Title of Invention	WATER STORAGE DEVICE HAVING A POWERED ANODE AND METHOD THEREOF
Abstract	[00]l A water heater having a powered electrode and a method of controlling the water heater. The water heater includes a tank to hold water, a heating element, an electrode, and a control circuit. The control circuit includes a variable voltage supply, a voltage sensor, and a current sensor. The control circuit is configured to controllably apply a voltage to the electrode, determine the potential of the electrode relative to the tank with the voltage sensor when the voltage does not power the electrode, determine a current applied to the tank after the voltage powers the electrode, determine a conductivity state of the water in the tank based on the electrode potential and the current, and define the voltage applied to the powered electrode based on the conductivity state. The control circuit of the water heater can also determine the water heater is in a dry-fire state.

Title of Invention

WATER STORAGE DEVICE HAVING A POWERED ANODE AND METHOD THEREOF

Abstract

[00]l A water heater having a powered electrode and a method of controlling the water heater. The water heater includes a tank to hold water, a heating element, an electrode, and a control circuit. The control circuit includes a variable voltage supply, a voltage sensor, and a current sensor. The control circuit is configured to controllably apply a voltage to the electrode, determine the potential of the electrode relative to the tank with the voltage sensor when the voltage does not power the electrode, determine a current applied to the tank after the voltage powers the electrode, determine a conductivity state of the water in the tank based on the electrode potential and the current, and define the voltage applied to the powered electrode based on the conductivity state. The control circuit of the water heater can also determine the water heater is in a dry-fire state.

Full Text	2 BACKGROUND [00] 1 The invention relates to a water storage device having a powered anode and a method of controlling the water storage device. [00] 2 Powered anodes have been used in the water heater industry. To operate properly, a powered anode typically has to resolve two major concerns. First, the powered anode should provide enough protective current to protect exposed steel within the tank. The level of exposed steel will vary from tank to tank and will change during the lifetime of the tank. Second, the protective current resulting from the powered anode should be low enough to reduce the likelihood of excessive hydrogen. [00]3 There are at least two techniques currently available in the water heater industry for using a powered anode to protect a tank. One technique adjusts anode voltage levels based on the conductivity of the water. However, this technique does not measure the protection level of the tank and tanks with excessive exposed steel could be inadequately protected. The second technique periodically shuts off the current to the anode electrode and uses the electrode to "sense" the protection level of the tank. This technique adapts to the changing amount of exposed steel in the tank, but does not adapt to changing water conductivity levels. In addition, this technique can have problems in high conductivity waters since currently produced titanium electrodes with mixed metal oxide films have a tendency to drift in their reference voltage measurements in high conductivity water. It would be beneficial to have another alternative to the just-described techniques. SUMMARY [00] 1 In one embodiment, the invention provides a water heater including a tank to hold water, an inlet to introduce cold water into the tank, an outlet to remove hot water from the tank, a heating element (e.g., an electric resistance heating element or a gas burner), an electrode, and a control circuit. The control circuit includes a variable voltage supply, a voltage sensor, and a current sensor. The control circuit is configured to controllably apply a voltage to the electrode, determine a potential of the electrode relative to the tank when the voltage does not power the electrode, determine a current applied to the tank after the voltage powers the electrode, 2A determine a conductivity state of the water in the tank based on the applied voltage and the current, and define the voltage applied to the electrode based on the conductivity state. [00] 2 In another embodiment, the invention provides a method of controlling operation of a water storage device. The method includes the acts of applying a voltage to an electrode, ceasing the application of the applied voltage to the electrode, determining the potential of the electrode relative to the tank after the ceasing of the application of the applied voltage, determining a conductivity state of the water, defining a target potential for the electrode based on the conductivity state, and adjusting the applied voltage to have the electrode potential emulate the target potential. [00]3 In another embodiment, the invention provides another method of controlling operation of a water heater. The method includes the acts of applying a voltage to an electrode, acquiring a signal having a relation to the applied voltage, determining whether the water heater is in a dry-fire state based at least in part on the acquired signal, and preventing activation of a heating element when the water heater is in a dry-fire state. [00]4 Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [00] 1 Fig. 1 is partial-exposed view of a water heater embodying the invention. [00]2 Fig. 2 is a side view of an electrode capable of being used in the water heater of Fig. 1. [00]3 Fig. 3 is a electric schematic of a control circuit capable of controlling the electrode of Fig. 2. [00]4 Fig. 4 is a flow chart of a subroutine capable of being executed by the control circuit shown ill Fig. 3. DETAILED DESCRIPTION [00] 1 Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following 3 description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limited. The use of "including," "comprising" or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms "mounted," "connected," "supported," and "coupled" are used broadly and encompass both direct and indirect mounting, connecting, supporting, and coupling. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. [00]2 Fig. 1 illustrates a water heater 100 including an enclosed water tank 105, a shell 110 surrounding the water tank 105, and foam insulation 115 filling the annular space between the water tank 105 and the shell 110. A typical storage tank 105 is made of ferrous metal and lined internally with a glass-like porcelain enamel to protect the metal from corrosion. Nevertheless, the protective lining may have imperfections or, of necessity, may not entirely cover the ferrous metal interior. Under these circumstances, an electrolytic corrosion cell may be established as a result of dissolved solids in the stored water, leading to corrosion of the exposed ferrous metal and to reduction of service life for the water heater 100. [00]3 A water inlet line or dip tube 120 and a water outlet line 125 enter the top of the water tank 105. The water inlet line 120 has an inlet opening 130 for adding cold water to the water tank 105, and the water outlet line 125 has an outlet opening 135 for withdrawing hot water from the water tank 105. The water heater 100 also includes an electric resistance heating element 140 that is attached to the tank 105 and extends into the tank 105 to heat the water. The heating element 140 typically includes an internal high resistance heating element wire surrounded by a suitable insulating material and enclosed in a metal jacket. Electric power for the heating element 140 is typically supplied from a control circuit. While a water heater 100 having element 140 is shown, the invention can be used with other water heater types, such as a gas water heater, and with other water heater element designs. It is also envisioned that the invention or aspects of the invention can be used in other water storage devices. 4 [00]4 An electrode assembly 145 is attached to the water heater 100 and extends into the tank 105 to provide corrosion protection to the tank. An example electrode assembly 145 capable of being used with the water heater is shown in Fig. 2. With reference to Fig. 2, the electrode assembly 145 includes an electrode wire 150 and a connector assembly 155. The electrode wire 150 comprises titanium and has a first portion 160 that is coated with a metal-oxide material and a second portion 165 that is not coated with the metal-oxide material. During manufacturing of the electrode assembly 145, a shield tube 170, comprising PEX or polysulfone, is placed over a portion of the electrode wire 150. The electrode wire 150 is then bent twice (e.g., at two forty-five degree angles) to hold the shield tube in place. A small portion 175 of the electrode wire 150 near the top of the tank is exposed to the tank for allowing hydrogen gas to exit the shield tube. In other constructions, the electrode assembly 145 does not include the shield tube 170. The connector assembly 155 includes a spud 180 having threads, which secure the electrode rod assembly to the top of the water tank 105 by mating with the threads of opening 190 (Fig. 1). Of course, other connector assemblies known to those skilled in the art can be used to secure the electrode assembly 145 to the tank 105. The connector assembly also includes a connector 195 for electrically connecting the electrode wire 150 to a control circuit (discussed below). Electrically connecting the electrode assembly 145 to the control circuit results in the electrode assembly 145 becoming a powered anode. As is known to those skilled in the art, the electrode wire 150 is electrically isolated from the tank 105 to allow for a potential to develop across the electrode wire 150 and the tank 105. [00]5 An electronic schematic for one construction of the control circuit 200 used for controlling the electrode assembly 145 is shown in Fig. 3. The control circuit includes a microcontroller U2. An example microcontroller U2 used in one construction of the control circuit 200 is a Silicon Laboratories microcontroller, model no. 8051F310. As will be discussed in more detail below, the microcontroller U2 receives signals or inputs from a plurality of sensors, analyzes the inputs, and generates outputs to control the electrode assembly 145. In addition, the microcontroller U2 can receive other inputs (e.g., inputs from a user) and can generate outputs to control other devices (e.g., the heating element 140). As is known in the art, the Silicon Laboratories microcontroller, model no. 8051F310, includes a processor and memory. The memory includes one or more 5 modules having instructions. The processor obtains, interprets, and executes the instructions to control the water heater 100, including the electrode assembly 145. Although the microcontroller U2 is described having a processor and memory, the invention may be implemented with other devices including a variety of integrated circuits (e.g., an application-specific-integrated circuit) and discrete devices, as would be apparent to one of ordinary skill in the art. [00]6 The microcontroller U2 outputs a pulse-width-modulated (PWM) signal at P0.1. Generally speaking, the PWM signal controls the voltage applied to the electrode wire 150. A one hundred percent duty cycle results in full voltage being applied to the electrode wire 150, a zero percent duty cycle results in no voltage being applied to the electrode wire 150, and a ratio between zero and one hundred percent will result in a corresponding ratio between no and full voltage being applied to the electrode wire 150. [00] 7 The PWM signal is applied to a low-pass filter and amplifier, which consists of resistors R2, R3, and R4; capacitor C3; and operational amplifier U3-C. The low- pass filter converts the PWM signal into an analog voltage proportional to the PWM signal. The analog voltage is provided to a buffer and current limiter, consisting of operational amplifier U3-D, resistors R12 and R19, and transistors Ql and Q3. The buffer and current limiter provides a buffer between the microcontroller U2 and the electrode assembly 145 and limits the current applied to the electrode wire 150 to prevent hydrogen buildup. Resistor R7, inductor LI, and capacitor C5 act as a filter to prevent transients and oscillations. The result of the filter is a voltage that is applied to the electrode assembly 145, which is electrically connected to CON1. [00] 8 As discussed later, the drive voltage is periodically removed from the electrode assembly 145. The microcontroller deactivates the drive voltage by controlling the signal applied to a driver, which consists of resistor R5 and transistor Q2. More specifically, pulling pin P0.3 of microcontroller U2 low results in the transistor Ql turning OFF, which effectively removes the applied voltage from driving the electrode assembly 145. Accordingly, the microcontroller U2, the low- pass filter and amplifier, the buffer and current limiter, the filter, and the driver act as a variable voltage supply that controllably applies a voltage to the electrode assembly 145, resulting in the powered arrode. Other circuit designs known to 6 those skilled in the art can be used to controllably provide a voltage to the electrode assembly 145. [00]9 The connection C0N2 provides a connection that allows for an electrode return current measurement. More specifically, resistor R15 provides a sense resistor that develops a signal having a relation to the current at the tank. Operational amplifier U3-B and resistors R13 and R14 provide an amplifier that provides an amplified signal to the microcontroller U2 at pin Pl.l. Accordingly, resistor R15 and the amplifier form a current sensor. However, other current sensors can be used in place of the sensor just described. [00] 10 With the removal of the voltage, the potential at the electrode 145 drops to a potential that is offset from, but proportional to, the open circuit or "natural potential" of the electrode 145 relative to the tank 105. A voltage proportional to the natural potential is applied to a filter consisting of resistor R6 and capacitor C4. The filtered signal is applied to operational amplifier U3-A, which acts as a voltage follower. The output of operational amplifier U3-A is applied to a voltage limiter (resistor R17 and zener diode D3) and a voltage divider (resistor R18 and R20). The output is a signal having a relation to the natural potential of the electrode assembly 145, which is applied to microcontroller U2 at pin P1.0. Accordingly, the just-described filter, voltage follower, voltage limiter, and voltage divider form a voltage sensor. However, other voltage sensors can be used in place of the disclosed voltage sensor. [00]ll The control circuit 200 controls the voltage applied to the electrode wire 150. As will be discussed below, the control circuit 200 also measures tank protection levels, adapts to changing water conductivity conditions, and adapts to electrode potential drift in high conductivity water. In addition, when the control circuit 200 for the electrode assembly 145 is combined or in communication with the control circuit for the heating element 140, the resulting control circuit can take advantage of the interaction to provide additional control of the water heater. [00] 12 Fig. 4 provides one method of controlling the electrode assembly 145. Before proceeding to Fig. 4, it should be understood that the order of steps disclosed could vary. Furthermore, additional steps can be added to the control sequence and not all of the steps may be required. During normal operation, voltage is applied from the control circuit 200 to the electrode assembly 145. Periodically 7 (e.g., every 100 ms), an interrupt occurs and the control circuit enters the control loop shown in Fig. 4. [00] 13 With reference to Fig. 4, the control circuit 200 disables the voltage applied to the electrode assembly 145 (block 220). After disabling the voltage, the control circuit 200 performs a delay (block 225), such as 250 us, and determines an electrode potential (block 230). The control circuit 200 performs the delay to allow the electrode assembly 145 to relax to its open circuit. The microcontroller Ul then acquires this potential from the voltage sensor. The control circuit 200 then reapplies the voltage to the electrode assembly 145 (block 240). At block 240, the control circuit 200 determines whether the electrode potential is greater than a target potential. If the electrode potential is greater than the target potential, the control circuit proceeds to block 245; otherwise the control proceeds to block 250. [00] 14 At block 245, the control circuit 200 determines whether the applied voltage is at a minimum value. If the applied voltage is at the minimum, the control circuit 200 proceeds to block 255; otherwise the control circuit 200 proceeds to block 260. At block 260, the control circuit decreases the applied voltage. [00] 15 At block 250, the control circuit 200 determines whether the applied voltage is at a maximum value. If the applied voltage is at the maximum, the control circuit 200 proceeds to block 255; otherwise the control circuit proceeds to block 265. At block 265, the control circuit 200 increases the applied voltage. By decreasing or increasing the applied voltage at block 260 or 265, respectively, the control circuit 200 can indirectly adjust the electrode potential. Increasing the applied voltage will result in an increase in the tank potential measured by the electrode and decreasing the applied voltage will decrease the tank potential measured by the electrode. Therefore, the control circuit 200 can adjust the open circuit potential of the electrode until it reaches the target potential. Furthermore, as the characteristics of the water heater 100 change, the control circuit 200 can adjust the voltage applied to the electrode to have the open circuit potential of the electrode equal the target point potential. [00]16 At block 255, the control circuit acquires an electrode current. More specifically, the microcontroller Ul receives a signal that represents a sensed current form the current sensor. At block 270, the control circuit determines a conductivity state of 8 the water. For example, the conductivity state can be either a high conductivity for the water or a low conductivity for the water. To determine the conductivity state (either high or low), the microcontroller Ul divides the applied current by an incremental voltage, which is equal to the applied voltage minus the open circuit potential. If the resultant is less than an empirically set value, then the control circuit 200 determines the conductivity state is low and sets the target potential to a first value; otherwise the control circuit sets the target potential to a second value indicating a high conductivity state (block 275). The control circuit 200 can repeatedly perform the conductivity test during each interrupt (as shown in Fig. 4), periodically perform the conductivity test at a greater interval than the setting of the electrode voltage, or perform the conductivity test only during a startup sequence. Additionally, while only two set points are shown, it is envisioned that multiple set points can be used. It is also envisioned that other methods can be used to determine the conductivity state of the water. For example, a ratio of the applied current divided by the applied voltage can be used to determine the conductivity state. [00] 17 In addition to establishing a set point, the control circuit 200 can use the acquired current to determine whether the water heater 100 is in a dry-fire state. The term "dry fire" refers to the activation of a water heater that is not storing a proper amount of water. Activation of a heating element (e.g., an electric resistance heating element or a gas burner) of a water heater in a dry-fire state may result in damage to the water heater. For example, if water is not properly surrounding the electric resistance heating element 140, then the electric resistance heating element may burnout in less than a minute when voltage is applied to the heating element 140. Therefore, it is beneficial to reduce the likelihood of activating the heating element 140 if the water heater 100 is in a dry-fire state. If the acquired current is less than a minimum value (e.g., essentially zero), then it is assumed that the water heater 100 is not storing the proper amount of water and the control circuit 200 prevents the activation of the heating element 140. It is also envisioned that other methods for determining a dry-fire state can be used. For example, the control circuit 200 can be designed in such a fashion that the electrode potential will be approximately equal to the applied voltage under dry fire conditions. 