Abstract
A safety apparatus designed to prevent electric shock and protect equipment on or around marinas or docks. Said apparatus alerts and electrically isolates the marina or dock from the power source in the event a hazardous condition is detected. Safety hazards include, but are not limited to: Earth-ground fault, electricity in the water, high-water condition, or dock-break away condition. Comparing to prior art, the distinction of said invention is providing personal and equipment protection from all hazardous scenarios, and a fail-safe operation.
Claims
1. An apparatus, for marinas and docks, to alert and electrically isolate said marina or dock from the power source in the event a hazardous condition is detected, said apparatus comprising: hazard sensors including, but not limited to: Earth-ground fault, electricity in the water, high-water condition, and dock-shore breakaway; means of isolating all conductors, including the Earth-ground, to said marina or dock from the power source; a momentary button to reset the system in the event of a hazardous condition, and to test the operation of the system; a visual and audible alarm to alert nearby persons around said marina or dock that a hazard has occurred; a logic controller to process system inputs, and control outputs using Boolean logic functions; and a human machine interface (HMI) to remotely monitor and control said apparatus.
2. The apparatus of claim 1 wherein the means of detecting an Earth-ground fault is accomplished by using a voltmeter to measure voltage across a shunt resistor placed between the Earth-ground conductor and a reference electrode, and said voltmeter outputs a signal when the measured voltage exceeds the danger threshold.
3. The apparatus of claim 1 wherein the means of detecting electricity in the water is accomplished by using a voltmeter to measure a voltage gradient between two sets of insulated conductors; the end of each conductor is exposed, and placed in a body of water at a distance, dependent upon the conductivity of the water, away from an opposing conductor; and when a gradient voltage is measured, said voltmeter outputs a signal.
4. The apparatus of claim 1 wherein the means of detecting a high-water condition is accomplished by placing a float sensor at the electrical datum plane.
5. The apparatus of claim I wherein the means of detecting a dock-shore breakaway condition is accomplished by placing reed switches at every joint of the marina or dock walkway.
6. The apparatus of claim 1 wherein all hazardous condition sensors are wired as normally closed (N/C) circuits to the logic controller to achieve a fail-safe operation in the event of sensor or wiring failure.
7. The apparatus of claim 1 wherein the means of isolating all conductors to the marina or dock from the power source is accomplished by installing components capable of electrically breaking each conductor before the marina or dock (e.g., solenoids, relays, contactors, or shunt trip breakers) when any hazardous condition is detected.
8. The means of claim 7 wherein the isolation components' contactor circuits are normally open (N/O) to achieve a fail-safe operation in the event of component, equipment, or wiring failure.
9. The means of claim 7 wherein isolating the Earth-ground conductor from the power source excludes isolating the Earth-ground conductor to the marina or dock from the Earth-ground rod located adjacent to the marina or dock.
10. The apparatus of claim 1 wherein the remote human machine interface (HMI) is accomplished by an industrial data gateway communicating via internet, and serially linked to the logic controller.
11. The HMI of claim 10 comprised a graphical interface (GI) displaying real-time hazardous condition sensor states, and controllable output functions.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a block diagram portraying the overall flow of components in the described invention;
[0020] FIG. 2 is a schematic diagram of the components and circuitry required to achieve the claimed operation;
[0021] FIG. 3 is an overhead view of an installed apparatus described in the invention; and
[0022] FIG. 4 is a representation of the preferred embodiment of the control box described in the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The overall flow of the apparatus is portrayed in FIG. 1, and will generally remain constant even in deviations from the preferred embodiment described below. Programmable logic controller (PLC) 200 is the brain of the apparatus. PLC 200 receives signals from inputs 201. These include all hazard sensors and the momentary reset and test button. Hazard sensors include, but are not limited to: electricity in the water, Earth-ground fault, dock-shore breakaway condition, and high-water condition. Another input 201 example is a sensor to determine the position of the boat lift. PLC 200 uses input 201 signals in Boolean logic functions to control outputs 202. Outputs 202 include necessary safety components such as conductor isolation relays 305, audible alarm 303, and visual alarm 302. Outputs 202 may also include convenient features such as boat lift controls, lighting controls, and stereo controls.
[0024] The circuitry and components required for achieving an all-encompassing and redundant safety system for marinas and boat docks is displayed in FIG. 2. The simplified Boolean logic function of PLC 200 is an AND gate. All equipment safety sensors are inputs of the AND gate function. The equipment safety sensors are wired as normally closed circuits when no fault is occurring. If any of the equipment safety sensor circuits becomes open, the AND gate deactivates. When the AND gate is activated, the output of PLC 200 is triggering the conductor isolation relays 305 to turn on. The conductor isolation relays 305 are connected in series of all conductors, including the Earth ground conductor, from the power source. Conductor isolation relays 305 are normally open circuit devices. In the event of PLC 200 failure, wiring failure, or any relay 305 failure, this ensures a fail-safe operation. Visual alarm 302 and audible alarm 303 are activated by a NOT state of the output of PLC 200 AND gate. When a hazardous condition occurs, and the AND gate is deactivated, the alarms will be triggered. In order to reactivate the AND gate, after a fault occurs, all hazard sensor circuits must return to the closed state, and reset button 304 must be momentarily depressed. The use of reset button 304 is necessary to prevent looping fault occurrences. With no reset button 304, this could happen when a fault is removed by the isolation circuit, and then reoccurs after the power automatically restores. The other function of momentary button 304 is a test button. By means of PLC 200 programming, the AND gate is deactivated when the momentary button 304 is depressed for five seconds or more. This action allows the user to test functionality of the conductor isolation relays 305 and the alarms without having to create an actual fault.
