Abstract:
A galvanic monitor system uses two annunciators, such like light emitting diodes, to alert a boat operator of the current status of the boat&#39;s galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciators lights are used to inform the operator if the protection is proper or if the component to be protected is either being over protected or under protected.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to a system for monitoring a galvanic protection system and, more particularly, to a monitor system which provides an easily recognizable signal representing the current state of a galvanic protection system without the need for operator. 
     2. Description of the Prior Art 
     It is widely known to those skilled in the art that certain submerged components can experience galvanic corrosion when used in conjunction with a marine vessel, such as a boat. Various types of corrosion prevention systems are available to prevent galvanic corrosion of marine propulsion system components. These include sacrificial anodes and electrical systems that inhibit galvanic corrosion of marine components. When connected properly and operated in conformance with suggested procedures, these known prevention systems work adequately. However, if the galvanic corrosion system is not working properly, a boat operator generally will not be aware of this condition without some active involvement by the boat operator. As an example, a sacrificial anode may be missing or so severely depleted that it is ineffective. In addition, an electrical prevention system can experience a broken wire or a connection that is inadvertently loosened. Although one system is available in the prior art that permits an operator to actively cause a circuit to be completed to check certain characteristics of one particular type of electrical corrosion prevention system, no passive monitor is currently available that automatically informs a boat operator of a problem in a galvanic protection system without requiring the operator to first request the monitor to check the system. 
     U.S. Pat. No. 4,117,345, which issued to Balcom on Sep. 26, 1978, describes a marine ground isolator. The isolator selectively completes the current path through a ground connection. The preferred of the isolator includes a switch circuit connected in series between two portions of the ground connection and arranged so as to complete the current path therethrough only in response to an applied control signal. It further comprises means for monitoring the potential between the two portions of the ground connection and for applying the control signal to the switch circuit only when the absolute magnitude of the dc potential exceeds a first value or when the ac potential exceeds a second value. 
     U.S. Pat. No. 5,627,414 which issued to Brown et al on May 6, 1997, describes an automatic cathodic protection system using galvanic anodes. The automatic system uses sacrificial galvanic anodes to provide a controlled and optimum amount of cathodic protection against galvanic corrosion on submerged metal parts. Intermittently pulsed control circuitry enables an electro-mechanical servo system to control a resistive element interposed between the sacrificial anodes and the electrically bonded underwater parts. In an active mode of operation, a current is applied directly to the anodes to quickly establish the proper level of correction which is maintained during the passive mode. Incremental corrections are made over a period of time to provide stabilization of the protection and to conserve power. A visual indication of the amount of protection is available at all times. Circuitry and indicating devices are included which facilitate location and correction of potentially harmful stray currents and to prevent loss of sacrificial anodes to nearby marine structures. 
     U.S. Pat. No. 5,840,164, which issued to Staerzl on Nov. 24, 1998, discloses a galvanic isolator used to protect against galvanic corrosion of a submersible metal marine drive. The galvanic isolator is positioned between shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground, while maintaining the safety function of neutral ground. The galvanic isolator of the invention includes a blocking element positioned between the boat ground and the shore ground that can be switched between an open and a closed state by a trigger circuit. The trigger circuit closes the blocking element when the difference between the boat ground and the shore ground exceeds a threshold value, such as 1.4 volts. During operation of the galvanic isolator during the high fault current condition, power is dissipated only by the blocking element, rather than by the combination of the blocking element and the trigger device. In this manner, the galvanic isolator reduces the amount of power dissipated during high current conditions and therefore reduces the amount of heat generated by the galvanic isolator. 
