On Wed, Dec 10, 2008 at 6:28 PM, Richard Prosser wrote: > On 11/12/2008, John Ferrell wrote: >> I hired in to IBM in 1961. This scheme was used at that time for power >> supply regulation. That is, one pair of wires to deliver the power to its >> destination and a pair of sense wires back to the regulator where the supply >> was dynamically regulated. >> >> I thought it was simply clever industry practice. >> Looking at it from today's viewpoint it looks like they are patenting Ohm's >> Law. With today's legal system in the US it might work out for them... >> >> John Ferrell W8CCW >> > > We used a cable measurement system with a similar power suppy > connection. All went well until the sense wire connection broke and > the power supply started delivering 8 volts or so to about 500 TTL > chips. > Cost _a lot_ of money to rebuild but we ended up with a much more > reliable system in the end. Every Kelvin-connected power supply I've seen has resistor or a few hundred ohms between "force" and "sense" to prevent exactly this occurrence. But I suppose the "sense" wire could become loose and touch ground or something. Regards, Mark markrages@gmail -- Mark Rages, Engineer Midwest Telecine LLC markrages@midwesttelecine.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist