National Instruments SCXI-1121 Manuel D’Utilisation

© National Instruments Corporation

Figure 2-10.  Shunt Circuit

The shunting resistors R

 are socketed so that you can replace them with 

a resistor of another value to achieve the required changes. The R

 

resistors on your 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

 shunting 

resistor is –199 µ

ε

. Determine the change as follows:

1.

Determine the change caused by the shunting resistor using the 
following formula:

2.

Using the appropriate strain-gauge strain formula, and assuming that 
you have no static voltage, determine the equivalent strain that the 
R

SCAL 

should produce. For example, R

SCAL 

= 301 k

Ω

 and a 

quarter-bridge 120 

Ω

 strain gauge with a gauge factor of GF = 2 and 

 = 3.333 V and R = 120 

Ω

 produces the following result:

 = 0.3321 mV

Replacing the strained voltage with V

 in the quarter-bridge strain 

equation produces an equivalent –199 µ

ε

 of change.

SCAL

EX+

R

CH+

EX–

R

SCAL

SCXI-1321

R

g

R

R

CH–

+

(

)

+

(

)

+

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

2

----------

–

=