GB2126711A - Instrument for measuring electrical energy - Google Patents

Abstract

An instrument comprises a sheet 1 of polyvinylidene fluoride (PVDF) coated on its upper surface with optically reflective and electrically conductive strip electrodes, 2 to 5, and on its lower surface with an electrically conductive back electrode 6. A grating 7 is held substantially parallel to reflective strip electrodes, 2 to 5, so that an image of grating 7 is formed thereby. Light emitting from a light emitting diode 8 therefore forms a pattern of moire fringes in plane 10, when reflected by strip electrodes, 2 to 5. A D.C. potential is applied to the sheet 1. When an unknown voltage is applied to the sheet 1, a deflection 15 occurs, which causes movement of the moire fringes. A servomechanism adjusts the D.C. potential to counteract the deflection, so that the adjusted potential is substantially equal to the unknown voltage <IMAGE>

Description

SPECIFICATION An instrument for measuring electrical energy This invention relates to an instrument for measuring electrical energy. Such an instrument may be used to measure voltage, as a voltmeter, or current, as an ammeter.

It is known to provide current-measuring instruments with optical read-out, which can substantially improve the sensitivity of the instrument. An example of this type of instrument is a galvanometer, wherein a small angular deflection of a coil in a magnetic field is proportional to the current passing therethrough.

The deflection may be magnified by mounting a small mirror on the coil and by measuring the angular deflection of a beam of light reflected therefrom, which is proprotional to the deflection of the coil.

However, although the sensitivity of instruments of this type may be relatively high, there is obviously a limit to the sensitivity that these known instruments incorporating optical read-out are capable of providing.

It is therefore an object of the present invention to provide a more sensitive instrument for measuring electrical energy than those that have been provided heretofore.

According to the invention there is provided an instrument for measuring electrical energy including reflective means associated with a substrate responsive to electrical energy applied thereto so as to cause a deflection of the reflective means, a diffraction grating positioned substantially parallel to the reflective means so that an image thereof is formed by said reflective means, the diffraction grating and the image thereof forming an optical pattern when light is incident thereon and reflected thereby, means for detecting said optical pattern and movement thereof caused by said deflection of the reflective means when an unknown amount of electrical energy is applied to the substrate and means for utilising said movement to determine said unknown amount of electrical energy.

Preferably the substrate comprises a sheet of polyvinylidene fluoride (PVDF) disposed between a continuous electrically conductive back electrode and a number of optically reflective and electrically conductive strip electrodes, which can thus provide the reflective means. When electrical energy, such as an unknown voltage which is required to be measured, is applied between the continuous back electrode and some of the strip electrodes a deflection of the PVDF sheet, and thus of the reflective strip electrodes, can be caused.

A pattern of moire fringes may be formed in a certain plane, when light, emitted from a light source, is incident on the diffraction grating and the image thereof, formed by the reflective strip electrodes, and the light is reflected thereby.

Deflection of the reflective strip electrodes by application of the unknown voltage to the PVDF sheet can cause these moire fringes formed by the reflected light to move.

The ratio between the intensities of the emitted light and of the reflected light may be modulated and a servomechanism may be used to adjust an admixture of a DC potential, which is also applied to the PVDF sheet between the back electrode and the remaining reflective strip electrodes, with the modulation, so that the depth of the light modulation is a maximum. The phase of the moire fringes is then such that any small deflection in the PVDF sheet will produce a relatively large change in the relative intensity of the light. The D.C. potential can be adjusted by the servomechanism to counteract the deflection, so that the potential may be made substantially equal to the unknown voltage and can therefore be measured.

It will thus be realised that such a technique in accordance with the present invention may be used to provide a highly sensitive pico-ammeter, or a very high impedance voltmeter. In fact, it has been found that currents as low as 1 to 2 electrons per second may be measured and input impedances as high as 1018 ohms may be achieved.

Such an instrument may also be utilised in conjunction with a conventional low impedance voltmeter, so that the values of currents measured thereby can be obtained to a higher degree of accuracy.

