D-1
Appendix D
RTD Linearization
Introduction
This appendix discusses Fixed-385 and Custom-385 RTD measurements with the
2680 Series.
Fixed-385 RTD
The Fixed-385 RTD linearization uses segmented polynomials to approximate the
Callendar Van-Dusen equation for a 385 RTD. R
0
may be specified using the
Fluke DAQ software, 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-15 (for a PAI module) and
Table A-32 (for an FAI module) in Appendix A.
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