Specifications
2640A Specifications
A
A-13
2640A 2-Wire Resistance Measurement Specifications A-16.
The 2640A specifications for the 2-wire resistance measurement function is based
on the 4-wire resistance measurement specification (above) except you add a
nominal 5-Ohm (10-Ohm maximum) positive offset. This value varies for each
channel and with temperature (nominal +1%/ºC).
2640A RTD’s 4-Wire, per ITS-1990 Measurement Specifications A-17.
Tables A-18 and A-19 provide 2640A 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-18. 2640A 4-Wire RTD Temperature Coefficient
Specification Characteristic
Temperature Coefficient To calculate RTD accuracy for temperatures
between 28°C and 60°C, or -10°C and 18°C,
use a linear interpolation between the two
applicable points. e.g. if the applicable spec at
28°C is .2 and the spec at 60°C is .75, then the
specification at 40°C = (.75-.2)x(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-19. 2640A 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 (Note1) 0.003ºC 0.007ºC0.06ºC0.16ºC0.09ºC0.33ºC0.63ºC
0ºC (Note 1) 0.003ºC 0.007ºC0.09ºC0.20ºC0.13ºC0.53ºC0.86ºC
100ºC 0.003ºC 0.007ºC0.10ºC0.23ºC0.16ºC0.63ºC0.97ºC
300ºC 0.003ºC 0.007ºC0.14ºC0.3ºC0.21ºC0.83ºC1.2ºC
600ºC 0.003ºC 0.007ºC0.19ºC0.53ºC0.30ºC1.2ºC1.6ºC
1. The Custom 385 range is not recommended for use below -80ºC. (See Appendix D)
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