HK1084982B - Method for inhibiting corrosion of metal - Google Patents

Description

Method for inhibiting corrosion of metals

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patent application No. 10/010,402 (filed 12/7/2001), currently U.S. patent No. 6,875,336, which is a continuation-in-part application of U.S. patent application No. 09/527,552 (filed 3/17/2000), now U.S. patent No. 6,331,243, which is a continuation-in-part application of U.S. patent application No. 09/066,174, currently U.S. patent No. 6,046,515, which claims the rights of U.S. provisional application No. 60/044,898 (filed 25/4/1997), the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a method and apparatus for preventing oxidation of a metal object (article) in an oxidizing environment. More particularly, the present invention relates to an apparatus and method for generating surface currents on conductors to inhibit corrosion.

Background

In an oxidizing environment, the material accepts electrons and is reduced under suitable conditions. These electrons typically come from atoms of the metal object that are exposed to the oxidizing environment. The oxidizing environment is characterized by the presence of at least one chemical species, the atoms of which can be reduced in the environment by obtaining at least one electron originating from an atom of the metal. In the case of "donating" electrons, the metal is oxidized. As the oxidation process continues, the metal objects degrade to a point where they can no longer be used for their intended purpose.

On land, oxidation occurs in general, especially in bridges and vehicles, when they are exposed to salts which are spread on the road surface in cold climates to prevent the formation of ice. The salt melts the snow and ice and forms an aqueous salt solution. Iron or steel in bridges and vehicles is easily oxidized when exposed to a salt solution. The first visible sign of oxidation is the appearance of rust on the surface of the metal object. Continued oxidation can result in a weakening of the structural integrity of the metal object. If the oxidation is allowed to continue, the metal object will rust through and eventually disintegrate, or, in the case of metals in bridges, will become too brittle to support its load. This situation has become more severe in recent years as the concentration of pollutants has increased and the demand for lighter, more fuel efficient vehicles requiring thinner sheet metal and the abandonment of main architectures.

Brine solutions are also responsible for corrosion in marine environments and for oxidation of the hull of ships, subsea pipelines, and drilling and production platforms used in the oil industry.

Early methods of preventing corrosion relied on applying a protective coating (e.g., paint) to the metal object. Which prevents the metal from coming into contact with the oxidizing environment and thus prevents corrosion. However, over time, the protective coating may peel off and the oxidation process of the metal may begin. The only way to prevent the onset of oxidation is to reapply the coating. This is an expensive process in the best case: it is much easier to thoroughly coat automobile parts than to recoat an assembled automobile before assembling the automobile in a factory. In other cases, such as subsea pipelines, a recoating process is not possible.

Other methods of preventing oxidation include cathodic protection systems. Wherein the metal object to be protected is used as the cathode of the circuit. The metal object to be protected and the anode are connected to a source of electrical energy and the electrical circuit is completed from the anode to the cathode through the aqueous solution. The flow of electrons provides the necessary source of electrons to species in the aqueous solution that typically cause oxidation, thus reducing the "donation" of electrons from the metal (cathode) atom to be protected.

The invention of Byrne (U.S. patent No. 3,242,064) provides a cathodic protection system in which pulses of Direct Current (DC) are applied to a metal surface to be protected, such as the hull of a ship. The duty cycle of the pulses is varied to respond to various conditions of the water surrounding the hull of the vessel. Kipps (U.S. patent No. 3,692,650) discloses a cathodic protection system for use in well casings and pipes buried in conductive soil, the interior surfaces of tanks containing corrosive materials, and submerged portions of buildings. The system uses a short pulsed DC voltage and continuous direct current.

Prior art cathodic protection systems are not entirely effective for objects or structures immersed in a conductive medium, such as seawater. The reason for this is that local "hot spots" of corrosion development are improperly protected due to local changes in the shape of the protected structure and the concentration of oxidizing species in the aqueous environment, eventually resulting in the collapse of the structure. Cathodic protection systems are rarely used to protect metal objects that are not only partially immersed in a conductive medium, such as seawater or conductive soil. As a result, the bridge metal beams and the vehicle body cannot be effectively protected by these cathode systems.

Cowatch (U.S. Pat. No. 4,767,512) provides a method for the purpose of preventing corrosion of objects that are not immersed in a conductive medium. An electric current is applied to the metal object by processing the metal object into a cathode plate of a capacitor. This is achieved by a capacitance coupled between the metal object and the means for providing the dc pulse. The metal object to be protected and the means for providing a direct current pulse have a common ground. In its preferred embodiment, Cowatch discloses a device in which a DC voltage of 5,000 to 6,000 volts is applied to the anode plate of a capacitor separated from the metal object by a dielectric. A small, high frequency (1 khz) pulsed DC voltage is superimposed on the regulated DC voltage. Cowatch also indicates that the breakdown voltage of the dielectric material is about 10 kV.

Because of the safety hazard of high voltage applications to areas where humans and animals may come into contact with metal objects or any other part of the capacitive coupling, Cowatch requires the limitation of the maximum energy output of the present invention.

Cowatch discloses a two-stage device for obtaining a pulsed DC voltage. The first stage provides outputs of a higher voltage AC and a lower voltage AC. In the second phase, the two AC voltages are corrected to provide a high voltage DC with overlapping DC pulses. Cowatch uses at least two transformers, one of which is a push/pull saturated core transformer. The energy losses associated with this invention are high due to the use of transformers. According to the disclosed values in Cowatch, the efficiency can be very low (less than 10%). Dissipation of high heat also requires a method of heat dissipation. Furthermore, the invention requires a separate device for shutting down the device during the duration of non-use to prevent battery discharge.

Some of the problems associated with affecting submerged structures are caused by the growth of organisms. Mussels, for example, are a serious problem in municipal water supply systems and power plants. Due to its rapid growth, it blocks the water inlet required for the water supply system or the power plant to function properly, resulting in a reduction of the water flow. Expensive cleaning operations must be performed regularly. Barnacles and other organisms are well known for attachment to the hull of ships and submerged parts of other structures. Conventional means of dealing with these problems include the use of anti-fouling coatings and regular thorough cleaning. The coating may have undesirable environmental effects but the cleaning is an expensive process and the vessel needs to be taken out of service when cleaned. Neither of these methods is effective for long-term operation.

