SLC 5/05 slow processing with Panelview Plus 6

[Captain7]

I have an issue with an Allen Bradley SLC 5/05 program acting “slow”. A few months ago, I noticed an issue with a part of my PLC program not executing when it was supposed to based on what screen was open on my Panelview. A piece in the machine should be inserted at a specific encoder position. When a certain screen was selected, the position would be late. When I did a trend, the part would try to insert when the encoder value was between 90 and 110, like it was programmed. When the screen was changed, the part would insert between 105 and 125. I noticed the refresh rate for this screen was set to .25 seconds. I changed all the refresh rates to 1 second, and seemed to help a lot. However, there is still the occasional time when the insertion position is late. Any thoughts? Could the Panelview still be causing the issue? Why would the refresh rate affect the program speed?

Thanks

 

[OkiePC]

The SLC can have its scan time affected by communications. I would venture to guess that the HMI is reading a lot of scattered addresses if you can truly see a difference depending on which screen you're monitoring. Back in the olden days of DH+ and RIO comms I developed a good habit of paying attention to how my HMI addresses are organized. Keeping all the bits and bytes in tight continuous groups can make a huge difference in the performance of the operator interface on those old networks. Even on machines where the OEM made the addressing a random scattered mess I never saw it slow down a PLC5.

With the advent of Ethernet, folks are less careful since speed of comms usually is not noticeably affected by disorganization.

Sometimes you can cheat and toggle a bit to make things better:
See the RSLogix help file in regards to Comms Servicing Selection S:2/15

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