Liquid level detection device

Abstract

This technology provides a solution for addressing abnormalities that occur in the grounding electrode. [Solution] The liquid level detection device comprises a tank for storing liquid, a main ground electrode that is electrically grounded, a sub-ground electrode that is electrically grounded via a switch that can switch between a conductive state and a non-conductive state, a liquid level detection electrode, a voltage application means for applying a voltage to the liquid level detection electrode, a current detection circuit for detecting whether or not current flows through the liquid level detection electrode, and a control unit. The control unit is configured to perform a liquid level determination process that determines whether or not the liquid level in the tank has risen to a predetermined liquid level based on the current detection result, which is the detection result of the current detection circuit when the voltage application means applies a voltage to the liquid level detection electrode, and an abnormality determination process that determines that there is an abnormality in the main ground electrode when the current detection result when the switch is conductive and the current detection result when the switch is non-conductive are different by switching the conductive state / non-conductive state of the switch.

Description

Technical Field

[0004] , , ,

[0001] The technology disclosed in this specification relates to a liquid level detection device.

Background Art

[0002] Patent Document 1 includes a tank for storing a liquid, a grounding electrode that is electrically grounded and disposed in the tank, a liquid level detection electrode disposed in the tank, a voltage application means for applying a voltage to the liquid level detection electrode, a current detection circuit for detecting whether a current flows through the liquid level detection electrode, and a control unit. The control unit is configured to be able to execute a liquid level determination process for determining whether the liquid level in the tank has reached a predetermined liquid level or higher based on a current detection result that is a detection result of the current detection circuit when the voltage application means applies a voltage to the liquid level detection electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Normally, when the liquid level detection electrode is immersed in liquid, the liquid level detection electrode conducts to the reference potential via the liquid and the ground electrode. In this case, when a voltage is applied to the liquid level detection electrode, a current flows from the liquid level detection electrode to the ground electrode. Therefore, the liquid level detection device determines that the liquid level in the tank is above a predetermined level (i.e., the liquid level has reached a level where the liquid level detection electrode is immersed in the liquid) when a current flows through the liquid level detection electrode when a voltage is applied to it. However, if there is a problem with the ground electrode, even if a voltage is applied to the liquid level detection electrode while it is immersed in liquid, no current will flow from the liquid level detection electrode to the ground electrode, and the liquid level detection device may misjudge the liquid level in the tank. Misjudgment here means that, despite the liquid level detection electrode being immersed in liquid, the device determines that the liquid level in the tank has not reached a level where the liquid level detection electrode is immersed in liquid. In the liquid level detection device described in Patent Document 1, even if an abnormality like the one described above occurs in the ground electrode, it cannot be recognized, and therefore cannot be dealt with (for example, by notifying the abnormality or detecting the liquid level by an alternative method). This specification provides a technology that can deal with abnormalities occurring in the ground electrode. [Means for solving the problem]

[0005] In a first aspect of this technology, the liquid level detection device may include a tank for storing liquid, a main ground electrode that is electrically grounded and located inside the tank, a sub-ground electrode that is electrically grounded via a switch that can switch between a conductive state and a non-conductive state and located inside the tank, a liquid level detection electrode located inside the tank, a voltage application means for applying a voltage to the liquid level detection electrode, a current detection circuit for detecting whether or not current flows through the liquid level detection electrode, and a control unit. The control unit may be configured to perform a liquid level determination process that determines whether or not the liquid level in the tank has risen to or below a predetermined liquid level based on a current detection result, which is the detection result of the current detection circuit when the voltage application means applies a voltage to the liquid level detection electrode, and an abnormality determination process that determines that there is an abnormality in the main ground electrode when the current detection result when the switch is conductive and the current detection result when the switch is non-conductive are different by switching the conductive state / non-conductive state of the switch.

[0006] According to the above configuration, when the liquid level detection electrode is immersed in liquid, the liquid level detection electrode conducts to the reference potential not only through the liquid and the main ground electrode, but also through the liquid, the sub-ground electrode, and the switch. If the main ground electrode is functioning normally, when a voltage is applied to the liquid level detection electrode, current flows from the liquid level detection electrode to the main ground electrode through the liquid. Therefore, whether the switch is in a conductive or non-conductive state, current flows to the liquid level detection electrode when a voltage is applied, so the current detection result will be the same. On the other hand, if there is a malfunction in the main ground electrode, current may not flow from the liquid level detection electrode to the main ground electrode even when a voltage is applied to it. In this case, the current detection result when a voltage is applied to the liquid level detection electrode will differ depending on the state of the switch. This is because, when the liquid level detection electrode is immersed in liquid, if the switch is conductive, current flows from the liquid level detection electrode through the liquid to the sub-ground electrode, but if the switch is not conductive, no current flows from the liquid level detection electrode to the sub-ground electrode. Therefore, with the above configuration, if the current detection result when a voltage is applied to the liquid level detection electrode differs depending on the state of the switch, it is possible to determine that there is an abnormality in the main ground electrode. This allows for the recognition and countermeasures to be taken when an abnormality occurs in the main ground electrode.

