In our plant we have several remote I/O systems driven with a RM-201 module in a C1000 PLC. In the last few years we have been having more problems with the remote systems, especially after a power outage. The RM-201 module has an indicator for a proper terminator resistance. When the line is checked with an ohm-meter the resistance is correct (60 ohms) but when power is applied the module indicates multiple terminators. This problems is occurring in different areas of the plant and changing cards has no effect. I also know our sister plant in Taiwan has the same issues (they have simular equipment). Omron has not been helpful. Has anyone had this problem or can offer suggestions for trouble-shooting?
Thanks in advance,
Jerry Hayden
Carlex Glass Co.

 

Jerry, your problem is not unique.

The key here was the problem occurs after a power failure.

When the RM201 powers up, it "looks for the nodes that are powered up" and "looks for it's terminators"

If power restores to the RM201 before the slave racks or I/O - it gets REALLY UNHAPPY.

I know of plants that have put an On-Delay timer on the power supply to their CPU rack (that houses that RM201) to ensure after a power failure it is the last thing to power up. Sounds crazy but it works - if that is the source of your problem.

Also, it may be that in large loads starting in your plant cause changes in ground potentials between PLC areas. Are you goig building-to-building? Consider using a pair of Wired to Fiber bridges to Galvanically isolate the bus.

Also, you mentioned you had a C1000H. That PLC is about 12-15 years old. Maybe time to have a look at a control system refit? $ per I/O point are much lower today than back in the mid nineties. If you add up your comined downtime, you may have bought both your plants new PLCs by now.

Paul Burke
[email protected]
(former Omron Employee)