Construction Thermistors are manufactured from oxides of nickel, manganese, iron, cobalt, magnesium, titanium and other metals. All are available epoxy encapsulated and color coded, with two 3" leads.Thermistors with 0.2°C interchangeability also are available encased in a 2" long waterproof PFA tube; order by adding 100 to the part number. For example: 44005 is a standard 3000 ohm thermistor; 44105 is a PFA-encased thermistor with the same temperature/resistance values. Stiff wire is placed in the tube so that, with slight finger pressure, it can be bent to any configuration. For PFA-encased thermistors, consult the factory.
Stability Finished thermistors are chemically stable and not significantly affected by aging or exposure to strong fields of hard nuclear radiation. Time Constant -The time required for a thermistor to indicate 63% of a newly impressed temperature is called the time constant. For a thermistor suspended by its leads in a “well stirred” oil bath, it is 1 sec. max., or 2.5 sec. max. for PFA-encased thermistors, and in still air it is 10 sec. max., or 25 sec. max. for PFA units.
Dissipation Constant The power in milliwatts required to raise a thermistor 1°C above the surrounding temperature is the dissipation constant. For all thermistors suspended by their leads in a “well stirred” oil bath, it is 8 mw/ °C min., or 1 mw/°C min. in still air. Operating Temperature -Maximum operating temperature is 150°C. Long-term stability studies show that extended operation or continued cycling above 90°C will cause thermistors with values less than 2252 ohms at 25°C to exceed tolerances eventually. Thermistors 44030, 44031, 44032 and 44033 are designed for operation below 75°C. They will operate safely up to 100°C, but extended use above 75°C may cause a change in resistance. Storage temperature for thermistors is from -80 to 120°C.
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