2645A Four-Wire Rtd Per Its-1990 Measurement Specifications; 2645A Thermocouple Per Its-1990 Measurement Specifications - Fluke 2640A Service Manual

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2645A Four-Wire RTD per ITS-1990 Measurement Specifications

Tables 1-37 and 1-38 provide 2645A specifications for the four-wire Resistance-
Temperature Detector (RTD) measurement function. The four-wire measurements use 2
input channels a decade apart, e.g., channels 4 and 14. There is no two-wire RTD
capability for the 2645A.
Specification
Temperature Coefficient
Temperature
-200°C
0°C
100°C
300°C
600°C

2645A Thermocouple per ITS-1990 Measurement Specifications

Tables 1-39 to 1-40 provide 2645A specifications for the thermocouple measurement
function per ITS-1990.
Specification
Input Impedance
Open Thermocouple Detect
Temperature Coefficient
1-24
Table 1-37. 2645A Four-Wire RTD 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. For example, if the applicable specification at
28°C is 0.2 and the specifications at 60°C is 0.75, then the
specification at 40°C =(.75-.2)x(40-28)/(60-28)+.2=.406.
Table 1-38. 2645A Four-Wire RTD Specifications
Resolution
Slow Fast
0.03°C 0.06°C
0.03°C 0.06°C
0.03°C 0.06°C
0.03°C 0.06°C
0.03°C 0.06°C
Table 1-39. 2645A Thermocouple General Specifications
100 MΩ minimum in parallel with 300 pF
Operates by injecting a small ac signal into the input after each
measurement. A thermocouple resistance greater than 1 k to 10k is
detected as an open input.
To calculate Thermocouple accuracy for temperatures between 28°C
and 60°C, or -10°C and 18°C, use a linear interpolation between the
two applicable points. For example, if the applicable specification at
28°C is 0.6 and the specification at 60°C is 1.1, then the specification
at 40°C is =(1.1-0.6)x(40-28)/(60-28)+0.6=0.7875.
Characteristic
Accuracy, 3σ
90 Day
18°C to 28°C 18°C to 28°C
Slow Fast
0.16°C 0.25°C 0.25°C
0.20°C 0.31°C 0.31°C
0.23°C 0.34°C 0.34°C
0.30°C 0.41°C 0.41°C
0.53°C 0.63°C 0.63°C
Characteristic
1 Year 1 Year
-10°C to 60°C
Slow Slow Fast
0.62°C 1.10°C
0.85°C 1.30°C
0.95°C 1.40°C
1.18°C 1.70°C
1.62°C 2.12°C
1-34.
1-35.