EP0828687A1

EP0828687A1 - Ozone generator with in-line sensor

Info

Publication number: EP0828687A1
Application number: EP95919291A
Authority: EP
Inventors: William E. Davidson
Original assignee: Vasogen Inc
Current assignee: Vasogen Inc
Priority date: 1995-05-26
Filing date: 1995-05-26
Publication date: 1998-03-18
Also published as: JPH11505797A; WO1996037432A1; AU2520095A

Abstract

An apparatus for generating ozone from an oxygen supply. The apparatus comprising grids mounted in an enclosure and a high voltage circuit coupled to the grids for generating an electric field. The high voltage circuit receives AC power and includes a control circuit for producing a linearly controlled high voltage output from the AC feed for energizing the grids. The apparatus also includes an in-line sensor for determining the level of ozone being produced without affecting the ozone concentration. The high voltage circuit is also suitable for other applications where a precisely controlled high voltage output signal is needed.

Description

OZONE GENERATOR WITH IN-LINE SENSOR

This invention relates to apparatus for generating ozone gas, and more particularly to an apparatus with an in-line sensor which is suitable for applications in which the concentration of ozone gas needs to be carefully controlled.

In the art, ozone generators are well-known. United States Patent 5,052,382, which issued to Wainwright on October 1, 1991, describes an apparatus for the controlled generation and administration of ozone gas. The apparatus disclosed by Wainwright comprises a generator for generating the ozone, a monitor for monitoring the ozone, a dosage device for providing the amount of ozone and a computer for controlling operation of the apparatus.

While Wainwright discloses an ozone generating apparatus suitable for medical application, there are aspects which affect the performance and accuracy of the device. The monitor or sensor taught by Wainwright comprises an ultra violet light source and a strobed detector. The detector is strobed by a zeon light source, but according to Wainwright, it may be strobed by another light source. As will be understood by those skilled in the art, this arrangement comprises an intrusive measurement technique. According to this technique, the ozone and oxygen gas stream is exposed to ultra violet light. The UV light interacts with the ozone and the amount of UV light which is measured by the sensor will be dependent on the concentration of the ozone gas. Because there is an interaction between the UV light and the ozone gas, the UV light affects the concentration of the ozone gas which is produced by the generator. Therefore, the ozone generator taught by Wainwright is not well-suited for applications where the ozone concentration must be very accurately controlled, nor is the Wainwright device suited for an application where the ozone sensor is in-line with the treatment. It is object of the present invention to provide an apparatus for generating ozone gas having an electronic circuit capable of carefully controlling the_. amount of ozone being generated. It is another object of the present invention to provide an apparatus for generating ozone gas having a non-intrusive sensor for sensing the concentration of the ozone gas being produced. It is another object of the present invention to provide an ozone sensor which can be located "in-line" with the treatment path.

According to one aspect of the present invention, there is provided an apparatus for generating ozone from an oxygen supply, said apparatus comprising: (a) an enclosure having an inlet for receiving said oxygen supply and an outlet for releasing said ozone and said oxygen; (b) a plurality of grids mounted inside said enclosure and said grids being separated by plates; (c) energizer means for energizing said grids, said energizer means having a control input for receiving a control signal and an input port for connecting to a power source; and (d) said energizer means including generator means for generating a high voltage output coupled to said grids for energizing said grids and producing an electric field, and said generator means being responsive to said control signal.

According to another aspect of the present invention, there is provided a bridge network and control circuit for linearly controlling an AC signal. The apparatus for linearly controlling an AC signal comprising (a) a bridge network having an input port for receiving an AC signal, and said bridge network including a switching control input and a bridge output port; (b) a control circuit having an input for receiving a control signal and an output coupled to the switching control input of said bridge network, and said control circuit having means for generating a switching control signal at said output for switching said bridge network and producing a controlled power signal at said bridge output port; and (c) a transformer having an output port and an input port coupled to the output port of said bridge output port and means responsive to said controlled power signal for producing a high voltage output signal at said output port.

Reference will now be made to the drawings which illustrate, by way of example, a preferred embodiment of the present invention,

FIGURE 1 is a diagrammatic illustration of an apparatus according to a specific embodiment of the present invention; and

FIGURE 2 is a schematic diagram of the control circuitry for the embodiment shown in Fig. 1.

