Magnetic flowmeter coil driver and method
First Claim
1. In a magnetic flowmeter comprising a body adapted to be connected in a flow system for flow of liquid therethrough, coil means for generating a magnetic field in the path of the fluid flowing through the body, voltage means for applying a voltage waveform across the coil means to generate the magnetic field, the strength and direction of the magnetic field being a function of the applied voltage waveform, said voltage means including means for periodically reversing the polarity of the voltage applied across the coil means to reverse the direction of the magnetic field, electrode means disposed transverse to the path of the fluid for detecting an induced voltage caused by the flow of the fluid through the magnetic field, the magnitude of the induced voltage being generally proportional to the rate of flow of said fluid, the improvement comprising:
- the voltage means including means for applying a first, relatively high voltage across the coil means for a controlled length of time to build the coil current to a desired level and means for applying a second, relatively low voltage across the coil means after the application of the high voltage to maintain the coil current at the desired level, so that the voltage waveform includes for each cycle half a relatively high voltage portion and a relatively low voltage portion;
means for sampling coil current; and
means responsive to differences in consecutive coil current samples for substantially eliminating such differences in subsequent coil current samples by changing the length of time the relatively high voltage is applied across the coil means.
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Accused Products
Abstract
A magnetic flowmeter includes circuitry for applying a first relatively high voltage across the electromagnet coils of the meter for a controlled length of time to build the coil current to a desired level and circuitry for applying a second, relatively low voltage across the electromagnet coils after the application of the high voltage to maintain the coil current at the desired level. The coil current is sampled at predetermined times during the application of the relatively low voltage and the length of time the relatively high voltage is applied is varied to eliminate differences in consecutive coil current samples. The actual level of the coil current is controlled by a magnetic amplifier which includes a saturable reactor. The voltage waveform applied to the electromagnetic coil reverses in polarity each half cycle due to a bridge circuit which is connected to a power supply of a single polarity.
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Citations
31 Claims
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1. In a magnetic flowmeter comprising a body adapted to be connected in a flow system for flow of liquid therethrough, coil means for generating a magnetic field in the path of the fluid flowing through the body, voltage means for applying a voltage waveform across the coil means to generate the magnetic field, the strength and direction of the magnetic field being a function of the applied voltage waveform, said voltage means including means for periodically reversing the polarity of the voltage applied across the coil means to reverse the direction of the magnetic field, electrode means disposed transverse to the path of the fluid for detecting an induced voltage caused by the flow of the fluid through the magnetic field, the magnitude of the induced voltage being generally proportional to the rate of flow of said fluid, the improvement comprising:
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the voltage means including means for applying a first, relatively high voltage across the coil means for a controlled length of time to build the coil current to a desired level and means for applying a second, relatively low voltage across the coil means after the application of the high voltage to maintain the coil current at the desired level, so that the voltage waveform includes for each cycle half a relatively high voltage portion and a relatively low voltage portion; means for sampling coil current; and means responsive to differences in consecutive coil current samples for substantially eliminating such differences in subsequent coil current samples by changing the length of time the relatively high voltage is applied across the coil means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of driving the coils in a magnetic flowmeter having a body adapted to be connected in a flow system for flow of liquid therethrough and coils for generating a magnetic field in the path of the fluid flowing through the body, the method comprising:
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cyclically applying a relatively high voltage and a relatively low voltage across the coils; sensing the current through the coils during a portion of the cycle when only the relatively low voltage is being applied across the coils; increasing the length of time the relatively high voltage is applied during subsequent cycles when the current sensed during the time the relatively low voltage is applied across the coils rises slightly during the time said relatively low voltage is applied; and decreasing the length of time the relatively high voltage is applied during subsequent cycles when the current sensed during the time the relatively low voltage is applied across the coils falls slightly during the time said relatively low voltage is applied. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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24. In a magnetic flowmeter comprising a body adapted to be connected in a flow system for flow of liquid therethrough, coil means for generating a magnetic field in the path of the fluid flowing through the body, voltage means for applying a voltage waveform across the coil means to generate the magnetic field, the strength and direction of the magnetic field being a function of the applied voltage waveform, electrode means disposed transverse to the path of the fluid for detecting an induced voltage caused by the flow of the fluid through the magnetic field, the magnitude of the induced voltage being generally proportional to the rate of flow of the fluid, the improvement comprising:
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the voltage means including means for applying a first, relatively high voltage across the coil means for a controlled length of time to build the coil current to a desired level and means for applying a second, relatively low voltage across the coil means after the application of the high voltage to maintain the coil current at the desired level so that the voltage waveform includes a relatively high voltage portion and a relatively low voltage portion for each cycle; means for sensing coil current; and means for regulating the coil current during the low voltage portion of each cycle, said regulating means including a saturable reactor connected to the low voltage applying means for controlling the voltage applied by the low voltage applying means, the saturable reactor being responsive to the current sensed by the current sensing means. - View Dependent Claims (25, 26, 27)
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28. In a magnetic flowmeter comprising a body adapted to be connected in a flow system for flow of liquid therethrough, coil means for generating a magnetic field in the path of the fluid flowing through the body, voltage means for applying a voltage waveform across the coil means to generate the magnetic field, said voltage means including means for applying a first, relatively high voltage across the coil means to build the coil current to a desired level and low voltage applying means for applying a second, relatively low voltage across the coil means after the application of the high voltage to maintain the coil current at the desired level, so that the voltage waveform includes for each cycle half a relatively high voltage portion and a relatively low voltage portion, the strength and direction of the magnetic field being a function of the applied voltage waveform, said voltage means including means for periodically reversing the polarity of the voltage applied across the coil means to reverse the direction of the magnetic field, electrode means disposed transverse to the path of the fluid for detecting an induced voltage caused by the flow of the fluid through the magnetic field, the magnitude of the induced voltage being generally proportional to the rate of flow of the fluid, the improvement comprising:
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the polarity reversing means including four electronic switching elements, each having a pair of load current terminals and a control terminal for controlling the flow of current between its associated load current terminals, the load current terminals of the switching elements being connected in a bridge configuration with the coil means connected across two, opposite nodes of the bridge and the other two nodes of the bridge being connected to a single polarity voltage source and to a circuit common respectively; and means for regulating the current flowing through the coil means during the relatively low voltage portion of the cycle, said regulating means including a saturable reactor connected to the low voltage applying means for controlling the voltage applied by the low voltage applying means. - View Dependent Claims (29, 30, 31)
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Specification