[0025] FIG. 1 also shows PLC 200 communicating with the industrial data gateway 203 via a serial connection. Industrial data gateway 203 runs a human machine interface (HMI) 204. The HMI 204 is a graphical interface (GI) displaying input 201 states, and output 202 control functions. PLC 200 reports input 201 states to the industrial data gateway 203, which then sends the data via an internet connection to the HMI 204. When an output control function of the HMI 204 is used, it sends the data to industrial data gateway 203 via internet connection. Industrial data gateway 203 then communicates the output control function to the PLC 200 via serial connection. The industrial data gateway 203 also alerts a marina or boat dock operator via email 205 when a safety hazard has occurred.
[0026] FIG. 3 portrays a diagram of an overhead view of an installed apparatus. Actual installations will vary dependent upon multiple factors such as dock size, dock location, and conductivity of the water. The preferred embodiment of a standard apparatus install is described. D represents the dock or marina. S refers to the shore in which D is attached. DR represents the dock ramp, which connects D to S. W, refers to the body of water that D is floating on. Control box 105 is located on S, and is a watertight enclosure housing all environmentally sensitive electronics such as PLC 200, industrial data gateway 203, voltmeters 301A,B, conductor isolation relays 305, shunt resistor 306, momentary reset and test button 304, and necessary power supply and circuit protection components. The preferred embodiment of control box 105 is portrayed in FIG. 4. The preferred embodiment shows visual alarm 302 and audible alarm 303 located on the face of control box 105, but the two alarms could also be located on D. Utility conductors from the power source are routed out of dock breaker box 106, and into control box 105 to receive protection from the conductor isolation relays 305. The protected conductors are then routed from control box 105 back into dock breaker box 106 before being routed out to D. Earth-ground rod 106 is located adjacent to control box 105. In the event of the conductor isolation relays 305 isolating D from the power source, Earth-ground rod 106 remains connected to D to continue providing ground fault protection and lightning protection for all equipment.
[0027] Float sensor 103 is one of the hazard sensors. It is located on or near S, and placed level with the electrical datum plane. The construction of float sensor 103 must be heavy-duty to be able to handle harsh conditions. In the event of a high-water condition, the circuit state of float sensor 103 changes from normally closed to open. This signals PLC 200 that a high-water condition has occurred. The circuit is wired normally closed to provide redundancy in the event of sensor failure, or wiring failure. This function protects dock workers and first responders responding to an emergency situation.
[0028] FIG. 3 also depicts two dock-shore breakaway sensors 102. The dock-shore breakaway sensor 102 is a heavy-duty reed switch. These switches 102 are placed at every moveable joint. Typically, there will be one placed between D and DR, and one placed between DR and S. In the event any joint becomes separated, the corresponding switch circuit state changes from normally closed to open. This signals PLC 200 that a dock-shore breakaway condition has occurred. The circuit is wired normally closed, and all switches 102 are wired in series to provide redundancy in the event of switch failure, or wiring failure. This function protects dock workers and first responders responding to an emergency situation.
[0029] The next component depicted in FIG. 3 is the reference electrode 104. It may be of the water or soil variety. The depicted example shows reference electrode 104 placed in W. Reference electrode 104 is used to detect the most common safety hazard, an Earth ground fault. Reference electrode 104 provides a reference point for voltmeter 301B to measure the Earth-ground circuit. This is a common knowledge method used in both marine and plumbing applications to detect corrosion causing stray voltages. Due to floating voltages on the Earth-ground circuit from the utility lines, shunt resistor 306 is connected between reference electrode 104 and the Earth-ground circuit to prevent false fault readings. As seen in FIG. 2, voltmeter 301B positive input is connected to Earth-ground side of shunt resistor 306, and voltmeter 301B negative input is connected to the reference electrode 104 side of shunt resistor 306. The resistance value of shunt resistor 306 is chosen to resemble the resistance of a human body when immersed in water. That value is 500 ohms. The dangerous current threshold of a Class B GFCI device is 6ma. Using that current value, and the resistance value of shunt resistor 306, in ohm's law (voltage=currentresistance), the dangerous voltage threshold is calculated to be 3V. When 3V is measured by voltmeter 301B, alarm output circuit state of voltmeter 301B is changed from normally closed to open. This signals PLC 200 that an Earth-ground fault has occurred. The alarm output circuit is wired normally closed to provide redundancy in the event of voltmeter 301B failure, or wiring failure.
[0030] The final components depicted in FIG. 3 are the electricity in the water probes 101A and 101B. The two sets of probes are insulated conductors with the ends exposed and permanently fixed in W. Probes 101A are connected to voltmeter 301A positive input, and probes 101B are connected to voltmeter 301A negative input. When a gradient voltage of 100 mV or more is measured by voltmeter 301A, alarm output circuit state of voltmeter 301A is changed from normally closed to open. This signals PLC 200 that electricity in the water has been detected. The alarm output circuit is wired normally closed to provide redundancy in the event of voltmeter 301A failure, or wiring failure. The measurement of gradient voltages to detect stray voltages is a common knowledge method used for corrosion prevention and livestock protection. Every conductor within a probe set, 101A or 101B, is wired in parallel with the other conductors of that set. The amount of conductors per set is determined by the size of the dock and the detection radius R1 of each probe. Radius R1 is a variable distance dependent upon the conductivity of the water. A sufficient amount of probes are installed to create a safety perimeter around the dock. Most lakes and rivers have low conductivity, so the ability to add probes is crucial to achieve full protection for different setups of D.
