Out of curiosity, I tried to find something that might do the job. The only PTC thermistor I could find was from Digikey (mfr GE Infrastructure) with a transition temperature in the right range was 70C and rated at only 25 volts, and that was 50 Ohms at 25C :-(
D. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David C. Partridge Sent: 10 September 2008 18:12 To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Ancient OCXO in scope calibrator. Now that's an interesting thought. How should one go about specifying such a part? Do you have any experience of doing this? We'd be looking at (I guess) a turnover from almost short circuit to darn near open circuit over a range of a few degrees centred on 75 celsius. Do such beasties exist? If it's relevant there are two heater windings, one for 230V, one for 115V though both do go through the thermostat. This rather surprised me as I would have expected two windings and only use one for 115V, and switch the second in series for 230V, but if I'm reading the circuit diagram right (not g'teed) this isn't what happens (it's on the last schematic page which is the power supply for those who've donwloaded the manual from BAMA). There's also something connected between the two windings which looks a bit like two cup-hooks - what this is I'm not sure. I don't recognise the symbol at all, it could just represent the bimetal strip part of the thermostat. I also don't quite understand the point of the capacitor at the top end of the 230V winding. Cheers Dave _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
