PanelBuilder32 3-Position Maintained Selector

[Bill Dolan 0]

I am trying to emulate a 3-position maintained selector switch and wondered if someone might recommend an approach.

[panic mode 246]

it's been a long time since I've used PB32 but is I recall you can use multistate pushbutton

[JRoss 84]

In general I avoid using a multi-state push-button to emulate a multi-position selector switch. Because it is a single button, it forces you to cycle through a series of states until you reach the one you want. In some cases this doesn't matter, but there are times when this can have unfortunate effects. For example, let's say you are emulating a Hand-Off-Auto switch (the most common one I see). Hand usually turns the device on, whereas Auto does not necessarily. If Auto is in an off state, then switching back and forth between Auto and Off will also cycle you through the Hand state, momentarily pulsing the device on. If Auto is in an on state, then switching back and forth between Auto and Hand will also cycle you through the Off state, momentarily pulsing the device off. Of course, there are ways to program around this, using state-change time delays, and things like that. However, I find it easier to eliminate the selector switch altogether. I would use one of the following approaches, and there may be others. 1. Multiple interlocked buttons. The Panelview Plus has an object specifically for this, but you can roll your own in most HMIs. I've seen this done with a graphic of a selector switch showing the position, and the buttons arrayed around the graphic. That's if you really want the old school look. 2. A pop-up with selector switches. This is actually a variation on the previous version, but doesn't take up as much real estate. Put some kind of indicator or graphic showing the current state, then overlay an invisible goto-screen button that opens a pop-up showing the available options. EDIT: And then I noticed that you said Panelbuilder32. Same basic principles apply, but I don't think the Interlocked Pushbutton object existed on the old Panelviews. In that case I would roll your own with two or three maintained pushbuttons and use some logic in the PLC to interlock them. Let me know if you need a more elaborate explanation. Edited 23 Jan 2014 by JRoss

[Bill Dolan 0]

Thanks Jeremy. This was very helpful. I had thought of what you mentioned in your EDIT comment. It would seem that three pushbuttons will consume a fair amount of real estate on the Panelview 1000 - though I could use a GO to screen button as you suggest. I also thought of a listbox object with three states.

[b_carlton 61]

As far as a 'Hand - Off - Auto' application with a multi-state use 4 states 'Hand - Off - Auto - Off' so that you go through 'Off' always between 'Hand' and 'Auto' just like on a 3 position physical switch. Let the PLC combine the two seperate 'Off' states into a single one.

[chantecler 15]

Hi, In a physical selector switch you unavoidably must pass through all intermediate positions when moving from one position to another. I personally like to use an Inc/Dec Numeric Entry Object for this purpose. I am attaching two files showing how. In this example you have an integer limited to three possible values (1, 2 & 3) and use the up and down arrows to move from one value to another. Bye SelectorSwitch.PBA SelectorSwitch.RSS Edited 25 Jan 2014 by chantecler

[JRoss 84]

Some other great ideas here! Definitely worth considering. I still prefer my approach (of course...), mainly because I think that passing through intermediate states is a weakness of a physical selector switch, and since we're hopefully already improving a system, why not take it a step further? Another two-button approach to a Hand-Off-Auto would be to have two maintained pushbuttons, one for Hand, one for Auto. If both are off, then you are in the Off state. Use some PLC logic to make sure you don't get both on at the same time, then you're done!