CA2365955A1 - Plasma analyser - Google Patents
Plasma analyser Download PDFInfo
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- CA2365955A1 CA2365955A1 CA 2365955 CA2365955A CA2365955A1 CA 2365955 A1 CA2365955 A1 CA 2365955A1 CA 2365955 CA2365955 CA 2365955 CA 2365955 A CA2365955 A CA 2365955A CA 2365955 A1 CA2365955 A1 CA 2365955A1
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- plasma
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- microdischarges
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/0006—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature
- H05H1/0081—Investigating plasma, e.g. measuring the degree of ionisation or the electron temperature by electric means
Abstract
A plasma analyser is disclosed for analysing the behaviour of a plasma discharge or corona discharge at the electrode of a non-thermal plasma or corona discharge reactor. This is done by providing instantaneous, real time voltage and current measurements at the electrode and multiplying them to obtain real time power values. The power values are then integrated over time to give energy values of the microdischarges occurring at the electrode. The values of current, power and energy are then compared with preselected threshold values and the microdischarges that exceed these values are counted. A method for controlling the plasma or corona discharge reaction is also disclosed by adjusting electrical parameters of the pulser that provides electrical energy to the reactor according to a modelling program that optimizes the reaction at the electrode.
Description
PLASMA ANALYSER
FIELD OF THE INVENTION
This invention relates to an analyser for analysing the behaviour of plasma discharge, which is also called "corona discharge", occurring at the electrode of a non-thermal or cold plasma reactor or a corona discharge reactor. The invention also includes a method providing real time statistical quantification of the non-thermal plasma behaviour in order to control the reaction occurring at the electrode.
BACKGROUND OF THE INVENTION
There are a number of prior art references describing non-thermal plasma or corona discharge reactors for carrying out various chemical reactions.
One such reactor is disclosed in U.S. Patent No. 3,798,457, where it is used as an ozone generator and the corona discharge occurs between a pair of spaced-apart electrodes.
Another such reactor, using plasma for cracking or synthesizing gases, is disclosed in U.S. Patent No. 5,817,218, in which cold or non-thermal plasma is generated in a gap between two electrodes, one of which carries a catalyst suitable for the desired chemical reaction, such as production of ethylene from methane.
A still further such apparatus is disclosed in U. S. Patent No. 6,159,432, where a non-thermal plasma generated by corona discharge between a pair of electrodes is used to convert methane or natural gas to higher level hydrocarbons.
Applicant's own Canadian Patent Application No. 2,353,752 filed July 25, 2001 and entitled "Production of Hydrogen and Carbon from Natural Gas or Methane using Barrier Discharge Non-Thermal Plasma" also discloses an apparatus having two concentric elongated electrodes and a concentric dielectric barrier connected to one of them so that non-thermal plasma can be produced within the gap between one of the electrodes and the barrier, for dissociating methane or natural gas into its constituents, hydrogen and carbon.
S In all above mentioned prior art references, the corona discharge or the non-thermal plasma is obtained from a pulser or a similar high frequency power supply source. None of these references, however, allows to analyse the electrical efficiency of the plasma reaction to provide real time quantification of the cold plasma behaviour in order to accurately monitor the plasma induced processes and make required adjustments to the pulser so as to optimize the reaction.
Some attempts have been made to improve the corona discharge reaction by means of a control system. For Example, U.S. Patent No. 5,822,981 provides a corona discharge reactor with an automatic control system that controls power generation characteristics, such as voltage, resonator frequency, pulse width and repetition rate, 1 S by means of a computer that reads relevant input data from various sensors, such as engine sensors and tailpipe sensors.
Also, Canadian Patent Application No. 2,236,769 discloses an ozone generator with a corona discharge and a control circuit that comprises circuitry to electrically control the voltage and the frequency applied to the pulse generating device producing the corona discharge. For this purpose, it uses a micro-controller which controls ozone production with electrical signals, and a voltage regulator controlled by an analog signal which determines the peak voltage of the pulses applied to the ozone generator and it is stated that the ozone production is proportional to the amplitude of the applied pulses. However, neither of these references analyses plasma or corona discharge behaviour in real time at the electrode within the reactor, and provides a possibility to adjust the same, also in real time.
OBJECTS AND SL;IMMARY OF 'THE INVENTION
It is an object of the present invention to provide a plasma analyser that produces real time quantification of non-thermal or cold plasma behaviour or corona discharge behaviour at the electrode in a plasma or corona discharge reactor.