[0007] In a second aspect of this technology, in the first aspect, the liquid level detection electrode may include a first liquid level detection electrode and a second liquid level detection electrode. In the vertical direction, the lower end of the first liquid level detection electrode may be positioned below the lower end of the second liquid level detection electrode in the tank. In the abnormality determination process, the control unit may determine that there is an abnormality in the main ground electrode if the current detection result when the switch is in a conductive state and the voltage application means applies a voltage to the first liquid level detection electrode is different from the current detection result when the switch is in a non-conductive state and the voltage application means applies a voltage to the first liquid level detection electrode.

[0008] If the liquid level detection electrode is not immersed in liquid, no current will flow through it even if a voltage is applied, and therefore the abnormality detection process will not function effectively. With the above configuration, when there are multiple liquid level detection electrodes, the abnormality detection process is performed using the current detection result of the electrode that extends further down in the tank (i.e., the liquid level detection electrode that is immersed in the liquid first). This makes it less likely that a situation will occur in which the abnormality detection process does not function effectively.

[0009] In a third aspect of this technology, in the first or second aspect described above, the control unit may maintain the switch in a conductive state if it determines that there is an abnormality in the main ground electrode.

[0010] With the above configuration, if there is a problem with the main ground electrode, the sub-ground electrode can function as a substitute for the main ground electrode. For example, when a voltage is applied to the liquid level detection electrode during liquid level determination processing, current can be made to flow from the liquid level detection electrode to the sub-ground electrode through the liquid.

[0011] In a fourth aspect of this technology, in any one of the first to third embodiments described above, if the control unit determines that there is an abnormality in the main ground electrode, it may cause a predetermined notification device to notify it of the abnormality in the main ground electrode.

[0012] With the above configuration, if there is an abnormality in the main ground electrode, the user can be notified. This allows, for example, the user to be prompted to resolve the abnormality in the main ground electrode.

[0013] In a fifth aspect of this technology, in any one of the first to fourth embodiments described above, the liquid level detection device may be incorporated into a combustion heat source. The combustion heat source may include a combustor, a latent heat exchanger that recovers the latent heat of the combustion gas generated in the combustor to heat a heat transfer medium, and a neutralizing agent that neutralizes the drain generated in the latent heat exchanger. The tank may store the drain, after it has been neutralized by the neutralizing agent, as the liquid.

[0014] When a calcium-based neutralizing agent is used, the calcium component contained in the neutralizing agent may be stored in the tank along with the drain. In this case, positively charged calcium components may adhere to the surface of the main ground electrode, which functions as the cathode in the liquid level determination process, potentially forming a film on the surface of the main ground electrode. This film insulates the main ground electrode from the surrounding liquid, potentially preventing current from flowing from the liquid level detection electrode to the main ground electrode even when a voltage is applied to the liquid level detection electrode. With the above configuration, it is possible to determine that there is an abnormality in the main ground electrode in such a case.

[0015] In a sixth aspect of this technology, in the fifth aspect described above, if the control unit has not performed the abnormality determination process and has not determined that there is an abnormality in the main ground electrode, the switch may be kept in a non-conductive state.

[0016] When the switch is in a conductive state, the sub-ground electrode functions as a cathode in the liquid level determination process, just like the main ground electrode. Therefore, if the sub-ground electrode is kept in a conductive state, calcium components may adhere to the sub-ground electrode, just like to the main ground electrode. In contrast, with the above configuration, the sub-ground electrode is not kept in a conductive state unnecessarily, thus suppressing the adhesion of calcium components to the sub-ground electrode.

[0017] In a seventh aspect of this technology, in the fifth or sixth aspect described above, the control unit may execute the abnormality determination process when a request to start combustion in the combustor occurs.

[0018] According to the above configuration, the control unit performs abnormality detection processing at appropriate time intervals. This makes it possible to check at appropriate time intervals whether or not there is an abnormality in the main ground electrode. [Brief explanation of the drawing]

[0019] [Figure 1] This diagram schematically shows the configuration of the water heater 2 according to the embodiment. [Figure 2] It is a diagram schematically showing the configuration of the liquid level detection device 90 incorporated in the water heater 2 according to the embodiment. [Figure 3] It is a flowchart of the drain discharge process executed by the microcomputer 70 of the water heater 2 according to the embodiment. [Figure 4] It is a flowchart of the combustion standby process executed by the microcomputer 70 of the water heater 2 according to the embodiment. [Figure 5] It is a flowchart of the abnormality determination process executed by the microcomputer 70 of the water heater 2 according to the embodiment. [Figure 6] It is a diagram schematically showing the mechanism for the microcomputer 70 of the water heater 2 according to the embodiment to determine that there is an abnormality in the main ground electrode 62.

Modes for Carrying Out the Invention

[0020] (Embodiment) The water heater 2 shown in FIG. 1 heats the water supplied from the water supply pipe 4 and sends it out to the hot water supply pipe 6. The hot water supply pipe 6 is connected to a hot water supply location such as a faucet or a bathtub.

[0021] The water heater 2 includes a water pipe 8, a flow sensor 10, a water volume servo 12, a gas burner 14, a sensible heat exchanger 16, a latent heat exchanger 18, a temperature sensor 20, a drain pan 22, a neutralizer 24, and a control unit 26.

[0022] The control unit 26 is configured to be communicable with the remote controller 28. The remote controller 28 is arranged in a bathroom or the like. The remote controller 28 includes an operation unit 30 operable by the user, a display unit 32 for displaying various information related to the water heater 2, and an audio output unit 34 for outputting various information related to the water heater 2 as audio.