9 [00] 18 Thus, the invention provides, among other things, a new and useful water heater and method of controlling a water heater. Various features and advantages of the invention are set forth in the following claims. 10 [00] 19 WE CLAIM:: 1. A method of controlling the operation of a water storage device, the water heater comprising a tank and an electrode, the method comprising: applying a voltage to the electrode; ceasing the application of the applied voltage to the electrode; determining the potential of the electrode relative to the tank after the ceasing of the application of the applied voltage; determining a conductivity state of the water; defining a target potential for the electrode based on the conductivity state; and adjusting the applied voltage to have the electrode potential relative to the tank emulate the target potential. 2. A method as set forth in claim 1 wherein the method further comprises determining a current applied to the tank resulting from the applied voltage, wherein determining a conductivity state of the water is based at least in part on the applied voltage and the applied current. 3. A method as set forth in claim 1 wherein the method further comprises determining a current applied to the tank resulting from the applied voltage, wherein determining a conductivity state of the water comprises the acts of dividing one of the applied voltage and the applied current by the other of the applied voltage and the applied current. 4. A method as set forth in claim 3 wherein determining a conductivity state of the water further comprises determining whether the resultant indicates a first conductivity state or a second conductivity state. 5. A method as set forth in claim 4 wherein defining a target potential comprises setting the target potential to a first value if the conductivity state is a first conductivity state and setting the target potential to a second value if the conductivity state is a second conductivity state. 6. A method as set forth in claim 1 wherein the method further comprises acquiring a current applied to the tank resulting from the applied voltage, wherein determining a 11 conductivity state of the water includes the acts of calculating a difference voltage with the applied voltage and the electrode potential relative to the tank and dividing one of the difference voltage and the applied current by the other of the difference voltage and the applied current. 7. A method as set forth in claim 6 wherein determining a conductivity state of the water further comprises determining whether the resultant indicates a first conductivity state or a second conductivity state. 8. A method as set forth in claim 7 wherein defining a target potential comprises setting the target potential to a first value if the conductivity state is a first conductivity state and setting the target potential to a second value if the conductivity state is a second conductivity state. 9. A water heater comprising: a tank to hold water; an inlet to introduce cold water into the tank; an outlet to remove hot water from the tank; a heating element; an electrode; and a control circuit comprising a variable voltage supply, a voltage sensor, and a current sensor, and being configured to controllably apply a voltage to the electrode, determine the potential of the electrode relative to the tank when the voltage does not power the electrode, determine a current applied to the tank after the voltage powers the electrode, determine a conductivity state of the water in the tank based on the applied voltage and the current, and define the voltage applied to the powered electrode based on the conductivity state. 10. A water heater as set forth in claim 9 wherein the powered electrode comprises an electrode wire comprising titanium. 12 11. A water heater as set forth in claim 10 wherein the electrode wire comprises a first portion having a metal oxide coating surrounding the titanium and a second portion without a metal oxide coating. 12. A water heater as set forth in claim 11 wherein a tube surrounds at least a portion of the second portion. 13. A water heater as set forth in claim 12 wherein the electrode wire includes at least one bend to hold the tube in place. 14. A water heater as set forth in claim 9 wherein the control circuit comprises a microcontroller having a processor and a memory. 15. A water heater as set forth in claim 9 wherein the variable voltage supply comprises a pulse width modulator and a filter. 16. A water heater as set forth in claim 9 wherein the control circuit determines a conductivity state of the water heater by being further operable to divide one of the applied voltage and the applied current by the other of the applied voltage and the applied current and determine whether the resultant indicates a first conductivity state or a second conductivity state. 17. A water heater as set forth in claim 16 wherein the control circuit defines the voltage by being further operable to set a target potential to a first value if the conductivity state is a first conductivity state and set the target potential to a second value if the conductivity state is a second conductivity state, and wherein the control circuit controllably applies a voltage to the powered electrode by adjusting the applied voltage to result in the electrode potential emulating the target potential. 13 18. A water heater as set forth in claim 9 wherein the control circuit determines a conductivity state of the water by being further operable to calculating a difference voltage with the applied voltage and the electrode potential, divide one of the difference voltage and the applied current by the other of the difference voltage and the applied current, and determine whether the resultant indicates a first conductivity state or a second conductivity state. 19. A water heater as set forth in claim 18 wherein the control circuit defines the voltage by being further operable to set a target potential to a first value if the conductivity state is a first conductivity state and set the target potential to a second value if the conductivity state is a second conductivity state, and wherein the control circuit controllably applies a voltage to the powered electrode by adjusting the applied voltage to result in the electrode potential emulating the target potential. 20. A method of controlling the operation of a water heater, the water heater comprising a tank, a heating element, and an electrode, the method comprising: applying a voltage to the electrode; acquiring a signal having a relation to the applied voltage; determining whether the water heater is in a dry-fire state based at least in part on the acquired signal; and preventing activation of the heating element when the water heater is in a dry-fire state. 21. A method as set forth in claim 20 wherein the water heater further comprises a sensor electrically connected to the tank, and wherein acquiring a signal comprises acquiring a signal using the sensor. 22. A method as set forth in claim 21 wherein the sensor is a current sensor, and wherein acquiring a signal using the sensor comprises sensing a current applied to the tank. 23. A method as set forth in claim 22 wherein sensing a current occurs when the voltage is applied to the electrode. 14 24. A method as set forth in claim 20 wherein determining whether the water heater is in a dry-fire state includes determining whether the signal is less than a threshold, the threshold indicating a dry-fire state. 25. A method as set forth in claim 20 wherein the water heater further comprises a sensor electrically connected to the powered electrode, and wherein acquiring a signal comprises acquiring a signal using the sensor. 26. A method as set forth in claim 25 wherein the sensor is a voltage sensor, and wherein acquiring a signal using the sensor comprises sensing a potential of the powered electrode relative to the tank. 27. A method as set forth in claim 26 wherein the method further comprises ceasing application of the applied voltage, and wherein sensing the potential occurs after the ceasing the application of the applied voltage. 28. A method as set forth in claim 27 wherein determining whether the water heater is in a dry-fire state includes determining whether the sensed potential is less than a threshold, the threshold indicating a dry-fire state. 29. A method as set forth in claim 20 wherein the electrode protects the tank from corrosion. 30. A method as set forth in claim 20 wherein the heating element comprises at least one of an electric resistance heating element and a gas burner. [00]l A water heater having a powered electrode and a method of controlling the water heater. The water heater includes a tank to hold water, a heating element, an electrode, and a control circuit. The control circuit includes a variable voltage supply, a voltage sensor, and a current sensor. The control circuit is configured to controllably apply a voltage to the electrode, determine the potential of the electrode relative to the tank with the voltage sensor when the voltage does not power the electrode, determine a current applied to the tank after the voltage powers the electrode, determine a conductivity state of the water in the tank based on the electrode potential and the current, and define the voltage applied to the powered electrode based on the conductivity state. The control circuit of the water heater can also determine the water heater is in a dry-fire state.

