WO1997014973A1

WO1997014973A1 - Method and apparatus for utilizing dielectric breakdown for indirect measurement purposes

Info

Publication number: WO1997014973A1
Application number: PCT/IB1996/001122
Authority: WO
Inventors: Ove K. Dunder
Original assignee: Lifetech Corporation
Priority date: 1995-10-20
Filing date: 1996-10-21
Publication date: 1997-04-24
Also published as: AU7143396A; CA2235256A1; JPH11513798A

Abstract

A device for measuring the breakdown of a dielectric in the presence of high voltage, for measuring e.g. ozone production in an ozone generator using the corona discharge principle. Corona discharge pulses in an ozone generator are capacitively sensed. Low frequencies are filtered out of the sensed signal. Electrical noise from the transformer circuitry is isolated by an optical coupler with an isolated direct current power supply. The filtered signal is then amplified and transformed to a DC voltage. After calibration to the actual ozone being produced, the DC output can be directly related to the ozone produced in the generator and used to display and/or control the ozone production.

Description

METHOD AND APPARATUS FOR UTILIZING DIELECTRIC BREAKDOWN FOR INDIRECT MEASUREMENT PURPOSES

FIELD OF THE INVENTION

The present invention relates to apparatus and methods which utilize the breakdown of a dielectric in the presence of high voltage for indirect measurement purposes, and more specifically relates to apparatus and methods for indirectly measuring the production of ozone by an ozone generator using the corona discharge principle.

In many application areas, it is desirable to evaluate the breakdown of a dielectric in order to effectively measure the products that are created by the breakdown. For example, the breakdown of a gas dielectric in the presence of high voltage will create products of that breakdown that are chemically related to the original dielectric. An example is the production of ozone (0₃) by the high voltage breakdown of oxygen (0₂) in ^"a typical corona discharge ozone generator.

In many application areas of ozone, it is imperative that ozone concentration and production be accurately measured. Photospectrometers, using a direct ultraviolet absorbance method, are the most common means of measuring the concentration of ozone. Other instruments that are used include: caloπmetπc instruments using a number of different chemical dyes in water, instruments for measuring changes in dielectric constant due to ozone, C0₂ lasers, luminescent methods, coulombometπc gas analysers, polarographic instruments, calorimetπc instruments, and amperometnc instruments. Instruments used for measuring ozone in most applications must be economical and must be able to continuously measure the absolute concentration values of ozone without significant drift over time. Consequently, the above-listed instruments suffer from a number of disadvantages.

One of the disadvantages of the above-listed instruments is that they are not feasible in smaller ozone generator installations due to economic considerations. Also, such previous instruments, including photospectrometers, experience drift in their outputs over time in comparison with a reference instrument. Similarly, such previous instruments are sensitive to physically adverse conditions. Furthermore, the relatively heavy weight and large physical size of most of such previous instruments are a problem during installation where space and portability are important. Additionally, it is common in such ozone sensors to require a complicated interface in order to convert the chemical, optical, heat, etc. inputs to a linear electncal output signal.

Accordingly, it would be desirable to provide a means for measuring ozone production in an ozone generator using the corona discharge principle to avoid the aforesaid difficulties.

SUMMARY OF THE INVENTION

tn accordance with the present invention the breakdown of a dielectric in the presence of high voltage is utilized to measure parameters of interest The dielectric may be a gas, a liquid or a solid. The purpose of the measurement can be to measure the breakdown products of the dielectric, or to measure the physical or chemical properties of the dielectric, in a preferred aspect of the invention, the measurement of the dielectric breakdown provides a means to measure the production of ozone in an ozone generator using the corona discharge principle.

Pursuant to the invention corona electrical discharge pulses from a winding in a voltage transformer providing electrical charging pulses to a high voltage discharge apparatus are sensed, and an electncal signal is generated in accordance with the sensed pulses The electπc signal is converted into a direct current (D.C.) voltage the level of which is a function of the frequency of occurrence and magnitude of said sensed electrical discharge pulses and thereby a measure of dielectric oreakdown product production in said high voltage discharge apparatus. The D.C. voltage level may be calibrated against measured dielectric breakdown product production in the apparatus, to enable measurement of the actual dielectric breakdown product production from the measured

D.C. voltage level.

