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21

M, C, T

Vishay Dale

Document Number: 33003

Revision 22-Sep-04

For technical questions, contact thermistor1@vishay.com

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.

Example: 1M1002-5, +70°C resistance = (Resistance factor for curve 1 at 70°C is .1990) X (10000 ohm resistance at 25°C)

= 1990 ohms.

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

Point match resistance tolerances at temperatures other than

25ºC 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

tables and is added to the point match temperature, i.e., ±

1% Tol. at 25ºC + ± 2.6% at -30ºC for Curve 1 equals a total

tolerance of ± 3.6% at -30ºC.

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 10ºC

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

contact factory if interested in this Excel™ spreadsheet.

POINT MATCH TOLERANCE

COMPUTER AIDS FOR THERMISTOR SELECTION

FIGURE 2

POINT MATCH TOLERANCES VS. TEMPERATURE

TEMPERATURE

25

NOMINAL R VS. T

MAX. R VS. T

MIN. R VS. T

PIVOT POINT

(CALIBRATION TEMPERATURE)

NTC Thermistors, Coated