How to set a bit and leave it

[pb-edm]

The company I work for recently took over tech support for a SCADA PC that has Lookout 6.1. Our customer is a small town's Utilities department.

A new pumphouse communicates back to the Public  Utilities SCADA PC using radio ethernet.  We've found that when setting command bits (Ack alarms, Reset alarms, disable/enable alarms, manual/auto mode  change) the radio transmission introduces a delay factor.  However, when  clicking a pushbutton object to set a bit, Lookout resets the bit  almost immediately and long before the remote pumphouse PLC receives the  command.

I've looked at and tried the .snapdelay option, set  the pushbuttons to latch their outputs, and examined the Lookout.ini settings but have not  achieved the desired result.  I want to set a bit high with a pushbutton, and leave it high until (optonally) logic in the PLC resets it back to zero. The opposite action would also be desireable, set and stick 0 from a 1 state. In this way, the action would be like a true toggle.

I want  Lookout to just get out of the way and not manipulate the output at  all: accept the set bit and leave it  alone completely. I checked the sample  applications, NI website knowledge base and discussion groups, but nothing comes  close to explaining how to set and leave a bit in Lookout. Flip-flop objects, one-shot objects and the .snapdelay feature are not suitable to this purpose. Why does Lookout not contain a simple toggle capability?

Can anyone please advise me of a method that will provide what I need?

pb-edm

[Rkdomer]

Have you tried using a Latchgate object?

[pb-edm]

No latchgate -- it's not appropriate.  I'm NOT looking for a dual input, single output.  I'm looking for a single bit input object or method, with a single bit output holding at the state it has been changed to.

[Bob_L]

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pb-edm wrote:. 

"However, when  clicking a pushbutton object to set a bit, Lookout resets the bit  almost immediately and long before the remote pumphouse PLC receives the  command."

Its a pushbutton. It clears when you stop pushing it.

"Why does Lookout not contain a simple toggle capability?"

Switch. Use remote position source with a URL referencing a PLC bit. Snap delay may be needed and PLC can set and clear the bit as well.

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[jbesselm]

It sounds like what you want is a Toggle switch that looks like a push button. Try creating a switch object and remote it to the bit in your PLC. For the display option select a graphic for the on state that looks like a depressed button and for the off state an un-depressed button there are some in image navigator. When you click on the button it should set the bit in the PLC and stay there until either you click it again or something else resets the bit. If you have previously set a snap using a connection to the snap delay datamember and then cleared it, you may have to explictly either turn off snap (snap delay=0) or set a sufficiently long delay. How long does your radio communication take? If you look in the event log you should see all that is going on.

[pb-edm]

Thank you for the suggestion.

The radio delay I'm working with is about 2 to 5 seconds, sometimes a little longer.

I was at the customer's site earlier this week and tried several things.  Almost nothing worked.  I noticed a while ago that a SnapDelay of 0 does NOT disable it on any of the pushbutton objects I created in the app. 

I did see in the Lookout Readme Notes file that the unwanted snapback behavior when using remote connections has been a "feature" since version 6.0.  The readme contains several possible workarounds, none of which work (as mentioned in my original post). 

A set of configurations I found in another application worked for half the objects I newly created, and did not work for the other half -- about 15 objects in total, all pushbuttons.  In the pushbutton object properties, I set connections for .enable, .resetvalue and .value to the remote PLC address. When the pushbutton object is clicked, the desired value is forced continuously until a change of state is registered in the PLC.  But like I said, it only works about half the time.

Obviously this IS a bug.  I'm hoping Lookout pulls up its socks and issues a patch.  We don't have ours/our customer's time to waste on something that is accomplished without a second thought in other products.

-pb-edm

[jbesselm]

I think that the push button object is designed as a momentary contact device, whereas the switch object is designed as a maintained device. While they are both switches they have different applications. I would agree that other HMI products have things that look like push buttons but have settings for toggle, switch when depresses, or released etc. In lookout the Switch object behaves as a toggle. I think that when you set a push button as "toggle" in other packages you are actually creating a toggle switch. Its really a matter of semantics. When you release the push button it will attempt to force the bit it is remoted to off.

Is your radio system polled or report by exception?  Based on your communication times I'm guessing polled. When you click the button with snap delay set to 0 it will remain depressed until the remoted bit becomes set, but then since you have released the button it will try to reset the bit but the button will remain depressed until the remote bit returns to off. All this on a radio system could be quite a lot of transmissions bouncing back and forth.

I suspect that if you try the switch object you'll get better results and performance.