It is an object of the present invention to provide corrosion protection of metal objects even if the object to be protected is not immersed in an electrolyte. Another object of the invention is to accomplish this without exposing humans or animals to the risk of high voltage. In addition, the device should also be energy efficient, thus reducing power consumption and not requiring any special means for heat dissipation. It should also have a battery voltage monitor as part of the circuit that turns off the pulse amplifier if the battery voltage drops below a predetermined threshold, thus conserving battery power. This is particularly useful because corrosion under cold weather conditions is more likely to occur due to exposure to salts used to melt ice on the road surface, which also results in a greater demand on the battery at vehicle start-up. In addition to cold climates, high temperatures and humidity also cause increased corrosion and increased battery power requirements for vehicle start-up. It is another object of the present invention to inhibit the growth of organisms on submerged structures. Finally, another object of the invention is to prevent circuit damage if the device is accidentally in contact with a battery having a reversed polarity.

Therefore, it is desirable to provide improved control of corrosion protection.

Disclosure of Invention

It is an object of the present invention to obviate or mitigate at least one disadvantage of previous corrosion inhibition methods. In particular, it is an object of the present invention to provide a circuit and a method for reducing the corrosion rate of a metal object.

In a first aspect, the present invention provides a method of reducing the rate of oxidation of a metal object. The method comprises the following steps: generating an electrical waveform; coupling an electrical waveform to a metal object; and inducing a surface current on the entire surface of the metal object in response to the electrical waveform. The electrical waveforms have predetermined characteristics and are generated by a DC voltage source such that each waveform has a transient AC component.

In an embodiment of the present aspect, the coupling step includes driving the electrical waveform through at least two contact points on the metal object, the generating step may include generating the electrical waveform having a shape for generating an AC component, and the electrical waveform may include a resonant frequency of the metal object. In another embodiment of the present aspect, the coupling step can include capacitively coupling the electrical waveform from a first terminal connected to the metal object to a second terminal, wherein the second terminal is connected to a ground terminal of the DC voltage source.

In another embodiment of the present aspect, the step of capacitively coupling may include charging a capacitor from the DC voltage source and discharging stored charge of the capacitor through the metal object to a ground connection between the DC voltage source and the metal object in response to the electrical waveform. In another aspect of this embodiment, the capacitor may be mechanically charged, a first terminal of the capacitor may be connected to the metal object, and a second terminal of the capacitor may be connected to a region of the metal object remote from the ground connection, and the polarity of the DC voltage source is reversed after discharging the stored charge.

In an alternate embodiment of the present aspect, the capacitively coupling step can include charging a capacitor from the DC voltage source and discharging stored charge of the capacitor to a distribution capacitor coupled to the metal object in response to the electrical waveform, wherein the induced surface current moves in a first direction in response to an accumulation of stored charge on the distribution capacitor. In one aspect of this embodiment, the coupling step can include moving a magnetic field over the metal object at a frequency corresponding to the predetermined frequency of the signal pulses.

According to another alternative embodiment of the present aspect, the coupling step may include transmitting an RF signal corresponding to the electrical waveform received by the metal object through an antenna, the generating step may include generating the electrical waveform having rise and fall times of about 200 nanoseconds, and the generating step may include generating a unipolar DC electrical waveform or a bipolar DC electrical waveform.

In a second aspect, the present invention provides a circuit for reducing the rate of corrosion of a metal object. The circuit includes a charging circuit having a DC voltage source, and a current generating circuit coupled to the metal object. The charging circuit has a DC voltage source for providing a capacitive discharge, wherein terminals of the DC voltage source are connected to the metal object. The current generating circuit is coupled to the metal object for receiving and shaping a capacitive discharge from the charging circuit, the current generating circuit coupling the shaped capacitive discharge to the metal object to induce a surface current therein.

In an embodiment of the present aspect, the charging circuit may include a capacitor in parallel with the DC voltage source, and a switching circuit for coupling the capacitor to the DC voltage source in a charging position for charging the capacitor, the switching circuit coupling the capacitor to an output in a discharging position for discharging the capacitor. The current generating circuit may include an impedance device coupled between the output and the metal object for providing a shaped current waveform to which a surface current induced as the shaped current waveform is applied. The DC voltage source may include a polarity switch circuit for reversing the polarity of the DC voltage source.

In one aspect of the embodiment, the current generating circuit may include a distribution capacitor coupled to the metal object, an impedance device coupled between the output and the distribution capacitor, the impedance device to provide a shaped current waveform, the distribution capacitor to receive charge from the shaped current waveform to induce the surface current, and a discharge circuit to discharge the charge of the distribution capacitor to the terminal to induce a second surface current in a direction opposite the surface current. The discharge circuit may include a second impedance device coupled between the distribution capacitor and a discharge switch circuit that selectively couples the second impedance device to the terminal. The distributed capacitor may include at least two parallel independent plates, wherein each of the at least two parallel independent plates has a different surface area.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGS. 1A and 1B are prior art circuit diagrams of Cowatch;

FIG. 2 is a schematic view of the apparatus of the present invention;

FIGS. 3A, 3B and 3C are circuit diagrams of a preferred embodiment of the present invention;

FIG. 4 is an alternative embodiment of the present invention;

FIG. 5 is a preferred embodiment of the preferred phase compensation of the present invention;

FIG. 6 is a circuit for capacitively coupling an electrical waveform to a metal object according to an embodiment of the present invention;

FIG. 7 is a circuit for capacitively coupling an electrical waveform to a metal object according to another embodiment of the present invention; and

FIG. 8 is a graph of corrosion potential versus time for a test panel and a control panel.