     U.S. Pat. No. 5,747,892, which issued to Staerzl on May 5, 1998, discloses a galvanic isolator fault monitor. The system and method for testing and monitoring the operation of a galvanic isolator are provided by this device. The isolator is positioned between shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground. The monitoring system transmits a test current through the galvanic isolator at specific time intervals to test the effectiveness of the galvanic isolator. The monitoring system includes a first counter that outputs an enabling signal after a period of time. The enabling signal allows a test current to flow through the galvanic isolator for a brief period of time determined by a second counter. As the test current flows through the galvanic isolator, a current sensing circuit measures the test current and activates an alarm if the test current flowing through the galvanic isolator falls outside a predetermined range. In this manner, the monitoring system of the invention monitors and periodically tests a galvanic isolator. 
     U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, describes a cathodic protection controller. The control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water. 
     U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for marine propulsion device. The monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode. 
     The United States patents described above are hereby explicitly incorporated by reference in the description of the present invention. 
     A booklet titled “Everything you need to know about marine corrosion” and published by the Quicksilver Marine Parts and Accessories Division of Mercury Marine, which is a division of the Brunswick Corporation, provides a detailed description on the electrochemistry of marine corrosion and also describes numerous techniques and devices available for the prevention of marine corrosion. 
     Notwithstanding the existence of many different systems for the prevention of galvanic corrosion of marine components, it would be significantly beneficial if a monitoring system could be provided that did not require active participation by a boat operator but provided a visual signal of the present operating condition of the galvanic corrosion prevention system. 
     SUMMARY OF THE INVENTION 
     A preferred embodiment of the present invention provides a marine galvanic protection monitor that comprises an electrode disposed in noncontact association with a component to be protected from corrosion. It also comprises a first comparator connected in signal communication with the electrode and with a first reference signal, the first comparator providing a first output signal which is representative of the relative magnitudes of the voltage potentials of the electrode and the first reference signal. The monitor further comprises a second comparator connected in signal communication with the electrode and with a second reference signal to provide a second output signal which is representative of the relative magnitudes of the voltage potentials of the electrode and the second reference signal. The first and second comparators are connected in signal communication with the component to be protected from corrosion. 
     A particularly preferred application of the present invention is in conjunction with a marine propulsion unit that serves as the component to be protected from corrosion. The marine propulsion system can be a stern drive unit or an outboard motor. 
     In one particularly preferred embodiment of the present invention, the first output signal and the second output signal are both high when the voltage potential of the electrode is higher than the first reference signal. Furthermore, the second output signal is high when the voltage potential of the electrode is higher than the second reference signal. The first output signal is high when the voltage potential of the electrode is lower than the second reference signal. 
     A battery can be connected in electrical communication with the electrode, with the first comparator, and with the second comparator. The electrode can be attached to a transom of a boat to which the component to be protected from corrosion is also attached. 
     In a preferred embodiment of the present invention, a first annunciator is connected in electrical communication with the first output signal and a second annunciator is connected in electrical communication with the second output signal. The annunciators can be light emitted diodes (LED&#39;s). Certain types of LED&#39;s can provide two different color outputs in a single component. If the two outputs are red and green, for use as the first and second annunciators, a combined first and second output can be yellow to indicate the presence of both the first and second output signals in a high state. 
     In order to conserve electrical energy, an oscillator can be connected in electrical communication with the first and second annunciators to periodically deactivate the first and second annunciators independently of the state of the first and second output signals. 
     The present invention provides the method for monitoring a marine galvanic protection system that comprises the steps of providing an electrode disposed in non-contact association with the component to be protected from corrosion, comparing a voltage potential of the electrode with a first reference signal, provided a first output signal which is representative of the relative magnitudes of the voltage potentials of the electrode and the first reference signal, comparing a voltage potential of the electrode with a second reference signal, and providing a second output signal which is representative of the relative magnitudes of the voltage potentials of the electrode and the second reference signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the figures, in which: 
     FIG. 1 shows a corrosion prevention system known to those skilled in the art; 
     FIG. 2 shows one application of the present invention with a certain type of corrosion prevention system; 
     FIG. 3 shows an alternative application of the present invention in conjunction with a system using only a sacrificial anode; and 
     FIG. 4 is an electrical schematic of a circuit usable in conjunction with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the description of the preferred embodiment, like components will be identified by like reference numerals. 
