TFPT

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Revision: 14-Jan-2020

4

Document Number: 33017

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RATIO FORMULA

RT = R25 x (9.0014 x 10-1 + 3.87235 x 10-3 (°C)-1 x T + 4.86825 x 10-6 (°C)-2 x T2 + 1.37559 x 10-9 (°C)-3 x T3)

T(°C) = 28.54 x (RT/R25)3 - 158.5 x (RT/R25)2 + 474.8 x (RT/R25) - 319.85)



RATIO TOLERANCE EXAMPLES:

At 40 °C, ratio = 1.063 ± 0.5 % (0.005)



so, ratio = 1.058 to 1.068

At 125 °C, ratio = 1.460 ± 3 % (0.044)



so, ratio = 1.416 to 1.504

At intermediate temperatures, the ratios can be gradually

adapted, for example at 105 °C the ratio tolerance will be

± 2.5 %.

For total resistance tolerance, the specific R25 tolerance

needs to be multiplied with the ratio tolerance, for example

a 100R 1 % at 25 °C will have a maximum resistance at

125 °C of 100R x 1.463 x 1.03 x 1.01 = 152.2

.

RATIO RT/R25

POWER DERATING

Note

• Zero power is considered as measuring power max. 1 % of rated

power P70

TCR TYPICAL VALUE

RATIO TOLERANCES

LOW TEMP.

HIGH TEMP.

TOL.

-55 °C

+150 °C

± 4 %

-40 °C

+125 °C

± 3 %

-20 °C

+85 °C

± 2 %

0 °C

+55 °C

± 1 %

+12 °C

+40 °C

± 0.5 %

10

100

1000

10000

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

-75 -50 -25

0

25

50

75 100 125 150

Axis Title

Temperature (°C)

Max.

Min.

10

100

1000

10000

0

10

20

30

40

50

60

70

80

90

100

110

-75 -50 -25

0

25 50 75 100 125 150 175

Axis Title

Temperature (°C)

10

100

1000

10000

3600

3700

3800

3900

4000

4100

4200

4300

4400

4500

4600

4700

4800

-75 -50 -25

0

25 50 75 100 125 150 175

Axis Title

Temperature (°C)