(Solved): Q. 2 The circuit shown in Fig.Q. 2 represents that of a strain gauge bridge driven by an excitatio ...

Q. 2 The circuit shown in Fig.Q. 2 represents that of a strain gauge bridge driven by an excitation voltage

. Each of the four strain gauges is such that, in response to an applied force, the strain produces a change in electrical resistance given by

. The arrangement of the gauges is such that two devices increase in resistance while the other two decrease in resistance, as indicated in the Fig. (a) Open the circuit at the bridge output nodes

and

, and determine expressions for the Thevenin equivalent voltage source

and the Thevenin equivalent resistance

. Hence give an expression the output voltage

. You may assume that

is sufficiently small so that second order effects can be neglected, ie.

[18 marks] (b)

represents a bridge voltage measuring instrument. Deriving any expression used, what value should

take if maximum power is to be transferred to the instrument?