urgent help needed

awalinski

Member
Join Date
Sep 2002
Posts
38
Hi everyone!

I have a EZ-TOUCH screen (Automation Direct) connected to SLC 5/05 on a RS232 port.
It works fine, but from time to time all of a sudden we are getting communication loss between them.
The message tells me that the screen is not getting an answer to it's inquiary. Tech support sais that it is only possible if the port setup changes, but no one is touching anything, so how?
The plc is connected through Ethernet to another plc (peer-to-peer).
Is it possible that too many messages being read by my plc from the other can cause somehow plc not responding to the screen?
Any suggestions how to solve the issue are desperately needed and awaited.
Thanks
 
Communication loss could be due to electrical noise on the serial cable. Are you using a good quality shielded cable?

If there are too many data requests for the SLC to handle immediately, it may have to buffer them. If the buffer overflows, you could lose communications while it resets. If the EZTouch has alarms configured, you could try increasing the time between updating alarms. I don't enough about the details of the EZTouch to know whether or not that's possible.

If your screens display data from several different memory types (N7, B3, I, O) you could try rewriting them so that they use fewer types per screen, or at least make the addresses consecutive.
 
It looks exactly like you said. It first happened when we were reading big chunk from Master plc.
Is there anything else I can do in processor setup or program to solve this issue? Rewritting alarms is not possible, the plant is already running and quick fix is needed.
 
The communications setup for the EZTouch has parameters for 'poll time' and 'timeout'. If your process monitoring can take being a little slower, try raising these.
 
Bernie! Thanks!
I talked to Tech support, but no one mentioned this.
I certainly will try it at the first opportunity ( which may not present itself for some time).
Do you know if the error will reset itself automatically, or the power has to be cycled?
 
awalinski,
Do not overlook the small things. It could also be that you have an internal broken wire in the communications cable. It is surprising how often this occurs. Any cable that gets flexed several times is subject to having one of the conductors break, with the ends touching. It may work okay -- most of the time. Then due to temperature change, vibration, or just Murphy's Law, the ends become disconnected. I have seen this many times. The last time was in the cable going to my computer mouse! You might want to buy a spare cable and swap it out just in case this is the problem.
 

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