Full Text

2
BACKGROUND
[00] 1 The invention relates to a water storage device having a powered anode and a
method of controlling the water storage device.
[00] 2 Powered anodes have been used in the water heater industry. To operate properly,
a powered anode typically has to resolve two major concerns. First, the powered
anode should provide enough protective current to protect exposed steel within the
tank. The level of exposed steel will vary from tank to tank and will change
during the lifetime of the tank. Second, the protective current resulting from the
powered anode should be low enough to reduce the likelihood of excessive
hydrogen.
[00]3 There are at least two techniques currently available in the water heater industry
for using a powered anode to protect a tank. One technique adjusts anode voltage
levels based on the conductivity of the water. However, this technique does not
measure the protection level of the tank and tanks with excessive exposed steel
could be inadequately protected. The second technique periodically shuts off the
current to the anode electrode and uses the electrode to "sense" the protection
level of the tank. This technique adapts to the changing amount of exposed steel
in the tank, but does not adapt to changing water conductivity levels. In addition,
this technique can have problems in high conductivity waters since currently
produced titanium electrodes with mixed metal oxide films have a tendency to
drift in their reference voltage measurements in high conductivity water. It would
be beneficial to have another alternative to the just-described techniques.
SUMMARY
[00] 1 In one embodiment, the invention provides a water heater including a tank to hold
water, an inlet to introduce cold water into the tank, an outlet to remove hot
water from the tank, a heating element (e.g., an electric resistance heating element
or a gas burner), an electrode, and a control circuit. The control circuit includes a
variable voltage supply, a voltage sensor, and a current sensor. The control circuit
is configured to controllably apply a voltage to the electrode, determine a potential
of the electrode relative to the tank when the voltage does not power the electrode,
determine a current applied to the tank after the voltage powers the electrode,

2A
determine a conductivity state of the water in the tank based on the applied voltage
and the current, and define the voltage applied to the electrode based on the
conductivity state.
[00] 2 In another embodiment, the invention provides a method of controlling operation
of a water storage device. The method includes the acts of applying a voltage to
an electrode, ceasing the application of the applied voltage to the electrode,
determining the potential of the electrode relative to the tank after the ceasing of
the application of the applied voltage, determining a conductivity state of the
water, defining a target potential for the electrode based on the conductivity state,
and adjusting the applied voltage to have the electrode potential emulate the target
potential.
[00]3 In another embodiment, the invention provides another method of controlling
operation of a water heater. The method includes the acts of applying a voltage to
an electrode, acquiring a signal having a relation to the applied voltage,
determining whether the water heater is in a dry-fire state based at least in part on
the acquired signal, and preventing activation of a heating element when the water
heater is in a dry-fire state.
[00]4 Other aspects of the invention will become apparent by consideration of the
detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[00] 1 Fig. 1 is partial-exposed view of a water heater embodying the invention.
[00]2 Fig. 2 is a side view of an electrode capable of being used in the water heater of
Fig. 1.
[00]3 Fig. 3 is a electric schematic of a control circuit capable of controlling the
electrode of Fig. 2.
[00]4 Fig. 4 is a flow chart of a subroutine capable of being executed by the control
circuit shown ill Fig. 3.
DETAILED DESCRIPTION
[00] 1 Before any embodiments of the invention are explained in detail, it is to be
understood that the invention is not limited in its application to the details of
construction and the arrangement of components set forth in the following

3
description or illustrated in the following drawings. The invention is capable of
other embodiments and of being practiced or of being carried out in various ways.
Also, it is to be understood that the phraseology and terminology used herein is for
the purpose of description and should not be regarded as limited. The use of
"including," "comprising" or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as well as additional
items. The terms "mounted," "connected," "supported," and "coupled" are used
broadly and encompass both direct and indirect mounting, connecting, supporting,
and coupling. Further, "connected" and "coupled" are not restricted to physical or
mechanical connections or couplings, and can include electrical connections or
couplings, whether direct or indirect.
[00]2 Fig. 1 illustrates a water heater 100 including an enclosed water tank 105, a shell
110 surrounding the water tank 105, and foam insulation 115 filling the annular
space between the water tank 105 and the shell 110. A typical storage tank 105 is
made of ferrous metal and lined internally with a glass-like porcelain enamel to
protect the metal from corrosion. Nevertheless, the protective lining may have
imperfections or, of necessity, may not entirely cover the ferrous metal interior.
Under these circumstances, an electrolytic corrosion cell may be established as a
result of dissolved solids in the stored water, leading to corrosion of the exposed
ferrous metal and to reduction of service life for the water heater 100.
[00]3 A water inlet line or dip tube 120 and a water outlet line 125 enter the top of the
water tank 105. The water inlet line 120 has an inlet opening 130 for adding cold
water to the water tank 105, and the water outlet line 125 has an outlet opening
135 for withdrawing hot water from the water tank 105. The water heater 100 also
includes an electric resistance heating element 140 that is attached to the tank 105
and extends into the tank 105 to heat the water. The heating element 140 typically
includes an internal high resistance heating element wire surrounded by a suitable
insulating material and enclosed in a metal jacket. Electric power for the heating
element 140 is typically supplied from a control circuit. While a water heater 100
having element 140 is shown, the invention can be used with other water heater
types, such as a gas water heater, and with other water heater element designs. It
is also envisioned that the invention or aspects of the invention can be used in
other water storage devices.

