Mark If you can't disconnect or ground the interfaces, you might try installing ferrites (e.g., clamp on type or empirical test fixtures found in product sample kits) on the sensitive circuit cables. This will help attenuate the peak voltages coupled to your circuits. Whether this will be sufficient to protect your circuits is another question, but you can determine how much attenuation you will get using a network analyzer and current probes to inject a low level current, and measure the effect at the sensitive circuit interface (with and without the ferrites) using a probe closely matched to the first. You will need to make sure that the ferrites are sized sufficiently to handle the current that you expect to see on the cable shield. DB
> ---------- > From: Price, Ed[SMTP:ed.pr...@cubic.com] > Reply To: Price, Ed > Sent: Tuesday, October 12, 1999 3:39 PM > To: 'm...@cjbdev.demon.co.uk'; emc-p...@ieee.org > Subject: RE: EMI from nearby welding > > > Mark: > > "Old" CMOS design may not have much protection. I would suggest that you > play it conservatively. Unplug the cluster of input wires from your > controller. Or, pull the boards from the backplane if you can. If this is > somehow impossible, I would short the inputs to ground using wire braid or > an impromptu woven wad of bronze wool. > > Regards, > > Ed > > > > -----Original Message----- > > From: m...@cjbdev.demon.co.uk [SMTP:m...@cjbdev.demon.co.uk] > > Sent: Tuesday, October 12, 1999 9:30 AM > > To: emc-p...@ieee.org > > Subject: EMI from nearby welding > > > > > > The query I'd like to put to the readers of this list is not exactly > > EMC related, but is close enough that I hope you'll forgive me > > asking. > > > > Can anyone give me an idea of the voltages likely to be induced > > in the unprotected input wiring of a process plant control system, > > when welding is carried out nearby? Or point me to a resource > > that may give me some help? > > > > The welding cables will be close (within a metre of the inputs to > > the control system, perhaps even touching the control system > > metal case). The welding transformer will be tens of metres > > away. The process plant control system is an old logic design > > based around 4000 series CMOS. > > > > The control system will not be energised when the welding is > > going on, so my main worry is induced voltages/currents blowing > > up the CMOS. Should I worry, or sleep happy? > > > > All advice gratefully received (except if someone tells me to throw > > away the control system and get something better protected, as > > that's not an option...) > > > > Regards, Mark > > -- > > Mark Hone > > > > Wellman CJB Limited Email: m...@cjbdev.demon.co.uk > > Airport Service Road Tel: +44 (0)2392 629239 (Direct) > > Portsmouth, Hampshire Tel: +44 (0)2392 664911 > > PO3 5PG, ENGLAND Fax: +44 (0)2392 697864 > > > > --------- > > > :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) > Ed Price > ed.pr...@cubic.com > Electromagnetic Compatibility Lab > Cubic Defense Systems > San Diego, CA. USA > 619-505-2780 (Voice) > 619-505-1502 (Fax) > Military & Avionics EMC Services Is Our Specialty > Shake-Bake-Shock - Metrology - Reliability Analysis > :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > jim_bac...@monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators). > > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
