Explain the strengths of instrumentation amplifiers

Question

a) Explain the strengths of instrumentation amplifiers compared to differential amplifiers in signal conditioning.

b) A 50 V range voltmeter is connected across the terminals A and B of the circuit shown in Figure 1 The voltmeter has a resistance of 1000 kΩ.

i) Find the open circuit voltage and output impedance of the circuit.

ii) Find the reading of the voltmeter, the percentage loading error and the accuracy.

Figure: Loading effect due to shunt connected voltmeter

c) The signal conditioning circuit shown in Figure 2 is used to measure the strain resulting from deflection of a steel bar The voltage V_o, is measured to be 100 mV and the gauge factor is 2.0. Modulus of elasticity for steel is 30 x 10⁶psi (pounds per square inch).

The resistances are R = 25kΩ and aR = 50Ω.

Calculate (i) gain of the instrumentation amplifier (ii) change in resistance, ΔR (iii) ΔR/R (iv) strain ΔL/L and (v) stress.

Figure: Signal conditioning circuit