     FIG. 1 shows a known type of galvanic protection system that is available in commercial quantities from the Quicksilver division of Mercury Marine which, in turn, is a division of the Brunswick Corporation. It shows a controller  10  that is connected in electrical communication with a power source, such as a battery  12 , which provides DC power to an electrode  14 . Although not directly related to the galvanic protection system, FIG. 1 also shows a trim position sender  16  connected in electrical communication with the battery  12  and with a trim gauge  18 . A currently available monitor  20  can be connected to the controller  10  in order to allow an operator to press a button  22  to see if power is available to the electrode  14  from the battery  12 . If the connection is made properly and power is available from the battery  12 , an annunciator light  26  is energized. The monitor  20  does not actually determine the voltage potential in the water surrounding a component to be protected from galvanic corrosion. Instead, the monitor  20  informs the operator that the battery  12  is connected properly to the anode  14 . In addition, the monitor  20  requires that the operator actively press the button  22  in order to activate the annunciator light  26 . 
     FIG. 2 is a highly schematic representative of the rear portion of a boat  30  with a stern drive unit  34  attached to the transom  36  of the boat  30 . A propeller  40  is attached to a propeller shaft of the stern drive unit  34  to propel the boat  30 . A controller  10 , which is generally similar to that described above in conjunction with FIG. 1, is electrically connected to an anode  14  that is located under the surface of the water and attached to the transom  36  of the boat  30 . The controller  10  is connected to the battery  12  and to a reference electrode  44 . Although the type of controller  10  is not limiting to the present invention, some controllers  10  are available which are capable of measuring the voltage field in the water proximate the reference electrode  44  and using that signal to control the magnitude of the signal provided at the anode  14 . A system for preventing galvanic corrosion of marine components is available from the Quicksilver division of the Mercury Marine division of the Brunswick Corporation. This system is referred to as the MerCathode system and it provides an automatic, permanent protection against galvanic corrosion. A solid state device, such as the controller  10 , operates with power provided by a 12 volt battery  12 . The galvanic protection system provides protection by impressing a reverse blocking current that stops the destructive flow of galvanic currents through the water in the vicinity of the stem drive unit  34 . 
     Galvanic corrosion occurs when two dissimilar metals are grounded, or connected electrically to each other and immersed in an electrolyte, such as sea water. Electrons flow from the more chemically active metal, such as aluminum, to the less chemically active metal, such as stainless steel, through the external connection or ground. Positively charged ions move from the anode and negatively charged ions move from the cathode through the electrolyte, such as sea water. The result of this process is the dissolving of the anode, or aluminum stern drive housing component. By providing an opposing current through the conductive liquid, the MerCathode system essentially blocks the ions from leaving the more chemically active material, which is generally the aluminum metal of the stern drive  34  housing. The MerCathode consists of a controller  10 , a reference electrode  44 , and an anode  14 , or electrode. The reference electrode  44  senses the corrosion potential of the drive in the water and regulates the controller  10  to keep the protective current within a prescribed range for optimum blocking and, hence, optimal corrosion protection. The protective current from the battery  12  is emitted into the water via the controller  10  and the anode  14 . The surface of the anode  14  is generally platinum coated so that it will not corrode due to the current flow, like sacrificial anodes would under these same circumstances. The MerCathode system automatically adjusts itself to compensate for changes in corrosion potential caused by variations in water temperature, velocity, and conductivity. It also compensates for changes in the condition of the paint on the drive unit  34 . 
     Although galvanic protection systems, such as the MerCathode protection system, work effectively in most circumstances, it is always possible that a portion of the system may become damaged. For example, the anode  14  can be damaged or inadvertently disconnected from the circuit. Similarly, the battery  12  may become drained or disconnected from the circuit. Any of these circumstances can cause the galvanic protection normally provided by the system to be disabled. 
