Table 3. socket to channel relationship – National Instruments SCXI-1321 User Manual

Page 13

SCXI-1321 Terminal Block Installation Guide

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 R

SCAL

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 R

SCAL

provided on the terminal block have a 301 k

Ω

±1% value.

Assuming a quarter-bridge strain-gauge configuration with a gauge factor
of GF = 2, the equivalent strain change introduced by the R

SCAL

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 R

SCAL

should

provide. For example, R

SCAL

= 301 k

Ω and a quarter-bridge 120 Ω strain

Table 3. Socket to Channel Relationship

Channel

Shunt Resistor Socket

R10

change

SCAL

(

)

SCAL

(

)

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