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US 7,072,776 B2Granted
Method of regulating resistance in a discontinuous time hot-wire anemometer
AssigneeTexas Instruments Incorporated
InventorsTobin D. Hagan, David J. Baldwin, William E. Grose
Life of this patent
Estimating the term…
Abstract
A system and method are provided to regulate resistance in a discontinuous time hot-wire anemometer. The solution removes supply voltage dependency on the mass airflow output signal. Operating the hot-wire anemometer using discontinuous time regulation offers lower system power, but introduces an inverse supply dependent term in the associated transfer function. This effect is removed by multiplying the output signal via a supply dependent signal.
Claims14
An anemometer comprising:
- a bridge circuit having a hot wire sensing resistor, a pair of input terminals, and a pair of output terminals, the hot wire sensing resistor operational to change its resistance in response to air flowing past it, unbalancing the bridge circuit and causing a differential signal to appear across the bridge circuit output terminals;
- a first differential amplifier coupled to the output terminals of the bridge circuit, the first differential amplifier configured to generate an output signal in response to the differential signal at the bridge circuit output terminals;
- a switching circuit operational to cycle a supply voltage to the input terminals in response to the first differential amplifier output signal and further in response to a discontinuous time control signal, such that current does not flow continuously through the hot wire sensing resistor;
- wherein the switching circuit comprises:
- a switching transistor;
- a second differential amplifier responsive to the first differential amplifier output signal and the discontinuous time control signal to turn the switching transistor on and off such that the supply voltage is intermittently connected to the bridge circuit;
- further comprising an intermediate output voltage circuit connected to the bridge circuit and operational to generate an anemometer output voltage
- V
- O
- =
- (
- R
- 1
- R
- 1
- +
- R
- H
- )
-
- (
- K
- V
- BAT
- )
- ,
- where VO is the anemometer output voltage, RH is the hot wire sensing resistor, R1 is a bridge circuit resistor in the same arm as hot wire sensing resistor RH, K is constant determined at a given air flow rate, and VBAT is the anemometer supply voltage.
24 more elements
An anemometer comprising:
- a bridge circuit having a pair of input terminals, a pair of output terminals and a hot wire sensing resistor;
- a switching circuit operational to cycle supply current through the hot wire sensing resistor to regulate its resistance and to control power dissipation in the hot wire sensing resistor;
- wherein the switching circuit comprises:
- a switching transistor;
- a first differential amplifier coupled to the bridge circuit output terminals, the first differential amplifier configured to generate an output signal in response to a differential signal at the bridge circuit output terminals;
- a second differential amplifier operational in response to the first differential amplifier output signal and further in response to a discontinuous time control signal, to turn the switching transistor on and off such that a bridge circuit supply voltage is controlled to limit the power dissipation in the hot wire sensing resistor;
- further comprising an intermediate output voltage circuit connected to the bridge circuit, the intermediate output voltage circuit operational to generate an anemometer output voltage represented by
- V
- O
- =
- (
- R
- 1
- R
- 1
- +
- R
- H
- )
-
- (
- K
- V
- BAT
- )
- ,
- where VO is the anemometer output voltage, RH is the hot wire sensing resistor, R1 is a bridge circuit resistor in the same arm as hot wire sensing resistor RH, K is constant determined at a given air flow rate, and VBAT is the anemometer supply voltage.
24 more elements
An anemometer comprising:
- a bridge circuit having a pair of input terminals, a pair of output terminals and a hot wire sensing resistor;
- and
- means for discontinuous time cycling a supply current through the hot wire sensing resistor to regulate its resistance and control power dissipation in the hot wire sensing resistor;
- further comprising means for generating an inverse supply voltage dependent anemometer output signal.
1 more element
A method of regulating resistance in a hot-wire anemometer, the method comprising the steps of:
- providing a hot-wire anemometer having a hot-wire sensing resistor;
- controlling current flow through the hot-wire sensing resistor in response to a discontinuous time control signal to regulate the resistance of the hot-wire sensing resistor;
- further comprising the step of controlling the current flow through the hot-wire sensing resistor in response to a hot-wire anemometer output voltage represented as:
- V
- O
- =
- (
- R
- 1
- R
- 1
- +
- R
- H
- )
-
- (
- K
- V
- BAT
- )
- ,
- where VO is the anemometer output voltage, RH is the hot wire sensing resistor, R1 is a bridge circuit resistor in the same arm as hot wire sensing resistor RH, K is constant determined at a given air flow rate, and VBAT is the anemometer supply voltage.
20 more elements
A method of regulating resistance in a hot-wire anemometer, the method comprising controlling current flow in discontinuous time through a hot-wire sensing resistor to regulate the resistance of the hot-wire sensing resistor,
- wherein controlling current flow in discontinuous time through a hot-wire sensing resistor is responsive to a hot-wire anemometer output voltage represented as:
- V
- O
- =
- (
- R
- 1
- R
- 1
- +
- R
- H
- )
-
- (
- K
- V
- BAT
- )
- ,
- where VO is the anemometer output voltage, RH is the hot wire sensing resistor, R1 is a anemometer bridge circuit resistor in the same arm as hot wire sensing resistor RH, K is constant determined at a given air flow rate, and VBAT is a anemometer supply voltage.
18 more elements
Dependencies are inferred from the claim text.