     The present invention provides a monitor  50  which is connected to the electrode  44  which, as described above, is disposed in non-contact association with a component, such as the stern drive unit  34 , to be protected from corrosion. The monitor  50  is also connected in electrical communication with the battery  12  and with the component to be protected from corrosion. Line  56  is the connection between the monitor  50  and the component to be protected from corrosion. Line  58  is the connection between the monitor  50  and the electrode  44 . 
     Also shown in FIG. 2 are two annunciators. A first annunciator  60  informs the boat operator if the galvanic protection current provided by the anode  14 , or any other protection source is within a preselected range that has been determined to be effective. More specifically, the first annunciator  60 , when activated, represents a state in which the voltage sensed by the electrode  44  is either too high or too low. A second annunciator  62  is activated by the monitor  50  when the voltage sensed by the electrode  44  is sufficiently high (i.e. not too low) to provide protection to the stern drive unit  34 . However, in a preferred embodiment of the present invention, the second annunciator  62  is also activated when the voltage sensed by the electrode  44  is actually too high for the intended purposes of the system. 
     Although FIG. 2 shows the present invention used in association with the controller  10  and anode  14  of a galvanic protection system, such as a MerCathode, it should be understood that the monitor does not require the use of this type of galvanic protection system. 
     FIG. 3 illustrates the present invention used in association with a marine propulsion system that is not equipped with a galvanic protection system, such as the MerCathode, but is instead protected solely by a sacrificial anode (not shown in FIG.  3 ). The monitor  50  is shown connected to the battery  12  and also to the grounded component to be protected from corrosion which, in this case, is a stern drive unit  34 . The monitor  50  is also connected to the reference electrode  44  by line  58 . The two annunciators,  60  and  62 , are provided to signal the boat operator and inform the operator of the operating status of the galvanic protection system, which in this case comprises only a sacrificial anode. 
     With reference to FIGS. 2 and 3, it can be seen that the monitor  50  remains connected to both the stern drive unit  34  and the reference electrode  44  regardless of whether the galvanic protection system of the controller  10  and anode  14  is used. Therefore, it should be understood that the present invention is able to monitor the current galvanic protection status of a component to be protected from corrosion regardless of the type of protection system being used. 
     FIG. 4 is an electrical schematic of a circuit that is suitable for performing the function of the present invention. In the following description of FIG. 4, the component values and identification specified refer to one particularly preferred embodiment of the circuit and are not limiting to the present invention. As is well understood by those skilled in the art, the absolute magnitudes of the components and the particular types of components used in the circuit of FIG. 4 can be changed without adversely affecting the operation of the present invention as long as certain relationships and characteristics of the components are maintained. 
     FIG. 4 shows the battery  12  connected to a line  56  that is intended to be connected to the component to be protected from corrosion, such as the stern drive housing  34  described above in conjunction with FIGS. 2 and 3. The diode D 1  restricts the direction of the current and resistor R 1 , which is 20 kΩ, operates as a current limiter to protect diode D 2 . Diode D 2  is a Zenner diode identified by type number 1N5231. It is a 5.1 volt Zenner diode that maintains a voltage of 5.1 volts at point P 1  in the circuit. Resistor R 3  is 100 kΩ, resistor R 4  is 7.5 kΩ, and resistor R 5  is 20 kΩ. These three resistors form a bridge  72  which provides preselected voltage potentials on line  74  of 1.1 volts and on line  76  of 0.8 volts. These references are used as the first and second reference signals, respectively. The first reference signal on line  74  is connected to the inverting input of a first comparator  81 . The second reference signal on line  76  is connected to the non-inverting input of a second comparator  82 . As can be seen, the reference electrode  44  is connected by line  58  to the non inverting input of the first comparator  81  and to the inverting input of the second comparator  82 . Resistor R 2  is a current limiting resistor to protect the circuit in the event of a disconnection of any of the terminals. Resistor R 2  is 100 kΩ. If the voltage potential of the reference electrode  44  is higher than the first reference signal on line  74 , a first output signal is provided on line  91 , through diode D 3  and resistor R 6 , to a first annunciator  101 . Resistor R 6  is 510 Ω. Therefore, the first annunciator  101  is activated at any time when the voltage potential of the electrode  44  on line  58  is greater than the first reference voltage on line  74 . 
