Nickel sensors are more stable than thermistors, but not as stable as platinum. The cost is more attractive than Pt, tho.
I'd consider staying analog with a DC bridge and a PID control op-amp. You don't need a highly accurate voltage source for the bridge because null is null, whatever the excitation voltage. Of course, you'll want a stable null for the op-amp, too. You do need a highly stable set of bridge resistors for a stable temperature. In the old days, precision, stable resistors were wound on ceramic forms by soldering a loop of e.g. constantan wire to the lead wires at each end of the form. Then you pull the loop at the center so that you can wind it on the core in a non-inductive manner. Inductance doesn't matter, but you want to finish the winding with the center bent double and sticking out a few inches from the core. Attach the lead wires to a measuring device with sufficient precision and accuracy, and hope that the winding has slightly more resistance than you want. Now take a razor blade and short the center wires closer to the winding. The resistance should go down. When you find the spot that gives the right resistance, remove the insulation and solder the wires together. Don't even think of using any kind of variable resistor to adjust the bridge null. What you want is a stable temperature near the value that gives the least crystal tempco. Yes, this is also how to make a meter shunt, but you'll be using much finer wire. The best thing to do might be to find an antique precision resistance bridge. It will have many such resistors in it, and you might be able to avoid winding altogether. Please write for details. Bill Hawkins -----Original Message----- From: Perry Sandeen Sent: Wednesday, November 10, 2010 11:03 PM List, Looking for a stable temperature sensor I first went to YSI. They have sold their sensor products to. Measurement Specialties, Inc. Perusing their site I came upon a Ni1000 SOT temperature sensor. It is a nickel based unit that has a basic resistance of 1K ohms at 20 degrees C and rising to 1482 ohms at 80 degrees C. . It has close to a 6 ohm change per degree. I tried to find one of their distributors without success. Entering the part number in Google, I found it is also made by ZETEX. ZETEX calls it an IC TEMP SENSOR NI1000 SOT23-3. The Digi-Key catalog as part number is ZNI1000CT ND. They are $2.77 each. The ZETEX data sheet has a nice circuit for a digital thermometer. Perhaps a LM 331 precision voltage-to-frequency IC or using a change in a bridge circuit to a varactor on a VCXO might provide the lack of aging problems that exist with a thermistor when precisely trying to obtain a temperature-to-frequency conversion. _______________________________________________ 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.