[0023] The water supply pipe 8 has its upstream end connected to the water supply pipe 4 and its downstream end connected to the hot water supply pipe 6. The water supply pipe 8 is equipped with, in order from the upstream side, a flow sensor 10, a water volume servo 12, a latent heat exchanger 18, a sensible heat exchanger 16, and a temperature sensor 20. The flow sensor 10 detects the flow rate of water flowing through the water supply pipe 8. The water volume servo 12 adjusts the flow rate of water flowing through the water supply pipe 8. The temperature sensor 20 detects the temperature of the water after it has passed through the sensible heat exchanger 16.

[0024] The gas burner 14 burns fuel gas supplied from a fuel source (not shown), such as city gas, to generate combustion gas. The sensible heat exchanger 16 recovers the sensible heat of the combustion gas generated by the gas burner 14 and heats the water in the water pipe 8. The latent heat exchanger 18 recovers the latent heat of the combustion gas generated by the gas burner 14 and heats the water in the water pipe 8.

[0025] Drain generated in the latent heat exchanger 18 drips into the drain pan 22. The drain that drips into the drain pan 22 is sent to the neutralizer 24 via the drain recovery passage 36. The neutralizer 24 comprises a first tank section 38 to which the downstream end of the drain recovery passage 36 is connected, and a second tank section 42 adjacent to the first tank section 38 via a partition wall 40. The drain sent to the neutralizer 24 via the drain recovery passage 36 is first stored in the first tank section 38. The first tank section 38 is filled with a neutralizing agent (not shown) such as calcium carbonate. As a result, the drain is neutralized in the first tank section 38. The first tank section 38 is also equipped with a trap structure 44. Normally, the space upstream of the trap structure 44 and the space downstream of the trap structure 44 are separated by the drain stored in the first tank section 38. When the liquid level of the drain stored in the first tank section 38 reaches the height of the upper end of the partition wall 40, the drain flows from the first tank section 38 to the second tank section 42 and is stored in the second tank section 42. The upstream end of the discharge channel 46 is connected to the lower part of the second tank section 42. The downstream end of the discharge channel 46 is connected to a predetermined discharge point (for example, a sewer). A discharge pump 48 is installed in the middle of the discharge channel 46. When the discharge pump 48 is driven, the drain stored in the second tank section 42 is discharged to the discharge point via the discharge channel 46. When the discharge pump 48 is stopped, the drain does not flow to the discharge point. In addition, the upstream end of the overflow channel 50 is connected to the side of the second tank section 42. The downstream end of the overflow channel 50 is connected to the discharge point. When the liquid level of the drain stored in the second tank section 42 rises and reaches the height of the upstream end of the overflow passage 50, the drain is discharged to the discharge point via the overflow passage 50. This prevents the drain stored in the neutralizer 24 from flowing back into the drain recovery passage 36. An electrode unit 60 is also provided inside the second tank section 42.

[0026] As shown in Figure 2, the electrode unit 60 comprises a main ground electrode 62, a sub-ground electrode 64, a low liquid level detection electrode 66, and a high liquid level detection electrode 68. The main ground electrode 62 is electrically grounded. The sub-ground electrode 64 is electrically grounded via a grounding switch 76, which will be described later. Here, "grounding" refers to being connected to the reference potential GND in the control unit 26. Inside the second tank section 42, the lower end of the main ground electrode 62, the lower end of the sub-ground electrode 64, and the lower end of the low liquid level detection electrode 66 are at approximately the same height. The lower end of the high liquid level detection electrode 68 is at a higher position than the lower end of the main ground electrode 62, the lower end of the sub-ground electrode 64, and the lower end of the low liquid level detection electrode 66.

[0027] The control unit 26 includes a microcontroller 70, a current limiting circuit 71, a voltage application circuit 72, a current detection circuit 74, and a grounding switch 76. The microcontroller 70 consists of a CPU, memory, etc., and controls the operation of each part of the water heater 2.

[0028] The current limiting circuit 71 and the voltage application circuit 72 are provided between the power supply 200 and the low liquid level detection electrode 66 and the high liquid level detection electrode 68, respectively. The current limiting circuit 71 is provided between the power supply 200 and the voltage application circuit 72. The current limiting circuit 71 limits the current flowing through the voltage application circuit 72 to a predetermined current (for example, 80 μA) or less.

[0029] The voltage application circuit 72 includes a first voltage application switch 78, a first diode 80, a second voltage application switch 82, and a second diode 84. When the first voltage application switch 78 is ON, it causes conduction between the power supply 200 and the low liquid level detection electrode 66. In this case, the voltage of the power supply 200 is applied to the low liquid level detection electrode 66. When the first voltage application switch 78 is OFF, it causes deconduction between the power supply 200 and the low liquid level detection electrode 66. In this case, the voltage of the power supply 200 is no longer applied to the low liquid level detection electrode 66. The first voltage application switch 78 is normally OFF. The first diode 80 is provided between the first voltage application switch 78 and the low liquid level detection electrode 66, allowing current to flow from the first voltage application switch 78 to the low liquid level detection electrode 66, and preventing current from flowing from the low liquid level detection electrode 66 to the first voltage application switch 78. The second voltage application switch 82, when turned ON, conducts between the power supply 200 and the high liquid level detection electrode 68. In this case, the voltage of the power supply 200 is applied to the high liquid level detection electrode 68. The second voltage application switch 82, when turned OFF, deconducts between the power supply 200 and the high liquid level detection electrode 68. In this case, the voltage of the power supply 200 is no longer applied to the high liquid level detection electrode 68. The second voltage application switch 82 is normally OFF. The second diode 84 is provided between the second voltage application switch 82 and the high liquid level detection electrode 68, allowing current to flow from the second voltage application switch 82 to the high liquid level detection electrode 68, and preventing current from flowing from the high liquid level detection electrode 68 to the second voltage application switch 82.