4
[00]4 An electrode assembly 145 is attached to the water heater 100 and extends into the
tank 105 to provide corrosion protection to the tank. An example electrode
assembly 145 capable of being used with the water heater is shown in Fig. 2.
With reference to Fig. 2, the electrode assembly 145 includes an electrode wire
150 and a connector assembly 155. The electrode wire 150 comprises titanium
and has a first portion 160 that is coated with a metal-oxide material and a second
portion 165 that is not coated with the metal-oxide material. During
manufacturing of the electrode assembly 145, a shield tube 170, comprising PEX
or polysulfone, is placed over a portion of the electrode wire 150. The electrode
wire 150 is then bent twice (e.g., at two forty-five degree angles) to hold the shield
tube in place. A small portion 175 of the electrode wire 150 near the top of the
tank is exposed to the tank for allowing hydrogen gas to exit the shield tube. In
other constructions, the electrode assembly 145 does not include the shield tube
170. The connector assembly 155 includes a spud 180 having threads, which
secure the electrode rod assembly to the top of the water tank 105 by mating with
the threads of opening 190 (Fig. 1). Of course, other connector assemblies known
to those skilled in the art can be used to secure the electrode assembly 145 to the
tank 105. The connector assembly also includes a connector 195 for electrically
connecting the electrode wire 150 to a control circuit (discussed below).
Electrically connecting the electrode assembly 145 to the control circuit results in
the electrode assembly 145 becoming a powered anode. As is known to those
skilled in the art, the electrode wire 150 is electrically isolated from the tank 105
to allow for a potential to develop across the electrode wire 150 and the tank 105.
[00]5 An electronic schematic for one construction of the control circuit 200 used for
controlling the electrode assembly 145 is shown in Fig. 3. The control circuit
includes a microcontroller U2. An example microcontroller U2 used in one
construction of the control circuit 200 is a Silicon Laboratories microcontroller,
model no. 8051F310. As will be discussed in more detail below, the
microcontroller U2 receives signals or inputs from a plurality of sensors, analyzes
the inputs, and generates outputs to control the electrode assembly 145. In
addition, the microcontroller U2 can receive other inputs (e.g., inputs from a user)
and can generate outputs to control other devices (e.g., the heating element 140).
As is known in the art, the Silicon Laboratories microcontroller, model no.
8051F310, includes a processor and memory. The memory includes one or more

5
modules having instructions. The processor obtains, interprets, and executes the
instructions to control the water heater 100, including the electrode assembly 145.
Although the microcontroller U2 is described having a processor and memory, the
invention may be implemented with other devices including a variety of integrated
circuits (e.g., an application-specific-integrated circuit) and discrete devices, as
would be apparent to one of ordinary skill in the art.
[00]6 The microcontroller U2 outputs a pulse-width-modulated (PWM) signal at P0.1.
Generally speaking, the PWM signal controls the voltage applied to the electrode
wire 150. A one hundred percent duty cycle results in full voltage being applied to
the electrode wire 150, a zero percent duty cycle results in no voltage being
applied to the electrode wire 150, and a ratio between zero and one hundred
percent will result in a corresponding ratio between no and full voltage being
applied to the electrode wire 150.
[00] 7 The PWM signal is applied to a low-pass filter and amplifier, which consists of
resistors R2, R3, and R4; capacitor C3; and operational amplifier U3-C. The low-
pass filter converts the PWM signal into an analog voltage proportional to the
PWM signal. The analog voltage is provided to a buffer and current limiter,
consisting of operational amplifier U3-D, resistors R12 and R19, and transistors
Ql and Q3. The buffer and current limiter provides a buffer between the
microcontroller U2 and the electrode assembly 145 and limits the current applied
to the electrode wire 150 to prevent hydrogen buildup. Resistor R7, inductor LI,
and capacitor C5 act as a filter to prevent transients and oscillations. The result of
the filter is a voltage that is applied to the electrode assembly 145, which is
electrically connected to CON1.
[00] 8 As discussed later, the drive voltage is periodically removed from the electrode
assembly 145. The microcontroller deactivates the drive voltage by controlling
the signal applied to a driver, which consists of resistor R5 and transistor Q2.
More specifically, pulling pin P0.3 of microcontroller U2 low results in the
transistor Ql turning OFF, which effectively removes the applied voltage from
driving the electrode assembly 145. Accordingly, the microcontroller U2, the low-
pass filter and amplifier, the buffer and current limiter, the filter, and the driver act
as a variable voltage supply that controllably applies a voltage to the electrode
assembly 145, resulting in the powered arrode. Other circuit designs known to

6
those skilled in the art can be used to controllably provide a voltage to the
electrode assembly 145.
[00]9 The connection C0N2 provides a connection that allows for an electrode return
current measurement. More specifically, resistor R15 provides a sense resistor
that develops a signal having a relation to the current at the tank. Operational
amplifier U3-B and resistors R13 and R14 provide an amplifier that provides an
amplified signal to the microcontroller U2 at pin Pl.l. Accordingly, resistor R15
and the amplifier form a current sensor. However, other current sensors can be
used in place of the sensor just described.
[00] 10 With the removal of the voltage, the potential at the electrode 145 drops to a
potential that is offset from, but proportional to, the open circuit or "natural
potential" of the electrode 145 relative to the tank 105. A voltage proportional to
the natural potential is applied to a filter consisting of resistor R6 and capacitor
C4. The filtered signal is applied to operational amplifier U3-A, which acts as a
voltage follower. The output of operational amplifier U3-A is applied to a voltage
limiter (resistor R17 and zener diode D3) and a voltage divider (resistor R18 and
R20). The output is a signal having a relation to the natural potential of the
electrode assembly 145, which is applied to microcontroller U2 at pin P1.0.
Accordingly, the just-described filter, voltage follower, voltage limiter, and
voltage divider form a voltage sensor. However, other voltage sensors can be used
in place of the disclosed voltage sensor.
[00]ll The control circuit 200 controls the voltage applied to the electrode wire 150. As
will be discussed below, the control circuit 200 also measures tank protection
levels, adapts to changing water conductivity conditions, and adapts to electrode
potential drift in high conductivity water. In addition, when the control circuit 200
for the electrode assembly 145 is combined or in communication with the control
circuit for the heating element 140, the resulting control circuit can take advantage
of the interaction to provide additional control of the water heater.
[00] 12 Fig. 4 provides one method of controlling the electrode assembly 145. Before
proceeding to Fig. 4, it should be understood that the order of steps disclosed
could vary. Furthermore, additional steps can be added to the control sequence
and not all of the steps may be required. During normal operation, voltage is
applied from the control circuit 200 to the electrode assembly 145. Periodically

