FORM 2
The Patents Act 1970
(39 of 1970) &
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13) TITLE OF THE INVENTION:
PIEZOELECTRIC SENSOR DEVICE
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra . INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED


A) TECHNICAL FIELD
[0001] The present invention generally relates to sensor devices and particularly to magnetic sensor devices. The present invention more particularly relates to a piezoelectric sensor device used for sensing the magnetic field generated from the electric current flowing through an electrical conductor and sensing the magnitude of the current flowing through an electrical conductor using the magnetic field and piezoelectric principle. The piezoelectric sensor is used widely in sensing, metering and protection devices in electrical industry.
B) BACKGROUND OF THE INVENTION
[2] Generally a current sensor is a device that detects electrical current flowing through an electrical conductor and generates a signal proportional to the electrical current. There is a variety of techniques used for measuring electrical current flowing through a conductor. Usually the conventional technique of current measurement includes current transformers which can be rather bulky due to thick iron cores. Further the method of using current transformers is expensive.
[3] There is another method that includes a resistor in series with the electrical conductor. This method allows the current to flow through the resistor and measures the voltage-drop across the resistor to calculate the amount of current. In this method, the resistance of the resistor is not easily altered. Hence the dynamic change of sensitivity of the sensor is difficult to achieve. Resistive heating during high current measurements over longer time periods is a major issue.
[4] Another method uses a magneto-resistive sensor. The magneto-resistive sensor is a device that changes its resistance in the presence of a magnetic field. A disadvantage of this approach is that the resistance change of a magneto-resistive material is not sensitive to polarity. Hence the direction or phase of the current flow
2

cannot be determined. Further disadvantages include a limited linear range and poor temperature characteristics.
[5] Also other techniques like Hall Effect sensors also need to be assisted with magnetic cores to focus on the magnetic fields. A current flowing through a conductor produces a magnetic field. The magnetic field is concentrated by placing a magnetic core around the conductor. A Hall Effect sensor placed in a gap in the magnetic core is used to measure the strength of the magnetic field. The magnetic core is required because of the low sensitivity of the Hall Effect sensor and limits the miniaturization of the sensor.
[6] With the focus on design of the next generation smaller sensing devices for metering and protection in electrical power line systems, there is a need to provide a robust, reliable, compact and consistent sensor system and method for sensing the current. Also there is a need to provide a self powered current sensor which consumes less space and solves the problem of temperature rise effectively and efficiently.
[7] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECTS OF THE INVENTION
[8] The primary object of the present invention is to develop a magnetic sensor such as piezoelectric current sensor device for sensing of the magnitude of the current flowing through an electrical conductor dynamically.
[9] Another object of the present invention is to develop a piezoelectric current sensor device which is a robust, reliable and accurate sensor to measure the Alternating Current (AC) flowing through an electrical conductor.

[10] Yet another object of the present invention is to develop a piezoelectric current sensor device which solves the problem of temperature rise effectively,
Yet another object of the present invention is to develop a self powered piezoelectric current sensor device consuming less space and providing complete isolation from the power line.
[12] Yet another object of the present invention is to develop a self powered piezoelectric sensor device for sensing the magnetic field generated from electric current flowing through an electrical conductor and sensing the magnitude of the current flowing through an electrical conductor using the magnetic field and piezoelectric principles
[13] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0014] The various embodiments of the present invention provide a magnetic sensor device such as a piezoelectric current sensor device for sensing the magnitude of the current flowing through an electrical conductor using the magnetic field and piezoelectric principle. The magnetic sensor is used for sensing the magnetic field generated from electric current flowing through an electrical conductor and sensing the magnitude of the current flowing through an electrical conductor using the magnetic field and piezoelectric principles.
[0015] According to one embodiment of the present invention, a piezoelectric current sensor system has a current carrying conductor. An insulating base is arranged over the current carrying conductor. A piezoelectric sensor assembly is arranged over the insulating base. An insulated adhesive layer is provided on the

