US3783687A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Electromagnetic flowmeter with square-wave excitation
Assignee: Fischer and Porter Co
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Filing: 1972-05-26
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Granted: 1974-01-08
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Expires: 1992-05-26
Abstract
Abstract An electromagnetic flowmeter system wherein liquid to be measured is conducted through a flow tube to intersect a transverse magnetic field produced by an electromagnet, the voltage induced in the fluid being transferred to a pair of electrodes mounted at diametrically opposed points on the tube. To avoid spurious voltages arising from stray couplings between the electromagnetic and the loop constituted by the electrodes and the liquid extending therebetween, without, however, causing polarization of the electrodes, the electromagnet is energized by a low-frequency square wave. This wave is produced by applying the output voltage of an unfiltered full-wave rectifier to the electromagnet and periodically reversing the voltage polarity at a low-frequency rate by means of an electronic switch, filtration of the applied voltage being effected largely by the electromagnet induction. Since the steady state field produced by the square wave is disrupted by switching transients occurring at the points of reversal, the converter to which the signal from the electrodes is applied includes a demodulator which is gated synchronously with an electronic switch to yield an output only when the magnet flux achieves a steady state condition.
Inventors
- 👤 E Mannherz
- 👤 H Riester
- 👤 R Schmoock
- 👤 J Yard
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 21:29
CPC Classifications
G; G01; G01F; G01F1/00; G01F1/56; G01F1/58; G01F1/60; G01F15/00; G01F15/06; G01F15/065; G01F15/068
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
239 words
An electromagnetic flowmeter system comprising: A. an electromagnetic flowmeter primary including a flow tube having a pair of electrodes mounted at diametrically-opposed positions, and an electromagnet provided with a coil to produce a transverse magnetic field within said tube, the voltage induced in the liquid passing through said tube and intersecting said field being transferred to said electrodes to provide a flow-induced signal, B. means to excite said electromagnet, including a full-wave rectifier connectable to an a-c power line having a predetermined frequency and producing an unfiltered d-c voltage, and switching means to periodically apply said unfiltered d-c voltage to said coil at a rate which is low relativE to said predetermined frequency whereby a steady state field is periodically established in said flow tube except at the points of switching when transients are created whose duration is a function of the inductance of said coil, said electromagnet having sufficient inductance to effectively filter said rectified d-c voltage, and C. a secondary coupled to said electrodes and responsive to said flow-induced signal to provide an output signal indicative of liquid flow rate, said secondary including a demodulator to convert said flow-induced signal into a d-c voltage, and pulsatory means to synchronize the operation of said demodulator with said switching means so as to activate said demodulator only during the periods in which the magnetic field is in a steady state condition, said demodulator being blocked during said transient intervals.
Claim 2
Dependent Claim
239 words
An electromagnetic flowmeter system comprising: A. an electromagnetic flowmeter primary including a flow tube having a pair of electrodes mounted at diametrically-opposed positions, and an electromagnet provided with a coil to produce a transverse magnetic field within said tube, the voltage induced in the liquid passing through said tube and intersecting said field being transferred to said electrodes to provide a flow-induced signal, B. means to excite said electromagnet, including a full-wave rectifier connectable to an a-c power line having a predetermined frequency and producing an unfiltered d-c voltage, and switching means to periodically apply said unfiltered d-c voltage to said coil at a rate which is low relativE to said predetermined frequency whereby a steady state field is periodically established in said flow tube except at the points of switching when transients are created whose duration is a function of the inductance of said coil, said electromagnet having sufficient inductance to effectively filter said rectified d-c voltage, and C. a secondary coupled to said electrodes and responsive to said flow-induced signal to provide an output signal indicative of liquid flow rate, said secondary including a demodulator to convert said flow-induced signal into a d-c voltage, and pulsatory means to synchronize the operation of said demodulator with said switching means so as to activate said demodulator only during the periods in which the magnetic field is in a steady state condition, said demodulator being blocked during said transient intervals.
Claim 3
Dependent Claim
26 words
A system as set forth in claim 1, wherein said predetermined frequency is at least 50 Hz and said switching rate is less than 10 Hz.
Claim 4
Dependent Claim
20 words
A system as set forth in claim 1, wherein said switching means is constituted by electronic solid state switching devices.
Claim 5
Dependent Claim
37 words
A system as set forth in claim 3, wherein said solid state switching devices are activated by low-frequency pulses produced by a divider circuit coupled to said a-c power line, said line frequency serving as a clock.
Claim 6
Dependent Claim
25 words
A system as set forth in claim 4, wherein said pulsatory means to synchronize the operation of said demodulator is coupled to said divider circuit.
Claim 7
Dependent Claim
28 words
A system as set forth in claim 1, wherein said switching means is arranged to periodically reverse the polarity of the rectified voltage applied to said magnet coil.
Claim 8
Dependent Claim
31 words
A system as set forth in claim 1, wherein said secondary includes a summing junction to which is applied said flow-induced signal and a feedback signal to produce an error signal.
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) | 1977-01-07 | 1977-07-09 | 1978-01-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-07 | 1981-07-09 | 1982-01-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-07 | 1985-07-09 | 1986-01-08 | $7700.00 | Window Closed / Lapsed |