The present invention can be realized with a dielectric breakdown circuit comprising a capacitive transducer, a first high pass filter, an optical coupler powered by an isolated direct current power supply, a two-stage radio frequency (RF) amplifier, a second high pass filter, an amplifier/diode pump, a linearizer, a low pass filter and a scaling amplifier. The capacitive transducer is coupled to the secondary winding of a high voltage transformer, which is used to provide high voltage pulses to a corona discharge ozone generator. The capacitive transducer thus capacitively senses individual corona discharge pulses that are imposed on the voltage signal of the secondary winding of the high voltage transformer. Lower frequencies, such as the high voltage drive frequency, are filtered out of the capacitive transducer signal in the first high pass filter. The optical coupler electrically isolates the processing circuitry from the high voltage transformer coupling. An isolated direct current power supply separates the power source of the optical coupler from the power source used for the processing circuitry, thereby reducing electrical noise induced by the transformer circuitry. The capacitive transducer signal is then amplified in the two-stage RF amplifier. Low frequencies are further reduced in the second high pass filter. The direct current voltage is amplified and voltage ripple is reduced in the amplifier/diode pump. The linearizer provides a voltage-dependent adjustment to the gain of the amplifier/diode pump to create linear voltage output values. Any remaining voltage ripple in the direct current voltage is reduced in the low pass filter, then amplified in the scaling amplifier for input to a analog-to-digital converter and then to a microprocessor. A photospectrometer or other device is used to calibrate the direct current voltage values in relation to the actual level of ozone being produced. The direct current voltage is then directly related to the formation of dielectric breakdown products in the presence of high voltage.

In summary, in the preferred embodiment, corona discharge pulses in an ozone generator are capacitively sensed. First, low frequencies are filtered out of the sensed signal. The sensed signal is then electrically isolated by an optical coupler, amplified, rectified, linearized, filtered and amplified again into a ripple-free direct current voltage signal. After calibration to the actual ozone being produced, this direct current voltage signal is directly related to ozone production in the ozone generator.

From the above descriptive summary it is apparent how the present invention overcomes the shortcomings of the above-mentioned prior art.

Accordingly, an object of the present invention is to provide cost effective apparatus and methods to measure the breakdown of a dielectric in the presence of high voltage, thereby providing a very cost effective measuring and signal conditioning circuit.

Another object of the present invention is to provide apparatus and method for measuring the breakdown products that are created by the breakdown of the dielectric.

Another object of the present invention is to provide apparatus and method for measuring ozone production in an ozone generator using the corona discharge principle.

Another object of the present invention is to provide an instrument for the aforementioned purposes, which is comprised completely of solid state electronics and is therefore very rugged.

Another object of the present invention is to provide for the aforementioned purposes a very light weight and compact instrument, which is suitable for installations where space and portability is important.

Another object of the present invention is to provide for the aforementioned purposes a completely solid state instrument with a linear output signal.

Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description and claims, in conjunction with the accompanying drawings which are appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a fuller understanding of the present invention, reference may now be made to the appended drawings. The drawings should not be construed as limiting the present invention, but are intended to be exemplary only.

Figure 1 is a schematic block diagram of a dielectric breakdown measurement circuit according to the present invention which may be used for measurement of ozone production; and Figure 2 is a schematic block diagram of a high voltage transformer with a capacitive transducer affixed thereto according to the present invention.

DETAILED DFSCRIPTION OF THF EFERRED FMRODIMENT

Referring to Figure 1 , there is shown a schematic block diagram of a dielectric breakdown measurement circuit 10 according to the present invention. The dielectric breakdown measurement circuit 10 comprises a capacitive transducer assembly 1 2, a first high pass filter 14, an optical coupler 16 powered by an isolated direct current power supply 18, a two-stage radio frequency (RF) amplifier 20, a second high pass filter 22, an amplifier/diode pump 24, a linearizer 26, a low pass filter 28 and a scaling amplifier 30. The output from amplifier 30 may be provided to an analog-to-digital (A/D) converter 32, which in turn provides a signal to a microprocessor 34.

The capacitive transducer assembly 12 is a capacitive coupling to the secondary winding of a high voltage transformer, which is used to provide high voltage pulses to a corona discharge ozone generator. Such a corona discharge ozone generator is disclosed in U.S. Patent No. 5,094,882, entitled Ozone Generator, which issued March

10, 1 992, and such a high voltage transformer is disclosed in U.S. Patent No. 5,443,800, entitled Pulse Train Generating Circuit for Control of an Ozone Generating Means, which issued August 22, 1995. The disclosures of these patents, which have a common inventor with the present invention, are hereby incorporated by reference herein.