piezoelectric assembly. A ferromagnetic plate is mounted over the insulated adhesive layer.
[16] The piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force generated on the ferromagnetic plate when a current is passed through the conductor. The piezoelectric disc generates a signal proportional to the square of the primary current passed through the current carrying conductor- The upper electrode and the lower electrode are metallic foils. The upper electrode and the lower electrode are copper foils. The shape and the size of the piezoelectric disc are designed to generate adequate voltage drop for the desired current level. The shape and the size of the fercomagaetic plate ate designed, to adjust th£ response of the piezoelectric sensor. The output wires are attached to the upper electrode and to the lower electrode.
[17] An insulating filler is arranged above the ferromagnetic plate. An upper damp is provided above the insulating filler. The clamp is designed to provide the necessary pre-loading for the correct operation of piezoelectric disc.
[18] According to another embodiment of the present invention, a piezoelectric current sensor system sensor system has a current carrying conductor. An insulating base is arranged over the current carrying conductor. A piezoelectric sensor assembly is provided over the insulating base. A ferromagnetic plate is mounted directly over the piezoelectric assembly.
[19] The piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force on the ferromagnetic plate when current is passed through the conductor. The upper electrode and the lower electrode are metallic foils. The upper electrode and the lower electrode are


copper foils. The signal from the piezoelectric disc is tapped from the lower electrode and the ferromagnetic plate.
[20] According to one embodiment, a piezoelectric current sensor device includes a piezoelectric crystal in the form of disc, a ferromagnetic plate, first and second flat copper electrodes, insulating fillers, and a cover made up of insulating material. The piezoelectric disc is sandwiched between the first and second copper electrodes for tapping the varying charge across the disc. The first and second copper electrodes are connected to separate output wires. The ferromagnetic plate is adhered with the insulating fillers firmly on top of the upper copper electrode.
[21] The whole assembly is then inserted into the cover made of insulating material without changing the sequence. Then the cover with the whole assembly is bolted on a current carrying conductor using screws. The current carrying conductor is covered with an insulating base to isolate the piezoelectric disc from the live current path.
[22] A minimal static load is required to apply above the upper copper electrode as preloading is necessary for piezoelectric operation. The assembly automatically sets the preloading for the piezoelectric disc. The piezoelectric disc properties are chosen such that the adequate voltage drop (mV) is generated for desired current levels. The response of the piezoelectric current sensor is also adjusted by varying the shape and size of the ferromagnetic plate.
When an alternating current (AC) flows through the electrical conductor, a magnetic field is generated around the electrical conductor. The ferromagnetic plate which is placed above the upper copper electrode responds to the changing magnetic field. As a result, the ferromagnetic plate gets attracted towards the electrical conductor during the first half cycle of the AC current. Due to the movement of ferromagnetic plate, a force is imparted on the piezoelectric disc placed under the ferromagnetic material. The piezoelectric disc converts this force into a corresponding potential drop across the faces of the piezoelectric disc. Hence

the generated voltage drop from the piezoelectric disc is directly proportional to the square of the primary current flowing through the electrical conductor.
[24] When the AC cycle reaches to zero current, the attraction between the ferromagnetic plate and the electrical conductor also reaches to zero. Thus the force imparted upon the piezoelectric disc also reduces to zero momentarily. The same phenomenon is again repeated during the next half cycle of the AC current. Hence a dynamically changing force is imparted on to the piezoelectric disc as the current flows through the electrical conductor. The frequency of this force as well as the output of the piezoelectric disc is always twice the frequency of the sinusoidal primary current to be sensed.
[25] Then the piezoelectric disc converts the Cyclic force generated by the ferromagnetic plate into a corresponding potential voltage drop across the faces of the piezoelectric disc. The voltage drop is then sensed by the upper and lower copper electrodes and sent via the output wires. Further the output of the piezoelectric disc is amplified through a charge amplifier. Upon the sufficient amplification, the signal conditioning unit is designed in a way such that it evaluates the square root of the input signal. A DC offset is also necessary to nullify the effect of the pre-loading given to the piezoelectric disc. Thus the processed signal replicates a scaled version of the current flowing through the electrical conductor. The output of the piezoelectric current sensor may be forwarded to any metering unit for annunciation as needed or for any other signal processing application.
E) BRIEF DESCRIPTION OF THE DRAWINGS:
[26] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

