Basic Shunt Calibration

Illustrated below is the Wheatstone bridge circuit in its simplest form.

Basic Wheatstone bridge circuit.

With the bridge excitation provided by the constant voltage , the output voltage, , is always equal to the voltage difference between points A and B:

And,

   Eq.(514.1) 

Or, in more convenient, nondimensional form:

Eq.(514.1a) 

It is evident from the form of Eq.(514.1a) that the output depends only on the resistance ratios and , rather than on the individual resistances. Furthermore, when = , the output is zero and the bridge is described as resistively balanced. Whether the bridge is balanced or unbalanced, Eq.(514.1a) permits calculating the change in output voltage due to decreasing any one of the arm resistances by shunting. The equation also demonstrates that the sign of the change depends on which arm is shunted. For example, decreasing by shunting , or increasing by shunting will cause a negative change in output. Correspondingly, a positive change in output is produced by shunting or (increasing , and decreasing , respectively).

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