A further object is to control the reaction taking place in the plasma or corona discharge reactor by electrical modelling that correlates the results obtained from the plasma analyser with optimum electrical parameters of the high frequency power supply.
Other objects and advantages of the invention will become apparent from the following description of the invention.
In essence, the plasma analyser of the present invention provides means for instantaneous measurement of electrode voltage (v) and of electrode current (i) in a 1 S non-thermal or cold plasma or corona discharge reactor, and a fast multiplier for multiplying the instantaneous v values by the instantaneous i values to obtain instantaneous power (p) values of the plasma or corona discharge. Then, a fast integrator is provided for integrating the v x i = p values over time to give energy (e) values of the plasma or corona microdischarges in the reactor. Thus, peak current, peak power and peak energy of the plasma or corona discharges are available through this analyser in real time and can be compared also in real time by means of a fast comparator, with preselected threshold values. The discharges that exceed a specified threshold can then be counted by a fast counter and used to control the plasma reaction. The plasma analyser of the present invention, therefore, gives an instantaneous "photograph" of the plasma or corona discharge behaviour, which can then be adjusted in real time to optimize the reaction.
The present invention also provides a method of controlling a reaction at an electrode of a non-thermal plasma or corona reactor to which high frequency electrical power is supplied from a high frequency power supply or pulser to produce plasma or corona microdischarges at the electrode that induce the reaction.
This method comprises:
(a) measuring voltage (v) at the electrode in real time as the reaction proceeds;
(b) measuring current (l) at the electrode in real time as the reaction proceeds;
(c) multiplying v x l by means of a fast multiplier to obtain instantaneous power (p) values;
(d) integrating the v x l = p values over time of the microdischarges by a fast integrator to give energy (e) values of the microdischarges;
(e) comparing in real time the l, p and/or a values against preselected l, p and/or a threshold values;
(f) counting the microdischarges that exceed the predetermined threshold values; and (g) adjusting electrical parameters of the power supply or pulser in real time so as to optimize the reaction at the electrode.
The electrical parameters of the pulser may be adjusted by computer according to a predetermined model which correlates the obtained l, p and/or a counts with the electrical parameters required for optimum reaction results.
FIELD OF THE INVENTION
This invention relates to an analyser for analysing the behaviour of plasma discharge, which is also called "corona discharge", occurring at the electrode of a non-thermal or cold plasma reactor or a corona discharge reactor. The invention also includes a method providing real time statistical quantification of the non-thermal plasma behaviour in order to control the reaction occurring at the electrode.
BACKGROUND OF THE INVENTION
There are a number of prior art references describing non-thermal plasma or corona discharge reactors for carrying out various chemical reactions.
One such reactor is disclosed in U.S. Patent No. 3,798,457, where it is used as an ozone generator and the corona discharge occurs between a pair of spaced-apart electrodes.
Another such reactor, using plasma for cracking or synthesizing gases, is disclosed in U.S. Patent No. 5,817,218, in which cold or non-thermal plasma is generated in a gap between two electrodes, one of which carries a catalyst suitable for the desired chemical reaction, such as production of ethylene from methane.
A still further such apparatus is disclosed in U. S. Patent No. 6,159,432, where a non-thermal plasma generated by corona discharge between a pair of electrodes is used to convert methane or natural gas to higher level hydrocarbons.
Applicant's own Canadian Patent Application No. 2,353,752 filed July 25, 2001 and entitled "Production of Hydrogen and Carbon from Natural Gas or Methane using Barrier Discharge Non-Thermal Plasma" also discloses an apparatus having two concentric elongated electrodes and a concentric dielectric barrier connected to one of them so that non-thermal plasma can be produced within the gap between one of the electrodes and the barrier, for dissociating methane or natural gas into its constituents, hydrogen and carbon.
S In all above mentioned prior art references, the corona discharge or the non-thermal plasma is obtained from a pulser or a similar high frequency power supply source. None of these references, however, allows to analyse the electrical efficiency of the plasma reaction to provide real time quantification of the cold plasma behaviour in order to accurately monitor the plasma induced processes and make required adjustments to the pulser so as to optimize the reaction.
Some attempts have been made to improve the corona discharge reaction by means of a control system. For Example, U.S. Patent No. 5,822,981 provides a corona discharge reactor with an automatic control system that controls power generation characteristics, such as voltage, resonator frequency, pulse width and repetition rate, 1 S by means of a computer that reads relevant input data from various sensors, such as engine sensors and tailpipe sensors.
