Fluke NetDAQ 2645A - Manual (Page 247)

RTD Linearization
Custom-385 RTD
D
D-3
Using the Custom-385 RTD with Other Platinum RTDs D-4.
Although the Custom-385 RTD linearization uses a
β
and
δ
from a 385 RTD,
other RTD types can be used. The Custom-385 linearization will compensate for
the change in
α
, but errors will be introduced due to the difference in the
δ
and
β
coefficients of the RTD and the fixed coefficients. Figure D-2 shows the accuracy
envelope for a 375 RTD. Because of the error introduced by the approximation
and the difference in
δ
it is recommended that the use of the 375 RTD be limited
to temperatures between -100
°
C and 300
°
C. Figure D-3 shows the accuracy
envelope for a 391 RTD and Figure D-4 shows the accuracy envelope for a 392
RTD. Due to errors introduced by the approximation and the difference in
δ
it is
recommended that the use of the 391 RTD and 392 RTD be limited to
temperatures between -100
°
C and 600
°
C.
2645A
2640A
-100 -50 0 50 100 150 200 250 300
Temperature - Degrees C
Accuracy Envelope: Custom RTD, 375 Probe
1 Year Slow: 18-28 Degrees C
Alpha: 0.00375 Delta: 1.605 Beta: 0.16
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Error - Degrees C
1.0
Figure D-2. 375 RTD