OTU without an OTL?

[kcox1980 2]

Is it possible to latch a bit directly from an HMI without an OTL instruction in the logic? The PLC platform is RSLogix5000 and we are running a version of PanelView though I'm not sure off the top of my head which version it is. 

We have some automated tape heads on our line that can be disabled remotely while they change rolls but to re-enable it they have to walk all the way back to the HMI. I've been tasked with providing a remote enable function which I thought would be easy enough until I started looking at the logic and was unable to find the latch instruction.

[TimWilborne 108]

Yes. usually you will have options such as "momentary on" or "turn on".  The "turn on" would turn the bit on in the PLC without turning it back off when the button is release.  That would be similar to a OTL.

[kcox1980 2]

Just now, TWControls said:

Yes. usually you will have options such as "momentary on" or "turn on".  The "turn on" would turn the bit on in the PLC without turning it back off when the button is release.  That would be similar to a OTL.

I was afraid of this. We do not currently have a developers license for modifying the HMI project, so if I were to add an OTL instruction to the PLC would it cause any kind of conflict?

Edited 3 Oct 2016 by kcox1980

[TimWilborne 108]

Yes, I think you are on the right track though it may help to post your code.

[kcox1980 2]

Not really much to it. What I have in mind for the modification is just an XIC bit with an ONS for my remote enable button and an OTL to match the HMI command address. There are a total of 4 tape heads with identical logic FYI.

Edited 3 Oct 2016 by kcox1980

[PLCMentor.com 60]

Should not be a problem with that.  You need to confirm that the HMI is just setting the bit.  Sometimes we will add catches in the program if the HMI or SCADA system has a history or tendency to leave bits on periodically.  Looking at the wording, these appear to be disables.  It may be that the programmer is continuously unlatching the bit to disable the function and override the HMI.  If the HMI is setting the bit and leaving it or even has separate set and reset function, you should be able to get away with putting some PLC logic that will operate in a similar manner.  Keep in mind that the HMI will still be able to set and reset that bit.  If you are looking to being able to do that functionality from both places, then it looks like you have what you need.  The HMI will set the bit or your PLC will set the bit.  If you want either the PLC or HMI to be able to reset the bit, then you will want to use a oneshot in your PLC logic to insure that it does not override a reset from the HMI.  Once again - this assumes that the HMI is setting the bit and not acting as a momentary and setting the bit and resetting it after a predetermined time period.

[kcox1980 2]

Just now, PLCMentor.com said:

Should not be a problem with that.  You need to confirm that the HMI is just setting the bit.  Sometimes we will add catches in the program if the HMI or SCADA system has a history or tendency to leave bits on periodically.  Looking at the wording, these appear to be disables.  It may be that the programmer is continuously unlatching the bit to disable the function and override the HMI.  If the HMI is setting the bit and leaving it or even has separate set and reset function, you should be able to get away with putting some PLC logic that will operate in a similar manner.  Keep in mind that the HMI will still be able to set and reset that bit.  If you are looking to being able to do that functionality from both places, then it looks like you have what you need.  The HMI will set the bit or your PLC will set the bit.  If you want either the PLC or HMI to be able to reset the bit, then you will want to use a oneshot in your PLC logic to insure that it does not override a reset from the HMI.  Once again - this assumes that the HMI is setting the bit and not acting as a momentary and setting the bit and resetting it after a predetermined time period.

While I can't look at the internals of the HMI project, based on the behavior of the machine I believe that it is just setting the bit. The tape heads can be disabled either by an HMI button or a physical button near the head itself, however the only way to re-enable them currently is by an HMI button. Again, I can't confirm the behavior of the HMI disable buttons but the physical buttons are momentary I believe(I'll double check that, I was sure until I typed it out haha).