Is it bad to have multiple identical inputs on an HMI?

[TheRooster]

Hello all,

I know its not good practice to have duplicate destructive bits when writing plc code, but I'm wondering about writing to the same tag with two buttons on an HMI? Right now I have 3 servo screens, in all 3 you can input a desired position, press a button to go to it, or press a button to go home. The tags are just HMIPB.GoHome or HMIin.MoveTo and start a servo move after some logic. I literally just copied and pasted the inputs/buttons, but now I'm concerned it may cause issues down the line.

 

[plvlce]

I don't think I've ever seen an HMI where this was an issue. Usually a button only does anything on change of state. When you press the button, it tells the PLC to change the associated bit to a 1. When you release it, it tells it to set it to 0.* The other buttons have no effect until you press/release them.

Numeric inputs and the like similarly write their value once, when you press enter, and don't change anything in the PLC when not interacted with.

To put it another way, tying multiple buttons to the same tag is like wiring buttons in parallel to the same physical input. When any of them is pushed, the input goes on, but the PLC can't tell which one the input came from.

One thing to keep in mind is that depending on the HMI and how you have it set up the displayed state of your buttons may reflect the state of the individual buttons, or of the input as a whole, eg having one button pushed may cause all of them to show as 'pushed'.

*assuming momentary pushbutton

 

[TheRooster]

Ahh okay, the wiring in parallel analogy makes sense, thanks for the reply.