Reference is first made to Figure 1 which shows an ozone generator 1 according to the present invention. The ozone generator 1 is suitable for the generation of carefully measured amounts of ozone gas and has particular though by no means exclusive application to medical applications. The apparatus and particularly the control circuit have wider applicability, such as applications where high voltage needs to be carefully controlled.

As shown in Figure 1, the ozone generator 1 comprises a housing or enclosure 10. The housing 10 is formed from PTFE material commonly known as Teflon™, preferably medical grade. Teflon is preferred because it is an inert substance which is impervious to ozone and preferably the housing 10 is milled from a solid block of Teflon™. The housing 10 can also be made from Kynar™ material available from the Pennwalt Corporation and other compositions such as CPCVC or silicon which are of medical grade. As shown, the housing 10 includes a lid 12 which is also made from medical grade Teflon™. The lid 12 is attached to the enclosure 10 by secure fasteners 14, for example, precision screws. The enclosure 10 includes an inlet port 16 and an outlet port 18. The inlet 16 provides the input for oxygen gas 24 and is coupled to an oxygen supply tank 20 through a gas flow control valve 22. The gas flow control valve 22 is coupled to control circuit 32 through a stepper motor 23 or other appropriate actuator. A flow meter 25 is also included which provides the rate of flow of the oxygen gas 24 into the enclosure 10. The outlet port 18 provides an output for gas 26 comprising oxygen and ozone produced by the generator 1. As shown in Figure 1, a temperature sensor 19 can also be provided to sense the temperature inside the enclosure 10. The control circuit 32 uses the temperature readings to control the production of ozone.

The ozone generator 1 includes a series of grids or electrodes 28a,28b,28c which are mounted in a spaced relationship inside the chamber 11 formed by the enclosure 10 as shown in Figure 1. Preferably, the grids or electrodes 28a,28b,28c are made from high-grade stainless steel. A pair of mica sheets 30a,30b separate the grids 28. The ozone generator 1 has a control circuit and power supply module 32. The control circuit 32 is powered by conventional AC power 34, i.e. mains supply. The control circuit 32 has a high voltage output 36 which connects to the grids 28a,28b,28c. The control circuit 32 biases the grids 28a,28b,28c to a high voltage level to produce an electric field which causes the formation of ozone gas 0₃ in the stream of oxygen 24 which enters the chamber 11 through the inlet port 16 and passes over the electrodes 28. The circuit 32 uses the gas flow control valve 22 to regulate the amount of oxygen 24 entering the chamber 11. The ozone generator 1 can also include a relay 33 (Figure 2) as a safety feature which is activated by the control circuit 32 to enable the high voltage feed to the electrodes 28.

Reference is next made to Figure 2, which shows the control circuit 32 in more detail. The control circuit 32 preferably comprises a microprocessor-based circuit suitably programmed for operating the gas flow control valve 22 and the ozonizer 1.

As shown in Figure 2, the control circuit 32 comprises a microcontroller 38, a high voltage drive circuit 40, a high voltage transformer 42, and a sensing circuit 44. The high voltage drive circuit 40 is connected to the transformer 42 which produces the high voltage output for biasing the grids 28. The sensing circuit 44 is coupled to the output of the transformer 42 and is used by the microcontroller 38 to determine the amount of ozone gas 0₃ being generated as will be described below.

The high voltage drive 40 has an input 46 connected to an output port of the microcontroller 38 for receiving a control signal 48. The control signal 48 comprises a pulse train which is generated by the microcontroller 38. The high voltage drive circuit 40 as shown in Figure 2 comprises a bridge network 50 and a bridge control circuit 52. The bridge network 50 comprises four diodes 50a, 50b, 50c, 50d connected in a bridge configuration. As shown in Figure 2, the bridge network 50 couples the "live" AC voltage 34 to the primary winding of the high voltage transformer 42. The current flowing in the primary winding of the transformer 42 is controlled by the circuit 52 which is coupled to the other port 54 of the bridge 50. The current which flows in the bridge 50 and primary winding induces a voltage in the secondary winding of the high voltage transformer 42 which biases the grids or electrodes 28 (Figure 1) .