[0030] The current detection circuit 74 detects whether or not current flows through the low liquid level detection electrode 66, and also detects whether or not current flows through the high liquid level detection electrode 68. Specifically, the current detection circuit 74 detects whether or not current flows through the conductive path between the current limiting circuit 71 and each of the first voltage application switch 78 and the second voltage application switch 82.

[0031] The grounding switch 76 conducts between the sub-grounding electrode 64 and the reference potential GND when it is ON, and deconducts between the sub-grounding electrode 64 and the reference potential GND when it is OFF. The grounding switch 76 is normally OFF.

[0032] In this embodiment, the electrode unit 60 and the control unit 26 are collectively referred to as the liquid level detection device 90.

[0033] (Drain discharge treatment: Figure 3) The microcomputer 70 repeatedly performs the drain discharge process shown in Figure 3 while the main power supply of the water heater 2 is ON. The drain discharge process is a process in which the discharge pump 48 is driven when the liquid level of the drain stored in the second tank section 42 (also called the tank liquid level) becomes high, and the drain is discharged to the discharge point.

[0034] In S2, the microcontroller 70 waits for a predetermined waiting time. In this embodiment, the microcontroller 70 waits for a first waiting time (e.g., 1 second) if combustion by the gas burner 14 is in progress, and waits for a second waiting time (e.g., 5 seconds) which is longer than the first waiting time, if combustion by the gas burner 14 has stopped. After S2, the process proceeds to S4.

[0035] In S4, the microcontroller 70 applies voltage to the high liquid level detection electrode 68 (see Figure 2) by switching the second voltage application switch 82 (see Figure 2) to ON. At the same time, the microcontroller 70 monitors the detection result of the current detection circuit 74 (see Figure 2) to determine whether or not current has flowed through the high liquid level detection electrode 68. After that, the microcontroller 70 switches the second voltage application switch 82 to OFF. After S4, the process proceeds to S6.

[0036] In S6, the microcontroller 70 applies voltage to the low liquid level detection electrode 66 (see Figure 2) by switching the first voltage application switch 78 (see Figure 2) to ON. At the same time, the microcontroller 70 monitors the detection result of the current detection circuit 74 (see Figure 2) to determine whether or not current has flowed through the low liquid level detection electrode 66. After that, the microcontroller 70 switches the first voltage application switch 78 to OFF. After S6, the process proceeds to S10.

[0037] In S10, the microcontroller 70 determines whether or not current flowed through the high liquid level detection electrode 68 (see Figure 2) when a voltage was applied to it in S4. If current flowed through the high liquid level detection electrode 68 (YES), the process proceeds to S12.

[0038] In S12, the microcontroller 70 determines that the tank liquid level is above the height of the lower end of the high liquid level detection electrode 68 (also called the high liquid level). After S12, the process proceeds to S14.

[0039] In S14, the microcontroller 70 drives the discharge pump 48 (see Figure 1). The discharge pump 48, which was driven in S14, continues to drive until it is stopped in S22. While the discharge pump 48 is running, the drain stored in the second tank section 42 is discharged to the discharge point via the discharge passage 46 (see Figure 1). As a result, the liquid level in the tank decreases. After S14, the process returns to S2.

[0040] If no current flows through the high liquid level detection electrode 68 in S10 (NO), the process proceeds to S16. In S16, the microcontroller 70 determines whether or not current flowed through the low liquid level detection electrode 66 (see Figure 2) when a voltage was applied to it in S6. If current flows through the low liquid level detection electrode 66 (YES), the process proceeds to S18.

[0041] In S18, the microcontroller 70 determines that the tank liquid level is above the height of the lower end of the low liquid level detection electrode 66 (also called the low liquid level) and below the high liquid level. After S18, the process returns to S2.

[0042] If no current is flowing through the low liquid level detection electrode 66 in S16 (NO), the process proceeds to S20. In S20, the microcontroller 70 determines that the tank liquid level is below the low liquid level. After S20, the process proceeds to S22.

[0043] In S22, the microcontroller 70 stops the discharge pump 48 unless it has already stopped. When the discharge pump 48 is stopped, the drain does not flow to the discharge point. Therefore, when the drain flows into the second tank section 42, the tank liquid level rises. After S22, the process returns to S2.

[0044] (Combustion standby process: Figure 4) If the main power supply of the water heater 2 is ON and combustion by the gas burner 14 is stopped, the microcomputer 70 executes the combustion standby process shown in Figure 4.

