Pushbuttons

I didnt check the forums so forgive me if it is out there already. I was wondering if anyone has an idea how I could solve this problem.
Problem=I am programming a panelview plus v.7.055. I am using a Maintained pushbutton to control a valve to open. I was wondering if there is a way that I could get the PB to write zero when the valve opens. The controller is an Allen Bradley 1756-l72.The Logix version is 20.01. I am using Factory Talk Studio 7.00 (CPR 9 SR 6)
Thanks,
Buzzen

Hello,

Could you please explain in a bit more detail what you mean when you say:

get the PB to write zero when the valve opens

Click to expand...

1)where do you want to write this 0 to?
2)are you wanting to write this 0 when the PB is pressed or do you actually have some type of feedback and want to write the 0 once you have confirmation the valve is really open?

I am no expert but it would seem that either way this would be done in the plc software not the HMI.

(actually looking at your post again it seems that you may be asking if once the valve is open can the maintained PB be deactivated.) (Is this what you mean?)

Forgive all the questions but I get burned alot when I assume I know what someone is talking about.

why not use a momentary pushbutton and use the plc logic to seal in the circuit to open the valve?

regards,
james

With A/B touchscreens, I have always had to use an indicator tag that is not the same as the controlled tag (forgive my generic terminology). If your button uses one tag for both indicator status and control, then the panelview will ASSuME it knows what is going on with the tag and may deceive the viewer in certain situations.

I also tend to use more momentary buttons and even still sometimes add logic in the PLC to ensure they "drop out" in case of communications loss.

This is pure speculation, but: I am not clear whether your valve is a simple discrete output, or something like a motorized actuator with end limits that eventually result in it reaching a position.

More info please.

["This is pure speculation, but: I am not clear whether your valve is a simple discrete output, or something like a motorized actuator with end limits that eventually result in it reaching a position"]end of quote

The valve is a motorized valve, that uses an output from the plc. It is a limitorque so it has programmable stops. When it gets an open or closed command it will continue to open and close until it reaches the designated stops.

(actually looking at your post again it seems that you may be asking if once the valve is open can the maintained PB be deactivated.) (Is this what you mean?)

Yes that's it exactly. I was trying to not have to re-write the logic that is there, that is why I was curious if this can even be done. Besides it's fun...

If you have a signal from the valve when its open move is complete, use a ons with an un-latch on the bit that is being set by the button.

-[valve open]---[ons]---(U)-

Hmmm...interesting concept I will go explore that option now. Thanks

If you have a signal from the valve when its open move is complete, use a ons with an un-latch on the bit that is being set by the button.

Click to expand...

If you are truly using a maintained button from the HMI then most likely you will not have a OTL (Latched Output) to unlatch.
You could set another instruction on the rung to make the output go false once you recieve feedback that the valve is Open/Closed, but the button input would still be true all the time. (Maintained)

Most likely you are going to have a OTE (normal output) and this output is held true as long as the input from the maintained button is true.

You could change the Maintained button to a Non-Maintaied button. Then one-shot latch and unlatch instructions for the valve operation output.

Or use seal-in with additional instructions to break the seal-in once the valve has reached max travel.

Either way you will need to make changes to the PLC code.

I dont think you can manipulate a maintained button on a PV from within the PLC Code, or from withing FTVME.

Maybe it is possible to set up some type of expression or code from within FTVME, I have never done this so not sure.
IT just makes more since if you dont want the button maintained, then dont write the plc program to used a maintained button to start with.

Maybe others more experienced can shed some light on if you can manuipulate a maintained button, if this can be done I would also be interested in knowing how, just to know.

But I dont see why you would want to write it in such a manner, this would make it harder to follow the logic when trouble shooting and there are easier ways to skin this cat.

BCS

Gomez_ said:

If you have a signal from the valve when its open move is complete, use a ons with an un-latch on the bit that is being set by the button.

-[valve open]---[ons]---(U)-

Click to expand...

I tried this using the emulator an found it worked fine.

I tried this using the emulator an found it worked fine.

Click to expand...

I must be missing something here, so excuse my ignorance if I am.

What exactly did you unlatch in the PLC program to change the state of a maintained Push Button from a Panelview??

Maybe I dont see it, but the Maintained button would just be a XIC instruction on a rung, that is held true by the button being activated on the PV. (at least this is my understanding of how this works)

How are you unlatching this button on the PV from the PLC?

Just curious.

BCS

Bering C Sparky said:

What exactly did you unlatch in the PLC program to change the state of a maintained Push Button from a Panelview??

Click to expand...

You unlatch whatever tag the button is maintaining.

Maybe others more experienced can shed some light on if you can manuipulate a maintained button, if this can be done I would also be interested in knowing how, just to know

Click to expand...

Here's how HMI pushbuttons work "under the hood".

For a momentary pushbutton, when the operator touches the button object the HMI writes a value of 1 to the corresponding tag in the PLC. Later when the operator's finger leaves the button object, the HMI writes a value of 0 to the PLC tag.

For a maintained pushbutton, the associated action could be "Turn on", "Turn off" or "Change state". In any case there is only one action each time the operator touches/releases the button object. If the button action is "Turn on", the HMI writes a 1 to the PLC tag. Something else is required to turn the tag off. That could be ladder logic as was suggested in the posts in the thread. Or it could be another button object on the HMI screen set up turn the PLC tag off. If the action associated with touching the button is "Change state" the HMI must first read the current state of PLC tag and then write the opposite value to the tag.

BCS, you appear to be of the opinion that when a button object action is set to "Maintained", the HMI repeatedly writes a value of 1 to the PLC tag. That is not what happens.

Ok, I looked for the smiley face that is eating his hat but did not find that one. LOL

So I am still a bit confused about how you would change the state of a XIC from within the PLC code.

] [ --------------( )


If the XIC is being made true by touching the PB on the PV. What are you writing to make it false.??

This can be done if you all say it can, I just dont have my head wrapped around it.

EDIT:
Can you use a OTU instruction to unlatch something that is not an output and is not presently latched as an OTL??
Or is the maintained button directly written to the OTE and not the XIC in this case.

Again I appologize for my ignorance on this one, but I still dont see it.

Thanks
BCS

Here's my example in RSLogix 5000