National Instruments SCXI-1321 用户手册

gauge with a gauge factor of GF = 2, V

 = 3.3 V, and R = 120 

Ω produces 

the following:

 = 0.3321 mV

Replacing the strained voltage by V

 in the quarter-bridge strain 

equation produces an equivalent 199 

µε of change. Refer to the NI-DAQ 

User Manual for more information on voltage to strain conversion 
equations.

CJC is used only with thermocouples and provides improved accuracy of 
temperature measurements. The CJC temperature sensor, mounted in the 
SCXI-1321, outputs 10 mV/°C and has an accuracy of ±0.9 °C over the 
0 to 55 °C temperature range. To determine the temperature, use the 
following formulas:

where V

 is the temperature sensor output voltage, and T (°F) and 

T (°C) are the temperature readings in degrees Fahrenheit and degrees 
Celsius, respectively.

Use the average of a large number of samples to obtain the most accurate reading. 

Noisy environments require averaging for greater accuracy. You cannot use virtual 
channels to take the readings.

You can enable the CJC sensor in one of two ways depending on the input 
mode configuration of the SCXI-1121. Jumper W5 switches the 
temperature sensor output between MTEMP (multiplexed mode) and 
DTEMP (parallel mode) modes. In MTEMP mode, you must scan the 
cold-junction temperature independently of the other AI channels on the 
SCXI-1121 using the LabVIEW Getting Started Analog Input VI, available 
in 

examples\daq\run_me.llb

, with the channel string 

ob0 ! sc1 ! md1 ! mtemp

. This reads the temperature sensor on the 

terminal block connected to the module in slot 1 of SCXI chassis 1.

You then can average several measurements of the cold-junction 
temperature and use this average to compensate for the cold junction of the 
thermocouple. Using this averaging method compensates for temperature 
variations during the measurement period and makes the CJC temperature 
more accurate.

T (

°C)

100 V

×

=

T (

°F)

T (

°C) 9

×

5

-------------------------

32

+

=