     With continued reference to FIG. 4, the second comparator  82  compares the electrode voltage on line  58  to the second reference voltage on line  76 . If the electrode  44  is at a voltage potential greater than the second reference signal on line  76 , a low signal is provided on line  92  and this, through the operation of comparator  110 , causes a high signal on line  93  to activate the second annunciator  102 . Resistor R 7  is 510 Ω. 
     If the voltage potential of the electrode  44  is too low, the second annunciator  102  is not activated. Also, if the voltage potential of the electrode  44  is too low, the first annunciator is activated by the output on line  92  through diode D 4  and resistor R 6 . 
     In summary, the first and second annunciators,  101  and  102 , operate in the following manner to inform the operator of the marine vessel the existing status of the galvanic protection system. If the voltage potential of the electrode  44 , on line  58 , is too low, the first annunciator  101  is energized and the second annunciator  102  is deenergized. If the voltage potential of the electrode  44 , on line  58  is too high, both the first and second annunciators,  101  and  102 , are energized. If the voltage potential of the electrode  44 , on line  58 , is proper and between the two reference signals on lines  74  and  76 , the first annunciator  101  is deenergized and the second annunciator  102  is energized. Therefore, in essence, the first annunciator  101  is energized when the voltage potential of the electrode  44  is either too high or too low. The second annunciator  102  is energized when the voltage potential of the electrode  44  is greater than the minimum reference set at line  76 , although possibly too high. 
     An oscillator circuit  120  provides a periodic deenergization of both the first and second annunciators,  101  and  102 , to conserve electrical power provided by the battery  12 . Resistor R 8 , which is 10 kΩ, and resistor R 9 , which is 100 kΩ, are used to set a reference voltage for the oscillator  120 . Resistor R 10 , which is 1 MΩ, resistor R 11 , which is 100 kΩ, and capacitor C 1  which is 6.8 μF combine with each other to set a duty cycle for the oscillator  120 . The output from operational amplifier  126  deenergizes the first and second annunciators,  101  and  102 , by preventing current flow through them. In a particularly preferred embodiment of the present invention, the duty cycle of the first and second annunciators,  101  and  102 , is approximately 10%. These blinking lights inform the operator of a marine vessel of the status of the protection system. 
     In FIG. 4, reference numeral  72  identifies the bridge used to set the two reference signals on lines  74  and  76 , reference numeral  140  identifies the first comparator circuit, reference numeral  142  identifies the second comparator circuit, and reference numeral  150  identifies the annunciators,  60  and  62 . 
     In summary of the above description of FIG. 4, if the second annunciator  62  is energized and blinking while the first annunciator  60  is continually deenergized, the boat operator is informed of the fact that the galvanic protection system is operating properly. If both annunciators,  60  and  62  are energized, the system is overprotecting the component to be protected from corrosion and can therefore cause other types of damage to the system. If only the first annunciator  60  is energized, the component to be protected is being underprotected by the galvanic protection system. 
     Although the present invention is described as incorporating two individual annunciators,  60  and  62 , as the first and second annunciators of the circuit, it should be understood that certain types of multi-colored annunciators are available for these purposes. For example, a tricolored LED is available from Industrial Devices, Inc. in commercial quantities. These components are identified as models 4361H1/5 and 5361H3/5. These single components provide red, green, and amber in a common three lead package. An annunciator of this type can be used in place of the first and second annunciators described above. 
     Although the present invention has been described with particular detail and illustrated to show one preferred embodiment of the present invention, it should be understood that alternative embodiments are also within its scope.