Issue with HMI Browser Client

dtrillo

Hello. When using HMI Browser Client, with two buttons as start stop signal for two bool variables, I found that if I do a short click they sometimes don't perform the start/stop change on the output. I checked HMI web server settings and changed Data poll interval to the lowest possible and it still happens (thought that was the setting I needed to change but it seems it isn't). I also checked the PLC Data List status and sometimes I'm able to see the value changing to "TRUE" in the start/stop signal associated to the buttons but yet no change on the output they act on, and other times I wasn't even able to see any change, they stayed with "FALSE" value. It only happens with short click, if I hold click for like at least half a second it always works. What am I missing that causes this?

Martin [PLCnext Technology Team]

I guess you are using the "Behaviour" section of the button properties to assign the boolean variable to the button, rather than using a Dynamic to do this.

In this case the likely cause of the problem is that one message is sent from the broswer to the PLC as soon as the button is pressed, and another message as soon as the button is released. If the button is pressed and released too quickly, the PLC will get the "On" and "Off" messages so close together, that the program that processes the button state may miss these transitions altogether. You can think of this problem in a similar way to the problem of a hardware button, wired to a digital input on the PLC, that is pressed and released too quickly.

If you want to make sure the signal from the HMI is never missed, you could latch the button, and turn off the boolean variable in the PLC when the button-press has been handled.

Hope this helps.

dtrillo

Thanks Martin. I was indeed using behaviour and not dynamics. I tried with dynamics action on pressed and action on released, but had the same issue. I guess the solution you present with latching is the only option. Thanks for your answer, it helps.