Also, Canadian Patent Application No. 2,236,769 discloses an ozone generator with a corona discharge and a control circuit that comprises circuitry to electrically control the voltage and the frequency applied to the pulse generating device producing the corona discharge. For this purpose, it uses a micro-controller which controls ozone production with electrical signals, and a voltage regulator controlled by an analog signal which determines the peak voltage of the pulses applied to the ozone generator and it is stated that the ozone production is proportional to the amplitude of the applied pulses. However, neither of these references analyses plasma or corona discharge behaviour in real time at the electrode within the reactor, and provides a possibility to adjust the same, also in real time.
OBJECTS AND SL;IMMARY OF 'THE INVENTION
It is an object of the present invention to provide a plasma analyser that produces real time quantification of non-thermal or cold plasma behaviour or corona discharge behaviour at the electrode in a plasma or corona discharge reactor.
A further object is to control the reaction taking place in the plasma or corona discharge reactor by electrical modelling that correlates the results obtained from the plasma analyser with optimum electrical parameters of the high frequency power supply.
Other objects and advantages of the invention will become apparent from the following description of the invention.
In essence, the plasma analyser of the present invention provides means for instantaneous measurement of electrode voltage (v) and of electrode current (i) in a 1 S non-thermal or cold plasma or corona discharge reactor, and a fast multiplier for multiplying the instantaneous v values by the instantaneous i values to obtain instantaneous power (p) values of the plasma or corona discharge. Then, a fast integrator is provided for integrating the v x i = p values over time to give energy (e) values of the plasma or corona microdischarges in the reactor. Thus, peak current, peak power and peak energy of the plasma or corona discharges are available through this analyser in real time and can be compared also in real time by means of a fast comparator, with preselected threshold values. The discharges that exceed a specified threshold can then be counted by a fast counter and used to control the plasma reaction. The plasma analyser of the present invention, therefore, gives an instantaneous "photograph" of the plasma or corona discharge behaviour, which can then be adjusted in real time to optimize the reaction.
The present invention also provides a method of controlling a reaction at an electrode of a non-thermal plasma or corona reactor to which high frequency electrical power is supplied from a high frequency power supply or pulser to produce plasma or corona microdischarges at the electrode that induce the reaction.
This method comprises:
(a) measuring voltage (v) at the electrode in real time as the reaction proceeds;
(b) measuring current (l) at the electrode in real time as the reaction proceeds;
(c) multiplying v x l by means of a fast multiplier to obtain instantaneous power (p) values;
(d) integrating the v x l = p values over time of the microdischarges by a fast integrator to give energy (e) values of the microdischarges;
(e) comparing in real time the l, p and/or a values against preselected l, p and/or a threshold values;
(f) counting the microdischarges that exceed the predetermined threshold values; and (g) adjusting electrical parameters of the power supply or pulser in real time so as to optimize the reaction at the electrode.
The electrical parameters of the pulser may be adjusted by computer according to a predetermined model which correlates the obtained l, p and/or a counts with the electrical parameters required for optimum reaction results.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in a preferred embodiment with reference to the appended drawings in which:
Fig. 1 is a general diagram of a set-up using non-thermal or cold plasma or corona discharge in a dissociation reaction and indicating where the voltage and current are to be measured;
Fig. 2 is an electrical diagram showing the arrangement of the set-up using resistive voltage divider to measure voltage and current sensing resistor to measure current, and including other devices required for the purposes of the invention.
Fig. 3 is a diagram illustrating in greater detail the analyser set-up of the present invention;
Fig. 4 is a diagram similar to that of Fig. 3, but providing a description of the various analyser box connections; and Fig. 5A and Fig. 5B are graphs illustrating typical corona voltage and current waveforms for long pulse width high impedance pulser and short pulse width low impedance pulser respectively.
DETAILED DESCRIPTION OF THE I)VVENTION
In the drawings, Fig. 1 illustrates a non-thermal or cold plasma or corona discharge set-up having an electrode 10 with a first grid 12 and a second grid 14, and a dielectric element 16. A gap is provided between the dielectric element 16 and the grids 12 and 14 of the electrode, where the plasma or corona microdischarges take place. In this particular embodiment, a dissociation reaction is shown with the reactant 18 being introduced into the gap between the electrode and the dielectric at one end and the dissociated products 20, 22 exiting at the other end.
