US4059014A
Expired / Lapsed
US
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Electromagnetic flowmeter
Assignee: Yokogawa Electric Corp
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Filing: 1976-11-18
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Granted: 1977-11-22
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Expires: 1996-11-18
Abstract
Abstract An electromagnetic flowmeter in which the fluid to be metered is conducted through a flow tube where it intersects a magnetic field established by an electromagnet. A pair of electrodes each having a relatively large surface area are mounted at diametrically-opposed positions in the flow tube whereby the electromotive force induced in the fluid and detected by the electrodes when the fluid velocity profile is non-uniform, is averaged and an electromotive force proportional to average flow velocity is obtained. The electromagnet is energized by a low-frequency wave produced by applying the output of a full-wave rectifier coupled to a commercial power line to the excitation coils of the electromagnet through an electronic switching element that acts to periodically chop the full-wave rectified voltage in accordance with high-frequency pulses whose frequency is higher than the power line frequency, the duty cycle thereof being gradually modulated by a low-frequency wave whose frequency is less than the power line frequency.
Inventors
- 👤 Takashi Torimaru
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 10:39
CPC Classifications
G; G01; G01F; G01F1/00; G01F1/56; G01F1/58; G01F1/60
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
193 words
In an electromagnetic flowmeter comprising: A. a flow tube through which a fluid to be metered is conducted to intersect a magnetic field therein which is transverse to the direction of flow and is produced by an electromagnet having excitation coils; B. a pair of electrodes mounted at diametrically-opposed positions in said tube, said electrodes each having a relatively large surface area whereby the electromotive force induced in the fluid intersecting the field and detected by the electrodes is averaged to minimize the effect of a non-uniform flow velocity on the accuracy of the meter; and C. an excitation system for supply current to said coils, said system being constituted by: a. a power source energized by a commercial a-c power line having a predetermined frequency and providing a direct voltage; b. electronic switching means interposed between said direct voltage source and said coils; c. control means to effect an on-off operation of said switching means at a pulse rate which is higher than the frequency of said a-c line; and d. means gradually changing the duty cycle of said control means at a low-frequency rate which is less than said line frequency.
Claim 2
Dependent Claim
193 words
In an electromagnetic flowmeter comprising: A. a flow tube through which a fluid to be metered is conducted to intersect a magnetic field therein which is transverse to the direction of flow and is produced by an electromagnet having excitation coils; B. a pair of electrodes mounted at diametrically-opposed positions in said tube, said electrodes each having a relatively large surface area whereby the electromotive force induced in the fluid intersecting the field and detected by the electrodes is averaged to minimize the effect of a non-uniform flow velocity on the accuracy of the meter; and C. an excitation system for supply current to said coils, said system being constituted by: a. a power source energized by a commercial a-c power line having a predetermined frequency and providing a direct voltage; b. electronic switching means interposed between said direct voltage source and said coils; c. control means to effect an on-off operation of said switching means at a pulse rate which is higher than the frequency of said a-c line; and d. means gradually changing the duty cycle of said control means at a low-frequency rate which is less than said line frequency.
Claim 3
Dependent Claim
25 words
An excitation system as set forth in claim 1, wherein said power source is constituted by a full-wave rectifier coupled to said a-c power line.
Claim 4
Dependent Claim
24 words
An excitation system as set forth in claim 2, wherein said means to gradually change the duty cycle is constituted by a sinusoidal-wave generator.
Claim 5
Dependent Claim
48 words
An excitation system as set forth in claim 3, wherein said sinusoidal wave generator is constituted by a frequency divider coupled to the output of said full-wave rectifier to produce low-frequency rectangular pulses which are applied to a filter to convert the rectangular pulses to a sinusoidal wave.
Claim 6
Dependent Claim
52 words
In an electromagnetic flowmeter as set forth in claim 4, wherein said sinusoidal wave is applied to a current controller and compared therein with the sinusoidal voltage produced across a resistor connected in series with said coils to produce an error signal for regulating the high-frequency pulses applied to said switching means.
Claim 7
Dependent Claim
19 words
An excitation system as set forth in claim 1, wherein said switching means is constituted by a switching transistor.
Claim 8
Dependent Claim
45 words
In an electromagnetic flowmeter as set forth in claim 1, wherein said electrodes are coupled to a signal converter including a voltage divider that divides the signal derived from said electrodes with a reference signal derived from a resistor in series with said excitation coils.
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) | 1980-11-21 | 1981-05-23 | 1981-11-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-11-21 | 1985-05-23 | 1985-11-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-11-21 | 1989-05-23 | 1989-11-22 | $7700.00 | Window Closed / Lapsed |