Test & Soldering Equipment On-line Store

D.E.V.I.C.E.
(Wiki)Calculators
Services

Instrumentation amplifier

The instrumentation amplifier is a differential amplifier with the same input resistance and the ability to adjust the gain by changing the value of only one resistor in the negative feedback circuit (Fig. 1).

Fig. 1. Instrumentation amplifier

Compared to the differential amplifier, the instrumentation amplifier circuit is significantly more complicated, but adjusting the gain is reduced to selecting the resistance of only one resistor R₁. The rest of the circuit can be implemented on a single crystal, which increases the accuracy of measurements.

The gain of the measuring amplifier is calculated using the formula:

V_out = (2 × R / R₁ + 1) × (V_in1 – V_in2)

The measuring amplifier has a number of important advantages:

If R₁ is removed from the circuit (thus, in the calculation, R₁ = infinity), the gain of the measuring amplifier becomes equal to one, and the output voltage (V_out) will be equal to the difference in voltages at the inputs (V_in1 – V_in2).
If you apply a voltage of V_in1 = 0 V to the upper input of the measuring amplifier, it can be used as an inverting amplifier with high input resistance.
If you apply a voltage of V_in2 = 0 V to the lower input of the measuring amplifier, it can be used as a normal non-inverting amplifier.
High input resistance allows you to connect a resistor adder to each input, as in the summing amplifier circuit. The above features allow you to use the circuit as a universal operational amplifier. Measuring amplifiers are manufactured by industry as ready-made microcircuits.