You are using an instrumentation amplifier with V1 = 21.23 mV, V2 = 43.54 mV, R4 = 3000 ohms, R3 = 500 ohms, R2 = 2000 ohms and R1 = 200 ohms. What is Vout in millivolts? (Type in an integer)
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Answer:
Instrumentation amplifier is a kind of differential amplifier with additional input buffer stages. The addition of input buffer stages makes it easy to match (impedance matching) the amplifier with the preceding stage. Instrumentation are commonly used in industrial test and measurement application. The instrumentation amplifier also has some useful features like low offset voltage, high CMRR (Common mode rejection ratio), high input resistance, high gain etc. The circuit diagram of a typical instrumentation amplifier using opamp is shown below.
instrumentation amplifier using aopam
A circuit providing an output based on the difference between two inputs (times a scale factor) is given in the above figure. In the circuit diagram, opamps labelled A1 and A2 are the input buffers. Anyway the gain of these buffer stages are not unity because of the presence of R1 and Rg. Op amp labelled A3 is wired as a standard differential amplifier. R3 connected from the output of A3 to its non inverting input is the feedback resistor. R2 is the input resistor. The voltage gain of the instrumentation amplifier can be expressed by using the equation below.
Voltage gain (Av) = Vo/(V2-V1) = (1 + 2R1/Rg ) x R3/R2