Symmetrical bridge circuit for measuring mass air flow

Abstract

A symmetrical bridge circuit having a sensing leg means and a compensation leg means for measuring mass air flow in the input of an internal combustion engine utilizes the same type of sensing and compensation elements with the same temperature coefficients. The sensing leg means and the compensation leg means are coupound circuits each having a conventional bridge leg and a voltage divider leg. The conventional bridge leg outputs are connected through voltage follower circuits controlling the input of the voltage divider legs. The conventional leg of the sensing leg means contains the sensing element and the voltage output therefrom is a function of a first factor. The voltage divider leg connected to the output of the voltage follower circuit further divides the voltage output by a second factor. The compensation element is connected in the voltage divider leg of the compensation leg means. The voltage output of the conventional leg of the compensation leg means is a function of a second factor and the voltage output from the voltage divider is a function of the first factor. The outputs of the voltage dividers control a power driver means supplying power to the bridge circuit. The output stage of the bridge circuit compares the voltage supplied by the power driver means with a fixed reference voltage to generate an analog signal representing the mass of the air flowing across the sensing element. The symmetrical bridge circuit does not require compensating capacitors and special amplification circuits for the compensation legs.