Detailed Description

The present invention generally provides a method for reducing the rate of corrosion in a metal object by inducing a surface current across the entire surface of the metal object. The surface current may be induced by directly or indirectly applying an electrical waveform (electronic waveform) having an AC component in response to the electrical waveform generated by the circuit. The electrical waveform has a time varying component having characteristics such as frequency spectrum, repetition rate, rise/fall time, pulse, sinusoid, and a combination of pulse and sinusoid. The negative terminal of the metal body and a suitable power source, such as a DC voltage (battery), is grounded. The positive terminal of the DC voltage source is connected to an electronic circuit that passes a low voltage electrical waveform to a conductive terminal connected to the metal body. The time-varying AC component in the electrical waveform used to induce the surface current is effective in suppressing corrosion, and therefore its generation is advantageous. Alternative methods of inducing surface currents include direct capacitor discharge via a metal body, or movement of an electromagnetic field on a metal body, or by generating a signal with a suitable waveform from an RF source attached to a transmitting antenna so that the transmitted signal can be received by the metal body.

According to embodiments of the present invention, the generation of an electrical waveform having a shape conduction to generate the time-varying (AC) component is effective to reduce the oxidation rate. The electrical waveform may, but need not, include a frequency at which the metal object resonates. The electrical waveform of the unipolar pulses with a nominal period of 100uS, a width of 3uS and rise and fall times of about 200 nanoseconds has proven effective in preventing corrosion even when the electrolyte is absent. It is known that: i) it has been determined that the surface current induced on the metal body by the electrical waveform is responsible for the reduced corrosion rate; and i) in principle, any electrical waveform having an AC component can induce a surface current on a metal object when properly coupled thereto. Thus, it should be clear that the possible number of suitable electrical waveforms suitable for reducing the rate of corrosion is virtually unlimited. These surface currents can be attributed to skin effect phenomena, where high frequency currents have a tendency to distribute themselves with higher current densities near the surface of the conductor than in its core.

The invention is best understood by first referring to prior art methods of preventing oxidation of metals by capacitive coupling. Fig. 1A shows a circuit diagram of a push/pull saturated core transformer for the invention of Cowatch. Typically, terminal 1 is connected to the positive side of the vehicle's electrical system and terminal 2 is connected to the negative side of the vehicle's electrical system. The output of transformer 81 has three taps 21, 22 and 23. Tap 21 provides the system ground, 22 provides 12 volts AC and 23 provides 400 volts AC. The output from the first stage is fed to a second stage, a rectified pulsator, the circuit diagram of which is shown in fig. 1B. A 400 volt AC supply 50 from 23, a 12 volt AC connection 51 from 22 and a ground connection 21 to 52. The output of the rectified pulsator (between 77 and 73) is 400 volts DC with 12 volt pulses superimposed on the 400 volts DC.

The specific configuration of the circuits of fig. 1A and 1B is now described. In fig. 1A, core 81, capacitor 4 and resistor 5 at connection 3 are connected in parallel to terminal 1. A transistor 6, a diode 7, a capacitor 8 and a resistor 9 are also connected in parallel to the resistor 5. Capacitor 4, transistor 6, diode 7, transistor 10 and diode 11 are connected in parallel to connection 2 to the negative side of the electrical system of the vehicle. The transistor 10 is connected at point 12 (input to the primary winding) to a second winding 14 which surrounds a saturable ferrite core transformer 81. Transistor 10 is also connected to a third winding 15 around transformer 81 at point 13 (output feedback). Capacitor 8 and resistor 9 are connected at point 16 (from the feedback output) to a third winding 15 around transformer 81. Transistor 6 is connected at point 17 (input to the primary winding) to a first winding 18 around transformer 81. The first coil 18 and the second coil 14 are each 7 turns of 20 gauge wire. The third coil 15 is 9 turns of 20 gauge wire. The fourth coil 19 is 225 turns of No. 30 wire and the fifth coil 20 is 10 turns of No. 30 wire.

In fig. 1B, diodes 59 and 60 are connected in parallel to 400 volts AC input at point 50. The 12 volt AC input at point 51 is connected in parallel to diodes 53 and 54. Diodes 55, 56, 57 and 58 are connected in parallel to system ground at the input of point 52. Capacitors 61 and 62, resistor 65, SCR76, diode 69 and first coil 78 connected at point 71 to a surrounding pulse transformer core 80 are connected in parallel with diodes 53, 56, 57 and 60. Capacitor 61, resistor 67 and resistor 66 are connected in parallel to diodes 54 and 55. A capacitor 62 and a transistor 75 are connected in parallel to the resistor 67. Resistor 66 is connected to transistor 75. Resistor 65 and SCR76 are connected in parallel to transistor 75. Resistor 68 is connected in parallel to diodes 58 and 59. SCR76, diode 69 and capacitor 64 are connected in parallel to resistor 68. Capacitor 64 is connected at point 72 to a first coil 78 that surrounds a pulse transformer core 80. A second coil 79 surrounding the pulse transformer core 80 is connected to the diode 70 at point 74. High voltage rectifier diode 70 is connected to output point 77. The ratio of the number of turns of the first coil 78 to the number of turns of the second coil 79 around the pulse transformer core 80 is 1: 125.

The prior art invention provides high voltage DC with low voltage pulses superimposed on the high voltage DC to the anode plate of a capacitor connected between 73 and 77. The anode plate of the capacitor is separated from and coupled to the grounded metal object by a capacitive spacer.

FIG. 2 is a functional block diagram illustrating the operation of the apparatus of the present invention. Battery 101 is a DC power source for the present invention. One terminal of the battery is connected to ground 103. The positive terminal of the battery is connected to the reverse voltage protector 105. The reverse voltage protector prevents reverse battery voltage from being accidentally applied to other circuits and damaging elements.

The power regulator 107 converts the battery voltage to the appropriate voltage required by the microprocessor 111. In a preferred embodiment, the voltage required by the microprocessor is 5.1 volts DC. The battery voltage monitor 109 compares a reference voltage (12 volts DC in the preferred embodiment) to the battery voltage. If the battery voltage is higher than the reference voltage, the microprocessor 111 activates the pulse amplifier 113 and the power indicator 115. When the pulse amplifier is activated by a pulse signal having a positive output of the microprocessor, an amplified pulse signal having a positive output is generated by the pulse amplifier and transmitted to the pad 117. The pad 117 is capacitively coupled to the metal object 119 to be protected. When the power indicator 115 is activated, the power LED in the power indicator is turned on as an indicator that the pulse amplifier is activated. Of course, when the battery voltage falls below the reference voltage, all circuits except the circuit that detects the battery voltage may be turned off to minimize power consumption. If the battery voltage is too low, the use of the battery voltage monitor 109 prevents the depletion of the battery.

