here is the link to that thread, perhaps something in there will be beneficial to you.

http://www.plctalk.net/qanda/showthread.php?t=93406

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Old March 9th, 2015, 11:44 AM   #17
Elcan
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Quote:
Originally Posted by Bering C Sparky View Post
I got schooled a bit on this same subject the other day.
Here is the link to that thread, perhaps something in there will be beneficial to you.

http://www.plctalk.net/qanda/showthread.php?t=93406

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Thank you for the link, Bering.

My case is a momentary Start button on a G3 Red Lion HMI used to start a motor, and sometimes (very infrequently, fortunately) this HMI button gets the PLC bit stuck. This means the motor cannot be stopped.
I haven't tried any alternative code yet, but I was thinking about using the motor running feedback signal to unlatch the Start bit. Comments?

As a work around, I asked the plant operator to push the Start button again, and it fixed the problem. It makes sense: when you press the momentary button the HMI is asking the PLC to set and reset the bit, so it clears the bit.

I'm still interest in seeing specific codes you guys have been using to deal with stuck bits when you start/stop motors.

Thank you!

Last edited by Elcan; March 9th, 2015 at 11:47 AM.
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Old March 9th, 2015, 12:32 PM   #18
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Here is how I have handled HMI push buttons in the past that I am worried about toggling a bit and leaving it true.
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Old March 10th, 2015, 09:06 AM   #19
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Here's what I've done and it seems to work.
The OIT_Start is the bit associated with the Start button on the HMI. You can see that I unlatch it with the Running_Aux bit (bit that tells if the motor is running).
Like I said in a previous post, a quick fix if I don't implement this code to reset the stuck bit, is to push the Start button again: it will clear the bit. At least this works with my Red Lion HMI.

I hope this helps and I will appreciate your comments and any other ideas.
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Old March 14th, 2015, 09:40 AM   #20
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JUST INFO I THOUGHT MAY HELP SOMEONE?...
We have worked for the last year on a project using 2 Redlion G3 15 inch HMIs. There was a constant issue with one where buttons would appear stuck.. They would show on the screen as on but in the PLC as off and very random. After a great deal of struggles we were finally able to get REDLION to see the same problem. They found a driver issue between the HMI and the Allen Bradley (compac logix) PLC. After they fixed the driver and we updated the firmware we have not seen this issue again. I have actually found or identified (3) separate driver related issues over the years with 3 different manufactures of PLC / HMI / INV. So I guess everyone is human and after you have drove yourself crazy trying to find your problem check with the makers!!! But you have to prove it to them!!! Hope this helps someone...
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Old March 14th, 2015, 10:49 AM   #21
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Quote:
Originally Posted by REHJ View Post
JUST INFO I THOUGHT MAY HELP SOMEONE?...
We have worked for the last year on a project using 2 Redlion G3 15 inch HMIs. There was a constant issue with one where buttons would appear stuck.. They would show on the screen as on but in the PLC as off and very random. After a great deal of struggles we were finally able to get REDLION to see the same problem. They found a driver issue between the HMI and the Allen Bradley (compac logix) PLC. After they fixed the driver and we updated the firmware we have not seen this issue again. I have actually found or identified (3) separate driver related issues over the years with 3 different manufactures of PLC / HMI / INV. So I guess everyone is human and after you have drove yourself crazy trying to find your problem check with the makers!!! But you have to prove it to them!!! Hope this helps someone...
Don't trust that the issue is fixed, as it isn't just a "Driver Issue". Take the safe route, and just forcibly unlatch any momentary HMI bit immediately after it has been used in the program.

It is simply irresponsible if you don't.
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Old March 16th, 2017, 04:40 PM   #22
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It can happen to any HMI

I've seen this on at least a dozen different HMIs and SCADA packages communicating with various PLC manufactures on different networks, not just Ethernet. The more complex the system the more it seems to happen so I suspect it's a CPU/network usage issue.

The only sure-fire way I'm aware of to *not* get a stuck PB is have the PLC turn the bit off every time or monitor it and turn it off if it's on too long.