[27] FIG. 1 illustrates an exploded perspective view of a piezoelectric current sensor system according to one embodiment of the present invention.
[28] FIG. 2 illustrates a side sectional view of a piezoelectric current sensor system according to one embodiment of the present invention.
[29] FIG. 3 illustrates a side sectional view of a piezoelectric current sensor system according to another embodiment of the present invention.
[30] FIG. 4 illustrates a graph representing a waveform drawn from the output signal of the piezoelectric current sensor for a particular current flowing through the conductor according to one embodiment of the present invention.
[31] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention,
F) DETAILED DESCRIPTION OF THE INVENTION
[32] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
The various embodiments of the present invention provide a magnetic sensor such as a piezoelectric current sensor device for sensing the magnitude of the current flowing through an electrical conductor using the magnetic field and the piezoelectric principle. According to one embodiment of the present invention, a

piezoelectric current sensor system has a current carrying conductor. An insulating base is arranged over the current carrying conductor. A piezoelectric sensor assembly is arranged over the insulating base. An insulated adhesive layer is provided on the piezoelectric assembly. A ferromagnetic plate is mounted over the insulated adhesive layer.
[34] The piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force generated on the ferromagnetic plate when a current is passed through the conductor. The piezoelectric disc generates a signal proportional to the square of the primary current passed through the current carrying conductor. The upper electrode and the lower electrode are metallic foils. The upper electrode and the lower electrode are copper foils. The shape and the size of the piezoelectric disc are designed to generate adequate voltage drop for the desired current level. The shape and the size of the ferromagnetic plate are designed to adjust the response of the piezoelectric sensor. The output wires are attached to the upper electrode and to the lower electrode,
[35] A set of insulating fillers is arranged above the ferromagnetic plate. An upper clamp is provided above the insulating filler.
[0036J According to another embodiment of the present invention, a piezoelectric current sensor system sensor system has a current carrying conductor. An insulating base is arranged over the current carrying conductor. A piezoelectric sensor assembly is provided over the insulating base. A ferromagnetic plate is mounted directly over the piezoelectric assembly.
[0037] The piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force on the ferromagnetic plate; when current is passed through the conductor. The upper electrode and the

lower electrode are metallic foils. The upper electrode and the lower electrode are copper foils. The signal from the piezoelectric disc is tapped from the lower electrode and the ferromagnetic plate.
[38] According to one embodiment, a piezoelectric current sensor device includes a piezoelectric crystal in the form of disc, a ferromagnetic plate, first and second flat copper electrodes, insulating fillers, and a cover made up of insulating material, The piezoelectric disc is sandwiched between the first and second copper electrodes for tapping the varying charge across the disc. The first and second copper electrodes are connected to separate output wires. The ferromagnetic plate is adhered with the insulating fillers firmly on top of the upper copper electrode.
[39] The whole assembly is then inserted into the cover made of insulating material without changing, the sequence. Then the cover with the whole assembly is bolted on a current carrying conductor using screws. The current carrying conductor is covered with an insulating base to isolate the piezoelectric disc from the live current path.
[40] A minimal static load is required to apply above the upper copper electrode as preloading is necessary for piezoelectric operation. The assembly automatically sets the preloading for the piezoelectric disc. The piezoelectric disc properties are chosen such that the adequate voltage drop (mV) is generated for desired current levels. The response of the piezoelectric current sensor is also adjusted by varying the shape and size of the ferromagnetic plate.
[0041] When an alternating current (AC) flows through the electrical conductor, a
magnetic field is generated around the electrical conductor. The ferromagnetic plate which is placed above the upper copper electrode responds to the changing magnetic field. As a result, the ferromagnetic plate gets attracted towards the electrical conductor during the first half cycle of the AC current. Due to the movement of ferromagnetic plate, a force is imparted on the piezoelectric disc placed under the ferromagnetic material. The force (F) is derived from the equation,


Where 'F' is force generated at the ferromagnetic plate, 'm' is magnetic moment in the ferromagnetic plate and 'B' is magnetic field intensity generated by current flow.
[42] Now, the magnetic moment 'm' is also a function of the shape of the ferromagnetic plate and the magnetic field 'B'. Hence the force is directly proportional to the square of the magnetic field as given in the equation.