When the present invention is used to protect a metal object, such as an automobile body, the gasket 117 has a backing material made of a suitable dielectric, which in this case is similar to fine fiber glass and is attached to the object 119 by a high dielectric strength silicone adhesive. In a preferred embodiment, the substrate adhesive combination has a breakdown voltage of at least 10 kilovolts. The adhesive is preferably a fast-curing adhesive that is sufficiently curable within 15 minutes to secure the dielectric material to the metal object.

The details of the device shown in fig. 3A-3C are better understood by an overview of the invention in fig. 2. The nodes labeled with numbers 147, 149, 151, 153, 155, 157, and 159 in fig. 3A are connected to the correspondingly labeled nodes in fig. 3C. The positive terminal of a typical automotive battery powered unit is connected to a terminal 133 on the connection plate 131. The negative terminal of the battery is connected to the vehicle body ("ground") and to a terminal 137 on the connection plate 131. The pad 117 of fig. 2 is connected to a terminal 139 on the connection plate 131 when the metal object 119 to be protected in fig. 2 is connected to ground. The vehicle battery, gasket 117 and protected metal object 119 and their connections are not shown in fig. 3A.

The reverse voltage protection circuit 105 of fig. 2 includes the diode D of fig. 3A₃And D₄. In a preferred embodiment of the invention, D₃And D₄Is an IN4004 diode. Those skilled in the art will appreciate that with the diode configuration shown, the voltage at point 141 is not at a significant negative voltage relative to ground, even though the battery is connected to the connection board 131 having the opposite polarity. Which protects the electronic components from damage and improves the prior art. As shown in FIG. 3A, the VCC voltage source is connected to R₁、R₂、C₁、D₁And a common terminal for the VCC input of microprocessor 145.

The power regulator circuit 107 in fig. 2 is composed of a resistor R₁Zener diode D₁And a capacitor C₁And (4) preparing. Which converts the nominal battery voltage of 13.5 volts to the 5.1 volts required by the microprocessor. In a preferred embodiment, R₁Has a resistance of 330 Ω, C₁Capacitance with 0.1 muF and D₁Is an IN751 diode. As is well known to those skilled in the art, zener diodes have a high stable voltage drop for a wide range of currents.

Capacitor C₈、C₉And C₁₀And functions to filter the battery voltage and the reference voltage. In a preferred embodiment, each has a value of 0.2 μ F. C₈And C₉Can be replaced by a single capacitor having a value of 0.2 muf.

The battery voltage monitor includes a resistor R₂、R₃、R₄、R₅And R₆And a capacitor C₄And C₅. The voltage is monitored by a comparator in the microprocessor 145. Voltage divider comprising a resistor R₂And R₃Providing a pin P of a microprocessor 145₃₃Is stable reference. In a preferred embodiment, R₂And R₃Each having a resistance of 100K omega. Thus, with the Zener diode D₁At pin P of the microprocessor, a reference voltage of 5.1 volts₃₃Will be 2.55 volts. In the preferred embodiment, microprocessor 145 is Z86ED4M manufactured by Zilog.

The battery voltage is controlled by a resistor R₅And R₆Divided and applied to comparator input pin P₃₁And P₃₂. In a preferred embodiment, R₅Has a resistance of 180K omega and R₆With a resistance of 100K omega. The comparator in microprocessor 145 will be at pin P₃₁And P₃₂By R₅And R₆Divided battery voltage versus pin P₃₃The divided reference of 2.55 volts. Only at pin P₃₁And P₃₂Is reduced to be lower than the voltage at pin P₃₃The microprocessor senses the low battery voltage and stops sending signals to the pulse amplifier (discussed below). Via a resistor R₄Pin P₀₀Is connected to a resistor R₅And R₆The necessity of the contact point of (A) is increased because the comparator is only reflected on the pin P₃₁And P₃₂Is reduced to be lower than the voltage at pin P₃₃Of the reference voltage. Pin P₀₀The pulses are generated by the microprocessor at between about 0 volts and 5 volts per second. When pin P₀₀At zero volts, resistor R in the preferred embodiment₄With a resistance of 100K omega, then when the battery voltage is below 11.96 volts, at pin P₃₁And P₃₂Is lower than at pin P₃₃A reference voltage of 2.55 volts. When pin P₀₀At 5 volts, at P₃₁And P₃₂Is higher than 2.55 volts. In this way, the microprocessor can sense low battery voltage under continuous operation. Capacitor C₄And C₅Providing AC filtering of these voltages.

Those skilled in the art will appreciate that the cycling pin P is used between two voltage levels₀₀And a resistor R₄This is not necessary in other microprocessors whose comparators reflect the actual difference between the reference voltage and the battery voltage, rather than the transition of the battery voltage below the reference voltage.

The use of a microprocessor to generate pulses of DC voltage and a battery voltage monitor to shut down the device when the battery voltage falls below a reference level is an improvement over prior art approaches. However, those skilled in the art will appreciate that there are logic circuits known in the art, such as oscillator/pulse generator circuits, which may be used to generate pulses. The power indicator comprises an LED D₂Transistor Q₅And a resistor R₇、R₈And R₉. Transistor Q₅From at pin P₀₂Is driven by the positive output of the microprocessor. When the transistor Q₅When turned on, LED D₂And (4) brightening. If the battery voltage drops to the nominal 12V, the microprocessor will be on pin P₀₂Non-positive output and LED D₂And closing. When the battery voltage rises above the nominal 12 volts, the microprocessor will turn on pin P₀₂With positive output and LED D₂And (4) opening.

In the preferred embodiment, Q₅Is a 2N3904 transistor, R₇Having a resistance of 3.9 K.OMEGA.₈Has a resistance of 1K omega, and R₉Has a resistance of 10K omega.

