US3922912A
Expired / Lapsed
US
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Anemometers
Assignee: National Research Development Corp UK
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Filing: 1974-02-25
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Granted: 1975-12-02
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Expires: 1994-02-25
Abstract
Abstract An anemometer is described in which a pulse of electric current is passed through a first wire to heat gas passing over the wire. Two further wires on either side of the first wire are connected in a bridge circuit to sense the heated gas. The velocity of the gas is indicated by automatically measuring the time between the heating pulse and the sensing of the heated gas by one of the further wires. In order to reduce the effect of signals induced electromagnetically in the sensing wires by the heating pulse an inhibit circuit constructed to introduce as little disturbance as possible, is coupled between the bridge and the time measuring circuits. The inhibit circuit has two paths which are both operative until after the induced pulse has occurred. The outputs from these paths are as far as possible, equal and opposite, and therefore cancel until one path is rendered inoperative before the pulse to be sensed occurs.
Inventors
- 👤 Leslie John Stanley Bradbury
- 👤 Nicholas Liptay Wagner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 04:43
CPC Classifications
G; G01; G01P; G01P13/00; G01P13/02; G01P5/00; G01P5/18
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
201 words
Apparatus for measuring the velocity of fluids, including electrical heating means for locally heating a flowing fluid for short intervals in response to current pulses passed through the heating means, a temperature sensitive element for providing an electrical signal dependent on the temperature of the fluid, the temperature sensitive element being in operation positioned, at least partially, in the path of heated fluid from the heating means, means for detecting changes in the said electrical signal, timing means for providing an indication of the duration of the intervals between each current pulse and each consequent change in the said electrical signal, and an inhibit circuit comprising means for combining, in opposition, signals along two substantially electrically equivalent paths each of which is coupled to receive the said electrical signal, one of the said paths including switch means having continuity means for providing continuity in the said one path and control means for controlling the continuity means to provide continuity when each of the current pulses occurs for an interval which terminates before the heated fluid is expected to reach the temperature sensitive element, the means for combining signals being coupled to pass its output signal to the means for detecting changes.
Claim 2
Dependent Claim
201 words
Apparatus for measuring the velocity of fluids, including electrical heating means for locally heating a flowing fluid for short intervals in response to current pulses passed through the heating means, a temperature sensitive element for providing an electrical signal dependent on the temperature of the fluid, the temperature sensitive element being in operation positioned, at least partially, in the path of heated fluid from the heating means, means for detecting changes in the said electrical signal, timing means for providing an indication of the duration of the intervals between each current pulse and each consequent change in the said electrical signal, and an inhibit circuit comprising means for combining, in opposition, signals along two substantially electrically equivalent paths each of which is coupled to receive the said electrical signal, one of the said paths including switch means having continuity means for providing continuity in the said one path and control means for controlling the continuity means to provide continuity when each of the current pulses occurs for an interval which terminates before the heated fluid is expected to reach the temperature sensitive element, the means for combining signals being coupled to pass its output signal to the means for detecting changes.
Claim 3
Dependent Claim
86 words
Apparatus according to claim 1 wherein the heating means includes a first wire, the temperature sensitive element includes a second wire, a further temperature sensitive element which includes a third wire is provided, the third wire being located on the opposite side of the first wire to the second wire, the second and third wires being connected as adjacent arms in a four arm electrical bridge, with the other arms being formed by electrical resistors, and the bridge output being coupled to the said inhibit circuit.
Claim 4
Dependent Claim
35 words
Apparatus according to claim 2 wherein the first, second and third wires are positioned, spaced apart from one another, with the second and third wires parallel to one another but orthogonal to the first wire.
Claim 5
Dependent Claim
17 words
Apparatus according to claim 3 wherein the three wires are positioned at the end of a probe.
Claim 6
Dependent Claim
53 words
Apparatus according to claim 3 including a wide-band differential amplifier having one input terminal coupled to one output terminal of the bridge, and the other input terminal coupled to the other bridge output terminal, the output of the said wide-band differential amplifier being coupled to the said two paths of the inhibit circuit.
Claim 7
Dependent Claim
27 words
Apparatus according to claim 1 wherein the heating means includes a first wire, and the temperature sensitive element includes a second wire orthogonal to the first wire.
Claim 8
Dependent Claim
15 words
Apparatus according to claim 6 including a wide-band amplifier coupled to the temperature sensitive element.
Claim 9
Dependent Claim
48 words
Apparatus according to claim 3 wherein the said means for combining two signals in opposition includes a further differential amplifier with one input coupled to one of the two paths, the other input coupled to the other path, and output coupled to the said means for detecting changes.
Claim 10
Dependent Claim
42 words
Apparatus according to claim 3 wherein the continuity means includes an electronic switching element, and the control means is constructed to initiate the said current pulses and to render the switching element conductive for an interval, when each current pulse is initiated.
Claim 11
Dependent Claim
77 words
Apparatus according to claim 9 wherein the path which includes the switch means also includes a first shunt capacitor connected on the output side of the switch means to hold the voltage at the output of the switch means when the switch opens, the combined time constant of the switch means, when closed, and the first shunt capacitor being short compared with the interval between a current pulse and the time at which heated gas is sensed.
Claim 12
Dependent Claim
37 words
Apparatus according to claim 10 wherein the patH which does not include the switch means includes a variable resistor and a second shunt capacitor allowing the electrical characteristics of the two paths to be made substantially equivalent.
Claim 13
Dependent Claim
29 words
Apparatus according to claim 11 including first and second voltage-follower circuits connected between the first and second shunt capacitors, respectively, and the said means for combining signals in opposition.
Claim 14
Dependent Claim
45 words
Apparatus according to claim 9 wherein the means for detecting changes in an electrical signal includes a differentiating circuit, and first and second comparator circuits for detecting when the output signal from the differentiating circuit exceeds predetermined levels in one and the opposite polarities, respectively.
Claim 15
Dependent Claim
77 words
Apparatus according to claim 13 including first and second bistable circuits coupled to the outputs of the first and second comparator circuits, respectively, each bistable circuit being set to a first state when the output signal of the comparator to which it is connected indicates that one of the said predetermined levels has been exceeded, and each bistable circuit being connected to disable the comparator which it is not coupled to when in the said first state.
Claim 16
Dependent Claim
80 words
Apparatus according to claim 14 wherein the timing means includes a pulse oscillator, and a counter coupled to the pulse oscillator by way of a gate circuit, the gate circuit being connected to be opened by the timing control circuit each time a current pulse is initiated, and each bistable circuit being connected to close the said gate circuit on entering the said first state, and to be set to its second state each time a current pulse is initiated.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-12-01 | 1979-06-02 | 1979-12-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-12-01 | 1983-06-02 | 1983-12-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-12-01 | 1987-06-02 | 1987-12-02 | $7700.00 | Window Closed / Lapsed |