[wmpy]

First of all, let me say that my knowledge of and experience with electronics is very limited. I'm a CNC setup guy who often times needs to fix machines. I'm hoping someone with experience here can help with my problem.

Background:
Hardinge CHNC I lathe with Fanuc OT-B controller has been giving intermittent alarms: 930 CPU Interrupt or RAM (or ROM... I don't remember) Parity Error. Usually, I can shut down the machine, power up, and everything's fine. Sometimes, though, I need to clear the memory and reload all parameters, programs, offsets, etc. These alarms can happen a couple times a day, or I can go a few days without one. They always happen in the same part of the program, though. It's always during a collet open or collet close. The collet actuator is pneumatic which is controlled by a solenoid which is controlled by a relay. So, this tells me that I'm getting some sort of electrical interference from either the relays or the solenoid. I've tried swapping relays and replacing relays, but that hasn't worked.

A friend of mine suggested that I install an RC filter network on the suspect devices. Does this sound right? I had no idea what those were, so I tried doing some research, and learned a little, but not enough to figure out how to do it.

My question is where to install the RC filter network? across the coil of the relay? across the contacts of the relay? across the coil of the solenoid? I also don't understand how to specify the RC filter network. How do I determine the R and C values?

Thanks in advance for your help. I really look forward to getting this annoying problem fixed.

Robert

[Al_The_Man]

The RC snubber is usually fitted to AC coils and solenoids, .22µf with 100ohm in series.
Do a search for snubber here and should pull a few links up.
If the coil is DC you need a reverse EMF (reverse biased) diode across the coil itself.
Always fit as close to the coil as possible.
Al.

[wmpy]

The relay coils are DC. When I replaced the relays, I got ones of the same type, but with the "surge suppression diode" option. Is this the reverse-based diode you mention?

[Al_The_Man]

Sounds like they are already fitted, when using these types you need to make sure how they are polarized in order to hook them up the correct way.
Al.

[wmpy]

The relays are the plug-in type. They're IDEC RH2B-UD DC24V. Maybe I don't understand, but I don't see how they could be hooked up the wrong way. So, if my relay coils already have the diode suppression, what else could be causing my problem?

[Al_The_Man]

Im not saying they are hooked up wrong, just that if they are a new installation and the polarity is not observed you blow a P.S. fuse.
Make sure that the solenoids also have a snubber, if AC and a diode if DC.
Al.