The microprocessor also has a pin P when the battery voltage is above the nominal 12V₂₀An output pulse is generated. It is transmitted to a pulse amplifier comprising a resistor R₁₁-R₁₆And a transistor Q₁-Q₄. In the preferred embodiment, Q₁、Q₃And Q₅Is a 2N3904 transistor, Q₂And Q₄Is a 2N2907 transistor, R₁₁Having a resistance of 2.7 K.OMEGA.₁₂And R₁₃Each having a resistance of 1K omega, R₁₄And R₁₅Has a resistance of 390 Ω, and R₁₆Has a resistance of 1K omega. Capacitor R₇AC filtering for the pulse amplifier circuit is provided, and in the preferred embodiment, has a capacitance of 20 muf. The output of the pulse amplifier is applied via 139 in the connection plate 131 to a coupling pad 117 attached to the vehicle body. The output has a nominal amplitude of 12 volts.

The invention has no transformer, so it can reach high efficiency easily. Which reduces battery consumption and is an improvement over the prior art. In the preferred embodiment, pin P originates from the microprocessor₂₀Comprises pulses with nominal characteristics of 5V amplitude, 3 microseconds width and 10kHz repetition rate. For the pulsed electrical waveform, the rise and fall times of the amplified pulse signal applied to pad 117 determine its high frequency content and hence the temporal variation (temporal variation) in the electrical waveform. In the preferred embodiment, the rise time and fall time of each pulse forming the amplified pulse signal is about 200 ns.

The clock frequency of the microprocessor in the preferred embodiment is controlled by the inclusion of capacitor C₂And C₃And an inductor L₁Is determined. The circuit is more cost-effective than a quartz crystal used for controlling a microprocessor clock. Which is an improvement of the prior art. In the preferred embodiment, when the inductor L is used₁With an inductance of 8.2 muH, C₂And C₃With a capacitance of 100 pF. One skilled in the art will recognize other devices or circuits to provide the timing mechanism for the microprocessor.

Referring now to fig. 4, an alternate embodiment of the present invention is illustrated using an internal capacitor 160, leads 161 and posts 162 to deliver pulses to the metal object 119, rather than the capacitor pad 117. In fig. 4, the output of the pulse amplifier 113 is attached to the positive side of the capacitor 160. The negative side of capacitor 160 is attached to lead 161, which is attached to post 162. The output pulses from the pulse amplifier 113 are thus transmitted to the metal object 119 through a path formed by the capacitor 160, the wire 161, and the post 162 attached to the metal object 119.

Referring now to fig. 5, a preferred embodiment of the present invention is shown for a phase sensor and adjustment circuit for a system having two or more electrodes. The present invention provides two or more electrodes for attachment to a large metal structure, such as a water storage tank and a metal storage shed or a large vehicle. The first and second electrodes are attached to the metal structure or vehicle being treated so that the efficacy of the invention is applied at two or more points simultaneously. Each electrode applies a time-varying electrical waveform to the object being treated. A sinusoidal waveform is an example of a preferred waveform that may be applied, however any suitable waveform may be applied. A first electrode on the short cable is applied to one point on the metal object and a second electrode attached to the longer cable is applied to a second point on the metal object being treated. The phase sensor is used for adjusting signals, so that the phase synchronization relation of two applied signals is not influenced by different impedances of the long cable and the short cable. That is, the phase relationship of the signals applied to the metal object and the complex impedances of the first and second cables is determined, and the signals applied to each cable are phase compensated and adjusted so that the signals at the distal end of each cable are phase synchronized or are phase when applied to the metal object. A high voltage protection circuit is provided to protect the present invention from high voltage spikes or shocks. Variable speed flashing Light Emitting Diodes (LEDs) are provided to display full, critical, and low power levels.

As shown in fig. 5, first lead 161 and second lead 166 are driven by pulse amplifier 213 via signal lines 216 and 214, respectively, in response to signal pulses provided by microprocessor 111. Pulse amplifier 213 includes a phase delay circuit to adjust for any phase delay due to the impedance difference between cables 161 and 166, which may be of different lengths and therefore exhibit different impedances and phase delays. The different impedances in each cable tend to independently shift the phase of each output signal at the distal end of the cable when applied to the object via posts 162 or 167. Thus, the present invention provides phase compensation, i.e., phase sensing each output signal to the point of action of the stud or object, and appropriate phase compensation or delay to synchronize each output signal to phase. Thus, the present invention monitors and adjusts the phase of the output signal at each of the terminals 162 and 167. Otherwise, the applied signals are not phase synchronized and cause the output signal to be less effective. The phase of the signal applied by each stud is more effectively adjusted so that the peak value of each stud signal coincides with the peak value of the other studs applied to the metal object. Thus, the present invention ensures that each signal applied to each post of the metal object is phase synchronized.

The phase of each signal at each stud can be determined by attaching each stud 162 and 167 to phase sensor 170 to determine the phase relationship of each signal at each stud 162 and 167 after the signal passes through transfer cables 161 and 166 and capacitors 160 and 165. The microprocessor 111 determines the phase difference and sends a phase delay signal to the pulse amplifier 213, which applies the phase delay signal to the pulses sent to each cable so that the signals are phase synchronized when applied to the object via the posts. The phase sensor and pulse amplifier may also sense and adjust for differences in complex impedance between two applied signals. Similar circuitry is used to adjust the phase of the applied signal in this embodiment, where capacitive coupling is used to apply the signal to the object.

The power indicator 215 includes voltage sensing circuitry, a scintillator and voltage indication and an LED. The power indicator circuit causes the LED to blink at 1/8 hz when the supply voltage is 12 volts, and at 1/4 hz when the supply voltage is below 12 volts and above 11.7 volts, and at 1/2 hz when the supply voltage is below 11.7 volts. A surge protection circuit 172 is provided to protect the present invention from high voltages due to regulator failure or other high voltage sources.