The function of the bridge network 50 and the bridge control circuit 52 is to regulate the current flowing in the primary winding and thereby the high voltage induced in the secondary winding of the transformer 42 and applied to the grids 28. By regulating the high voltage applied to the grids 28, the amount of ozone gas 0₃ which is generated can be carefully controlled. As will be described, the bridge control circuit 52 together with the control signal 48 regulate both the shape and level of the high voltage signal which biases the electrodes 28, thereby providing accurate control for the production of ozone.

The bridge control circuit 52 comprises an input transistor 56, an isolation transformer 58 and an output transistor 60. The isolation transformer 58 is needed because the bridge network 50 is "floating" at 110 VAC (or 220 VAC) . The base of the transistor 56 forms the input 46 for receiving the control signal 48 from the microcontroller 38. The control signal 48 comprises a pulse train generated by the microcontroller 38. According to the invention, either the pulse width or the frequency of the control signal 48 can be varied to control the current flowing through the bridge 50 and the primary winding of the transformer 42. The pulse width (or frequency) of the control signal 48 is selected to produce a target ozone level and the actual amount of ozone being produced is determined through the sensing circuit 44. The collector of the transistor 56 is connected to the primary winding of the isolation transformer 58 so that the pulse train produced by the signal 48 is induced in the secondary winding of the transformer 58. The secondary winding of the transformer 58 is connected to a diode 62 and a capacitor 64. The diode 62 rectifies the output from the secondary winding of the isolation transformer 58 and charges the capacitor 64 to generate a DC voltage. The base of the output transistor 60 is connected to the capacitor 64 through a resistive divider formed from resistors 66,68. Another resistor 70 is connected to the emitter of the transistor 60 to limit the current flowing through the transistor 60. The values of the resistors are chosen to operate the output transistor 60 in the linear or active region. By operating the output transistor 60 in the active region, a sinusoidal output from the bridge 50 is produced thereby allowing precision linear control of the voltage output from the secondary winding of the transformer 42 which is applied to the grids or electrodes 28.

The sensing circuit 44 is coupled to the secondary winding of the high voltage transformer 42 and provides the microcontroller 38 with data for determining the amount of ozone gas 0₃ being produced. The microcontroller 38 uses this information to control the operation of the ozone generator 1. The microcontroller 38 can be programmed to respond to commands from another computer (not shown) or the microcontroller 38 can include an input panel (not shown) for manually setting the desired ozone gas level.

Figure 2 also shows the sensing circuit 44 in more detail. The sensing circuit 44 produces an output signal 72 corresponding to the discharges occurring in the chamber 11 which are also related to the production of ozone gas 0₃ from the oxygen 24. The microcontroller 38 uses the output 72 from the sensing circuit 44 to calculate the amount of ozone gas 0₃ being generated by the ozonizer 1. Each time there is a discharge between the electrodes 28 mounted in the chamber 11 (Figure 1) , a pulse is produced in the winding of the high voltage transformer 42. A pickup coil 74 is electromagnetically coupled to the winding of high voltage transformer 42 and pulses due to discharges will induce a current in the pickup coil 74. The sensing circuit 44 detects these pulses and produces the output 72 for the microcontroller 38.

Referring to Figure 2, the sensing circuit 44 comprises a diode 76, a capacitor 78, a resistor 80 and an operational amplifier 82. The operation amplifier 82 (op amp) is configured as a voltage follower or unity gain buffer and functions as an isolating circuit. The capacitor 78 is charged through the diode 76 by the induced voltage in the pickup coil 74 and provides an input voltage for the op amp 82. The op amp 82 produces a corresponding output pulse 72 which is inputted by the microcontroller 38. The microcontroller 38 includes program code which determines the amount of ozone 0₃ produced by the discharge by calculating the area of the pulse. The readings from the flow rate meter 25 are factored into the calculation. Preferably the temperature inside the enclosure 11 is also taken into account, i.e. as the temperature inside the enclosure 11 rises the voltage to the grids 28 needs to be increased. If the stream of oxygen 24 comprises medical grade oxygen then there is a direct correspondence between the input energy and the amount of ozone 0₃ generated. If the oxygen 24 does not comprise medical grade oxygen, i.e. pure oxygen, then a correction factor is introduced into the calculation.