The capacitive transducer assembly 12 capacitively senses individual corona discharge pulses that are imposed on the voltage signal of the secondary winding of the high voltage transformer. Lower frequencies, such as the high voltage drive frequency, are filtered out of the transducer signal in the first high pass filter 14. The optical coupler allows the passage of the transducer signal, while isolating the electrical noise present in the high voltage transformer circuitry. The isolated direct current power supply 1 8 aids in achieving this electrical isolation. The optical coupler 16 may be of a conventional type, based e.g. upon an LED light source and a spaced photodiode sensor. The transducer signal is then amplified in the two-stage RF amplifier 20. Low frequencies are further reduced in the second high pass filter 22. The voltage pulses are amplified and modulated by a diode pump circuit in the amplifier/diode pump 24, which provides a measure of the amplitude and frequency of the pulses. The linearizer 26 provides a voltage dependent adjustment to the gain of the amplifier/diode pump 24 to create linear voltage output values. Any remaining voltage ripple in the direct current voltage is reduced in the low pass filter 28. The direct current voltage is amplified in the scaling amplifier 30. After calibration to the actual dielectric product, e.g., ozone, being produced, the direct current voltage is now directly related to the breakdown of the dielectric in the presence of high voltage, and can then be converted into digital form by the A/D converter 32. The microprocessor 34 can then process the digital data so as to provide a display of the breakdown of the dielectric, which in the present embodiment is the amount of ozone being produced by the ozone generator. The microprocessor 34 can then control the rate of dielectric product, e.g. ozone, production in a high voltage ozone generator.

The direct current voltage levels provided from scaling amplifier 30 are calibrated to the actual levels of ozone being produced as measured by a conventional spectrophotometer. This is effected by establishing a series of points relating measured voltage levels to measured ozone concentrations. The established relationship thereby enables direct calibration of readout voltage levels in terms of ozone concentration.

It should be noted that the sequence of the signal conditioning described above may be varied and, in fact, some of the above-described signal conditioning functions may be omitted.

The overall function of the transducer signal conditioning in the dielectric breakdown measuring circuit 10 is to provide a means for converting sensed corona discharge pulses into a direct current voltage which is representative of the frequency and magnitude of occurrence of these corona discharge pulses. The generation of the corona discharge pulses is relatively uniform if the physical dimensions (i.e. gap size) of the ozone generator are held fixed and the composition and flow rate of gases flowing through the ozone generator are properly regulated. However, the actual amount of ozone production in the ozone generator is dependent on the frequency and magnitude of the corona discharge pulses. The present invention is therefore directed toward sensing corona discharge pulses and then converting the sensed corona discharge pulses into a direct current voltage having a voltage level that is representative of the frequency and magnitude of occurrence of the sensed corona discharge pulses and thereby directly related to the ozone production in the ozone generator.

It should be noted that the capacitive transducer assembly 12, which consists of an aluminum plate, need not be actually affixed to the insulating material surrounding the secondary winding in the high voltage transformer, but must merely be in close proximity to the secondary winding in the high voltage transformer so as to sense the individual corona discharge pulses.

Referring to Figure 2, there is shown a schematic block diagram revealing a typical physical relationship between a high voltage transformer 40 and a corona discharge pulse capacitive transducer 42 according to the present invention. The high voltage transformer 40 comprises a primary winding (not shown) and a high voltage secondary winding 44.

In this particular embodiment, the capacitive transducer 42 comprises an aluminum plate, approximately 10 x 10 mm square, which is fixed to the insulating material surrounding the high voltage secondary winding 44. The high voltage secondary winding 44 provides high voltage pulses to an ozone generator (not shown). These high voltage pulses produce corona discharges in the ozone generator. The capacitive transducer 42 capacitively senses these corona discharges as pulses of electrical charge from the high voltage secondary winding 44. These sensed corona discharge pulses may then be signal conditioned by the dielectric breakdown measurement circuit according to the present invention.

With the present invention now fully described, it can thus be seen that the objects set forth above are efficiently attained and, since certain changes may be made in the above-described embodiments without departing from the scope of the invention, it is intended that ali matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

WHAT IS CA AIMED IS:

1 . Apparatus for measuring dielectric breakdown product production in a high voltage discharge apparatus, said apparatus comprising:

means for sensing corona electrical discharge pulses from a winding in a voltage transformer providing electrical charging pulses to said high voltage discharge apparatus and generating an electrical signal in accordance with the sensed pulses; and

means for converting said electrical signal into a D.C. voltage the level of which is a function of the frequency of occurrence and magnitude of said sensed electrical discharge pulses and thereby a measure of dielectric breakdown product production in said high voltage discharge apparatus; and

means for calibrating said direct current voltage level against measured dielectric breakdown product production in said apparatus, to enable measurement of the actual dielectric breakdown product production from the measured direct current voltage level.

2. The apparatus as defined in claim 1 , wherein said means for sensing comprises a capacitive transducer coupling to said winding in said voltage transformer.

3. The apparatus as defined in claim 2, wherein said winding is a secondary winding.

4. The apparatus as defined in claim 1 , wherein said means for converting comprises a first high pass filter for filtering out lower frequencies from the electrical signal produced from said sensing means.

5. The apparatus as defined in claim 4, wherein said means for converting further comprises an optical coupler powered by an isolated direct current power supply, for receiving the signal from said first high pass filter, while isolating the processing cciirrccuuiittrrvy ffrroomm t thhee h hiiαghh v voollttaaαgee t trraannssffoorrmmeerr r cnouunplliinnπg.

