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2640A/2645A NetDAQ
Users Manual
A-22
2645A 2-Wire Resistance Measurement Specifications A-25.
The 2645A specifications for the 2-wire resistance measurement function is based
on the 4-wire resistance measurement specification (above) except you add a 700
to 1000 Ohm positive offset. This value varies for each channel and temperature
gradient (nominal +1%/ºC).
2645A 4-Wire RTD per ITS-1990 Measurement Specifications A-26.
Tables A-33 and A-34 provide 2645A specifications for the 4-wire Resistance-
Temperature Detector (RTD) measurement function. The 4-wire measurements
use 2 input channels a decade apart, e.g., channels 4 and 14.
Table A-33. 2645A 4-Wire RTD Temperature Coefficient
Specification Characteristic
Temperature Coefficient To calculate RTD accuracy for temperatures
between 28ºC and 60ºC, or -10ºC and 18ºC,
use a linear interpolation between the two
application points. e.g., if the applicable spec at
28ºC is .2 and the spec at 60ºC is .75, then the
specification at 40ºC is (.75-.2)*(40-28)/(60-28)
+ .2 = .55*(12/32)+.2 = .406.
Accuracy at -20°C Multiply the -10°C to + 60°C accuracy
specification by 2. After 1 hour warm-up. For
accuracy between -10°C and -20°C, interpolate
linearly.
Table A-34. 2645A 4-Wire RTD Specifications
Accuracy, 3σ ± ºC
Temperature Resolution
90 Day, 18ºC to
28ºC
1 Year,
18ºC to
28ºC
1 Year, -10ºC to
60ºC
Slow Fast Slow Fast Slow Slow Fast
-200ºC* 0.03ºC0.06ºC0.16ºC0.25ºC0.25ºC0.62ºC1.10ºC
0ºC* 0.03ºC0.06ºC0.20ºC0.31ºC0.31ºC0.85ºC1.30ºC
100ºC0.03ºC0.06ºC0.23ºC0.34ºC0.34ºC0.95ºC1.40ºC
300ºC0.03ºC0.06ºC0.30ºC0.41ºC0.41ºC1.18ºC1.70ºC
600ºC0.03ºC0.06ºC0.53ºC0.63ºC0.63ºC1.62ºC2.12ºC
* The Custom-385 range is not recommended for use below -80ºC. See Appendix D.