METHOD AND APPARATUS FOR CONTROLLING TEMPERATURE OF MEASURING RESISTOR FOR DETECTING FLOW RATE OF FLUID

PURPOSE: To accurately determine the flow rate of a fluid even when a power source voltage is unstable and insufficient by considering the size of a heating voltage ON or OFF controlled when a pulse duty ratio is determined. CONSTITUTION: A resistance value of a measuring resistance RS varies as cooling effect differs with changes in air flow rate (m) within a suction tube-of an internal combustion engine. A partial potential ratio of a potential divider 2 varies with the change of the resistance value and a measuring voltage US is generated accordingly. When a change occurs in the temperature of a suction flow, a thermosensitive resistance RK responds to correct a reference voltage UK. In this case, changes in the flow rate (m) cause the detuning of a bridge to change a bridge voltage UBr and the voltage UBr is processed by a controller 11 so that the flow rate (m) is extracted from an output 25. Then, the flow rate (m) is inputted into the controller to be used for the calculation of the optimum driving point for various running conditions. Then, to return the resistance RS to a working temperature after the detuning of the bridge, the voltage UBr is processed by the controller 11 to form a clock pulse.