H-O-A touchscreen?

dginbuffalo · Oct 16, 2013

Hello- looking for opinions. We typically provide a touchscreen on our control panels. What type of hardwired buttons or switches do you use with a touchscreen? We always provide an E-stop but I'm torn with providing H-O-A switches and run stop buttons when I could just program them on the touchscreen. I guess part of me thinks that if the touchscreen died, at least they could turn their system on and off if there were hardwired switches on the panel. Thoughts?

mendonsy · Oct 16, 2013

Depends on what your application is.
If the system can run without the operator interface, then you might consider it. A lot of them can't.
It may be less expensive to have a spare touchscreen than to build in all the hardware and wiring required for switches.

dginbuffalo · Oct 16, 2013

Project is a compressor with some auxiliary systems. they will be able to change the setpoint but I think that will pretty much stay the same once dialed in. All the aux systems will start on a group start with the compressor and do their thing. I don't see much operator interface happening on a regular basis.

Jmeadows7676 · Oct 16, 2013

One thing to remember any button that will be used alot, should be hardwired. Of course All estops should be too. It sounds like that want be a problem (I don't see much operator interface happening on a regular basis)

jseavers · Oct 16, 2013

Buttons or switches that have a high usage I try to install hardwired just to keep the screen on a HMI in good shape.

James Mcquade · Oct 16, 2013

dginbuffalo,
e-stops, e-stop resets, and certain other controls (depending on the machine) are required to be hard wired.

NFPA 79 - electrical standard for electrical machinery.

buttons on HMI terminals fail and stick in the on state. replaced 2 units for that reason.

since this is a compressor, I STRONGLY !! recommend hardwired e-stop and reset.

a friend of mine was severly injured by an air compressor because of safety issues. the company was found guilty of safety violations.

regards,
james

dginbuffalo · Oct 16, 2013

Yes- E stop definitely on panel.

By buttons on the HMI- I was referring to virtual pushbuttons on the screen. I never really use the side buttons except for changing pages.

brstilson · Oct 16, 2013

It depends. I usually provide an E-Stop because a hard-wired E-Stop is usually mandatory anyway. But I'd ask these questions:

1. How critical is this piece of equipment? How big of a deal would it be if it went down?
2. If it's a big enough deal, what does the customer need to do, at an absolute minimum, to keep it running?

An HMI exists to eliminate push buttons and selectors. It's not just component cost, but wiring and installation time, and more things to go wrong. My first instinct is to put them on the screen, but only if this is not a mission-critical piece of equipment.

curlyandshemp · Oct 16, 2013

If any of the HOA are connected to motors with feedback, make sure you have an IH( In Hand )alarm programmed for those motors. IH is determined whenever the PLC Motor Output is OFF, but the Running feedback is ON.

cjd1965 · Oct 16, 2013

Hi
The last compressor farm I did, the manual control was totally hard wired with Auto being under PLC control. This provided a means of running without the PLC because it was a critical system and they didn't want to pay for redundancy

Steve Etter · Oct 16, 2013

The only thing I want to add is the consideration for "touch". Sometimes an function requires that the operator is looking at the actual process rather than the screen when pressing or bumping a button. In those cases it is often preferable to use hardwired buttons rather than a touchscreen so that the operator can "feel" when the button actually pressed.

Clay B. · Oct 17, 2013

As several have said there are lots of reason to use and not use hardwired push buttons. One thing not mentioned is I/O. Whenever you use a push button you have to use an input on your PLC, that will drive the cost for it as well.

As a preference I prefer to always have Start Stop and HOA as switches and a green run light and red fault light as a minimum on any system I build. So any time I build I know I will use 3 inputs and 2 outputs as a minimum on my PLC.

The way I justify this is it saves on wear on the HMI. It is easier on the operator and it gives me flexibility on my HMI screens.

I did not mention E-stops as that should be a no brainer, its always a switch.

shooter · Oct 17, 2013

start/stop buttons are good, to prevent wear as operators push hard on screen when unit is not running immediatly, In the PLC make it that they have to push the button until unit is free of alarms like oilpressure etc.
then the light in button comes on to signal unit is running good.

H-O-A touchscreen?

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