A significant advantage of the sensing circuit 44 and microcontroller 38 arrangement according to the present invention is the capability to perform an ozone measurement "in-line". Because the measurement can be taken in-line, the problem of the ozone gas 0₃ being contaminated or altered by the measurement technique is eliminated. The microcontroller 38 can be implemented using the commercially available PIC16C71 microcontroller available from Microchip Technologies Inc. which has been suitably programmed to perform the processing steps according to the present method. The PIC16C71 controller is a single chip device comprising a microprocessor and "on-chip" program memory, data memory, input/output ports, timers and other on-chip resources.

The control loop for controlling the operation of the ozone generator l is preferably implemented as a closed control loop which is realized using a PID (Proportional plus Integral plus Derivative) control mode. A proportional control system operates by first determining the actual value of the quantity to be controlled and the desired value, i.e. set-point, and then applying a correction proportional to this difference. The microcontroller 38 controls the amount of ozone gas 0₃ being generated by regulating and monitoring the amount of oxygen 24 entering the chamber 11 and/or the voltage applied to the grids 28. The addition of the integral and derivative terms in the transfer function improves the performance of the control loop. For the ozone control loop, the derivative term is selected to compensate for the sequential lag of the output from electrodes 28 and the generation of ozone gas 0₃ in the chamber 11. The implementation of the control loop in software will be within the understanding of those skilled in the art and further explanation is not needed.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the presently discussed embodiments are considered to be illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

I CLAIM :

1. An apparatus for generating ozone from an oxygen supply, said apparatus comprising:

(a) an enclosure having an inlet for receiving said oxygen supply and an outlet for releasing said ozone and said oxygen;

(b) a plurality of grids mounted inside said enclosure and said grids being separated by plates;

(c) energizer means for energizing said grids, said energizer means having a control input for receiving a control signal and an input port for connecting to a power source; and

(d) said energizer means including generator means for generating a high voltage output coupled to said grids for energizing said grids and producing an electric field, and said generator means being responsive to said control signal.

2. The apparatus as claimed in claim 1, further including means for determining the amount of ozone being produced comprising sensor means coupled to the high voltage output of said generator means for sensing discharge current produced by interaction of said oxygen and said electric field in formation of said ozone, and means for calculating amount of ozone from the energy in said discharge current and concentration and flow rate of said oxygen supply.

3. The apparatus as claimed in claim 2, further including a temperature sensor for producing a temperature reading signal indicative of the temperature in said enclosure and said means for calculating being responsive to said temperature reading.

4. The apparatus as claimed in claim 1, wherein said generator means for generating a high voltage output comprises a transformer having an input port and an output port and a bridge network having an input for connecting to said power source and an output coupled to the input port of said transformer and a bridge control input, and said generator means including a switching circuit coupled to the bridge control input for switching said bridge network in response to said control signal to produce said high voltage output at the output port of said transformer.

5. The apparatus as claimed in claim 1, wherein said enclosure is formed from medical grade teflon material .

6. The apparatus as claimed in claim 1, 2 or 4, wherein said control signal comprises a pulse width modulated signal.

7. An apparatus for linearly controlling an AC signal, said apparatus comprising:

(a) a bridge network having an input port for receiving an AC signal, and said bridge network including a switching control input and a bridge output port;

(b) a control circuit having an input for receiving a control signal and an output coupled to the switching control input of said bridge network, and said control circuit having means responsive to said control signal for generating a switching control signal at said output for switching said bridge network and producing a controlled power signal at said bridge output port; and

(c) a transformer having an output port and an input port coupled to the output port of said bridge output port and means responsive to said controlled power signal for producing a high voltage output signal at said output port.

8. The apparatus as claimed in claim 7, wherein said means for generating a switching control signal comprises a transistor.

9. The apparatus as claimed in claim 7 or 8, wherein said control signal comprises a pulse width modulated signal.

10. The apparatus as claimed in claim 7 or 8, wherein said control signal comprises a square wave having a variable frequency.