As previously described in the description of the invention shown in FIG. 5, the microprocessor 111 may generate an electrical waveform, such as a series of pulses, for application to a metal structure. As previously mentioned, the electrical waveform has a time-varying component, and may be pulsed or sinusoidal, and have different characteristics such as a particular frequency spectrum, repetition rate, rise/fall times. In the present embodiment, the surface current generated or induced on the metal structure is effective to suppress corrosion of the metal structure. While the surface current may be generated in response to a time varying electrical waveform applied, the microprocessor 111 and pulse amplifier 113 provide a unipolar pulsed DC based signal. However, the fourier transform of the signal shows that in addition to the DC component, the signal also comprises a number of AC components. It is generally observed that the highest frequency component is found to be about 0.35/Trf, where Trf is the rise/fall time of the pulse, which is always low. Although a unipolar DC signal is used in this embodiment, a bipolar DC signal may be used instead and with equal efficacy. A unipolar signal refers to a signal that produces a voltage or current offset in only the positive or negative direction, whereas a bipolar signal refers to a signal that produces a voltage or current offset in both the positive or negative direction, such as a sinusoidal waveform.

Those skilled in the art will appreciate that in the field of digital signal communications, the lines carrying the digital signals may exhibit undesirable inductance and capacitance characteristics. It may behave as a resonant LC circuit that can cause unwanted transients and ringing of the signal at the receiving end of the circuit. The rise and fall times vary at high transfer rates, causing serious problems if left out. While attempts have been made by those skilled in the art of digital signal communication to minimize this effect, this transient state is preferred for embodiments of the present invention. The transient AC component of these pulsed forms of the electrical waveform increases the frequency component at which the effective LC circuit oscillates and thus increases the surface current generation which reduces the rate of corrosion. Note that the electrical waveform may have any shape as long as it has a time-varying (AC) component. Naturally, for a waveform in the form of a pulse, the microprocessor 111 can be set to provide a pulse signal of high frequency and short rise/fall time to generate the time-varying (AC) component. Of course, those skilled in the art will appreciate that any suitable high speed pulse generation circuit may be used in place of the microprocessor 111.

It is noted that surface current generation may be increased if the electrical waveform includes the frequency at which the metal object resonates. Because the vehicle is a complex electronic structure associated with AC electrical excitation, it may have electronic resonance at many frequencies generated by the electrical waveforms. The exact resonant frequency of the vehicle is determined by the structure of the vehicle and the parasitic capacitances and inductances present in the electrical circuit and the wires connecting the electrical circuit. Not only will surface currents be increased, which will radiate efficiently, converting the metal object into an effective antenna. In this manner, by selecting an appropriate waveform shape, and thus frequency spectrum, optimal corrosion inhibition can be obtained. However, those skilled in the art will appreciate that it is preferable to control this process to avoid RF interference problems.

In an alternative embodiment, high frequency components are not possible or desirable, and can be minimized by reducing the maximum rate of change present in the electrical waveform. For a pulse waveform, this means a reduction in the rise and fall times of the pulse. It is noted that a low duty cycle pulse shape with moderate rise and fall times is effective for inducing surface currents on the metal body being protected. Moderate rise and fall times are meant to be similar to those disclosed in embodiments of the present invention. In particular, it is noted that the rise and fall times of the pulse waveform with appropriate duration are primarily responsible for generating the surface current. Circuit techniques for minimizing signal rise/fall times are well known to those skilled in the art.

An alternative technique for generating surface currents in metal objects is to capacitively couple an electrical waveform directly to the metal object to induce surface current generation. Which can be achieved by direct discharge through a metal object or by electric field induced surface current generation. The following is a description of a circuit for capacitively coupling an electrical waveform to a metal object according to an embodiment of the present invention.

FIG. 6 shows a schematic diagram of a circuit for coupling an electrical waveform to a metal object by direct discharge, according to an embodiment of the invention. The circuit includes a charging circuit having a DC voltage source for providing a capacitive discharge, and a current generating circuit coupled to the metal object to receive and shape the capacitive discharge from the charging circuit. The terminals of the DC voltage source are connected to the metal object, and the current generating circuit applies a shaped capacitive discharge to the metal object for inducing a surface current therein. The capacitive coupling circuit 300 includes a DC voltage source 302, such as a battery, impedance devices 304 and 306, a capacitor 308, a switch 310, and a metal object 312. In the present embodiment, the DC voltage source 302, the impedance device 304, the capacitor 308, and the switch 310 form a charging circuit for providing a capacitive discharge from the capacitor 308 via the switch 310. In particular, capacitor 308 is connected in parallel with DC voltage source 302, and switch 310 couples capacitor 308 to DC voltage source 302 in a charging position for charging the capacitor, and to an output in a discharging position for discharging capacitor 308. In this embodiment, the output may be node "1" of switch 310, and the current generating circuit includes impedance device 306. Impedance device 304 limits current as capacitor 308 charges and impedance device 306 is used to shape the electrical waveform applied to metal object 312. Although not shown, the voltage source 302 includes a polarity switching circuit that reverses its polarity. Switch 310 is controlled to electrically connect the plates of capacitor 308 at either position 1 or position 2 in fig. 6. Preferably, the two terminals of the capacitor 308 are connected at a distance from each other on the metal object 312. Those skilled in the art will appreciate that the particular types and values of impedance devices 304, 306, capacitor 308, and voltage source 302 are design parameters. In other words, the value is selected to ensure that a surface current effective to reduce the corrosion rate of the metal object 312 is induced.

In operation, switch 310 is set to position 2 to charge capacitor 308 by voltage source 302 via impedance device 304. Assume in this embodiment that voltage source 302 starts with a negative terminal connected to the bottom plate of capacitor 308. When charging, switch 310 is switched to position 1 to discharge the stored charge via impedance device 306 via metal object 312. Thus, surface current is generated through the metal object, and positive charges on the top plate of the capacitor 308 are discharged through the metal object 312. Switch 310 is then switched back to position 2 and the polarity of voltage source 302 is reversed via the polarity switch circuit to cause the bottom plate of capacitor 308 to become positively charged. When the switch 310 is switched to position 1, a surface current in the opposite direction is generated through the metal object 312. Thus, as switch 310 switches between positions 1 and 2, charge is applied to and drawn from the metal object 312, and the polarity of voltage source 302 is reversed each time switch 310 returns to position 2.

