panelview button not always seen by plc

mrgees100peas

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Join Date
Aug 2016
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vermont
Posts
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Hi,

I have an application in factory talk view ME edition for a panel view+ 700 and a program in rxlogix studio 5000. I manage to make all my application work with the PLC animating fans, navigating screens, indicators light the works. Everything works great except for one button. The momentary button connects to one a XIC instruction in the PLC in only 1 RUNG and all it does is enable a clear command and unlatches a bit. The problem is that when I press it it doesn't always work. Sometimes it picks it up immediately and other times it takes a couple of tries. I think it is some sort of scan issue. I even made a trace to see if I could capture the signal but it doesn't pick it up. it does however, unlatches the bit and runs the Clear command but again, not consistently. Any suggestions?

I tried changing the maintain time on the momentary button and changing the maximum refresh rate both to lower and higher numbers but still no luck.
 
To Verify your button, place a Counter (CTU) in the same rung as the OTU instruction. Then press the button multiple times on the HMI and see if the count matches.
 
I dont know if this is possible on a panelview, but instead of setting the bit momentarily from the panel, only set (latch) the bit from the panel. Then in PLC code, evaluate the bit, and then reset (unlatch) it explicitly.
 
I dont know if this is possible on a panelview, but instead of setting the bit momentarily from the panel, only set (latch) the bit from the panel. Then in PLC code, evaluate the bit, and then reset (unlatch) it explicitly.

This is quite possible on a panelview, and is my preferred method for doing this kind of task. If it needs to be momentary, it needs to be a physical button, period. Otherwise, you have a large potential for a button to be stuck on.

Basically:
Button is pressed on HMI. The PLC sees that this button is pressed and sets the tag associated with it. Then, the PLC does what it needs to, unlatches the bit. The HMI reads that the bit is now unlatched and adjusts accordingly.
 
You cannot expect 'Real Time' (I/O Class) CPU 'reaction' to a tag broadcasted by a HMI application; depending of the FTVME application's complexity and the available bandwidth of the communications network (presuming it is Ethernet) there will be a variable 'lag' between the time the pushbutton changes states and the controller 'acknowledges' the state change.

If you need I/O type data exchange, use a physical push button connected to a PLC Input point.

If no I/O is available nearby, like Jesper suggested, in the Logix application, examine the HMI pushbutton (XIC) and, when 'true', 'latch' (OTL) a BOOL tag which's state will be used to implement the HMI pushbutton related logic; when the logic is implemented 'unlatch' (OTU) the PLC tag 'related' to the HMI pushbutton.
 
AAAHhh false alarm. It turns out there was more than one occurrence of the tag. The first one was attached to the first scan with the idea to do a reset one time only. Well, it was implemented wrong and it was forcing the desired bit off. The button then was working intermittently because coincidentaly it would pick up being set to one in the scan.
 

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