6. The apparatus as defined in claim 5, wherein said means for converting further comprises a first two-stage amplifier for receiving and amplifying the filtered signal from said optical coupler.

7. The apparatus as defined in claim 6, wherein said first two-stage amplifier is an RF amplifier.

8. The apparatus as defined in claim 6, wherein said means for converting further comprises a second high pass filter connected to the output of said two stage amplifier, for filtering out lower frequencies in said amplified signal.

9. The apparatus as defined in claim 8, wherein said means for converting comprises a second amplifier connected to the output of said second high pass filter for amplifying said D.C. voltage signal.

10. The apparatus as defined in claim 9, wherein said means for converting further comprises a diode pump for providing a measure of the amplitude and frequency of the said D.C. voltage signal.

1 1 . The apparatus as defined in claim 10, wherein said means for converting further comprises a linearizer for adjusting the actual values of the said D.C. signal to a linear range.

12. The apparatus as defined in claim 1 1 , wherein said means for converting further comprises a low pass filter for receiving the signal from said linearizer and filtering out higher frequencies in the D.C. voltage signal.

13. The apparatus as defined in claim 12, wherein said means for converting further comprises a scaling amplifier for receiving and amplifying said D.C. voltage signal.

14. An apparatus for measuring the breakdown of a dielectric in the presence of high voltage by sensing electrical pulses from a winding in a transformer and then converting said sensed electrical pulses into a D.C. voltage the level of which represents the magnitude of said sensed electrical pulses, said device comprising:

means for sensing electrical pulses from a winding in a transformer; and

means for converting said sensed electrical pulses into a D.C. voltage which is representative of the magnitude of said sensed electrical pulses.

15. An apparatus for measuring the breakdown of a dielectric in the presence of high voltage by sensing electrical pulses from a winding in a transformer and then converting said sensed electrical pulses into a D.C. voltage the level of which represents the frequency of occurrence and magnitude of said sensed electrical pulses, said device comprising:

-means for sensing electrical pulses from a winding in a transformer; and

means for converting said sensed electrical pulses into a direct current voltage which is representative of the magnitude and frequency of occurrence of said sensed electrical pulses.

16. An apparatus for measuring the breakdown of the dielectric in the presence of high voltage represents the frequency of occurrence and the magnitude of said sensed electrical pulses, said method comprising:

means for sensing electrical pulses from a winding in a transformer; and

means for converting said sensed electrical pulses into a D.C. voltage which is representative of the frequency of occurrence and the magnitude of said sensed electrical pulses.

17. A method for measuring the breakdown of a dielectric in the presence of high voltage by sensing electrical pulses from a winding in a transformer and then converting said sensed electrical pulses into a D.C. voltage the level of which is indicative of the frequency and magnitude of said sensed electrical pulses, said method comprising the steps of:

sensing electrical pulses from a winding in a transformer; and

converting said sensed electrical pulses into a D.C. voltage the level of which is representative of the frequency and magnitude of said sensed electrical pulses.

18. A method for measuring ozone production in an ozone generator using the corona discharge principle, said method comprising the steps of.

sensing electrical discharge pulses from a winding in a voltage transformer, said voltage transformer providing electrical charging pulses to a corona discharge ozone generator; and

converting said sensed electrical discharge pulses into a D.C. voltage the level of which is representative of the frequency and magnitude of said sensed electrical discharge pulses and thereby directly related to ozone production in said corona discharge ozone generator.

19. The method as defined in claim 18, further comprising the step of controlling ozone production in said corona discharge ozone generator based on the level of said direct current voltage by changing the rate at which said voltage transformer provides electrical charging pulses to said corona discharge ozone generator.

20. The method as defined in claim 19, further comprising the step of providing a display indicating the amount of ozone production in said corona discharge ozone generator based on the level of said direct current voltage.

21 . A method for measuring ozone production in a high voltage discharge apparatus, comprising:

sensing corona electrical discharge pulses from a winding in a voltage transformer providing electrical charging pulses to said high voltage discharge apparatus and generating an electrical signal in accordance with the sensed pulses;

converting said electrical signal into a D.C. voltage the level of which is a function of the frequency of occurrence and magnitude of said sensed electrical discharge pulses and thereby a measure of ozone production in said high voltage discharge apparatus; and

calibrating said direct current voltage level against measured ozone production in said apparatus, to enable measurement of the actual ozone production from the measured D.C. voltage level.

22. ^' The method of claim 21 , wherein said discharge pulses are sensed by a capacitive coupling.

23. The method of claim 22, wherein said winding sensed is a secondary winding.

24. The method of claim 21 , wherein said electrical signal being converted to said D.C. signal is conditioned by filtering out lower frequencies, and by passing the signal through an optical coupler powered by an isolated direct current power supply, for isolating the signal processing from the high voltage transformer coupling.