[0045] In S32, the microcontroller 70 determines whether a request to start combustion (i.e., a combustion start request) has been issued to the gas burner 14. For example, the microcontroller 70 determines that a combustion start request has been issued if the flow rate detected by the flow sensor 10 (see Figure 1) exceeds a predetermined combustion start flow rate. If no combustion start request has been issued (NO), the process repeats S32. If a combustion start request has been issued (YES), the process proceeds to S34.

[0046] In S34, the microcontroller 70 determines whether the main ground electrode abnormality flag, which indicates an abnormality in the main ground electrode 62 (see Figure 2), is set. For information on when the main ground electrode abnormality flag is set, please refer to the abnormality determination process described later. If the main ground electrode abnormality flag is not set (NO), the process proceeds to S36.

[0047] In S36, the microcontroller 70 executes the abnormality detection process shown in Figure 5.

[0048] (Anomaly detection process: Figure 5) When the abnormality detection process is initiated, the process proceeds to S52. In S52, the microcontroller 70 turns off the grounding switch 76 (see Figure 2), thereby making the connection between the sub-grounding electrode 64 (see Figure 2) and the reference potential GND non-conductive. The grounding switch 76, which was turned off in S52, remains off until the subsequent S54 is completed. After S52, the process proceeds to S54.

[0049] In S54, the microcontroller 70 turns on the first voltage application switch 78 to apply voltage to the low liquid level detection electrode 66 and obtains the current detection result from the current detection circuit 74 (i.e., whether or not current flows through the low liquid level detection electrode 66). After that, the microcontroller 70 switches the first voltage application switch 78 to OFF. In this embodiment, the current detection result obtained in S54 is also called the first current detection result. As shown in Figure 6, if the main ground electrode 62 is functioning normally, in case 1 (when the tank liquid level is above the low liquid level), the first current detection result is obtained indicating that current flows through the low liquid level detection electrode 66 (indicated by ○ in the table in Figure 6), and in case 2 (when the tank liquid level is below the low liquid level), the first current detection result is obtained indicating that no current flows through the low liquid level detection electrode 66 (indicated by × in the table in Figure 6). However, if there is an abnormality in the main ground electrode 62, a first current detection result will be obtained in both Case 1 and Case 2, indicating that no current is flowing through the low liquid level detection electrode 66. An example of such an abnormality is that the calcium component contained in the neutralizing agent adheres to the surface of the main ground electrode 62, forming a film that insulates the main ground electrode 62 from the drain. After S54 shown in Figure 5, the process proceeds to S56.

[0050] In S56, the microcontroller 70 turns on the grounding switch 76, thereby creating conductivity between the sub-grounding electrode 64 and the reference potential GND. The grounding switch 76, which was turned on in S56, remains ON until the completion of the following S58. After S56, the process proceeds to S58.

[0051] In S58, the microcontroller 70 turns on the first voltage application switch 78 to apply voltage to the low liquid level detection electrode 66 and acquires the current detection result from the current detection circuit 74 (i.e., whether or not current flows through the low liquid level detection electrode 66). Subsequently, the microcontroller 70 switches the first voltage application switch 78 to OFF and also switches the ground switch 76 to OFF. In this embodiment, the current detection result acquired in S58 is also called the second current detection result. In S58, whether or not there is an abnormality in the main ground electrode 62, if the sub ground electrode 64 and the low liquid level detection electrode 66 are functioning normally, in case 1 (when the tank liquid level is above the low liquid level), the second current detection result is acquired indicating that current flows through the low liquid level detection electrode 66, and in case 2 (when the tank liquid level is below the low liquid level), the second current detection result is acquired indicating that no current flows through the low liquid level detection electrode 66 (see Figure 6). This is because when the grounding switch 76 is turned ON, conduction occurs between the sub-grounding electrode 64 and the reference potential GND, causing the sub-grounding electrode 64 to function as a substitute for the main grounding electrode 62. After S58, the process proceeds to S60.

[0052] In S60, the microcontroller 70 determines whether the first current detection result obtained in S54 and the second current detection result obtained in S58 are different. As shown in Figure 6, if the main ground electrode 62 is functioning normally, the two current detection results will match in both Case 1 and Case 2. However, if there is a problem with the main ground electrode 62, the two current detection results will match in Case 2, but they will differ in Case 1. If the two current detection results match (NO), the abnormality detection process ends. If the two current detection results differ (YES), the process proceeds to S62 as shown in Figure 5.

[0053] In S62, the microcontroller 70 sets the main ground electrode abnormality flag. After S62, the abnormality detection process ends.

[0054] Once the abnormality detection process is complete, the process proceeds to S38 shown in Figure 4. In S38, the microcontroller 70 determines whether or not the main ground electrode abnormality flag is set. If the main ground electrode abnormality flag is not set (NO), the process proceeds to S40.

[0055] In S40, the microcontroller 70 turns off the grounding switch 76, thereby making the connection between the sub-grounding electrode 64 and the reference potential GND non-conductive. Furthermore, from S40 onward, the microcontroller 70 keeps the grounding switch 76 OFF, except when performing abnormality detection processing.

[0056] If the main ground electrode abnormality flag is set in S34 or S38 (YES), the process proceeds to S42. In S42, the microcontroller 70 notifies the remote control 28 that there is an abnormality in the main ground electrode 62. For example, the microcontroller 70 displays that there is an abnormality in the main ground electrode 62 on the display unit 32 of the remote control 28. Alternatively, the microcontroller 70 outputs an audio message to the audio output unit 34 of the remote control 28 indicating that there is an abnormality in the main ground electrode 62. After S42, the process proceeds to S44.