The invention will now be described in a preferred embodiment with reference to the appended drawings in which:
Fig. 1 is a general diagram of a set-up using non-thermal or cold plasma or corona discharge in a dissociation reaction and indicating where the voltage and current are to be measured;
Fig. 2 is an electrical diagram showing the arrangement of the set-up using resistive voltage divider to measure voltage and current sensing resistor to measure current, and including other devices required for the purposes of the invention.
Fig. 3 is a diagram illustrating in greater detail the analyser set-up of the present invention;
Fig. 4 is a diagram similar to that of Fig. 3, but providing a description of the various analyser box connections; and Fig. 5A and Fig. 5B are graphs illustrating typical corona voltage and current waveforms for long pulse width high impedance pulser and short pulse width low impedance pulser respectively.
DETAILED DESCRIPTION OF THE I)VVENTION
In the drawings, Fig. 1 illustrates a non-thermal or cold plasma or corona discharge set-up having an electrode 10 with a first grid 12 and a second grid 14, and a dielectric element 16. A gap is provided between the dielectric element 16 and the grids 12 and 14 of the electrode, where the plasma or corona microdischarges take place. In this particular embodiment, a dissociation reaction is shown with the reactant 18 being introduced into the gap between the electrode and the dielectric at one end and the dissociated products 20, 22 exiting at the other end.
This electrode arrangement 10 is wired to an electrical energy source by wires 24, 26. The voltage is then measured across the wires 24, 26 while the current is measured on one of the wires, for example, 26. The electrical energy source is a high frequency power supply or pulser 28. The driving pulses at the power supply 28 are the pulser applied to gates or bases of power transistors. Their amplitude is constant (about 10v), but their repetition rate (frequency) and duration (pulse width) can be varied manually or by computer. The output of the pulser 28 has a DC voltage which can also be varied manually or by computer from 0 to 200v and is switched on/off by the pulser and produces an AC waveform at the input or primary 32 of a high voltage transformer 30 (set-up ratio 1:50). The output or secondary 34 of the high voltage transformer 30 produces the plasma or corona voltage of variable frequency, amplitude and pulse width waveforms, which is impressed on the electrode 10.
Fig. 2 illustrates diagrammatically the electrical circuitry of the arrangement shown in Fig. 1, associated with a fast analog multiplier 40, a fast analog integrator 42, a fast comparator 44A for zero crossing, 44B for current, 44C for power and 44D
for energy, a fast counter 46 and a computer 48. As shown in Fig. 2, pulser 28 is connected by wires 24, 26 to the electrode producing a plasma or corona discharge 15. The voltage (v) across the grids of the electrode is measured in this case by a resistive voltage divider 36 and the current (i) is measured by a current resistor 38.
The voltage (v) and current (i) are designated herein by lower case letters because they are instantaneous values and, as such by convention of electrical engineering are written in lower case. The total power at the electrode is then determined by multiplication P = v x i, by means of the fast analog multiplier 40. The discharge duration can be anything between 100 nanoseconds and a few microseconds.
Fig. 2 illustrates diagrammatically the electrical circuitry of the arrangement shown in Fig. 1, associated with a fast analog multiplier 40, a fast analog integrator 42, a fast comparator 44A for zero crossing, 44B for current, 44C for power and 44D
for energy, a fast counter 46 and a computer 48. As shown in Fig. 2, pulser 28 is connected by wires 24, 26 to the electrode producing a plasma or corona discharge 15. The voltage (v) across the grids of the electrode is measured in this case by a resistive voltage divider 36 and the current (i) is measured by a current resistor 38.
The voltage (v) and current (i) are designated herein by lower case letters because they are instantaneous values and, as such by convention of electrical engineering are written in lower case. The total power at the electrode is then determined by multiplication P = v x i, by means of the fast analog multiplier 40. The discharge duration can be anything between 100 nanoseconds and a few microseconds.
Integrating the product of v x i over time, for example, by means of a fast analog integrator 42, will give the energy (e) of a particular discharge. Peak current, peak power and peak energy of the discharges are thus available in analog form in real time. These outputs are then compared to preselected threshold values, for example, by fast comparators 44B, 44C and 44D, which can be high speed differential comparators producing a standard digital pulse 0-Sv whenever a particular discharge parameter, namely peak current, peak power and/or peak energy exceeds a specified threshold. These digital pulses can then be counted, for example, by a fast digital counter 46 and the obtained numbers forwarded to a computer 48, such as a PC.
