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Temperature Sensors Platinum RTDs

36 Honeywell Sensing and Control 1-800-537-6945 USA 1-815-235-6847 International 1-800-737-3360 Canada

EFERENCE AND APPLICATION DATA

LATINUM RTD RESISTANCE VS. TEMPERATURE FUNCTION

LATINUM is a precious metal with a very stable and near linearesistance versus temperature function. While intrinsically lessensitive than thermistors or other metals, thin film RTDs provideery high base resistance and high device sensitivity.

latinums resistance versus temperature function is accuratelymodeled by the Callendar-Van Dusen equation. This equation

ses constants A, B and C, derived from resistance measure-ments at 0C, 100C and 260C.

allendar-Van Dusen Equation:

RT R0(1+AT+BT2100CT3+CT4)

RT Resistance () at temperature T (C)R0 Resistance () at 0CT Temperature in C

or T>0C, the quadratic formula can be used to solve for

emperature as a function of measured resistance with theesult:

0 R0BT2+R0AT+(R0RT) implies...

TR R0A+ R02A24R0B(R0RT)

2R0B

latinum RTDs are specified by resistance at 0C, R0, and alpha,, a term related to the temperature coefficient of resistance, orCR. The Callendar-Van Dusen constants A, B and C are de-ved from alphaand other constants, delta and beta, whichre obtained from actual resistance measurements. Commonallendar-Van Dusen constant values are shown in the table

elow:

ALLENDAR-VAN DUSEN CONSTANTS

Alpha, (C1) .003750 .00003 .003850 .0001

Delta, (C) 1.605 0.009 1.4999 0.007

Beta, * (C) 0.16 0.10863

A (C1) 3.81 103 3.908 103

B (C2) 6.02 107 5.775 107

C (C4)* 6.0 1012 4.183 1012

Both 0 and C 0 for T>0C

The definitions of the Callendar Van Dusen constants: A, B, C,and alpha, delta and beta (, and ), and their inter-relation-ships are given by the equations below. In all cases, the values ofthe constants and the fundamental accuracy and repeatability

performance of an RTD is determined by the repeatability of theempirically measured resistance values:

RO ROR100 R100 and R260 R260

A +

100B

1002CT

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