Fluke NetDAQ 2645A - Manual (Page 224)

2640A/2645A NetDAQ
Users Manual
A-14
2640A RTD’s 2-Wire per ITS-1990 Measurement Specifications A-18.
The 2640A specifications for the 2-wire Resistance-Temperature Detector (RTD)
measurement function is based on the 4-wire RTD measurement specification
(above) except you add a nominal 5-Ohm (roughly 13ºC ) positive offset. This
value varies for each channel and temperature gradient (nominal +0.4%/ºC). Also
note that the resistance of the RTD wiring adds directly to the error. After 100
million operations of a measurement channel, the offset will increase at an
indeterminate rate.
2640A Thermocouple per ITS-1990 Measurement Specifications A-19.
Tables A-20 to A-21 provide 2640A specifications for the thermocouple
measurement function per ITS-1990.
Table A-20. 2640A Thermocouple General Specifications
Specification Characteristic
Input Impedance 100 M
Ω
minimum in parallel with 300 pF
Open Thermocouple Detect Operates by injecting a small ac signal into the
input after each measurement. A thermocouple
resistance greater than 1k
Ω
to 10k
Ω
is
detected as an open input.
Temperature Coefficient To calculate thermocouple accuracy for
temperatures between 28
º C and 60 º C, or -10 º C
and 18 º C, use a linear interpolation between
the two applicable points. e.g., if the applicable
spec at 28
º C is .6 and the spec at 60 º C is 1.1,
then the spec at 40 º C = (1.1-.6)*(40-28)/(60-
28)+.6= .5* (12/32) + .6 = .7875.
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.