[0057] In S44, the microcontroller 70 turns on the grounding switch 76, thereby creating conductivity between the sub-grounding electrode 64 and the reference potential GND. The microcontroller 70 also keeps the grounding switch 76 ON from S44 onward. As a result, if there is a problem with the main grounding electrode 62, the sub-grounding electrode 64 will function as a substitute for the main grounding electrode 62.

[0058] After S40 or S44, the process proceeds to S46. In S46, the microcontroller 70 starts combustion in the gas burner 14. After S46, the combustion waiting process ends.

[0059] Furthermore, once the main ground electrode abnormality flag is set, it is retained even after the combustion standby process is completed or after the main power of the water heater 2 is turned OFF. The main ground electrode abnormality flag is cleared, for example, by maintenance personnel performing maintenance and inspection on the water heater 2. When the main ground electrode abnormality flag is cleared, the microcontroller 70 switches the ground switch 76, which had been kept ON since S44, to OFF.

[0060] (modified version) The liquid level detection device 90 in this embodiment may be incorporated into equipment or devices other than the water heater 2. For example, the liquid level detection device 90 may be incorporated into a gas-liquid dissolution device that dissolves gas in water. Alternatively, the liquid level detection device 90 may be incorporated into a heating device that provides heating by radiating heat from a heat transfer medium. In these cases, the tank in which the electrode unit 60 is provided is not limited to one that stores drain, but may also store other liquids (e.g., water, antifreeze).

[0061] (See Figure 5) In the abnormality determination process S54 and S58, the microcontroller 70 may, instead of obtaining the current detection result when a voltage is applied to the low liquid level detection electrode 66, obtain the current detection result when a voltage is applied to the high liquid level detection electrode 68. Therefore, the microcontroller 70 may determine that there is an abnormality in the main grounding electrode 62 if the current detection result when a voltage is applied to the high liquid level detection electrode 68 differs depending on whether the grounding switch 76 is ON or OFF. However, in this configuration, it is only possible to determine whether there is an abnormality in the main grounding electrode 62 when the high liquid level detection electrode 68 is submerged in liquid (i.e., when the tank liquid level is above the high liquid level). Normally, the tank liquid level is maintained below the high liquid level by the drain discharge process (see Figure 3). Therefore, situations in which it is possible to determine whether there is an abnormality in the main grounding electrode 62 (i.e., situations in which the tank liquid level is above the high liquid level) rarely occur. On the other hand, in the configuration of the embodiment, it becomes possible to determine whether or not there is an abnormality in the main ground electrode 62 when the low liquid level detection electrode 66 is immersed in liquid (i.e., when the tank liquid level is above the low liquid level). Therefore, the situation in which it is possible to determine whether or not there is an abnormality in the main ground electrode 62 (i.e., the situation in which the tank liquid level is above the low liquid level) occurs sufficiently. Accordingly, the configuration of the embodiment (i.e., the configuration in which the current detection result is obtained when a voltage is applied to the low liquid level detection electrode 66 in the abnormality determination process S54 and S58) is more advantageous than the configuration described as a modification (i.e., the configuration in which the current detection result is obtained when a voltage is applied to the high liquid level detection electrode 68 in the abnormality determination process S54 and S58).

[0062] (See Figure 2) In this embodiment, there were two liquid level detection electrodes (i.e., electrodes to which the voltage of the power supply 200 is applied via the voltage application circuit 72), namely a low liquid level detection electrode 66 and a high liquid level detection electrode 68. However, there may be one or three or more electrodes.

[0063] (See Figure 4) After S44 of the combustion standby process, the microcontroller 70 may keep the ground switch 76 OFF instead of keeping it ON. In this case, the microcontroller 70 may prohibit combustion by the gas burner 14 until the main ground electrode abnormality flag is cleared.

[0064] (See Figure 4) The combustion standby process S42 may be omitted. In other words, the microcontroller 70 does not need to be configured to notify the remote control 28 that there is an abnormality in the main ground electrode 62.

[0065] The microcontroller 70 may perform an abnormality detection process (see Figure 5) even if no combustion start request occurs. For example, the microcontroller 70 may perform the abnormality detection process immediately after the main power supply of the water heater 2 switches from OFF to ON. Alternatively, the microcontroller 70 may perform the abnormality detection process after S12 or after S18 of the drain discharge process (see Figure 3).

[0066] (Features of the example) In one or more embodiments, the liquid level detection device 90 includes a second tank section 42 (example of a tank) for storing liquid, a main grounding electrode 62 electrically grounded and located within the second tank section 42, a sub-grounding electrode 64 electrically grounded and located within the second tank section 42 via a grounding switch 76 (example of a switch) that can be switched between a conductive state (i.e., ON) and a non-conductive state (i.e., OFF), liquid level detection electrodes 66, 68 located within the second tank section 42, a voltage application circuit 72 (example of a voltage application means) for applying a voltage to the liquid level detection electrodes 66, 68, a current detection circuit 74 for detecting whether or not current flows through the liquid level detection electrodes 66, 68, and a microcontroller 70 (example of a control unit). The microcontroller 70 is configured to perform a liquid level determination process (i.e., S2, S4, S6, S10, S12, S16, S18, S20 of the drain discharge process) that determines whether the liquid level in the second tank section 42 has risen to or above a predetermined liquid level based on the current detection result, which is the detection result of the current detection circuit 74 when the voltage application circuit 72 applies voltage to the liquid level detection electrodes 66 and 68, and an abnormality determination process that switches the conduction state / non-conduction state of the grounding switch 76 and determines that there is an abnormality in the main grounding electrode 62 if the current detection result when the grounding switch 76 is in the conduction state is different from the current detection result when the grounding switch 76 is in the non-conduction state.

