AD DL-06 Input Failure

We are an OEM that uses the DL-06AR 120VAC Inputs on several of our machines. We have not had one single problem with them until now. I don't think it is the processor itself, but instead is an external wiring problem.

There are 16 various push buttons, sensors, and selector switches wired into the inputs on the unit, all from the same 120VAC source and same common. The failure was that input X0, which has a maintained E-Stop button wired into it, would fail. We sent a replacement plc figuring it was a fluke failure. 30 days later the same input failed. All other inputs still worked fine.

AD says that the only thing that would wipe out an input is an overvoltage condition, but why just the one input and not any others.

Any help would be appreciated, thanks.

We too had an input failure problem. The input was a monitor of an inductive circuit which was being turned on and off by a switch (actually an E-Stop). It turns out the inductive kick back during turn off was killing the input. A varistor across the device stopped the problems. Does your E-Stop ONLY go to the PLC? Or is this one contact of a multi contact switch where the other(s) do the actual turn off switching and this line is only an input?

"Or is this one contact of a multi contact switch where the other(s) do the actual turn off switching and this line is only an input?"

Yes, this is the case.

Have you checked the control voltage level? Could it be running at a higher than normal level? DL06 AC inputs are rated for 90 - 120 VAC. If this is the only input on the machine that's wired to a NC contact, it would be energized for a higher percentage of the day than any other. It could be the canary in the coal mine.

Sorry Bernie, I just talked to our electricians and they informed me that they only used one contact on the E-Stop and besides the input it also runs two good sized dump valves (inductive kick). Looks like they did not follow the prints. Thanks, you are a lifesaver.

The issue now is that there is not an extra wire to wire another contact in ( the button is not in the control panel). Could you explain the varistor trick in a little more detail. Thanks.

See Page 2-21 of the D0-06USER-M. If you don't have it it can be found here.

Be sure to read the last part of page 2-20 for WHY this is happening. Then the table at the top of 2-21 will show acceptable parts. By the way, the varistor (MOV) is most effective the closer it is to the source of the kick (the coils). Put one near each if needed.

I was having a problem similar to this and started using double stack terminals with MOVs built in. I wire all my valves this way now.

Thanks guys, you have been a great help. In the future we will isolate the inductive coils from the actual input. For the time being we will add a relay in the control box to isolate the input since we have a service guy on scene with a relay.