Three fixes I've seen and agree with:

1. Put OTU coil right after the NO/NC use of the PB tag in the same rung.
2. Add rung below with OTU, or composite at end of the routine with all OTU.
3. My favorite - alias all PB tags to the bits of an array of DINTs. Using simple (but clever?) compare logic monitor the array for stuck bits, reset stuck bit after desired "stuck on" time delay.
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Old March 17th, 2017, 05:48 AM   #23
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I had not originally followed this thread but the most recent post dragged me in. So I thank you for that.

Quote:
Originally Posted by Elcan
...This is an old post, but I would like to compile a good set of solutions for this issue...
While not customary here to revive old threads; in the interest of Elcan's request above I would like to mention the option that Rockwell introduced in Studio 5000 v27. Namely the HMIBC (HMI Button Control) instruction. This was introduced to combat the "stuck bit" anomaly, which is all too common across many of the different brands of Operator Interface products. As this feature is specific to Rockwell, and only their newer HMI products at that; it does not address the issue for their older HMI offerings. Nor does it address the specific issue mentioned here with the Red Lion HMI products, or any other, for that matter. The only reason I am mentioning it here is to point out the fact that they have least "acknowledged" (HMI pun) the problem and are attempting to "address" (pun no.2) the issue, going forward. Hopefully other manufacturers are or intend to do likewise. It may also be of interest if some are using the newer PanelView 5500 terminals but we're not aware of this feature.

Note: I have not used this new feature yet. So I cannot say with any certainty how successful it is, or not. I have my first PanelView 5500 sitting on my desk a couple of weeks now. It's to be used on a project later this year. I haven't gotten into it too deeply yet but I do intend soon to add it to a project's I/O Configuration and test this instruction. I tried to find time this week but you know how it goes. I'll try to get back to it the week after next as I'm in the UK next week on business.

I would still, in agreeance with others, strongly advise programmers to handle the resetting of HMI set "bits" programmatically. At least until we live in an automation world where this pest has been completely eradicated.

This is a previous thread on a similar topic which also outlines the operation of the HMIBC instruction...

"stuck key" anomaly RSLogixs5000v21

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Old March 17th, 2017, 08:03 AM   #24
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Quote:
Originally Posted by Elcan View Post
Hi all,
This is an old post, but I would like to compile a good set of solutions for this issue.
From the previous comments:

But if the HMI Push button is stuck, would this prevent the motor to start again?
Don't get fooled by the problem title. The HMI push button is not stuck. Many HMI's are configured so that when the operator selects the START (or other action item) button, the HMI tells the PLC to turn on a bit in the PLC. This bit is used to start the motor (or other actions). When the operator quits selecting the action, it is supposed to tell the PLC to turn off the bit in the PLC. But sometimes the PLC doesn't seem to get the turn off command, and the bit stays on. This could be due to a buggy HMI, communication problem, or other issue. Except for the case of buggy HMI, it is usually happens on very rare occasions, it is not repeatable. There were some HMI's that if the operator clicked on a button, but moved the cursor off the icon before he released the button, the turn bit off command did not get sent when he released the button.

The bit could get set back by having the HMI turn the bit ON then OFF again, but some systems are set up so that if the start bit is already on or the run status for the motor is on, the button to start the motor is not enabled. So the operator can't select the start bit to 'reset' the bit.
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Old March 17th, 2017, 08:25 AM   #25
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Quote:
Originally Posted by Elcan View Post
Nobody?
On the stuck from HMI, no. Because two things need to happen. The HMI should only set the bit....don't configure it as a momentary. Then the PLC resets the bit after using a one shot to generate an intermediate bit that's used in the code.
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Old March 17th, 2017, 10:57 AM   #26
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On the stuck from HMI, no. Because two things need to happen. The HMI should only set the bit....don't configure it as a momentary. Then the PLC resets the bit after using a one shot to generate an intermediate bit that's used in the code.
I disagree. When I press the STOP button on the HMI, I do not want the PLC to override my STOP. The STOP should come off when I release the button. The HMI should be set up so that the operator presses and release the stop even if the PLC shows the HMI stop already On.
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Old March 17th, 2017, 11:28 AM   #27
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Quote:
Originally Posted by proof View Post
I disagree. When I press the STOP button on the HMI, I do not want the PLC to override my STOP. The STOP should come off when I release the button. The HMI should be set up so that the operator presses and release the stop even if the PLC shows the HMI stop already On.
No matter what you do, any protocol connected set up can fail. Stuck Button Syndrome is ubiquitous. It may be nearly impossible on a RIO Panelview or one with an I/O connection as Ken described but that is because the PLC has a built in mechanism to override the I/O data in the event of a communication failure.