The invention will now be further described by way of example only with reference to the accompanying diagram, the single figure of which shows a preferred embodiment of the invention.

Referring to the figure, a PVDF sheet 1 is coated on its upper surface with a number of substantially identical optically reflective and electrically conductive strip electrodes, 2 to 5 inclusive, and the sheet 1 also has on its lower surface a continuous electrically conductive back electrode 6. A fine-pitch diffraction grating 7 is held in close proximity, and substantially parallel to the reflective strip electrodes, 2 to 5, on the PVDF sheet 1.

In this position, an image of the diffraction grating 7 is formed by the reflective strip electrodes, 2 to 5, so that an impression of two diffraction gratings, one superposed on top of the other is produced.

Light, emitted from a light emitting diode 8, is split by a beam splitter 9 and is incident on the diffraction grating 7 and the image thereof formed by the reflective strip electrodes, 2 to 5. Light reflected therefrom then forms, in a plane shown at 10, a pattern of moire fringes which is detected by a photodetector 11 positioned in the plane 10.

The intensity of the reflected light forming the moire fringes is thus measured by the photodetector 11 and the intensity of the emitted light from the light emitting diode 8 is measured by a photodetector 1 2. A ratio circuit (not shown) is used to derive the ratio between these two intensities measured by the photodetectors and this ratio is modulated at a frequency of approximately 1 KHz by applying a small AC potential between reflective strip electrodes, 2 and 4, and back electrode 6.

A servomechanism (not shown) is also used to adjust a small admixture of a DC potential with the 1 KHz modulation, so that the depth of the light modulation is a maximum.

In operation as a voltmeter, an unknown voltage is applied between reflective strip electrodes, 3 and 5, and back electrode 6, as well as the potential applied between strip electrodes 2 and 4 and back electrode 6, which causes the non-uniformly poled PVDF sheet 1 to deflect, as shown at end 14 thereof, whilst end 1 3 is kept fixed. This therefore provides a deflection as shown by dotted lines at 1 5.

Consequently, the reflective strip electrodes, 2 to 5, are also deflected, which causes a movement of the moire fringes in the plane 10, the movement being detected by the photodetector 11 as a change in the intensity of the light.

The servomechanism ensures that the phase of the moire fringes is such that any small deflection of the PVDF sheet 1 will produce a relatively large change in the light intensity detected by the photodetector 11, which thus provides the high sensitivity required. The servomechanism also provides a zero reference voltage for the spacing between the diffraction grating 7 and the upper surface of the PVDF sheet 1.

Due to the provision of the servomechanism, the DC potential applied to strip electrodes, 2 and 4, and back electrode 6 will be adjusted automatically to counteract the deflection produced by the unknown voltage applied to strip electrodes, 3 and 5, and back electrode 6.

Provided that all of the reflective strip electrodes, 2 to 5, are substantially identical, the adjusted D.C. potential will be substantially equal to the unknown voltage and can be measured using a known technique incorporating a conventional low impedance meter.

The present invention therefore provides a highly sensitive instrument for measuring electrical energy incorporating an optical technique in conjunction with a sheet of PVDF material, wherein currents as low as 1 to 2 electrons per second may be measured and input impedances as high as 1018 ohms may be achieved.

Claims (Filed 1 Sept. 83) 1. An instrument for measuring electrical energy including reflective means associated with a substrate responsive to electrical energy applied thereto so as to cause a deflection of the reflective means, a diffraction grating positioned substantially parallel to the reflective means so that an image thereof its formed by said reflective means, the diffraction grating and the image thereof forming an optical pattern when light is incident thereon and reflected thereby, means for detecting said optical pattern and movement thereof caused by said deflection of the reflective means when an unknown amount of electrical energy is applied to the substrate and means for utilising said movement to determine said unknown amount of electrical energy.

2. An instrument as claimed in claim 1 wherein said substrate comprises a layer of polyvinylidene fluoride.

3. An instrument as claimed in claim 1 or 2 wherein said substrate is disposed between an electrically conductive back electrode and a number of electrically conductive strip electrodes.

