[EMAIL PROTECTED] wrote: >Phil,
> I didn't believe that the thermoswitch was the problem, at first, > chiefly because of the simplicity of operation. Eventually, after > checking wiring, a carbon resistor that is in series with the > thermoswitch, and components around the inner oven control > circuitry, I removed the thermoswitch to the bench. > After hooking up to a ohmmeter and using a 60 watt light bulb as > the heat source, I found that I could duplicate the a pulsating > open / close as before. I first focused on the bulb leads and > eventually completely removed the old leads and rebuilt each one > and did all new soldering under magnification. The problem remains > the same. > I'm ready to move on at this point noting that this component > failure has me stumped and that the fault is most likely internal > to the thermoswitch (as strange as this seems). Years ago, when I > first saw how internal temperature worked using the mercury > thermometer switch, I remarked that it was one component that > would never fail. HA! That statement came back to haunt me. >Best, >Russ I have been following this thread with some interest, as I expect to have similar equipment in the future. What is amazing is how you discovered the problem! Like you, I would not have believed a mercury switch could fail. But a quick search showed the contact can oxidize, and gave several patents aimed at solving the problem: 1. Reduction of oxides in a fluid-based switch - US Patent 7071432, 07/04/2006 Often, oxides may form within the switch and inhibit proper functioning of the switch. For example, the oxides may increase or decrease the surface tension of the liquid metal, which may increase or decrease the energy required for the switch to change state. Oxides can lead to poor switch performance, and even switch failure, because they lessen or prevent a switching fluid from wetting surfaces it is supposed to wet. 2. Preventing corrosion degradation in a fluid-based switch - United States Patent 6781074, 08/24/2004 Liquid metal switches rely on the cleanness of the liquid metal for good performance. If the liquid metal forms oxide films or other types of corrosion product buildup within the switch, the proper functioning or performance of the switch may degrade or be inhibited. For example, the oxide film or other corrosion products may increase the surface tension of the liquid metal, which may increase the energy required for the switch to change state. Films of oxide and other corrosion products may increase the tendency for the liquid metal to wet to the substrate between switch contacts, thereby increasing undesirable short circuits in the switching operation. Build up of oxide and other corrosion products may also degrade the ability of the liquid metal to wet to the switch contacts, and thereby may increase the probability of undesirable open circuits in the switching operation. This is very interesting. Thanks for posting your experience. Best Regards, Mike Monett _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.