US 5,181,420 A · Hot wire air flow meter

Abstract

The present specification discloses a hot wire air flow meter with high circuit stability. The hot wire type air flow meter comprises a hot wire located in an air flow path to be measured and to which current is supplied from the external, a circuit for detecting a value of current flowing through the hot wire, an amplifying circuit including an inverting input terminal, a non-inverting input terminal to which a value detected in the current detecting circuit is applied, and an output terminal to which an output of an air-flow function is applied, a feedback circuit for supplying a feedback output to any terminal except the non-inverting input terminal of the amplifying circuit and controlling the output of the amplifying circuit to keep the temperature of the hot wire stable according to the output of the amplifying circuit, and a circuit for compensating for a phase of an output of the amplifying circuit contained in the feedback circuit.

Claims18

Dependent claims

A hot wire type air flow meter, comprising:

a hot wire to be located in an air flow path and to which a heating current is to be externally supplied;
means connected to said hot wire for detecting a value of heating current flowing through said hot wire;
amplifying means having an inverting input terminal (-), and a non-inverting input terminal (+) to which an output of said current detecting means is applied, for applying to an output terminal thereof a signal which is a function of air flow in the air flow path;
feedback means connected to supply a feedback output related to said heating current to said inverting input terminal of said amplifying means for controlling the output of said amplifying means to keep the temperature of said hot wire constant according to the output of said amplifying means;
and
means connected to said amplifying means and isolated from said detecting means for compensating for a phase of an output of said amplifying means;
wherein a buffer is provided between said feedback means and said compensating means.

4 more elements

A hot wire type air flow meter comprising:

a hot wire to be located in an air flow path;
means for supplying a heating current to said hot wire, including a control transistor for coupling a source of heating current to one end of said hot wire;
means connected to said hot wire for detecting a value of heating current flowing through said hot wire;
control means, including an amplifier having a non-inverting input terminal to which an output of said heating current detecting means is connected, an inverting input terminal, and an output terminal, for controlling said heating current supplying means to keep the temperature of said hot wire constant;
feedback means, including a series circuit of first and second resistors, connected to supply a current, which represents a level of said heating current, to said inverting input terminal of said amplifier;
compensating means connected to said amplifier for compensating for a phase of an output of said amplifier;
and
wherein said control means comprises a further amplifier having an inverting input terminal connected to a point of connection of said first and second resistors, a non-inverting input terminal connected to an output terminal of the first-mentioned amplifier and an output terminal connected to a control electrode of said control transistor.

5 more elements

A hot wire type air flow meter comprising:

a hot wire to be located in an air flow path;
means for supplying a heating current to said hot wire;
means connected to said hot wire for detecting a value of heating current flowing through said hot wire;
control means, including an amplifier having a non-inverting input terminal to which an output of said heating current detecting means is connected, an inverting input terminal, and an output terminal, for controlling said heating current supplying means to keep the temperature of said hot wire constant;
feedback means connected to supply a current, which represents a level of said heating current, to said output terminal of said amplifier;
and
compensating means connected to said amplifier for compensating for a phase of an output of said amplifier;
and
wherein said heating current supplying means includes a control transistor for coupling a source of heating current to one end of said hot wire, and wherein said feedback means comprises a series circuit of first and second resistors connected between said one end of said hot wire and said output terminal of said amplifier.

6 more elements

Dependencies are inferred from the claim text.

Hot wire air flow meter

Life of this patent

Hot wire air flow meter

Life of this patent

Abstract

Claims18