Appendix D

RTD Linearization

Introduction

D-1.

This appendix discusses Fixed-385 and Custom-385 RTD measurements with NetDAQ.

Fixed-385 RTD

D-2.

The Fixed-385 RTD linearization uses segmented polynomials to approximate the Callendar Van-Dusen equation for a 385 RTD. R0 may be specified via NetDAQ Logger but α, δ, and β are fixed. These fixed coefficients are the modified DIN

43760 coefficients that conform to ITS90:

α= 0.00385055 δ = 1.49978574 β = 0.10863383

The accuracy specifications of Fixed-385 measurements with a 385 RTD that matches the above coefficients are shown in Table A-34 in Appendix A.

D-1

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Fluke 2640A, 2645A user manual RTD Linearization, Fixed-385 RTD

2645A, 2640A specifications

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