adccommunitymod (AutomationDirect) asked a question.
Created Date: September 14,2010
Created By: dschlyer
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I have a 250-1 cpu with an EZAutomation color touch screen plugged into port 1. There is a short serial cable going to a bulkhead connector in the enclosure, a 50 ' long serial cable going to another bulkhead conn. in the little box the display is in, and then another short cable going to the display. (I have 150 units like this in the feild, but with the display in the local enclosure - this is one of 4 units that are like this, but only this one gives trouble) The screen responds erratically to the CPU, we get occasional "Communication Problems " messages, but more problematically at times when a screen button is pushed nothing happens. If you press several buttons, after awhile the actions may all be done as if the button presses were buffered, or maybe it will just sit there doing nothing forever, or maybe it will start to respond again without doing the 'bufferred ' actions. This is driving me CRAZY! The cable(s) have been replaced, grounds checked, screen changed out - anyone got any ideas? I probably will change to a CMore screen and go ethernet, but I still need to understand what is happening.
Created Date: September 14,2010
Created by: JoeW
RS-232 or 485?
Created Date: September 14,2010
Created by: dschlyer
Port 1 is only RS232, as far as I know...
Created Date: September 14,2010
Created by: JoeW
Ahh thats right, I must have just ignored the port 1 part. You mentioned you have a 50 ' run plus a few more for internal connections. Right there you are over the max length for 232 (50 '). Have you tried a shorter cable?
Created Date: September 14,2010
Created by: Do-more PE
50 ' for a RS-232 serial cable is pushing the limits of practical application. The spec says 100 ', but that is in a pure laboratory situation.
The problem with trying to get that sort of distance out of RS-232 is that RS-232 is a ground based signal with poor noise rejection properties. If the cable is near anything that generates a magnetic field, radiates electromagnetic noise, or if it is connected to anything that is poorly grounded, then you have issues.
Personally I would get an FA-ISOCON and convert that long run into a RS-422 or RS-485 signal that is noise tolerant.
Created Date: September 14,2010
Created by: dschlyer
Thanks, guys. I will try the converter and also shorten up the wiring. Really appreciate the input.
Created Date: September 14,2010
Created by: dschlyer
I have a 250-1 cpu with an EZAutomation color touch screen plugged into port 1. There is a short serial cable going to a bulkhead connector in the enclosure, a 50 ' long serial cable going to another bulkhead conn. in the little box the display is in, and then another short cable going to the display. (I have 150 units like this in the feild, but with the display in the local enclosure - this is one of 4 units that are like this, but only this one gives trouble) The screen responds erratically to the CPU, we get occasional "Communication Problems " messages, but more problematically at times when a screen button is pushed nothing happens. If you press several buttons, after awhile the actions may all be done as if the button presses were buffered, or maybe it will just sit there doing nothing forever, or maybe it will start to respond again without doing the 'bufferred ' actions. This is driving me CRAZY! The cable(s) have been replaced, grounds checked, screen changed out - anyone got any ideas? I probably will change to a CMore screen and go ethernet, but I still need to understand what is happening.