[0067] According to the above configuration, when the liquid level detection electrodes 66 and 68 are immersed in liquid, the liquid level detection electrodes 66 and 68 conduct to the reference potential GND not only through the liquid and the main ground electrode 62, but also through the liquid, the sub-ground electrode 64, and the ground switch 76. If the main ground electrode 62 is functioning normally, when a voltage is applied to the liquid level detection electrodes 66 and 68, current flows from the liquid level detection electrodes 66 and 68 to the main ground electrode 62 through the liquid. Therefore, whether the ground switch 76 is in a conductive or non-conductive state, current flows to the liquid level detection electrodes 66 and 68 when a voltage is applied to them, so the current detection result will be the same. On the other hand, if there is a malfunction in the main ground electrode 62, even if a voltage is applied to the liquid level detection electrodes 66 and 68, current may not flow from the liquid level detection electrodes 66 and 68 to the main ground electrode 62. In this case, the current detection result when voltage is applied to the liquid level detection electrodes 66 and 68 differs depending on the state of the grounding switch 76. This is because, when the liquid level detection electrodes 66 and 68 are immersed in liquid, if the grounding switch 76 is conductive, current flows from the liquid level detection electrodes 66 and 68 to the sub-grounding electrode 64 through the liquid, but if the grounding switch 76 is not conductive, no current flows from the liquid level detection electrodes 66 and 68 to the sub-grounding electrode 64. Therefore, with the above configuration, it is possible to determine that there is an abnormality in the main grounding electrode 62 by observing that the current detection result when voltage is applied to the liquid level detection electrodes 66 and 68 differs depending on the state of the grounding switch 76. This allows for recognition and countermeasures when an abnormality occurs in the main grounding electrode 62.

[0068] In one or more embodiments, the liquid level detection electrodes 66, 68 include a low liquid level detection electrode 66 (example of a first liquid level detection electrode) and a high liquid level detection electrode 68 (example of a second liquid level detection electrode). In the vertical direction, the lower end of the low liquid level detection electrode 66 is positioned below the lower end of the high liquid level detection electrode 68 within the second tank portion 42. In the abnormality determination process, the microcontroller 70 determines that there is an abnormality in the main grounding electrode 62 if the current detection result when the grounding switch 76 is in a conductive state and the voltage application circuit 72 applies voltage to the low liquid level detection electrode 66 (i.e., the second current detection result) is different from the current detection result when the grounding switch 76 is in a non-conductive state and the voltage application circuit 72 applies voltage to the low liquid level detection electrode 66 (i.e., the first current detection result).

[0069] If the liquid level detection electrodes 66 and 68 are not immersed in the liquid, no current will flow through them even if a voltage is applied, and the abnormality detection process will not function effectively. With the above configuration, the abnormality detection process is performed using the current detection result from the lower liquid level detection electrode 66 (i.e., the electrode that is immersed in the liquid first), which extends further down within the second tank section 42. This makes it less likely for situations in which the abnormality detection process does not function effectively to occur.

[0070] In one or more embodiments, if the microcontroller 70 determines that there is an abnormality in the main grounding electrode 62, it maintains the grounding switch 76 in a conductive state.

[0071] With the above configuration, if there is a problem with the main ground electrode 62, the sub-ground electrode 64 can function as a substitute for the main ground electrode 62. For example, when a voltage is applied to the liquid level detection electrodes 66 and 68 during the liquid level determination process, current can be made to flow from the liquid level detection electrodes 66 and 68 to the sub-ground electrode 64 through the liquid.

[0072] In one or more embodiments, if the microcomputer 70 determines that there is an abnormality in the main ground electrode 62, it causes a predetermined remote control 28 (an example of a notification device) to notify it of the abnormality in the main ground electrode 62.

[0073] According to the above configuration, if there is an abnormality in the main grounding electrode 62, the user can be notified. This allows the user to, for example, be prompted to resolve the abnormality in the main grounding electrode 62.

[0074] In one or more embodiments, the liquid level detection device 90 is incorporated into a water heater 2 (an example of a combustion heat source). The water heater 2 includes a gas burner 14 (an example of a combustion device), a latent heat exchanger 18 that recovers the latent heat of the combustion gas produced by the gas burner 14 to heat a heat transfer medium, and a neutralizing agent that neutralizes the condensate produced in the latent heat exchanger 18. A second tank section 42 stores the condensate as a liquid after it has been neutralized by the neutralizing agent.

