Russ, Also could it be a cold solder joint on the tubes connections, possibly look good but have a high resistance. That could account for an intermittent as you are describing. Sometimes we overlook the simplest of things. Phil
----- Original Message ----- From: "phil" <[EMAIL PROTECTED]> To: <time-nuts@febo.com>; <[EMAIL PROTECTED]> Sent: Wednesday, August 20, 2008 3:26 AM Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard > Russ, > In other words, you sound like you are not 100% sure it's the switch. A > shame you couldn't graph voltage and current going to the switch as it > cycles. Is it possible a cap or something else is intermittently failing > in > the circuit. Again I'm assuming with that resistance there is something > between it and the heater. Though I had one, I don't think I ever looked > inside the thing. > > I have seen some similar units (I think what you have) that use an almost > paper thin column of mercury. I would guess that is how they can achieve > the > fine resolution/precision. > > Phil > > > ----- Original Message ----- > From: <[EMAIL PROTECTED]> > To: <time-nuts@febo.com> > Cc: <[EMAIL PROTECTED]> > Sent: Wednesday, August 20, 2008 2:34 AM > Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard > > >> Phil, >> >> The details of the thermoswitch failure are not completely clear. >> Intermittently, the mercury column will pass the 78C point without >> causing >> circuit closure. Instead, a pulsating open / close with an internal >> resistance of 50K - 300K is observed. Circuit closure eventually happens >> at a temperature above 82C. Once an external failure, i.e. lead wiring, >> was ruled out, I used a borrowed microscope to view the internal >> structure >> of the thermoswitch. Unfortunately, this did not reveal the failure >> source. >> >> Russ >> >> -----Original Message----- >> From: phil <[EMAIL PROTECTED]> >> To: Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> Sent: Tue, 19 Aug 2008 9:33 pm >> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard >> >> >> >> Neville, >> good answer. Perhaps the original poster could supply a photo of his >> switch, >> perhaps more suggestions could be made. I think we had an old gr-1100 at >> one >> time, it was a 100kc unit. Needless to say it was scrapped years ago and >> I'm >> sure it's been melted down and sent back to the usa in tin cans or cars >> by >> now! I'm curious as to how the switch failed. I'm assuming it was a >> sealed >> unit. >> Phil >> >> ----- Original Message ----- >> From: "Neville Michie" <[EMAIL PROTECTED]> >> To: "Discussion of precise time and frequency measurement" >> <time-nuts@febo.com> >> Sent: Tuesday, August 19, 2008 7:46 PM >> Subject: Re: [time-nuts] Restoring GR 1120-AB Frequency Standard >> >> >> Hi, >> this is a second attempt at an answer, the first seemed to evaporate. >> Mercury-in -glass thermometers have formed the basis of a system of >> thermostats >> used constant temperature systems of very high performance. >> A major producer of contact thermometers was Jumo (maybe German). >> These thermometers had a thin wire that went down the capillary and >> contacted the mercury at the set temperature. The system could be >> accurate to >> 0.005 degree. The control algorithm is alien to modern EEs but used a >> large thermal mass and a fixed rate of heating to produce a slow >> temperature ramp. >> Fast response by the thermometer switching kept overshoot down to >> millidegrees. >> A cycle time of 5 or 10 seconds kept a very low amplitude temperature >> ramp running up and down >> with mean temperature held quite close. >> Locating the thermometer close to the heater caused a little over >> control which reduced overshoot and cycle amplitude. >> The thermometers had up to 30 mA run through the wire, but more >> modern units reduced this to 1mA. >> If the tip is corroded on your thermometer contact, maybe a higher >> resistance measuring circuit may >> still operate reliably. >> Good Luck with the unit, >> Neville Michie >> >> >> >> >> >> On 20/08/2008, at 9:17 AM, Mark Sims wrote: >> >>> >>> I suspect the only place you would find a replacement themoswitch >>> is in another unit. I also doubt that any current mechanical >>> switch will be anywhere near stable and accurate enough. >>> >>> I stand by my original comments: Built a solid state functional >>> replacement in the same form factor as the original unit. It will >>> be hidden inside the oven assembly where only you will know of the >>> dastardly deed that you did. If you ever find a replacement >>> switch, you can install it and bask in its originality. Until >>> then, bask in its solid state patch enabled oscillatude. >>> >>> A non-original part that restores a device to operating condition >>> is far superior to a dead unit... particularly if the part is not >>> visible. There are lots of zillion dollar antique cars winning >>> best-of-show with modern internal engine components (not to mention >>> bondo and fiberglass under the paint). >>> ---------------------------------------- >>> >>> _________________________________________________________________ >>> Be the filmmaker you always wanted to beearn how to burn a DVD >>> with Windows. >>> http://clk.atdmt.com/MRT/go/108588797/direct/01/ >>> _______________________________________________ >>> 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. >> >> >> _______________________________________________ >> 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. >> >> >> _______________________________________________ >> 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. >> > > > _______________________________________________ > 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. _______________________________________________ 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.