Two Op-Amp Differential Amp

This is an ideal circuit for sensor amplification. Strain Bridge circuits too. It is an instrumentation amplifier, means precision. High input impedance to a differential input signal source. The gain can be set with external resistors to over 1000. CMRR trim to match resistor network.

Circuit Two Op Amp Instrumentation Amplifier

I measure Instrumentation Amplifier like this – Tera Ohms Impedance, Pico Amps Bias Current. Micro Volts Offset Voltage. Here is a Interactive demo i built for such a configuration. The Input Impedance of this module is very high and is symmetric. This circuit can be used for strain gauges and for four wire measurements. If inputs are in mV use OP07. The merit is that it uses only 2 OpAmps yet has high differential Input Impedance.

Dual Op-Amp Differential Amp Tutorial

The Outputs of Opamps are low impedance but still have limits they cannot drive more than a few mA of Current into the Load. If low ohmic value loads are to be applied use external transistors as amplifiers. If inputs Vn-Vp are floating, outputs may be random or oscillating, it is good to have a bias network of 10M resistors to a potential even zero or common, this enables some Vout when input floats.