THERMAL FLOW RATE MEASUREMENT APPARATUS

摘要

PROBLEM TO BE SOLVED: To solve such a problem in heating current control due to sticking of a fluid drop to a heating resistor with a simple circuit configuration and furthermore, by reducing the number of parts. SOLUTION: A simple protection network, in which a voltage restriction element such as a Zener diode (or several diodes and resistors) is used, is built-in between a differential amplifier 2 of an operational amplifier 1 used in the feedback control of a heating resistor 47 and an output amplifier 4 as an output voltage restriction circuit 5. Only when a voltage to be inputted to a plus input terminal of the operational amplifier 1 becomes abnormally higher than the voltage to be inputted to a minus input terminal of the operational amplifier 1, the output voltage of the operational amplifier 1 is limited to a predetermined value.