7
(e.g., every 100 ms), an interrupt occurs and the control circuit enters the control
loop shown in Fig. 4.
[00] 13 With reference to Fig. 4, the control circuit 200 disables the voltage applied to the
electrode assembly 145 (block 220). After disabling the voltage, the control
circuit 200 performs a delay (block 225), such as 250 us, and determines an
electrode potential (block 230). The control circuit 200 performs the delay to
allow the electrode assembly 145 to relax to its open circuit. The microcontroller
Ul then acquires this potential from the voltage sensor. The control circuit 200
then reapplies the voltage to the electrode assembly 145 (block 240). At block
240, the control circuit 200 determines whether the electrode potential is greater
than a target potential. If the electrode potential is greater than the target potential,
the control circuit proceeds to block 245; otherwise the control proceeds to block
250.
[00] 14 At block 245, the control circuit 200 determines whether the applied voltage is at a
minimum value. If the applied voltage is at the minimum, the control circuit 200
proceeds to block 255; otherwise the control circuit 200 proceeds to block 260. At
block 260, the control circuit decreases the applied voltage.
[00] 15 At block 250, the control circuit 200 determines whether the applied voltage is at a
maximum value. If the applied voltage is at the maximum, the control circuit 200
proceeds to block 255; otherwise the control circuit proceeds to block 265. At
block 265, the control circuit 200 increases the applied voltage. By decreasing or
increasing the applied voltage at block 260 or 265, respectively, the control circuit
200 can indirectly adjust the electrode potential. Increasing the applied voltage
will result in an increase in the tank potential measured by the electrode and
decreasing the applied voltage will decrease the tank potential measured by the
electrode. Therefore, the control circuit 200 can adjust the open circuit potential
of the electrode until it reaches the target potential. Furthermore, as the
characteristics of the water heater 100 change, the control circuit 200 can adjust
the voltage applied to the electrode to have the open circuit potential of the
electrode equal the target point potential.
[00]16 At block 255, the control circuit acquires an electrode current. More specifically,
the microcontroller Ul receives a signal that represents a sensed current form the
current sensor. At block 270, the control circuit determines a conductivity state of

8
the water. For example, the conductivity state can be either a high conductivity
for the water or a low conductivity for the water. To determine the conductivity
state (either high or low), the microcontroller Ul divides the applied current by an
incremental voltage, which is equal to the applied voltage minus the open circuit
potential. If the resultant is less than an empirically set value, then the control
circuit 200 determines the conductivity state is low and sets the target potential to
a first value; otherwise the control circuit sets the target potential to a second value
indicating a high conductivity state (block 275). The control circuit 200 can
repeatedly perform the conductivity test during each interrupt (as shown in Fig. 4),
periodically perform the conductivity test at a greater interval than the setting of
the electrode voltage, or perform the conductivity test only during a startup
sequence. Additionally, while only two set points are shown, it is envisioned that
multiple set points can be used. It is also envisioned that other methods can be
used to determine the conductivity state of the water. For example, a ratio of the
applied current divided by the applied voltage can be used to determine the
conductivity state.
[00] 17 In addition to establishing a set point, the control circuit 200 can use the acquired
current to determine whether the water heater 100 is in a dry-fire state. The term
"dry fire" refers to the activation of a water heater that is not storing a proper
amount of water. Activation of a heating element (e.g., an electric resistance
heating element or a gas burner) of a water heater in a dry-fire state may result in
damage to the water heater. For example, if water is not properly surrounding the
electric resistance heating element 140, then the electric resistance heating element
may burnout in less than a minute when voltage is applied to the heating element
140. Therefore, it is beneficial to reduce the likelihood of activating the heating
element 140 if the water heater 100 is in a dry-fire state. If the acquired current is
less than a minimum value (e.g., essentially zero), then it is assumed that the water
heater 100 is not storing the proper amount of water and the control circuit 200
prevents the activation of the heating element 140. It is also envisioned that other
methods for determining a dry-fire state can be used. For example, the control
circuit 200 can be designed in such a fashion that the electrode potential will be
approximately equal to the applied voltage under dry fire conditions.

9
[00] 18 Thus, the invention provides, among other things, a new and useful water heater
and method of controlling a water heater. Various features and advantages of the
invention are set forth in the following claims.

10
[00] 19 WE CLAIM::
1. A method of controlling the operation of a water storage device, the water heater
comprising a tank and an electrode, the method comprising:
applying a voltage to the electrode;
ceasing the application of the applied voltage to the electrode;
determining the potential of the electrode relative to the tank after the ceasing of the
application of the applied voltage;
determining a conductivity state of the water;
defining a target potential for the electrode based on the conductivity state; and
adjusting the applied voltage to have the electrode potential relative to the tank
emulate the target potential.
2. A method as set forth in claim 1 wherein the method further comprises determining a
current applied to the tank resulting from the applied voltage, wherein determining a
conductivity state of the water is based at least in part on the applied voltage and the applied
current.
3. A method as set forth in claim 1 wherein the method further comprises determining a
current applied to the tank resulting from the applied voltage, wherein determining a
conductivity state of the water comprises the acts of dividing one of the applied voltage and
the applied current by the other of the applied voltage and the applied current.
4. A method as set forth in claim 3 wherein determining a conductivity state of the water
further comprises determining whether the resultant indicates a first conductivity state or a
second conductivity state.
5. A method as set forth in claim 4 wherein defining a target potential comprises setting
the target potential to a first value if the conductivity state is a first conductivity state and
setting the target potential to a second value if the conductivity state is a second conductivity
state.
6. A method as set forth in claim 1 wherein the method further comprises acquiring a
current applied to the tank resulting from the applied voltage, wherein determining a

11
conductivity state of the water includes the acts of calculating a difference voltage with the
applied voltage and the electrode potential relative to the tank and dividing one of the
difference voltage and the applied current by the other of the difference voltage and the
applied current.
7. A method as set forth in claim 6 wherein determining a conductivity state of the water
further comprises determining whether the resultant indicates a first conductivity state or a
second conductivity state.
8. A method as set forth in claim 7 wherein defining a target potential comprises setting
the target potential to a first value if the conductivity state is a first conductivity state and
setting the target potential to a second value if the conductivity state is a second conductivity
state.
9. A water heater comprising:
a tank to hold water;
an inlet to introduce cold water into the tank;
an outlet to remove hot water from the tank;
a heating element;
an electrode; and
a control circuit comprising a variable voltage supply, a voltage sensor, and a current
sensor, and being configured to
controllably apply a voltage to the electrode,
determine the potential of the electrode relative to the tank when the voltage
does not power the electrode,
determine a current applied to the tank after the voltage powers the electrode,
determine a conductivity state of the water in the tank based on the applied
voltage and the current, and
define the voltage applied to the powered electrode based on the conductivity
state.
10. A water heater as set forth in claim 9 wherein the powered electrode comprises an
electrode wire comprising titanium.

