Detects very small resistance changes in the blue resistor and converts it to voltage.
Emitter resistor sets the sensitivity; eg at 1k ohm, the range is about 0.001 to 0.02 ohms. Higher emitter resistor values increase the range up to 0.2 ohms.
Could work as a rough temp sensor; use a little loop of fine wire as a probe and heat will affect the resistance dramatically. The differential amplifier allows long wires to be attached to the probe being measured; any noise that affects both wires will not be amplified.
