Resonator sensors employing piezoelectric benders for fluid property sensing
First Claim
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1. A method of monitoring liquid viscosity to maintain the level of a liquid contained in a vessel comprising the steps of:
- (a) locating at least the vibrating portion of a piezoelectric bender in said vessel containing said liquid;
(b) applying a stimulation voltage to said bender at an amplitude and frequency to cause the bender to resonate;
(c) varying said stimulation voltage frequency as a function of said output voltage frequency to maintain said bender at resonance;
(d) monitoring an output voltage from said bender, the amplitude of said output voltage varying as an inverse function of the liquid viscosity, whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa;
(e) detecting when the output voltage amplitude signals a change in viscosity indicating that the bender is no longer in contact with said liquid; and
(f) automatically replenishing the liquid in said vessel when the liquid is no longer in contact with said bender.
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Abstract
Resonator sensors namely piezoelectric benders are used for sensing fluid viscosity and density. The benders are inserted into a liquid to be monitored. An input voltage is applied to the bender causing it to vibrate in the liquid at a resonant frequency. Output voltage amplitude or frequency are monitored to determine changes in viscosity and density, respectively. The device may be used as a liquid level sensor and to control alteration of the viscosity of the fluid as, for example, by connection with a supply of ink or solvent in an ink jet printing device.
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Citations
19 Claims
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1. A method of monitoring liquid viscosity to maintain the level of a liquid contained in a vessel comprising the steps of:
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(a) locating at least the vibrating portion of a piezoelectric bender in said vessel containing said liquid; (b) applying a stimulation voltage to said bender at an amplitude and frequency to cause the bender to resonate; (c) varying said stimulation voltage frequency as a function of said output voltage frequency to maintain said bender at resonance; (d) monitoring an output voltage from said bender, the amplitude of said output voltage varying as an inverse function of the liquid viscosity, whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa; (e) detecting when the output voltage amplitude signals a change in viscosity indicating that the bender is no longer in contact with said liquid; and (f) automatically replenishing the liquid in said vessel when the liquid is no longer in contact with said bender. - View Dependent Claims (2)
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3. Apparatus for monitoring liquid viscosity to maintain the level of a liquid contained in a vessel comprising:
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(a) a piezoelectric bender having an element which vibrates upon application of a stimulation voltage thereto and which is positioned to contact said liquid; (b) means for applying a stimulation voltage to said bender at an amplitude and frequency to cause said bender element to resonate and to produce an output voltage, (c) means for varying said stimulation voltage frequency as a function of said output voltage frequency to maintain said bender at resonance; (d) means for monitoring an output voltage from said bender, the amplitude of said output voltage varying as an inverse function of the liquid viscosity, whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa; (e) means for detecting when the output voltage amplitude signals a change viscosity indicating that the bender is no longer in contact with said liquid; and (f) means for automatically replenishing said vessel when said output voltage indicates that said bender is no longer in contact with said liquid. - View Dependent Claims (4)
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5. Apparatus for monitoring and maintaining the viscosity of a liquid comprising:
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(a) a piezoelectric bender having an element which vibrates upon application of a stimulation voltage thereto and which is positioned to contact said liquid; (b) means for applying a stimulation voltage to said bender at an amplitude and frequency to cause said bender element to resonate and to produce an output voltage, the amplitude of which varies as an inverse function of liquid viscosity whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa; (c) said means for applying including means for varying said stimulation voltage frequency responsive to said output voltage frequency to maintain said bender at its resonant frequency in said liquid; and (d) means for automatically altering the liquid viscosity responsive to the amplitude of said output voltage.
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6. A method for monitoring and maintaining the viscosity of a liquid comprising:
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(a) locating the vibrating portion of a piezoelectric bender in contact with said liquid; (b) applying a stimulation voltage to said bender at an amplitude and frequency to cause said bender to resonate and to produce an output voltage, the amplitude of which varies as an inverse function of liquid viscosity, whereby an increase in liquid viscosity produces a decrease in output voltage amplitude and vice-versa; (c) varying said stimulation voltage frequency as a function of said output voltage frequency to maintain said bender at resonance; and (d) automatically altering the liquid viscosity responsive to the amplitude of said output voltage.
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7. A resonator sensor for monitoring changes in the properties of a liquid such as density and viscosity comprising:
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(a) a one-port bender; (b) means for causing said bender to vibrate in said liquid at its resonant frequency; and (c) monitoring the changes in the electrical characteristics of said bender due to changes in the motional resistance of said liquid to determine changes in said liquid properties.
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8. A liquid sensing apparatus comprising:
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(a) a piezoelectric bender for immersion in the liquid; (b) a first circuit (62,64) for supplying an input voltage to said bender at a frequency to cause it to resonate; and (c) a second circuit (60) for monitoring an output voltage produced by said bender in response to said input voltage thereby to sense said liquid; (d) said first circuit(62)receiving said output voltage and following any change in the resonant frequency of said bender thereby to maintain the bender at resonance, said first circuit maintaining said input voltage amplitude substantially constant, independent of any change in the amplitude of said output voltage. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A liquid sensing apparatus comprising:
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(a) a piezoelectric bender for immersion in the liquid; (b) a first circuit (62,64) for supplying an input voltage to said bender at a frequency to cause it to resonate; and (c) a second circuit (60) for monitoring an output voltage produced by said bender in response to said input voltage thereby to sense said liquid; (d) said first circuit (62) receiving said output voltage and following any change in the resonant frequency of said bender thereby to maintain the bender at resonance, said first circuit including amplifying means for maintaining said input voltage below a predetermined level.
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Specification