12
11. A water heater as set forth in claim 10 wherein the electrode wire comprises a first
portion having a metal oxide coating surrounding the titanium and a second portion without a
metal oxide coating.
12. A water heater as set forth in claim 11 wherein a tube surrounds at least a portion of
the second portion.
13. A water heater as set forth in claim 12 wherein the electrode wire includes at least one
bend to hold the tube in place.
14. A water heater as set forth in claim 9 wherein the control circuit comprises a
microcontroller having a processor and a memory.

15. A water heater as set forth in claim 9 wherein the variable voltage supply comprises a
pulse width modulator and a filter.
16. A water heater as set forth in claim 9 wherein the control circuit determines a
conductivity state of the water heater by being further operable to divide one of the applied
voltage and the applied current by the other of the applied voltage and the applied current and
determine whether the resultant indicates a first conductivity state or a second conductivity
state.
17. A water heater as set forth in claim 16 wherein the control circuit defines the voltage
by being further operable to set a target potential to a first value if the conductivity state is a
first conductivity state and set the target potential to a second value if the conductivity state is
a second conductivity state, and wherein the control circuit controllably applies a voltage to
the powered electrode by adjusting the applied voltage to result in the electrode potential
emulating the target potential.

13
18. A water heater as set forth in claim 9 wherein the control circuit determines a
conductivity state of the water by being further operable to calculating a difference voltage
with the applied voltage and the electrode potential, divide one of the difference voltage and
the applied current by the other of the difference voltage and the applied current, and
determine whether the resultant indicates a first conductivity state or a second conductivity
state.
19. A water heater as set forth in claim 18 wherein the control circuit defines the voltage
by being further operable to set a target potential to a first value if the conductivity state is a
first conductivity state and set the target potential to a second value if the conductivity state is
a second conductivity state, and wherein the control circuit controllably applies a voltage to
the powered electrode by adjusting the applied voltage to result in the electrode potential
emulating the target potential.
20. A method of controlling the operation of a water heater, the water heater comprising
a tank, a heating element, and an electrode, the method comprising:
applying a voltage to the electrode;
acquiring a signal having a relation to the applied voltage;
determining whether the water heater is in a dry-fire state based at least in part on the
acquired signal; and
preventing activation of the heating element when the water heater is in a dry-fire
state.
21. A method as set forth in claim 20 wherein the water heater further comprises a sensor
electrically connected to the tank, and wherein acquiring a signal comprises acquiring a signal
using the sensor.
22. A method as set forth in claim 21 wherein the sensor is a current sensor, and wherein
acquiring a signal using the sensor comprises sensing a current applied to the tank.
23. A method as set forth in claim 22 wherein sensing a current occurs when the voltage
is applied to the electrode.

14
24. A method as set forth in claim 20 wherein determining whether the water heater is in a
dry-fire state includes determining whether the signal is less than a threshold, the threshold
indicating a dry-fire state.
25. A method as set forth in claim 20 wherein the water heater further comprises a sensor
electrically connected to the powered electrode, and wherein acquiring a signal comprises
acquiring a signal using the sensor.
26. A method as set forth in claim 25 wherein the sensor is a voltage sensor, and wherein
acquiring a signal using the sensor comprises sensing a potential of the powered electrode
relative to the tank.
27. A method as set forth in claim 26 wherein the method further comprises ceasing
application of the applied voltage, and wherein sensing the potential occurs after the ceasing
the application of the applied voltage.

28. A method as set forth in claim 27 wherein determining whether the water heater is in a
dry-fire state includes determining whether the sensed potential is less than a threshold, the
threshold indicating a dry-fire state.
29. A method as set forth in claim 20 wherein the electrode protects the tank from
corrosion.
30. A method as set forth in claim 20 wherein the heating element comprises at least one
of an electric resistance heating element and a gas burner.

[00]l A water heater having a powered electrode and a method of controlling the
water heater. The water heater includes a tank to hold water, a heating element, an
electrode, and a control circuit. The control circuit includes a variable voltage
supply, a voltage sensor, and a current sensor. The control circuit is configured to
controllably apply a voltage to the electrode, determine the potential of the
electrode relative to the tank with the voltage sensor when the voltage does not
power the electrode, determine a current applied to the tank after the voltage
powers the electrode, determine a conductivity state of the water in the tank based
on the electrode potential and the current, and define the voltage applied to the
powered electrode based on the conductivity state. The control circuit of the water
heater can also determine the water heater is in a dry-fire state.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=FRga5RkgFzBnBCWF8hrgkg==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

279143

Indian Patent Application Number

879/KOL/2005

PG Journal Number

02/2017

Publication Date

13-Jan-2017

Grant Date

12-Jan-2017

Date of Filing

23-Sep-2005

Name of Patentee

AOS HOLDING COMPANY

Applicant Address

1403 FAULK ROAD, SUITE 106-, WILMINGTON DELAWARE 19890, U.S.A.

Inventors:

#	Inventor's Name	Inventor's Address
1	KNOEPPEL RAY OLIVER	N8691 W316 PALAMINO CIRCLE HARTLAND, WISCONSIN 53029, U.S.A.
2	MURPHY MARK ALLAN	462 OAKLEY DRIVE, NASHVILLE, TENNESSEE 37220, U.S.A.
3	SISTINE THOMAS GERARD VAN	N74 W 15442 STONEWOOD DRIVE MENOMONEE FALLS, WISCONSIN 53051 U.S.A.

PCT International Classification Number

H05B 3/60

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10/950,851	2004-09-27	U.S.A.