Accordingly, the frequency at which capacitor 308 is charged and discharged may be controlled by microprocessor 111, and in particular by the electrical waveform provided by microprocessor 111. More particularly, the switch 310 and the switching circuit of the voltage source 302 may be controlled by an electrical waveform. Thus, the electrical waveform is effectively coupled to the metal object, as the discharge voltage of the capacitor 308 corresponds to the activation phase of the electrical waveform. In an alternative embodiment, a number of capacitors operating in parallel may be selectively connected to the metal object to ensure that surface currents are induced through the metal object 312, and the capacitors may be mechanically charged by the dielectric acting on the separate capacitor plates. Furthermore, those skilled in the art will appreciate that a bipolar voltage source may be used in place of the unipolar voltage source 302 described in FIG. 6 to eliminate the need for a polarity switch circuit.

FIG. 7 shows a circuit diagram for coupling an electrical waveform to a metal object by electric field induced surface current generation, according to an embodiment of the invention. The circuit includes a charging circuit having a DC voltage source to provide a capacitive discharge, and a current generating circuit coupled to the metal object to receive and shape the capacitive discharge from the charging circuit. The terminals of the DC voltage source are connected to a metal object, and the current generating circuit applies a shaped capacitive discharge to the metal object to induce a surface current therein. Circuit 350 includes the same elements shown in circuit 300 of fig. 6 and is arranged in the same configuration, but with the addition of a third impedance device 352, a second switch 354, and a distributed capacitor plate 356. In the present embodiment, the DC voltage source 302, the impedance device 304, the capacitor 308, and the switch 310 form a charging circuit for providing a capacitive discharge from the capacitor 308 via the switch 310. In particular, a DC voltage source 302, and a switch 310 are connected in parallel with the capacitor 308, coupling the capacitor 308 to the DC voltage source 302 in a charging position for charging the capacitor, and to an output in a discharging position for discharging the capacitor 308. In this embodiment, the output may be node "1" of switch 310. The current generating circuit includes impedance device 306, distributed capacitor plate 356, and a discharge circuit including impedance device 352 and switch 354. Impedance device 352 shapes the current signal as it discharges through switch 354, and distributed capacitor plate 356 may be a number of separate capacitor plates located at different locations along metal object 312. In a variation of the present embodiment, each individual capacitor plate forming distributed capacitor plate 356 may have its own impedance device 352 and switch 354. As in FIG. 6, those skilled in the art will appreciate that the particular types and values of impedance devices 304, 306, 352, capacitor 308, and voltage source 302 are design parameters selected to ensure efficient surface current generation. Furthermore, the surface area of each individual capacitor may be tailored (tailor) to produce the required surface current intensity for a particular location on the metal object 312. Tailoring may be desirable to compensate for the shape of the metal object 312 and/or components connected to the metal object 312, which may affect the distribution of surface currents.

In operation, when switch 354 is open, switch 310 is placed in position 2 to charge capacitor 308 through impedance device 304 by voltage source 302. Assume that the voltage source 302 in this embodiment has been configured such that its negative terminal is connected to the bottom plate of the capacitor 308. When switch 354 is open, switch 310 is switched to position 1 to distribute or share the stored charge through distribution capacitor plate 356 via impedance device 306. Thus, surface currents are generated via the metal object as the distributed capacitor plates 356 are charged. More specifically, as the distributed capacitor plate 356 charges, surface currents flowing in a first direction are induced. When switch 310 is in position 2, switch 354 is switched to a closed position to discharge distributed capacitor plate 356 and induce a surface current flowing in a second and opposite direction. Accordingly, when switch 310 is in position 2, capacitor 308 begins to charge. The cycle is then terminated by setting switch 354 to the on position.

Accordingly, the frequency at which the capacitor 356 is charged and discharged may be controlled by the microprocessor 111, and in particular by the electrical waveform provided by the microprocessor 111. More specifically, switches 310 and 354 may be controlled by an electrical waveform to maintain the aforementioned switching sequence. Thus, the electrical waveform is efficiently coupled to the metal object, as the distributed capacitor plate 356 charges and discharges at a frequency related to the frequency of the electrical waveform. Those skilled in the art will appreciate that microprocessor 111 may be configured to generate more than one electrical waveform such that each electrical waveform controls switches 310 and 354 in the appropriate sequence.

An advantage of this embodiment is that the flexibility of the surface current can be tailored at different locations of the metal object by adjusting the values of the individual capacitors and the values of the components of the distributed capacitor plates 356. Thus, the reduction in corrosion throughout the entire surface of the metal object can be maximized regardless of its shape or size.

The aforementioned techniques for generating surface currents in metal objects require a physical connection between the pulse signal generator circuit and the metal object. A non-contact method of generating a surface current may include generating an electromagnetic field to induce a surface current. For example, moving a magnetic field across a metal surface may induce eddy currents, some of which are surface currents. The magnetic field may be provided by a permanent magnet that can traverse the surface of the metal object at a frequency that can be controlled by the microprocessor 111. Thus, the signal pulse is efficiently coupled to the metal object as the means for generating a magnetic field moves over a specific area of the metal object in response to the activation phase of the signal pulse.

Another non-contact technique for generating surface currents involves transmitting a signal from an RF source via an antenna in an appropriate shape (waveform) so that the transmitted signal is received by the metal object. Accordingly, the signal pulses in this alternative embodiment may be used to generate an RF signal using known RF circuitry, which is then coupled to the metal object via the transmitted signal.

Thus, according to embodiments of the present invention, the rate of corrosion or oxidation of a metal object may be reduced by generating an electrical waveform having predetermined characteristics from a suitable waveform generation circuit powered by a suitable source of electrical energy (e.g., a DC voltage source). By coupling the generated electrical waveform to the metal object, a surface current is induced at the entire surface of the metal object. When the electrical waveform is not directly coupled to the metal object in capacitive coupling and non-contact technologies, it is considered to be indirectly coupled to the metal object when it can be used to control other elements to induce surface currents. Those skilled in the art will appreciate that the design of the circuit and device parameters must be carefully selected to ensure that nearby systems that are sensitive to time-varying digital signals are not disturbed.

Since surface currents can be generated with low DC voltage sources, embodiments of the present invention can be used in many practical applications since low voltage batteries, such as 12 volt DC batteries, are readily available and more popular than the high voltage sources required in the prior art.

To confirm the corrosion inhibition efficacy of the embodiments of the present invention, corrosion tests were performed on metal panels prepared for use as vehicle body panels. Surface current testing is performed on the vehicle to ensure that surface current is present when the device is activated to inhibit corrosion.

