Справочник Пользователя для Fluke 2640A

Users Manual

A-14

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.

Tables A-20 to A-21 provide 2640A specifications for the thermocouple
measurement function per ITS-1990.

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.