Thermal-type flowmeter for detecting flow rate of fluid

Abstract

A thermal-type flowmeter for detecting a flow rate of a fluid such as intake air flow rate in an internal combustion engine includes a voltage converting circuit for converting a flow-rate indicating voltage signal outputted from a flow-rate detecting sensor element into a voltage of a level falling within a predetermined range, a voltage-to-current converting circuit for converting the voltage into a current of magnitude which is proportional to a value of the flow-rate indicating voltage signal, a current-to-voltage converting circuit for converting the current mentioned above into a voltage signal for analogue-to-digital conversion, and a voltage adjusting circuit for increasing or decreasing the output voltage level of the voltage converting circuit in dependence on the value of the flow-rate indicating voltage signal. The voltage of a current source for the voltage-to-current converting circuit can be regulated so as to conform with the input voltage. The voltage-to-current converting circuit can be realized inexpensively by imparting a gain adjusting function thereto.

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