Hi Mani Ahmadi; Re: "At cryo temps all materials have less electrical resistance, and as you probably know some material are super conductive."
I guess there's a bunch of guys out on the internet that have it all wrong:
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The resistance of most common types of thermistor decreases as the temperature rises. They are called negative temperature coefficient, or ntc, thermistors. Note the -t° next to the circuit symbol. A typical ntc thermistor is made using semiconductor metal oxide materials. (Semiconductors have resistance properties midway between those of conductors and insulators.) As the temperature rises, more charge carriers become available and the resistance falls.
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users.dircon.co.uk
...It consists of a normal composite resistor (NTC) as temperature sensing element, a cryogenic valve and a box containing the hardware.
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As a sensing resistor we use a resistor of nominal 1000 ohm at room temperature, going to over 1350 ohm at liquid nitrogen temperature.
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nmr.de
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According to our senior sensor R engineer, Lake Shore's Cernox? ceramic oxynitride thin film over sapphire negative temperature coefficient (NTC) resistance temperature detectors (RTDs) are the best thing to happen to cryogenic thermometry in decade. With High Temperature Cernox?, a good product is now even better in the development of a cryogenic sensor that can withstand vacuum chamber bake-out temperatures to 140 °C.
Cernox? RTDs combine small size, fast thermal response time, and a wide useful temperature range with excellent resistance to repeated thermal cycling, ionizing radiation, and magnetic fields; flexible packaging options are also available. With these features, Cernox? RTDs offer significant advantages over comparable bulk or thick film resistance sensors at comparable cost for applications from below liquid helium to room temperature, from 0.3 to 325 K.
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lakeshore.com
-- Carl |