The computer 48, by simple subtraction, can deliver the number of discharges occurring between threshold setting #n in 49 and threshold #n + 1. A fast computer 44A
for a zero crossing channel is also provided to count the total number of microdischarges per second to evaluate the overall plasma activity, if desired.
The above described set up, therefore, provides an accurate essentially instantaneous or real time "photograph" of what happens in the plasma or corona discharge reaction. These purely electrical measurements have been found to be linked to physics and chemistry of the reaction taking place in the plasma or corona reactor. For example, the number of microdischarges must be increased when the flow of input reactant is increased or a number of high energy microdischarges should be increased for certain type of reactions, such as dissociation, and the like.
On this basis, providing a given microdischarge pattern can be implemented by a PC program following a relatively simple control algorithm, such as:
- Send initial corona voltage, corona frequency, corona pulsewidth values to electrode via pulser;
- Read analyser;
- Modify corona voltage, corona frequency, corona pulse width values according to discharge distribution;
- Stop when predetermined discharge distribution is attained (within desired tolerance).
Fig. 3 illustrates the analyser box 50 and its connections in greater detail, and Fig. 4 provides a descriptive outline of said connections. The potentiometers A, B, C
and D are used to adjust threshold voltages within desired ranges.
Potentiometer E is a spare potentiometer that can be used if one of the others malfunctions. The banana plugs A, B, C, D,. E, F, G, H, I, J and K provide connections to various devices used as part of the set-up of the present invention. Thus, plugs A, C, E and G connect to the digital voltmeter DVM 52 for DC threshold measurements. Plugs B, D, F and H
connect to the frequency counter 54 for discharge counting. The counter 54 in this case was of 0-10 Megahertz. Plugs I and K connect to a two channel oscilloscope 56 1 S for corona voltage and corona current visualization.
The analyser box 50 is also provided with switches for POWER ON/OFF and VOLTS DIVIDER and is connected to the electrode volts/amps connector 58 which is supplied with electrode voltage sense and electrode current sense. The corona voltage divider box 60 is also connected to the electrode. Finally, a line filter 62 is provided for noise suppression.
Fig. 5A and Fig. 5B illustrate typical corona voltage and current waveforms produced by long pulsewidth, high impedance pulser, and by short pulsewidth, low impedance pulser respectively. In both cases, alumina electrodes were used and the reactant was air. In both cases, the visual results were obtained by connecting the _g-oscilloscope as shown in Fig. 3 and looking at the corona voltage and current waveforms. It should be noted that voltage and current waveforms represent instantaneous values of voltages and currents at the electrode and that v is continuous, but i is not. The electric current, contrary to conventional electric circuitry, does not follow the electrode voltage waveform. The current waveforms are discrete jumps which occur randomly, with little correlation to electrode voltage. In other words, at a given instant, there can be an electrode voltage, but not current, i.e. no microdischarge. Moreover, the frequencies of currents are several orders of magnitude higher than the basic corona frequency. This is due to the fact that the electrode is not a mere passive capacitor; during discharge, it behaves Iike a high frequency generator. All this can be seen with an oscilloscope. Moreover, voltage and current waveforms can vary with pulser characteristics, high voltage transformer characteristics, corona pulse width, type of electrode used, type of reactant, and so on.
Examples of recording the number of discharges with the analyser of the present invention will now be given.
Recording the number of discharges as a function of current thresholds can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug G (current thresholds values);
- Connect frequency counter to banana plug H (number of discharges having current above given threshold value, 0.6 Amp/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 1.5 Amp) by e.g. 10 increments of 0.25v (0.150 Amp) and read on counter n = number of pulses/sec for each different level. Record values, which in this example were as follows:
Threshold, volts: Threshold, Amps:Number of discharge above threshold:
0.25 0.150 22322 0.50 0.300 15010 0.75 0.450 6789 1.0 0.600 3456 1.25 0.750 123 1.50 0.900 0 1.75 1.050 0 2.0 - -2.25 - -2.50 - -With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having currents of for example 0.075 Amp is 29334-22322 = 7012.