[43] The magnetic field 'B' is directly proportional to the primary current 'I' flowing through the electrical conductor. The primary current is directly related by the equation,

Where 'μ' is permeability of medium 'r' is distance from the conductor. Hence the
force 'F' is directly proportional to the square of the primary current flowing through the electrical conductor.

Then the piezoelectric disc converts this force into a corresponding potential drop across the faces of the piezoelectric disc. Then the potential drop across the piezoelectric disc is given as,

Where 'V' is voltage across the piezoelectric disc faces, 'g33' is piezoelectric property constant, 'Force' is force component perpendicular to the piezoelectric disc face, 'thickness' is thickness of the piezoelectric disc and 'radius' is the radius of the piezoelectric disc. Hence the generated voltage drop from the piezoelectric disc is directly proportional to the square of the primary current (I) flowing through the electrical conductor. This is given as,

[44] When the AC cycle reaches to zero current, the attraction between the ferromagnetic plate and the electrical conductor also reaches to zero. Thus the force imparted upon the piezoelectric disc also reduces to zero momentarily. The same phenomenon is again repeated during the next half cycle of the AC current. Hence a dynamically changing force is imparted on to the piezoelectric disc as the current flows through the electrical conductor. The frequency of this force as well as the output of the piezoelectric disc is always twice the frequency of the sinusoidal primary current to be sensed. For example, if the primary current is of 50 Hz frequency, then the output signal is of 100Hz.
[45] Then the piezoelectric disc converts the cyclic force generated by the ferromagnetic plate into a corresponding potential voltage drop across the faces of the piezoelectric disc. The voltage drop is then sensed by the upper and lower copper electrodes and sent via the output wires. Further the output of the piezoelectric disc is amplified through a charge amplifier. Upon the sufficient amplification, the signal conditioning unit is designed in a way such that it evaluates the square root of the input signal. A DC offset is also necessary to nullify the effect of the pre-loading given to the piezoelectric disc. Thus the processed signal replicates a scaled version of the current flowing through the electrical conductor. The output of the piezoelectric current sensor may be forwarded to any metering unit for annunciation as needed or for any other signal processing application.
FIG. 1 illustrates an exploded perspective view of a piezoelectric current sensor system according to one embodiment of the present invention. With respect to FIG. 1, the piezoelectric current sensor device includes a piezoelectric disc 102, copper electrodes 1041, 1042 and a ferromagnetic plate 108. The piezoelectric disc 102 is sandwiched between the copper electrodes 1041 and 1042. The ferromagnetic plate 108 is attached on the top of the upper copper electrode 1041. The copper electrodes 1041, 1042 are attached to probes 1061, 1062 respectively to sense the voltage drop across the copper electrodes 1041 and 1042.

[47] Further the piezoelectric current sensor device includes an insulating filler HO and a cover 112 made up of insufating materia?. The insulating filler is kept on top of the ferromagnetic plate 108. The whole assembly is then inserted into the cover 112 without changing the sequence. Then the cover 112 with the whole assembly is bolted on a current carrying conductor 114 using screws. The current carrying conductor 114 is covered with an insulating base to isolate the piezoelectric disc from the live current path.
[48] When an electrical current passes through the current carrying conductor 114, a magnetic field is generated around the current carrying conductor 114. Due to the magnetic field, the ferromagnetic plate 108 gets periodic attraction towards the current carrying conductor 114. The cyclic pulling force acting on the ferromagnetic plate 108 is directly proportional to square of the current flowing through the current carrying conductor 114. The cyclic pulling force generated by the ferromagnetic plate 108 is impinged on the piezoelectric disc 102. Since the cyclic pulling force is unidirectional in both phases of the sinusoidal current flow, the frequency of force on the piezoelectric disc 102 is twice as the input frequency of the current flowing through the current carrying conductor 114.
[49] Then the piezoelectric disc 102 converts the mechanical force into a voltage signal which is easily probed across the copper electrodes 1041, 1042 through the probes 1061, 1062. Thus the piezoelectric current sensor generates a voltage signal which is proportional to the square of the magnitude of the instantaneous current flowing through the electrical conductor.
[50] FIG. 2 illustrates a side sectional view of piezoelectric current sensor system according to one embodiment of the present invention. With respect to FIG. 2, a piezoelectric current sensor includes a piezoelectric disc 202, flat copper electrodes 2041, 2042, insulating fillers 2081, 2082 and a ferromagnetic plate 210. The piezoelectric disc 102 is sandwiched between the copper electrodes 2041 and 2042. The insulating filler 2081 is fixed on top of the upper copper electrode 2041

