2640A/2645A NetDAQ

Users Manual

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

Input Impedance

Open Thermocouple Detect

Characteristic

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 1kΩ to 10kΩ is detected as an open input.

Temperature Coefficient

Accuracy at -20°C

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 = (1.1-.6)*(40-28)/(60- 28)+.6= .5* (12/32) + .6 = .7875.

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.

A-14

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Fluke 2645A, 2640A user manual Table A-20 a Thermocouple General Specifications

2645A, 2640A specifications

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