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

[wa3frp at aol.com]

Sorry for missing enough detail on the original thermoswitch.

The original thermoswitch was a unique design that I have not seen 
elsewhere.  The Princo thermoswitch was a modified mercury thermometer 
with two electrodes installed.  When the temperature rises, the column 
of mercury comes into contact with both electrodes and completes the 
electric circuit.  The inner oven stays within  +/-0.05 degree C of 78C.

Since the design involved a mercury thermometer, the form factor is 
0.25 by 4.25 inches.




-----Original Message-----
From: Mark Sims <holrum at hotmail.com>
To: time-nuts at febo.com
Sent: Tue, 19 Aug 2008 1:54 pm
Subject: [time-nuts] Restoring GR 1120-AB Frequency Standard - Need



The original thermoswitch sounds like is is a mechanical switch,  so it 
can't be
all that accurate or stable.

I would use something like one of those TO-92 temperature sensor chips. 
 I would
probably use a 8 pin micro with an A/D to read it and drive a reed 
relay (or
transistor).  Analog people would use a comparator and voltage 
reference
chip/pot.
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