[51] and the insulating filler 2082 is fixed under the lower copper electrode 2042. The ferromagnetic plate 210 is attached on top of the insulating filler 2081.
[51] Further the piezoelectric current sensor device includes electrical probes 2061, 2062 which are connected to the copper electrodes 2041, 2042 respectively. The electrical probes 2061, 2062 are used to sense the voltage drop across the copper electrodes 2041 and 2042. The whole assembly is then fixed on the surface of a current carrying conductor 212.
[52] When the current passes through the current carrying conductor 212, a magnetic field is generated around the current carrying conductor 212. Due to the magnetic field, the ferromagnetic plate 210 in the piezoelectric current sensor is attracted towards the current carrying conductor 212. The cyclic pulling force acting on the ferromagnetic plate 210 is directly proportional to square of the current flowing through the current carrying conductor 212. Due to the cyclic pulling force, the ferromagnetic plate 210 provides a mechanical stress to the piezoelectric disc 202. Since the cyclic pulling force is unidirectional in both phases of the sinusoidal current flow, the frequency of force on the piezoelectric disc 202 is twice as the input frequency of the current flowing through the current carrying conductor 212.
[53] Then the piezoelectric disc 202 converts the mechanical force into a voltage signal which is easily probed across the copper electrodes 2041, 2042 through the electrical probes 2061, 2062. Thus the piezoelectric current sensor generates a voltage signal which is proportional to the square of the magnitude of the instantaneous current flowing through the electrical conductor.
[54] FIG. 3 illustrates a side sectional view of a piezoelectric current sensor system according to another embodiment of the present invention. With respect to FIG. 3, a piezoelectric current sensor includes a piezoelectric disc 302, a flat copper electrode 304, a ferromagnetic plate 306 and an insulating base 310. The piezoelectric disc 302 is sandwiched between the copper electrode 304 and the

[55] ferromagnetic plate 306. The insulating base 310 is fixed under the copper electrode 304 to provide a complete isolation for the piezoelectric current sensor from the power line.
[55] Further the piezoelectric current sensor device includes electrical probes 3081, 3082 which are connected to the ferromagnetic plate 306 and the copper electrode 304 respectively. The electrical probes 3081, 3082 are used to sense the voltage drop across the ferromagnetic plate 306 and the copper electrode 304. The whole assembly is then fixed on the surface of a current carrying conductor 312.
When the current passes through the current carrying conductor 312, a magnetic field is generated around the current carrying conductor 312. Due to the magnetic field, the ferromagnetic plate 306 in the piezoelectric current sensor is attracted towards the current carrying conductor 312. The cyclic pulling force acting on the ferromagnetic plate 306 is directly proportional to square of the current flowing through the current carrying conductor 312. Due to the cyclic pulling force, the ferromagnetic plate 306 forces a mechanical stress on the piezoelectric disc 302. Since the cyclic pulling force is unidirectional in both phases of the sinusoidal current flow, the frequency of force on the piezoelectric disc 302 is twice as the input frequency of the current flowing through the current carrying conductor 312.
[57] Then the piezoelectric disc 302 converts the mechanical force into a voltage signal which is easily probed across the fen-omagnetic plate 306 and the copper electrode 304 through the electrical probes 3081, 3082. Thus the piezoelectric current sensor generates a voltage signal which is proportional to the square of the magnitude of the instantaneous current flowing through the electrical conductor.
[58] FIG. 4 illustrates a graph representing a waveform drawn from the output signal of the piezoelectric current sensor for a particular current flowing through the conductor according to one embodiment of the present invention. With respect to

