How is it working? And more precisely what is the use of the schottky diodes? How the part with the temperature sensor and the shunt voltage reference is working?
The op amp is configured in a Howland circuit to generate a constant current independent of loop resistances and the supply voltage in the loop (within it's operating limits), with the current value proportional to the temperature of temp sensor U1.
The diodes put the circuit inside a diode bridge so that it works for either supply polarity.