2640A/2645A NetDAQ
Users Manual
D-2
Custom-385 RTD D-3.
The Custom-385 RTD linearization solves the Callendar Van-Dusen equation for
positive temperatures and uses a polynomial approximation to the Callendar Van-
Dusen equation for negative temperatures. In addition to R
0
, α may also be
specified via NetDAQ Logger. δ nd β are fixed. These fixed coefficients are the
modified DIN 43760 coefficients that conform to ITS90:
δ = 1.49978574
β = 0.10863383
Figure D-1 shows the accuracy envelope for a 385 RTD that has δ and β that
match the above coefficients. Because of the error introduced by the linearization
at low temperatures, it is recommended that use of the Custom-385 RTD type be
limited to temperatures between -100 and 600°C.
2645A
2640A
-100 0 100 200 300 400 500 600
Temperature - Degrees C
Accuracy Envelope: Custom RTD, 385 Probe
1 Year Slow: 18-28 Degrees C
Alpha: 0.00385055 Delta: 1.49978574 Beta: 0.10863383
-1.5
-1.0
-0.5
0.0
0.5
1.0
Error - Degrees C
1.5
Figure D-1. 385 RTD
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