4. An instrument as claimed in claim 3 wherein said strip electrodes are optically reflective, so as to provide said reflective means.

5. An instrument as claimed in any preceding claim wherein said optical pattern comprises a pattern of moire fringes.

6. An instrument as claimed in any preceding claim including means for modulating a ratio between the relative intensities of said incident light and said reflective light.

7. An instrument as claimed in claim 6 and including servo means for adjusting an admixture of a potential applied to said substrate with said modulation, so as to maximise the depth of said modulation.

8. An instrument as claimed in claim 7 wherein said servo means are arranged to adjust said potential so as to counteract said deflection, so that said potential is made substantially equal to said unknown amount of electrical energy.

9. An instrument substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. potential between reflective strip electrodes, 2 and 4, and back electrode 6. A servomechanism (not shown) is also used to adjust a small admixture of a DC potential with the 1 KHz modulation, so that the depth of the light modulation is a maximum. In operation as a voltmeter, an unknown voltage is applied between reflective strip electrodes, 3 and 5, and back electrode 6, as well as the potential applied between strip electrodes 2 and 4 and back electrode 6, which causes the non-uniformly poled PVDF sheet 1 to deflect, as shown at end 14 thereof, whilst end 1 3 is kept fixed. This therefore provides a deflection as shown by dotted lines at 1 5. Consequently, the reflective strip electrodes, 2 to 5, are also deflected, which causes a movement of the moire fringes in the plane 10, the movement being detected by the photodetector 11 as a change in the intensity of the light. The servomechanism ensures that the phase of the moire fringes is such that any small deflection of the PVDF sheet 1 will produce a relatively large change in the light intensity detected by the photodetector 11, which thus provides the high sensitivity required. The servomechanism also provides a zero reference voltage for the spacing between the diffraction grating 7 and the upper surface of the PVDF sheet 1. Due to the provision of the servomechanism, the DC potential applied to strip electrodes, 2 and 4, and back electrode 6 will be adjusted automatically to counteract the deflection produced by the unknown voltage applied to strip electrodes, 3 and 5, and back electrode 6. Provided that all of the reflective strip electrodes, 2 to 5, are substantially identical, the adjusted D.C. potential will be substantially equal to the unknown voltage and can be measured using a known technique incorporating a conventional low impedance meter. The present invention therefore provides a highly sensitive instrument for measuring electrical energy incorporating an optical technique in conjunction with a sheet of PVDF material, wherein currents as low as 1 to 2 electrons per second may be measured and input impedances as high as 1018 ohms may be achieved. Claims (Filed 1 Sept. 83)

1. An instrument for measuring electrical energy including reflective means associated with a substrate responsive to electrical energy applied thereto so as to cause a deflection of the reflective means, a diffraction grating positioned substantially parallel to the reflective means so that an image thereof its formed by said reflective means, the diffraction grating and the image thereof forming an optical pattern when light is incident thereon and reflected thereby, means for detecting said optical pattern and movement thereof caused by said deflection of the reflective means when an unknown amount of electrical energy is applied to the substrate and means for utilising said movement to determine said unknown amount of electrical energy.

2. An instrument as claimed in claim 1 wherein said substrate comprises a layer of polyvinylidene fluoride.

3. An instrument as claimed in claim 1 or 2 wherein said substrate is disposed between an electrically conductive back electrode and a number of electrically conductive strip electrodes.

4. An instrument as claimed in claim 3 wherein said strip electrodes are optically reflective, so as to provide said reflective means.

5. An instrument as claimed in any preceding claim wherein said optical pattern comprises a pattern of moire fringes.

6. An instrument as claimed in any preceding claim including means for modulating a ratio between the relative intensities of said incident light and said reflective light.

7. An instrument as claimed in claim 6 and including servo means for adjusting an admixture of a potential applied to said substrate with said modulation, so as to maximise the depth of said modulation.

8. An instrument as claimed in claim 7 wherein said servo means are arranged to adjust said potential so as to counteract said deflection, so that said potential is made substantially equal to said unknown amount of electrical energy.

9. An instrument substantially as herein described with reference to the accompanying drawing.