Hi. I am mechanical engineer , and I have presentation somewhere next week about sensor of my choosing. The thing is:I picked sensor which is a research project ,and the sensor is flow sensor,using hot wire technology . Not only this entire subject confuses me (measuring flow using heat exchange ? Sounds not the most accurate thing ),which confuses me the most is the circuitry designed to keep steady temperature of the "hot wire" resistor.And in that research,they have the circuit that confuses the hell out of me. Anyway,here it is : http://img401.imageshack.us/img401/5583/ld52.jpg [Broken] It has two wire sensors,to measure upstream an downstream.It measures nasal respiration. Now we learned in our class the basic circuit for keeping temperature of the hot wire constant,but this goes way beyond. Now upper and down circuits are the same,to reduce the response time.Anyway,beyond the fact the both are supposed to keep the temperature of the hot wire constant,and the final comperator is to detect the direction of the flow,I don't understand the choosing of circuitry.Why integral amplifier is used?Why the transistor afterwards? Thanks in advance.