[time-nuts] Restoring GR 1120-AB Frequency Standard

phil fortime at bellsouth.net
Wed Aug 20 03:45:00 EDT 2008


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" <fortime at bellsouth.net>
To: <time-nuts at febo.com>; <wa3frp at aol.com>
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: <wa3frp at aol.com>
> To: <time-nuts at febo.com>
> Cc: <fortime at bellsouth.net>
> 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 <fortime at bellsouth.net>
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at 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" <namichie at gmail.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at 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 at 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 at 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 at 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 at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there. 




More information about the time-nuts mailing list