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.

Tolerance Curves
The following curves indicate conformance to standard resistance-temperature values as a % of resistance and as a maximum interchangeability error expressed as temperature.

----------- Temperature ±C

_______ Resistance ±%

Thermistor Equation
Occasionally, it is advantageous to have a general mathematical expression for a thermistor. NEWPORT finds the following equation best represents thermistor behavior:

1 T	= A + B (LOGeR) + C(LOGeR)3

Where T = °Kelvin; R = resistance; A, B, C = fitting constants.

A, B and C may be found by writing three equations utilizing three known data sets: R1, T1; R2, T2; R3, T3; and solving for A, B, and C.

When -40°C < or equal to T1, T2, T3 < or equal to 150°C and | T2 – T1 | < or equal to 50°C, | T3 – T2 | < or equal to 50°C interpolation data generated by this equation will be accurate to ±0.01°C or better.