I'm in IT, and pretty unfamiliar with CNC technology, but I've been asked to troubleshoot our DNC system, and fix a problem we've been having. The system is horribly outdated. We have a Windows 95 box running this software sub-soft.com/dncplus.htm PC-DNC plus. This computer has a rocketport serial controller card, with breakout box. The breakout box connects to about 15 machines via RS232. No two machines are of the same brand and model, therefore we have have a wide range of different COM settings. Our machines are located as far as 50ft from the breakout box.

We have been getting communication errors in the form of, strings of charecters disappearing when sent across the link. This can occur anywhere in the program. The missing section is typically a line or two long. We used to receive errors like this constantly, but that was resolved (to some extent) when we replaced the computer. When this would occur, the computer in question would become unresponsive for around a second. You couldn't move the mouse cursor, etc. It seemed like a software problem at the time, and we have had some success with it since then. We have received a dozen errors on each machine since this replacement, where before we would have had hundreds by now. We used the same rocketport card as before.

We only recently began to realize that the problems are still occuring, because they are so infrequent. They are persistent though, and we worry that we're going to have a tool crash in to the work.

I'd like to replace all of our serial cables with ethernet, and use serial-ethernet adapters at the machine. Does this sound like a reasonable approach to this problem? Thing is, we really don't want to spend any money, but I feel like there might not be any way around it. We have the ethernet cable, and time, but it's the adapters we're worried about. Are there other approaches we could try first?

Sub-soft company is stilll on business these days, I'm sure they could help you with an upgrade to your whole system, but of course, money is required.

I'd like to spend the money. It's what I've been suggesting. The thing standing in my way is, it's not my decision. I've been asked to replace the computer again, if I can't make progress some other way. I think this path is a dead end. If I could show that professionals in this field agree, we need to spend the money, that would help.

Can anyone tell me about your own experience in a similar scenario? That is, you had programs being corrupted due to old rs232 wiring, then you upgraded to ethernet, and it solved the problem?

Does anyones experience all them to say with any confidence, an upgrade is in order? "This is what you have to do."

What's the quality of your cables? If you use braided shielding that can and should eliminate any noise slipping in. That is what this sounds like especially if you have foil shield.(Which will break down over time) If the old system is working fine why change? Speed wise you're not going to gain enough to matter even if your are machining high speed profile spline surfaces. Just a thought.

I would tend to agree with "Strat", that you might inspect the quality of the wiring, especially if it's over 10 yrs. old in a "shop" environment. It's possible that coolant, mist, etc. have broken down the insulation over the years and this could impact signal integrity. In addition I would suggest you check the routing of the cables with respect to the proximity to high voltage sources, motor leads, etc.. I have seen voltage transients cause some pretty bizarre issues with RS-232 communications. Finally, insure that the shield of the cable is only connected to pin 1 (assuming DB-25 connector) on ONE END of the cable, otherwise the possibility of ground loops is almost unavoidable.

All that being said, the reliability of RS-232 based communications in a factory environment is pretty good, provided that the above pitfalls are avoided. I have heard many people advise against running over 75 ft., but the driver IC's that are used in current equipment can usually handle a couple hundred feet. Of course, USB to RS-232 has it's own issues, but based upon the vintage of the equipment you seem to have, that is likely not a consideration.

As someone else mentioned, Suburban Machinery is still around (Suburban Machinery / Software Division Home Page) and Dan Fritz is a very helpful individual.