Recording the number of discharges as a function of power threshold can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug B (power thresholds values);
- Connect frequency counter to banana plug C (number of discharges having power above given threshold value, 9 kilowatts/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 22.5 kilowatts) by e.g. 10 increments of 0.25v (2.25 kw) and read on counter n = number of pulses/sec for each different level. Record values which in this example were as follows:
Threshold, volts: Threshold, kilowatts: Number of discharge above threshold:
0.25 2.25 30636 0.50 4.50 29048 0.75 6.65 12078 1.0 9 10978 1.25 11.25 560 1.50 13.50 120 1.75 15.75 0 2.0 18 0 S 2.25 20.75 0 2.50 22.5 0 With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having powers of for example 1.125 kw is 50345-30636 = 19709.
Recording the number of discharges as a function of energy thresholds can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug E (energy thresholds values);
- Connect frequency counter to banana plug F (number of discharges having current above given threshold value, 0.562 Joules/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 1.4 Joule) by e.g. 10 increments of 0.25v (0.140 J) and read on counter n = number of puises/sec for each different level. Record values which in this example were as follows:
Threshold, volts:Threshold, Joules:Number of discharge above threshold:
0.25 0.140 12670 0.50 0.280 5678 0.75 0.420 23 1.01 0.560 0 1.25 - -1.50 - -1.75 - -2.0 - -2.25 - -2.50 - -With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having energies of e.g. 0.070 J is 15006 -12670 = 2336.
E3~AMPLE 4 Recording the number of zero crossing discharges can be done as follows:
- Connect DVM at banana plug A and counter at banana plug B.
- Set threshold to about +0.100V.
- Read number of zero crossing discharges on counter.
- Zero crossing discharges can be used to evaluate roughly the plasma activity.
Patterns obtained by the analyser of the present invention as described above can be seen as providing plasma electrical signatures, taking into account the discontinuous nature of microdischarges. Once a given signature corresponding to optimum results is known, it can be adopted and reproduced by merely controlling a few electrical parameters.
The invention is not limited to the specific embodiments and examples described above, but includes various modifications obvious to those skilled in the art, without departing from the scope of the following claims.
The computer 48, by simple subtraction, can deliver the number of discharges occurring between threshold setting #n in 49 and threshold #n + 1. A fast computer 44A
for a zero crossing channel is also provided to count the total number of microdischarges per second to evaluate the overall plasma activity, if desired.
The above described set up, therefore, provides an accurate essentially instantaneous or real time "photograph" of what happens in the plasma or corona discharge reaction. These purely electrical measurements have been found to be linked to physics and chemistry of the reaction taking place in the plasma or corona reactor. For example, the number of microdischarges must be increased when the flow of input reactant is increased or a number of high energy microdischarges should be increased for certain type of reactions, such as dissociation, and the like.
On this basis, providing a given microdischarge pattern can be implemented by a PC program following a relatively simple control algorithm, such as:
- Send initial corona voltage, corona frequency, corona pulsewidth values to electrode via pulser;
- Read analyser;
- Modify corona voltage, corona frequency, corona pulse width values according to discharge distribution;
- Stop when predetermined discharge distribution is attained (within desired tolerance).
Fig. 3 illustrates the analyser box 50 and its connections in greater detail, and Fig. 4 provides a descriptive outline of said connections. The potentiometers A, B, C
and D are used to adjust threshold voltages within desired ranges.
Potentiometer E is a spare potentiometer that can be used if one of the others malfunctions. The banana plugs A, B, C, D,. E, F, G, H, I, J and K provide connections to various devices used as part of the set-up of the present invention. Thus, plugs A, C, E and G connect to the digital voltmeter DVM 52 for DC threshold measurements. Plugs B, D, F and H
connect to the frequency counter 54 for discharge counting. The counter 54 in this case was of 0-10 Megahertz. Plugs I and K connect to a two channel oscilloscope 56 1 S for corona voltage and corona current visualization.
The analyser box 50 is also provided with switches for POWER ON/OFF and VOLTS DIVIDER and is connected to the electrode volts/amps connector 58 which is supplied with electrode voltage sense and electrode current sense. The corona voltage divider box 60 is also connected to the electrode. Finally, a line filter 62 is provided for noise suppression.