[0075] When a calcium-based neutralizing agent is used, the calcium component contained in the neutralizing agent may be stored in the second tank section 42 along with the drain. In this case, positively charged calcium components may adhere to the surface of the main ground electrode 62, which functions as a cathode in the liquid level determination process, potentially forming a film on the surface of the main ground electrode 62. This film insulates the main ground electrode 62 from the surrounding liquid, potentially preventing current from flowing from the liquid level detection electrodes 66 and 68 to the main ground electrode 62 even when a voltage is applied to the liquid level detection electrodes 66 and 68. With the above configuration, it is possible to determine that there is an abnormality in the main ground electrode 62 in such a case.

[0076] In one or more embodiments, if the microcontroller 70 is not performing abnormality detection processing and does not determine that there is an abnormality in the main ground electrode 62, it maintains the ground switch 76 in a non-conductive state.

[0077] When the grounding switch 76 is in a conductive state, the sub-grounding electrode 64 functions as a cathode in the liquid level determination process, just like the main grounding electrode 62. Therefore, if the sub-grounding electrode 64 is kept in a conductive state, calcium components may adhere to the sub-grounding electrode 64, just like to the main grounding electrode 62. In contrast, with the above configuration, the sub-grounding electrode 64 is not kept in a conductive state unnecessarily, so the adhesion of calcium components to the sub-grounding electrode 64 can be suppressed.

[0078] In one or more embodiments, the microcontroller 70 performs an abnormality determination process when a request is received to start combustion in the gas burner 14.

[0079] With the above configuration, the microcontroller 70 performs abnormality detection processing at appropriate time intervals. This makes it possible to check at appropriate time intervals whether or not there is an abnormality in the main ground electrode 62.

[0080] The technical elements described herein or in the drawings demonstrate technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated herein or in the drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0081] 2: Water heater, 4: Water supply pipe, 6: Hot water pipe, 8: Water passage pipe, 10: Flow sensor, 12: Water volume servo, 14: Gas burner, 16: Sensible heat exchanger, 18: Latent heat exchanger, 20: Temperature sensor, 22: Drain pan, 24: Neutralizer, 26: Control unit, 28: Remote control, 30: Operation unit, 32: Display unit, 34: Audio output unit, 36: Drain recovery path, 38: First tank section, 40: Partition wall, 42: Second tank section, 44: Trap structure, 46: Exhaust Outlet path, 48: Discharge pump, 50: Overflow path, 60: Electrode unit, 62: Main ground electrode, 64: Sub ground electrode, 66: Low liquid level detection electrode, 68: High liquid level detection electrode, 70: Microcontroller, 71: Current limiting circuit, 72: Voltage application circuit, 74: Current detection circuit, 76: Ground switch, 78: First voltage application switch, 80: First diode, 82: Second voltage application switch, 84: Second diode, 90: Liquid level detection device, 200: Power supply

Claims

1. A tank for storing liquid, A main grounding electrode, which is electrically grounded and located inside the tank, A sub-grounding electrode is electrically grounded via a switch that can switch between a conductive state and a non-conductive state, and is located inside the tank. A liquid level detection electrode is placed inside the tank, A voltage application means for applying a voltage to the liquid level detection electrode, A current detection circuit for detecting whether or not current flows through the liquid level detection electrode, It includes a control unit, The control unit, A liquid level determination process that determines whether the liquid level in the tank has risen to or above a predetermined liquid level based on the current detection result, which is the detection result of the current detection circuit when the voltage application means applies a voltage to the liquid level detection electrode, A liquid level detection device configured to perform an abnormality determination process, which involves switching the conduction state / non-conduction state of the switch and determining that there is an abnormality in the main ground electrode if the current detection result when the switch is in the conduction state differs from the current detection result when the switch is in the non-conduction state.

2. The liquid level detection electrode includes a first liquid level detection electrode and a second liquid level detection electrode. In the vertical direction, the lower end of the first liquid level detection electrode is positioned below the lower end of the second liquid level detection electrode within the tank. Liquid level detection device according to claim 1, wherein in the abnormality determination process, the control unit determines that there is an abnormality in the main ground electrode when the current detection result when the switch is in a conductive state and the voltage application means applies a voltage to the first liquid level detection electrode is different from the current detection result when the switch is in a non-conductive state and the voltage application means applies a voltage to the first liquid level detection electrode.

3. The liquid level detection device according to claim 1, wherein the control unit maintains the switch in a conductive state when it determines that there is an abnormality in the main ground electrode.

4. The liquid level detection device according to claim 1, wherein the control unit, when it determines that there is an abnormality in the main ground electrode, causes a predetermined notification device to notify it of the abnormality in the main ground electrode.

5. The aforementioned liquid level detection device is incorporated into the combustion heat source unit. The aforementioned combustion heat source unit is Combustor and A latent heat exchanger recovers the latent heat of the combustion gas generated in the aforementioned combustor to heat a heat transfer medium, The system includes a neutralizing agent for neutralizing the drain generated in the latent heat exchanger, The liquid level detection device according to any one of claims 1 to 4, wherein the tank stores the drain after it has been neutralized by the neutralizing agent as the liquid.

6. The liquid level detection device according to claim 5, wherein the control unit maintains the switch in a non-conductive state when it has not performed the abnormality determination process and has not determined that there is an abnormality in the main ground electrode.

7. The liquid level detection device according to claim 5, wherein the control unit executes the abnormality determination process when a request to start combustion occurs in the combustor.

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