National Instruments SCXI-1321

z is the module slot of the SCXI-1121

w is the channel of the module that you want to engage the shunt and

take measurements

For example, if you want to measure the voltage at channel 0 with the shunt

resistor enabled, use the SCXI channel string

ob0 ! sc1 ! md1 ! shunt0.

You also can specify a list of channels by using

ob0 ! sc1 ! md1 ! shunt0:

, for example. Refer to the LabVIEW

Measurements Manual for information on using SCXI channel strings.

The shunting resistors RSCAL are socketed so that you can replace them with

a resistor of another value to achieve the required nulling range for your

application. The sockets and corresponding channels are shown in Table 3.

The factory installed RSCAL provided on the terminal block have a 301 kΩ

±1% value.

Assuming a quarter-bridge strain-gauge configuration with a gauge factor

of GF = 2, the equivalent strain change introduced by the RSCAL shunting

resistor is –199 µε.

Refer to the Traditional NI-DAQ User Manual for more information on

strain-gauge bridge configurations and formulas.

Use the following formula to determine the change due to this shunting

resistor:

Next, using the appropriate strain-gauge strain formula, and assuming that

you have no static voltage, determine the equivalent strain the RSCAL should

provide. For example, RSCAL = 301 kΩ and a quarter-bridge 120 Ω strain

Table 3. Socket to Channel Relationship

Channel Shunt Resistor Socket

0R4

1R6

2R8

3R10

Vchange

VexRdRSCAL Rg

+()

RgRSCAL RdRSCAL Rg

+()+

----------------------------------------------------------------- Vex

-------–=