The corrosion inhibition efficacy of the circuit embodiments of the present invention (meaning as a module from that point forward) was tested by scratching the panel to expose bare metal. The module, powered by a standard automotive battery, has its terminals connected to the back of the metal panel. Both the test panel and a similarly scribed "control" panel were continuously sprayed with saline solution for more than 500 hours. A reference electrode set to the position of each panel wiper monitors the potential of each panel during the duration of the test. Visual inspection clearly showed that the test panel experienced significantly less corrosion than the control panel, as evidenced by the lack of rust spots. In addition, the potential measurement of each panel showed that the test panel eventually reached a potential of about 150mV, which is more negative than the potential of the control panel. The results of the voltage potential (volts) versus time (hours) plot are shown in fig. 8, with test panel potentials shown in diamonds and control panel potentials shown in squares. Thus, it was concluded that the more negative potential of the test panel induced by embodiments of the present invention contributed to corrosion inhibition.

Surface current testing involves connecting the module to the vehicle and measuring the surface current using known techniques. In particular, one terminal of the module is connected to the driver side ground bolt of the vehicle and the other terminal of the module is connected to the dash panel bolt on the passenger side of the vehicle. A radio receiver with a calibration loop current probe is used to detect and measure surface currents at different locations of the vehicle body. The conclusion of this test is that the surface current is detectable over the entire surface of the vehicle.

Thus, according to the aforementioned embodiments of the present invention, the test confirmed that corrosion can be suppressed by generating surface current.

Although the embodiments of the present invention described above are effective in reducing the corrosion rate of metals in the absence of an electrolyte, they are also effective in the presence of an electrolyte. In addition, although a low voltage DC voltage source is described in the preferred embodiment of the present invention, a high voltage DC voltage source can be used with the same effect. Thus, embodiments of the present invention may be applied to large metal structures such as marine vessels having a metal outer shell.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (24)

1. A method of reducing the corrosion rate of a metal object comprising:

a) generating electrical waveforms having predetermined characteristics from a DC voltage source, each electrical waveform having a transient AC component;

b) capacitively coupling the electrical waveform to the metal object; and

c) inducing a surface current on the entire surface of the metal object in response to the electrical waveform.

2. The method of claim 1, wherein the step of coupling comprises driving the electrical waveform through at least two contact points on the metal object.

3. The method of claim 1, wherein the step of generating comprises generating an electrical waveform having a shape conduction for generating the AC component.

4. The method of claim 1, wherein the electrical waveform comprises a resonant frequency of the metal object.

5. The method of claim 1, wherein the step of coupling comprises capacitively coupling the electrical waveform from a first terminal connected to the metal object to a second terminal.

6. The method of claim 5, wherein the second terminal is connected to a ground terminal of the DC voltage source.

7. The method of claim 1, wherein the step of capacitively coupling comprises: in response to the electrical waveform, charging a capacitor by the DC voltage source and discharging stored charge of the capacitor through the metal object to a ground connection between the DC voltage source and the metal object.

8. The method of claim 7, wherein the capacitor is mechanically charged.

9. The method of claim 7, wherein the capacitor includes a first terminal connected to the metal object and a second terminal connected to an area of the metal object away from the ground connection.

10. The method of claim 7, wherein the polarity of the DC voltage source is reversed after discharging the stored charge.

11. The method of claim 1, wherein the step of capacitively coupling comprises: charging a capacitor by the DC voltage source and discharging stored charge of the capacitor to a distribution capacitor coupled to the metal object in response to the electrical waveform, the induced surface current flowing in a first direction in response to accumulation of stored charge on the distribution capacitor.

12. The method of claim 11, wherein the step of capacitively coupling further comprises: discharging the distributed capacitor in response to the electrical waveform, the induced surface current flowing in a second direction opposite the first direction in response to the discharging of the distributed capacitor.

13. The method of claim 1, wherein the step of coupling comprises transmitting an RF signal corresponding to the electrical waveform received by the metal object through an antenna.

14. The method of claim 1, wherein the step of generating comprises generating an electrical waveform having a rise time and a fall time of 200 nanoseconds.

15. The method of claim 1, wherein the step of generating comprises generating a unipolar DC electrical waveform.

16. The method of claim 1, wherein the step of generating comprises generating a bipolar DC electrical waveform.

17. A circuit for reducing the corrosion rate of a metal object, comprising:

a charging circuit having a DC voltage source for providing a capacitive discharge, terminals of the DC voltage source being connected to the metal object; and the number of the first and second groups,

a current generating circuit coupled to the metal object for receiving and shaping a capacitive discharge from the charging circuit, the current generating circuit coupling the shaped capacitive discharge to the metal object for inducing a surface current therein.

18. The circuit of claim 17, wherein the charging circuit comprises:

a capacitor coupled in parallel to the DC voltage source, an

A switching circuit for coupling the capacitor to a DC voltage source in a charging position for charging the capacitor, the switching circuit coupling the capacitor to an output in a discharging position for discharging the capacitor.

19. The circuit of claim 18, wherein the current generating circuit comprises an impedance device coupled between the output and the metal object for providing a shaped current waveform, a surface current induced as the shaped current waveform being applied to the metal object.

20. The circuit of claim 19, wherein the DC voltage source includes a polarity switch circuit for reversing the polarity of the DC voltage source.

21. The circuit of claim 18, wherein the current generating circuit comprises:

a distributed capacitor coupled to the metal object,

an impedance device coupled between the output and the distribution capacitor for providing a shaped current waveform, the distribution capacitor receiving charge from the shaped current waveform to induce the surface current, an

A discharge circuit for discharging charge from the distribution capacitor to the terminal for inducing a second surface current in a direction opposite to the surface current.

22. The circuit of claim 21, wherein the discharge circuit comprises:

a second impedance device coupled between the distribution capacitor and a discharge switch circuit for coupling the second impedance device to the terminal.

23. The circuit of claim 21, wherein the distributed capacitor comprises at least two independent plates in parallel.

24. The circuit of claim 23, wherein each of the at least two parallel independent plates has a different surface area.