Vibrating beam force transducer with automatic drive control
First Claim
1. A force transducer comprising:
- an oscillating sensing element having an output frequency indicative of the force applied to the sensing element, said sensing element having a variable electrical resistance;
means electrically coupled to said sensing element for electrically driving said sensing element to cause said sensing element to oscillate at a resonant frequency that is a function of the force applied to said sensing element, said driving means having means for amplifying electrical signals, said amplifying means having means for receiving input signals and means for providing output signals, said input signal receiving means being electrically coupled to said sensing element;
said electrical driving means having means for DC compensating said driving means for variations in the electrical resistance of the sensing means, said DC compensating means being electrically coupled between said input signal receiving means and said output signal providing means; and
said driving means having means separate from said DC compensating means for applying an AC drive signal to said sensing element to thereby cause said sensing element to oscillate, said AC drive signal applying means being electrically coupled between said output signal providing means and said sensing element, said AC drive signal applying means including a capacitor for preventing the flow of DC signals between said output signal providing means and said sensing means.
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Accused Products
Abstract
A vibrating beam force transducer is comprised of an oscillating sensing element having an output frequency indicative of the force applied to the sensing element. The sensing element has a variable electrical resistance which can vary in accordance with temperature fluctuations over the operating range of the transducer.
A drive circuit utilizes an AC drive signal source that is electrically coupled to the sensing element to drive the sensing element at its resonant frequency which is a function of the force applied to the sensing element. The drive circuit has a DC compensation circuit that alters the electrical characteristics of the drive circuit in response to variations in the electrical resistance of the sensing element.
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Citations
16 Claims
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1. A force transducer comprising:
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an oscillating sensing element having an output frequency indicative of the force applied to the sensing element, said sensing element having a variable electrical resistance; means electrically coupled to said sensing element for electrically driving said sensing element to cause said sensing element to oscillate at a resonant frequency that is a function of the force applied to said sensing element, said driving means having means for amplifying electrical signals, said amplifying means having means for receiving input signals and means for providing output signals, said input signal receiving means being electrically coupled to said sensing element; said electrical driving means having means for DC compensating said driving means for variations in the electrical resistance of the sensing means, said DC compensating means being electrically coupled between said input signal receiving means and said output signal providing means; and said driving means having means separate from said DC compensating means for applying an AC drive signal to said sensing element to thereby cause said sensing element to oscillate, said AC drive signal applying means being electrically coupled between said output signal providing means and said sensing element, said AC drive signal applying means including a capacitor for preventing the flow of DC signals between said output signal providing means and said sensing means. - View Dependent Claims (2, 3)
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4. A force transducer comprising:
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an oscillating sensing element having an output frequency indicative of the force applied to the sensing element, said sensing element having a variable electrical resistance; means electrically coupled to said sensing element for electrically driving said sensing element to cause said sensing element to oscillate at a resonant frequency that is a function of the force supplied to said sensing element, said driving means having means for amplifying electrical signals, said amplifying means having means for receiving input signals and means for providing output signals, said input signal receiving means being electrically coupled to said sensing element; said electrical driving means having means for DC compensating said driving means for variations in the electrical resistance of the sensing means,.said DC compensating means being electrically coupled between said input signal receiving means and said output signal providing means; and said driving means having separate from said DC compensating means for applying an AC drive signal to said sensing element to thereby cause said sensing element to oscillate, said AC drive signal applying means being electrically coupled between said output signal providing means and said sensing element, said AC drive signal applying means including means for preventing the flow of DC signals between said output signal providing means and said sensing means; wherein said DC compensating means further includes a variable resistance element, said DC compensating means being operative to vary the resistance value of said variable resistance element in response to variations in the electrical resistance of said element; wherein said variable resistance element includes a field effect transistor; and wherein said field effect transistor forms a part of a bridge circuit. - View Dependent Claims (5, 6, 7, 8, 9)
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10. A force transducer comprising:
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an oscillating sensing element having a frequency output indicative of the force applied to the sensing element, said sensing element having a variable electrical resistance; and drive means electrically coupled to the sensing element for causing the sensing element to oscillate at a resonant frequency that is a function of the force applied to the sensing element, said drive means comprising; a first voltage divider comprised of a resistance element electrically serially connected to said sensing element and having a first output node therebetween; a second voltage divider, comprised of at least two resistance elements electrically serially connected to each other with a second output node therebetween, said first and second voltage dividers being connected electrically in parallel at first and second input nodes; comparator means having inputs coupled to said first and second output nodes for determining the difference in output between said first and second output nodes and an output; compensating means coupled to said output and to said second voltage divider for altering the resistance of said second voltage divider in response to variations in the resistance of said sensing element; and AC drive signal applying means coupled to said output and to one of said input nodes for applying AC drive signals to said sensing element from said output while preventing the flow of DC signals between said output and said one of said input nodes. - View Dependent Claims (11, 12)
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13. A force transducer comprising:
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an oscillating sensing element having an output frequency indicative of the force applied to the sensing element, said sensing element having a variable electrical resistance; means including an amplifier electrically coupled to said sensing element for driving said sensing element to resonate at a frequency indicative of the amount of force applied to said sensing element, said driving means including means including a variable resistance element for biasing said amplifier, wherein said sensing element forms part of said biasing means, an AC feedback loop electrically coupled to an output of said amplifier and to said sensing element, said AC feedback loop being operative to prevent DC signals from being transferred therethrough, and a DC feedback loop electrically coupled to an output of said amplifier and to said variable resistance element; said DC feedback loop being operative to adjust the resistance of said variable resistance element in response to changes in the electrical resistance of said sensing element to thereby maintain said amplifier biased in a predetermined bias range. - View Dependent Claims (14, 15, 16)
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Specification