FIG. 4, a waveform graph is drawn between the measured output signals of the piezoelectric current sensor described in the present invention and time in seconds. A current in the order of 2400 A and 50Hz is Carried through the electrical conductor and the piezoelectric current sensor output signals are measured. The measured output signals of the piezoelectric current sensor are taken at volt scale in Y-axis and the time domain is taken at seconds scale in X-axis of the graph.
[59] The signal data shown in the graph have been artificially offset by the preloaded potential which is generated by the static loading of the piezoelectric disc at zero current flow in the conductor. From the graph, it is obvious that the frequency of the generated signal is 100 Hz. Since the cyclic pulling force is unidirectional in both phases of the sinusoidal current flow in the electrical conductor, the frequency of the output signal of the piezoelectric current sensor is twice as the input frequency of the current flowing through the electrical conductor.
G) ADVANTAGES OF THE INVENTION
[60] The various embodiments of the present invention provide a piezoelectric current sensor device for sensing the magnitude of the current flowing through an electrical conductor. According to one embodiment, the piezoelectric current sensor uses magnetic field and piezoelectric principles for sensing the current flow in the electrical conductor. The present invention is used for numerous sensing, metering and protection devices in electrical industry. With the focus on design of next generation smaller sensing devices for metering and protection in electrical power line systems, the present invention offers a robust, reliable and consistent method for sensing the current.
[61] The piezoelectric current sensor in the present invention is self powered, smaller in size and it consumes less space. The piezoelectric current sensor solves the problem of temperature rise comfortably. The piezoelectric current sensor provides a complete electrical isolation of the sensor from the live conductor. Using the piezoelectric current sensor of the present invention, a very high level of

[62] currents (i.e. greater than 10 kA) is measured by appropriate design of the ferromagnetic plate.
[62] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[63] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

Date: October 23, 2009
RAKESH PRABHU
Place: Bangalore.
Patent Agent

CLAIMS
What is claimed is:
1. A piezoelectric sensor system comprising: A current carrying conductor;
An insulating base arranged over the current carrying conductor A piezoelectric sensor assembly arranged over the insulating base; An insulated adhesive layer provided the piezoelectric assembly; and A ferromagnetic plate mounted over the insulated adhesive layer.
2. The sensor system according to claim 1, wherein the piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force generated on the ferromagnetic plate when a current is passed through the conductor.
3. The sensor system according to claim 1, wherein the piezoelectric disc generates a signal proportional to the square of the primary current passed through the current carrying conductor.
4. The sensor system according to claim 1, wherein the upper electrode and the lower electrode are metallic foils.
5. The sensor system according to claim 1, wherein the upper electrode and the lower electrode are copper foils.
6. The sensor system according to claim 1, wherein the shape and the size of the piezoelectric disc are designed to generate adequate voltage drop for the desired current level.
18

7. The sensor system according to claim 1, wherein the shape and the size of the ferromagnetic plate are designed to adjust the response of the piezoelectric sensor.
8. The sensor system according to claim 1, wherein output wires are attached to the upper electrode and to the lower electrode.
9. The sensor system according to claim 1, further comprising insulating filler arranged above the ferromagnetic plate.
10. The sensor system according to claim 1, further comprising an upper clamp provided above the insulating filler.
11. A piezoelectric sensor system sensor system comprising: A current carrying conductor;
An insulating base arranged over the current carrying conductor A piezoelectric sensor assembly provided over the insulating base; and A ferromagnetic plate mounted directly over the piezoelectric assembly.
12. The sensor system according to claim 11, wherein the piezoelectric sensor assembly has a piezoelectric disc sandwiched between an upper electrode and a lower electrode so that the piezoelectric disc generates a signal corresponding to the amplitude of the force on the ferromagnetic plate when current is passed through the conductor.
13. The sensor system according to claim 11, wherein the upper electrode and the lower electrode are metallic foils.
14. The sensor system according to claim 11, wherein the upper electrode and the lower electrode are copper foils.
19

15. The sensor system according to claim 11, wherein the signal from the piezoelectric disc is tapped from the lower electrode and the ferromagnetic plate.