Document Number: 33003

www.vishay.com

Revision: 12-Nov-09

107

M, C, T

NTC Thermistors, Radial Leaded and Coated

Vishay Dale

POINT MATCH TOLERANCE

The standard leaded thermistors are calibrated and tested at 25 °C to a tolerance of ± 5 % or ± 10 %; however, tighter tolerance,

point matched thermistors are readily available as are special point match temperatures to fit your application.

Since these thermistors have only one controlled point of reference (the point match temperature), the resistance at other

temperatures is given by the “Resistance vs. Temperature Conversion Tables” for the appropriate material curve. The resistance

value at any temperature is the ratio factor times the resistance at 25 °C. The resistance vs. temperature conversion tables can

Example: 09M1002JF, + 70 °C resistance = (Resistance factor for curve 9 at 70 °C is 0.1990) x (10 000

Ω resistance at 25 °C)

= 1990

Ω.

The tolerance of the resistance at any temperature is described by figure 2.

FIGURE 2

POINT MATCH TOLERANCES VS. TEMPERATURE

Point match resistance tolerances at temperatures other

than 25 ºC are not the same as the calibration temperature.

This difference is presented in figure 2.

The tolerance at any given temperature is the point match

tolerance + the MT ± % (manufacturing tolerance).

The MT ± % may be obtained from the R vs. T conversion

point match temperature, i.e., ± 1 % Tol. at 25 ºC + ± 2.6 %

at - 30 ºC for Curve 1 equals a total tolerance of ± 3.6 % at

- 30 ºC.

COMPUTER AIDS FOR THERMISTOR SELECTION

A spreadsheet is available for the Vishay thermistor materials that calculates beta, Steinhart-Hart equation constants A, B, and

C, the resistance at any temperature based upon the Steinhart constants or beta, the temperature equivalent of the resistance

reading, and resistance temperature coefficients.

This spread sheet will also calculate the total resistance tolerance of any point matched thermistor for temperatures in 10 ºC

increments, and the resistance tolerance at any temperature within the calibrated range of curve tracking thermistors. Please

25 °C

NOMINAL R vs. T

MAX. R vs. T

MIN. R vs. T

PIVOT POINT

(CALIBRATION TEMPERATURE)

TEMPERATURE