NetDAQ Users Manual

Specifications
2645A Specifications A
A-23
2645A Thermocouple per ITS-1990 Measurement Specifications A-27.
Tables A-35 to A-36 provide 2645A specifications for the thermocouple
measurement function per ITS-1990.
Table A-35. 2645A Thermocouple General Specifications
Specification Characteristic
Input Impedance 100 MΩ minimum in parallel with 150 pF
Open Thermocouple Detect Operates by injecting a small ac signal into the
input after each measurement. A thermocouple
resistance greater than 1 kΩ to 10 kΩ is
detected as an open input.
Temperature Coefficient To calculate Thermocouple accuracy for
temperatures between 28ºC and 60ºC, or -10ºC
and 18ºC, use a linear interpolation between
the two applicable points. e.g., if the applicable
spec at 28ºC is .6 and the spec at 60ºC is 1.1,
then the spec at 40ºC is (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.
Table A-36. 2645A Thermocouple Specifications
Accuracy ± ºC
Thermocouple
Resolution
18ºC to 28ºC-10ºC to 60ºC
90
Day
1 Year 1 Year
Type Temperature ºC Slow Slow Fast Slow Fast
J -100 to 80 .3 0.8 0.9 1.6 0.9 1.7
80 to 230 .2 0.7 0.8 1.4 0.9 1.5
230 to 760 .2 0.7 0.8 1.3 1.0 1.5
K -100 to -25 .4 1.0 1.1 2.0 1.2 2.1
-25 to 120 .3 0.8 0.9 1.7 1.0 1.8
120 to 1000 .3 0.9 1.1 1.8 1.5 2.2
1000 to 1372 .3 1.2 1.5 2.3 2.0 2.9
N -100 to -25 .5 1.4 1.5 2.8 1.5 2.9
-25 to 120 .5 1.1 1.3 2.3 1.3 2.4
120 to 1000 .4 1.0 1.1 2.0 1.2 2.1
1000 to 1300 .3 1.0 1.2 1.9 1.6 2.4