On a normal protocol link, you need to build that into the PLC logic. For a jog button, it can be slightly more tricky since you still need to use momentary buttons. I still use momentary buttons a lot but I also program the PLC to unlatch them immediately after use or after a time period.

I often use a timer with the TT bit (timer timing) as the driver for the button logic, and then examine the DN bit and OTU the HMI bit. Then if the HMI bit doesn't get stuck or gets held down too long, the TT bit will go false even if you don't unlatch the HMI bit.

Using a timer lets you monitor the logic whereas instantly unlatching it makes monitoring hard to do without other tricks.

But don't do what I recently did. I added some stuff to a small water plant on the fly and forgot to deal with the potential for a stuck button on the two new ones I added. Not only that, but once the mode change occurred, I made the button invisible. So the button (two hundred miles away) got "stuck" and I couldn't have the operator press it again because it was no longer showing! (Doh!)
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Old March 17th, 2017, 12:02 PM   #28
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No matter what you do, any protocol connected set up can fail. Stuck Button Syndrome is ubiquitous.

Not only that, but once the mode change occurred, I made the button invisible. So the button (two hundred miles away) got "stuck" and I couldn't have the operator press it again because it was no longer showing! (Doh!)
I must have better luck. In the last 10 years, I can only recall two instances where I had a 'stuck' bit that the operators couldn't clear. Once with RSView32, and once with Intouch. Both times, the HMI was set up similar to you except the buttons were still visible, but they didn't execute if the HMI bit was already on, or the device status correct. (its been long enough I don't remember the details). It may have happened at my plants more that twice, but when the HMI allowed the operator to click on the buttons and get things back in sink, and unstick the bits, I didn't find out there was ever a problem.

One other reason I don't like to see the PLC clear bit set by the HMI, is like you said. It makes troubleshooting harder. If the PLC turns it off, I can't see that the bit comes on if it's turned of with a one shot, or I have to be quick if it is from a timer.

I prefer to see that the HMI start latches a PLC start when the HMI start turns on, and the PLC start turns off when the motor starts, faults, or the HMI start turns off.
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Old March 17th, 2017, 12:12 PM   #29
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Quote:
Originally Posted by robertmee View Post
On the stuck from HMI, no. Because two things need to happen. The HMI should only set the bit....don't configure it as a momentary. Then the PLC resets the bit after using a one shot to generate an intermediate bit that's used in the code.
right again

especially ran into this in the oil fields when the hmi's were communicating over radio.

what was the cool trick I forgot where someone mapped them into a dint and used an xor instruction to basically do the oneshot reset thingy?
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Old March 17th, 2017, 12:24 PM   #30
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Quote:
Originally Posted by proof View Post
I must have better luck. In the last 10 years, I can only recall two instances where I had a 'stuck' bit that the operators couldn't clear. Once with RSView32, and once with Intouch. Both times, the HMI was set up similar to you except the buttons were still visible, but they didn't execute if the HMI bit was already on, or the device status correct. (its been long enough I don't remember the details). It may have happened at my plants more that twice, but when the HMI allowed the operator to click on the buttons and get things back in sink, and unstick the bits, I didn't find out there was ever a problem.

One other reason I don't like to see the PLC clear bit set by the HMI, is like you said. It makes troubleshooting harder. If the PLC turns it off, I can't see that the bit comes on if it's turned of with a one shot, or I have to be quick if it is from a timer.

I prefer to see that the HMI start latches a PLC start when the HMI start turns on, and the PLC start turns off when the motor starts, faults, or the HMI start turns off.

I second this.

I have not encountered any "stuck" HMI PBs on any new systems I have designed and implemented since the PB32-PVs and first generation of PV+s (before the 6.1 SQL data server)

However, I have never installed more than 1 HMI on any I/O data traffic network; any multi-HMI systems will always contain a segregated (physical or virtual) subnet dedicated to Broadcast type communication.

While "First-Scan" routines dedicated to unlatch all the potentially damaging or unsafe conditions generating tags are a must in every system, I don't believe programmatically accounting for a poor network bandwidth is a normal approach.
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