Way off topic - RS232 Filter?

Hi all,

This is way off topic, I know, and I hope y'all don't mind too much, but since it is communications related I thought it might be Ok.

I recently "fried" a CNC machine (~$9,000 worth of repair) when I replaced a UPS on a peripheral PC that is used to store parts programs. This PC is connected to the CNC via an RS232 cable and there is a small application that runs on the PC to suck the parts programs from the CNC and store them on the harddrive and then to poke them back into the CNC when needed.

Talking to the tech support guys from the CNC manufacturer, I am told that the serial cable between the two should remain disconnected whenever uploading or downloading is not happening. Had this been the case when I attached the new UPS, they say, the problem would not have happened (Yeah, right). The reason for keeping the cable disconnected, they say, is to protect against the effects of lightning, etc.

Anyway, this is a plant-floor machine. The PC is right there, on the plant floor, at the machine. The guy who uses it is the machine operator and he needs it when he needs it. What he doesn't need is to have to attach and disconnect the cable every time he uses it. I have no doubt that the cable will remain attached eventually.

Ok, finally...my question: Does anyone know of some kind of filter/buffer that goes inline with serial cables to protect against spikes and such caused by lightning, etc.? As far as liability is concerned, I am pretty sure the CNC manufacturer will not recognize anything short of their recommended procedure, but I cannot live with this procedure, either. I need to find some sort of reasonable way to realistically reduce the machines exposure and keep the cable attached at both ends.

Thanks,
Steve

Try optical isolation
http://www.bb-elec.com/protect_system/isolators.asp

Steve

As Ron stated above go for opto-isolation, but I thought that most 'modern' rs232 ports are opto-isolated as a matter of course, I might be wrong on this front, I await to be put right on this matter.

Paul

Looks Perfect

Thanks Ron,

This looks like exactly what I need. I will even try to get the CNC man to agree to it.

PLucas...Never heard that before, but then again, I never heard the opposite either.

Thanks.
Steve

Steve

I am sure that the ports on my laptop are opto-isolated and I am 99% sure that the rs232 port on the siemens CP340 comms module is also opto-isolated, so that is what I am basing my limited knowledge of our friendly 232 ports on

Paul

My experience is the opposite... I've seen laptops fried because they were plugged into their wall socket source which was on a different ground than the PLC on a machine.

B&B Electronics are my source as well for this sort of thing.

For a great technical overview of serial device isolation, read through Lynn A. Linse's tutorials at:

http://www.robustdc.com/

The Siemens CP340 comm port is galvanically isolated, the laptop may be but I would take time to triple check that because it is not a common feature for any computer system. I have fried alot of older computers playing around with things from the serial and parallel port. I have also seen laptops fried when connecting to things in a plant.

B & B is hard to beat, but if you want an alternate source for price or delivery comparisons try Black Box www.blackbox.com