Two Opamp Differential
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.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 COM this enables Vout when input floats.
Vout = (Vp - Vn) * (Rf+Ri)/Ri