Fig. 5A and Fig. 5B illustrate typical corona voltage and current waveforms produced by long pulsewidth, high impedance pulser, and by short pulsewidth, low impedance pulser respectively. In both cases, alumina electrodes were used and the reactant was air. In both cases, the visual results were obtained by connecting the _g-oscilloscope as shown in Fig. 3 and looking at the corona voltage and current waveforms. It should be noted that voltage and current waveforms represent instantaneous values of voltages and currents at the electrode and that v is continuous, but i is not. The electric current, contrary to conventional electric circuitry, does not follow the electrode voltage waveform. The current waveforms are discrete jumps which occur randomly, with little correlation to electrode voltage. In other words, at a given instant, there can be an electrode voltage, but not current, i.e. no microdischarge. Moreover, the frequencies of currents are several orders of magnitude higher than the basic corona frequency. This is due to the fact that the electrode is not a mere passive capacitor; during discharge, it behaves Iike a high frequency generator. All this can be seen with an oscilloscope. Moreover, voltage and current waveforms can vary with pulser characteristics, high voltage transformer characteristics, corona pulse width, type of electrode used, type of reactant, and so on.
Examples of recording the number of discharges with the analyser of the present invention will now be given.
Recording the number of discharges as a function of current thresholds can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug G (current thresholds values);
- Connect frequency counter to banana plug H (number of discharges having current above given threshold value, 0.6 Amp/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 1.5 Amp) by e.g. 10 increments of 0.25v (0.150 Amp) and read on counter n = number of pulses/sec for each different level. Record values, which in this example were as follows:
Threshold, volts: Threshold, Amps:Number of discharge above threshold:
0.25 0.150 22322 0.50 0.300 15010 0.75 0.450 6789 1.0 0.600 3456 1.25 0.750 123 1.50 0.900 0 1.75 1.050 0 2.0 - -2.25 - -2.50 - -With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having currents of for example 0.075 Amp is 29334-22322 = 7012.
Recording the number of discharges as a function of power threshold can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug B (power thresholds values);
- Connect frequency counter to banana plug C (number of discharges having power above given threshold value, 9 kilowatts/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 22.5 kilowatts) by e.g. 10 increments of 0.25v (2.25 kw) and read on counter n = number of pulses/sec for each different level. Record values which in this example were as follows:
Threshold, volts: Threshold, kilowatts: Number of discharge above threshold:
0.25 2.25 30636 0.50 4.50 29048 0.75 6.65 12078 1.0 9 10978 1.25 11.25 560 1.50 13.50 120 1.75 15.75 0 2.0 18 0 S 2.25 20.75 0 2.50 22.5 0 With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having powers of for example 1.125 kw is 50345-30636 = 19709.
Recording the number of discharges as a function of energy thresholds can be done as follows:
- Disconnect oscilloscope;
- Connect DVM to banana plug E (energy thresholds values);
- Connect frequency counter to banana plug F (number of discharges having current above given threshold value, 0.562 Joules/volt);
- Vary threshold values from 0 vdc to 2.5 vdc (0 to 1.4 Joule) by e.g. 10 increments of 0.25v (0.140 J) and read on counter n = number of puises/sec for each different level. Record values which in this example were as follows:
Threshold, volts:Threshold, Joules:Number of discharge above threshold:
0.25 0.140 12670 0.50 0.280 5678 0.75 0.420 23 1.01 0.560 0 1.25 - -1.50 - -1.75 - -2.0 - -2.25 - -2.50 - -With some error (which can be made as small as wanted by increasing the number of threshold selected), the number of discharges having energies of e.g. 0.070 J is 15006 -12670 = 2336.
E3~AMPLE 4 Recording the number of zero crossing discharges can be done as follows:
- Connect DVM at banana plug A and counter at banana plug B.
- Set threshold to about +0.100V.
- Read number of zero crossing discharges on counter.
- Zero crossing discharges can be used to evaluate roughly the plasma activity.
Patterns obtained by the analyser of the present invention as described above can be seen as providing plasma electrical signatures, taking into account the discontinuous nature of microdischarges. Once a given signature corresponding to optimum results is known, it can be adopted and reproduced by merely controlling a few electrical parameters.
The invention is not limited to the specific embodiments and examples described above, but includes various modifications obvious to those skilled in the art, without departing from the scope of the following claims.
