Piezoelectric transducer with improved sensing circuit

Claim 2

An improved sensing circuit for use with a transducer of the type which produces its full electrical output only when it is substantially unbiased by externally applied voltages or currents, said sensing circuit comprising, amplifying means coupled to said transducer and including at least two direct-coupled transistors and bias means for supplying a bias voltage for said transistors, said amplifying means being operative to amplify the current produced by said transducer while maintaining the voltage thereof; reference means coupled to said transducer for providing a reference voltage selected to establish a substantially zero voltage drop across said transducer under quiescent conditions; an output relay; and relay control means coupled to said amplifying means and adapted to energize said relay as said transducer signal exceeds a predetermined threshold voltage.

Claim 3

An improved sensing circuit in accordance with claim 1 wherein said bias means includes a first voltage divider for providing a bias voltage for said transistors sufficient to render them conductive in their linear range, and said reference means includes a second voltage divider for providing a reference voltage substantially equal to said bias voltage, said transducer being coupled between said second voltage divider and said transistors, whereby zero current flows through said transducer under quiescent conditions.

Claim 4

An improved sensing circuit in accordance with claim 2 further including a diode connected between said first voltage divider and said transistors and poled to allow conduction of said biasing current while preventing loading of said transducer by said first voltage divider.

Claim 5

An improved sensing circuit according to claim 1 wherein said amplifiEr includes at least two direct-coupled transistors each having base, emitter and collector terminals, the emitter of the first transistor being coupled to the base of the second transistor and the collectors of both transistors being connected together.

Claim 6

An improved sensing device for detecting stress applied to a deformable body, comprising a transducer including a pair of mounting means fixed to said body substantially in line with the stress to be detected and a piezoelectric material stationed between said mounting means for providing a DC signal having a voltage substantially proportional to the stress applied to said body; amplifying means coupled to said transducer for providing an output voltage which is linearly proportional to the voltage of the transducer signal; detector means coupled to said amplifying means for providing an output indication when said output voltage exceeds a predetermined threshold and capacitive means coupled across said piezoelectric material for charging as stress is applied to said body, and means coupled to said capacitive means for causing said capacitive means to discharge to a completely discharged level when the stress is removed from said body, whereby said transducer is conditioned to respond to stresses which are intermittently applied to and removed from said body.

Claim 7

An improved sensing device for detecting stress applied to a deformable body, comprising a transducer including a pair of mounting means fixed to said body substantially in line with the stress to be detected and a piezoelectric material stationed between said mounting means for providing a DC signal having a voltage substantially proportional to the stress applied to said body; amplifying means coupled to said transducer for providing an output voltage which is linearly proportional to the voltage of the transducer signal; detector means coupled to said amplifying means for providing an output indication when said output voltage exceeds a predetermined threshold and capacitive means coupled across said piezoelectric material for charging as stress is applied to said body, and means coupled to said capacitive means for causing said capacitive means to discharge to a completely discharged level when the stress is removed from said body, whereby said transducer is conditioned to respond to stresses which are intermittently applied to and removed from said body.

Claim 8

An improved sensing device according to claim 5 wherein said detector means includes a controlled rectifier having an anode, cathode and gate, and bias means coupled between said cathode and a point of reference potential for establishing said predetermined threshold; said amplifying means being coupled to the gate of said rectifier and being separated from said bias means by the gate-cathode circuit of said rectifier, whereby the output voltage from said amplifying means is substantially independent of the threshold level established for said detector means.

Claim 9

An improved sensing device for monitoring stresses which are intermittently applied to and removed from a deformable body, comprising, a transducer including a pair of brackets fixed to said body in line with the stress to be monitored and a piezoelectric material arranged between said brackets and adapted to produce a DC electrical output signal having a voltage proportional to the applied stress and a current; capacitive means coupled across said piezoelectric material for charging towards a predetermined voltage limit as stress is applied to said body and for completely discharging as stress is removed form said body, isolation means comprising amplifying coupled to said transducer for amplifying the current of said transducer output signal while maintaining the voltage thereof, bias means for said amplifying means, and unidirectional means for connecting said bias means to said amplifying means; an output relay; and relay control means coupled to said amplifying means and adapted to energize said relay when said transducer output signal exceeds a predetermined threshold voltage.

Claim 10

An improved sensing device for monitoring stresses which are intermittently applied to and removed from a deformable body, comprising, a transducer including a pair of brackets fixed to said body in line with the stress to be monitored and a piezoelectric material arranged between said brackets and adapted to produce a DC electrical output signal having a voltage proportional to the applied stress and a current; capacitive means coupled across said piezoelectric material for charging towards a predetermined voltage limit as stress is applied to said body and for completely discharging as stress is removed form said body, isolation means comprising amplifying coupled to said transducer for amplifying the current of said transducer output signal while maintaining the voltage thereof, bias means for said amplifying means, and unidirectional means for connecting said bias means to said amplifying means; an output relay; and relay control means coupled to said amplifying means and adapted to energize said relay when said transducer output signal exceeds a predetermined threshold voltage.

Claim 11

An improved sensing device according to claim 7 wherein said bias means provides a predetermined bias voltage and current for said amplifying means, further including a reference means for providing a reference voltage substantially equal to said bias voltage, said transducer being coupled between said reference means and said bias means, whereby substantially zero current flows through said transducer under quiescent conditions.

Claim 12

An improved sensing device according to claim 8 wherein said bias means and said reference means respectively comprise first and second voltage dividers, and said amplifying means comprises a pair of transistors connected to an emitter follower Darlington configuration.

Claim 13

An improved sensing device according to claim 9 wherein said unidirectional means comprise a diode connected between said first voltage divider and said transistors and poled to allow conduction of said bias current while preventing said fist voltage divider From loading said transducer, whereby said transducer output signal is impressed only on high impedances.

Claim 14

An improved sensing device according to claim 10 wherein at least one of said voltage dividers is a variable potentiometer having a wiper on which a divided voltage is present.

Claim 15

An improved sensing device according to claim 7 wherein said relay control means includes means for varying said predetermined threshold voltage in accordance with the amount of stress desired to be detected.

Claim 16

An improved sensing device according to claim 7 wherein said relay circuit means includes a variable voltage divider and a controlled rectifier having an anode terminal coupled to said relay, a cathode terminal referenced to said voltage divider, and a gate terminal connected to receive said amplified transducer signal, whereby conduction is initiated in said relay only when said transducer signal exceeds a threshold voltage established by said voltage divider.