Dan Rae wrote: > The 10811-60111 that came in my 5370B counter turned out to have an open > circuit Thermistor in it. This is a "non-replaceable" part in theory. > > However, nothing to lose, I have successfully substituted a Digikey Part > number: 317-1371 100 kOhm 1% Thermistor ( from Cantherm, part number: > MF51B104F3950 ). > > I measured the resistance of it at the target oven temperature, working > back from the selected value of R20 that was installed in mine, in this > case 0 Ohms for 84C. In fact this thermistor must be very similar to > the one used originally, since I only needed to use a value of 110 Ohms > for R20 to get bridge balance, instead of the short that was in there > previously. > > Good enough for me... > > Dan > > Dan
The real reasons that this part is labelled non replaceable are 1) its epoxied to the oven. 2) Setting R20 to the correct value actually requires plotting the OCXO frequency vs R20 and selecting R20 so that the OCXO frequency is located at the stationary point on the frequency vs R20 value plot. This requires a high resolution frequency measurement setup with a highly stable reference and takes considerable time as one has to allow the oven temperature to settle between adjustments to R20. Drift due to aging and ambient temperature changes limit the accuracy with which the OCXO turnover temperature can be achieved. Bruce _______________________________________________ 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.