Claims (10)
- A plasma analyser for analysing non-thermal plasma or corona discharge behaviour at an electrode where plasma or corona microdischarges occur, which comprises:
(a) means for instantaneous, real time measurement of voltage (v) at the electrode;
(b) means for instantaneous, real time measurement of current (i) at the electrode;
(c) a fast multiplier for multiplying v x i values to obtain real time power (p) values;
(d) a fast integrator for integrating the v x i = p values over time of the microdischarges to give energy (e) values thereof;
(e) a fast comparator for comparing in real time the i, p and/or a values against preselected i, p and/or a threshold values; and (f) a fast counter for counting the microdischarges that exceed the preselected threshold values. - 2. A plasma analyser according to claim 1, wherein the fast comparator also includes a zero crossing channel which sends zero-cross signals to the fast counter to count the total number of microdischarges per second.
- 3. A plasma analyser according to claims 1 or 2, further comprising a computer which uses output from the fast counter to adjust parameters of power supply to the electrode.
- 4. A plasma analyser according to claims 1, 2 or 3, in which the fast multiplier is an analog multiplier.
- 5. A plasma analyser according to any one of claims 1 to 4, in which the fast integrator is an analog integrator.
- 6. A plasma analyser according to any one of claims 1 to 5, in which the fast comparator is a high speed differential comparator.
- 7. A plasma analyser according to any one of claims 1 to 6, in which the fast counter is a digital counter.
- 8. A method of controlling a reaction at an electrode of a non-thermal plasma or corona reactor to which high frequency electrical power is supplied from a pulser to produce plasma or corona microdischarges at the electrode, which comprises:
(a) measuring voltage (v) at the electrode in real-time as the reaction proceeds;
(b) measuring current (i) at the electrode in real-time as the reaction proceeds;
(c) multiplying v × i by means of a fast multiplier to obtain instantaneous power (p) values;
(d) integrating the v ×i = p values over time of the microdischarges by a fast integrator to give energy (e) values thereof;
(e) comparing in real time the i, p and/or a values against preselected i, p and/or a threshold values;
(f) counting the microdischarges that exceed the predetermined threshold values; and (g) adjusting electrical parameters of the pulser in real time so as to optimize the reaction at the electrode; - 9. Method according to claim 8, further comprising measuring zero cross microdischarges at the electrode and counting the same to evaluate the overall plasma or corona activity.
- 10. Method according to claims 8 or 9, in which the electrical parameters of the pulser are adjusted by computer according to a predetermined model which correlates the obtained i, p and/or a counts with the electrical parameters required for optimum reaction results.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2365955 CA2365955A1 (en) | 2001-12-17 | 2001-12-17 | Plasma analyser |
| AU2002350311A AU2002350311A1 (en) | 2001-12-17 | 2002-12-13 | Plasma analyser |
| PCT/CA2002/001906 WO2003052432A2 (en) | 2001-12-17 | 2002-12-13 | Plasma analyser |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2365955 CA2365955A1 (en) | 2001-12-17 | 2001-12-17 | Plasma analyser |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2365955A1 true CA2365955A1 (en) | 2003-06-17 |
Family
ID=4170943
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2365955 Abandoned CA2365955A1 (en) | 2001-12-17 | 2001-12-17 | Plasma analyser |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU2002350311A1 (en) |
| CA (1) | CA2365955A1 (en) |
| WO (1) | WO2003052432A2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2707704B1 (en) * | 2011-05-13 | 2019-04-24 | DBD Innovations Pty Ltd | Method of analyzing a material |
| CN109298235B (en) * | 2018-08-17 | 2021-05-28 | 北京优诺信创科技有限公司 | Micro-discharge power dynamic tracking method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5017876A (en) * | 1989-10-30 | 1991-05-21 | The Simco Company, Inc. | Corona current monitoring apparatus and circuitry for A.C. air ionizers including capacitive current elimination |
| US5570175A (en) * | 1994-03-07 | 1996-10-29 | Ceram Optec Industries Inc. | Method for determination of degree of molecular dissociation in plasma using combined electrostatic measurement and emission spectroscopy |
| US5822981A (en) * | 1996-08-19 | 1998-10-20 | Hughes Electronics Corporation | Automatic control system and method for corona discharge pollutant destruction apparatus |
-
2001
- 2001-12-17 CA CA 2365955 patent/CA2365955A1/en not_active Abandoned
-
2002
- 2002-12-13 AU AU2002350311A patent/AU2002350311A1/en not_active Abandoned
- 2002-12-13 WO PCT/CA2002/001906 patent/WO2003052432A2/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO2003052432A3 (en) | 2003-09-12 |
| AU2002350311A1 (en) | 2003-06-30 |
| WO2003052432A2 (en) | 2003-06-26 |
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