JP2016180698A - Water detection electrode circuit, and hot-water heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To send an AC current to the water to be detected using a DC power supply.SOLUTION: Provided is a water detection electrode circuit 100 for sending an electric current to an electrode 10 immersed in the water to be detected and detecting the presence of the water to be detected, the water detection electrode circuit comprising: a first series circuit in which a first resistor 31, a third resistor 33, the electrode 10, a fourth resistor 34, and a first switch element 22a are connected in series in the order stated; a second series circuit in which a second resistor 35, the fourth resistor 34, the electrode 10, the third resistor 33, and a second switch element are connected in series in the order stated; a DC power supply for applying a voltage to both ends of the first series circuit, and to both ends of the second series circuit; an AD input port for detecting the potential of one or both of the connection point of the first resistor 31 and the third resistor 33 and the connection point of the second resistor 35 and the fourth resistor 34; and a control unit for making the short circuit duration of the first switch element and the short circuit duration of the second switch element approximately equal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water detection electrode circuit and a water heater, for example, a water detection electrode circuit provided in a neutralizer of a latent heat recovery type water heater.

  Hot water heaters used in kitchens and bathrooms are equipped with primary heat exchangers and secondary heat exchangers, and latent heat recovery type water heaters that reheat with secondary heat exchangers have come to be used. . The latent heat recovery type water heater is configured to neutralize acidic condensed water flowing out from the secondary heat exchanger with a neutralizer, and water is supplied to the neutralizer so that combustion gas does not leak from the neutralizer. A sealing structure is provided. For this reason, the latent heat recovery type water heater needs a water level detection electrode that detects whether sufficient dew condensation water is stored in the neutralizer before the burner is ignited. Patent Document 1 discloses an appropriate water level detection electrode, a dangerous water level detection electrode, and a minimum water level detection electrode in a water heater.

  The water detection circuit is a circuit that determines the presence or absence of water based on the electrical resistance of the electrode by passing a direct current through an electrode immersed in water (water to be detected) or by passing an alternating current using a transformer. Are known.

Japanese Patent No. 5146727 (paragraph 0088)

  In the AC energization method in which an alternating current is passed through the water to be detected, the current flowing through the electrode is reversed every fixed time, so it is difficult for the electrode to corrode due to electrolysis or to precipitate impurities dissolved in the water. Is unlikely to occur. However, the AC energization method using an AC transformer has the problems that the component parts are expensive and the area occupied by the components on the board is large. On the other hand, the DC energization method is configured using switch elements such as photocouplers and relays, so that circuit components are inexpensive and the area occupied by components on the board is small. However, in the DC energization method, since the current flowing through the electrode is always in a certain direction, electrode corrosion due to electrolysis and precipitation of impurities dissolved in water (detection target water) are likely to occur.

  This invention is made | formed in view of such a situation, and it aims at providing the water detection electrode circuit and water heater which can flow an alternating current to detection object water using DC power supply.

  In order to achieve the above object, the first invention is a water detection electrode circuit for detecting the presence or absence of the detection target water by passing a current through an electrode immersed in the detection target water, wherein the first resistor (31 ), A third resistor (33), the electrode (10), a fourth resistor (34), and a first switch element (phototransistor 22a) in series in this order, The second resistor (35), the fourth resistor (34), the electrode (10), the third resistor (33), and the second switch element (phototransistor 20a) are connected in series in this order. A connected second series circuit; both ends of the first series circuit; a DC power supply for applying a voltage to both ends of the second series circuit; the first resistor (31); and the third resistor A connection point with a resistor (33), and the second resistor (35) and the fourth resistor A potential detection circuit (for example, an A / D converter 156) that detects the potential of one or both of the connection points with the resistor (34), the short-circuit time of the first switch element, and the second switch And a control unit (152) that makes the short circuit time of the elements substantially equal. Here, the third resistor and the fourth resistor may be in a short-circuited state. Note that symbols and characters in parentheses are examples.

  The second invention is a water detection electrode circuit (104) for detecting the presence or absence of the detection target water by passing a current through the electrode (10) immersed in the detection target water, wherein the first movable contact is the first. When connected to the fixed contact, the second movable contact is connected to the third fixed contact, and when the first movable contact is connected to the second fixed contact, the second movable contact is connected to the fourth fixed contact. A two-circuit two-contact relay (51), a resistor (41) having one end connected to the first fixed contact and the fourth fixed contact, the other end of the resistor and the second fixed contact, and A DC power source that applies a DC voltage to the third fixed contact; a potential detection circuit (for example, an A / D converter 156) that detects a potential at a connection point between the resistor and the first fixed contact; The coil energization time and the non-energization time of the two-circuit two-contact relay are made substantially equal. And a unit (152), the electrode is characterized in that it is connected to the first movable contact on the second movable contact. Note that symbols and characters in parentheses are examples.

  The third invention is a water detection electrode circuit that detects the presence or absence of the detection target water by passing a current through the electrode immersed in the detection target water, and a series circuit in which a resistor and the electrode are connected in series. A switch circuit that reverses the direction of the current flowing through the electrode, a DC power source that applies a voltage to one end of the resistor, a potential detection circuit that detects the potential of the other end of the resistor, and the switch circuit It is characterized by comprising a control unit that makes the time for flowing the current in the positive direction to the electrode substantially equal to the time for flowing the reverse current.

  ADVANTAGE OF THE INVENTION According to this invention, an alternating current can be sent through detection object water using DC power supply. In addition, since a switch element is used, it is cheaper than an alternating current flowing using a transformer, and the component-occupied area is also reduced.

It is a circuit diagram of the water detection electrode circuit which is 1st Embodiment of this invention. It is a lineblock diagram of a water heater provided with the water detection electrode circuit which is a 1st embodiment of the present invention. It is a block diagram of the water heater which is 1st Embodiment of this invention. It is a timing chart which shows operation | movement of a water detection electrode circuit. It is a circuit diagram of the water detection electrode circuit which is a comparative example of the present invention. It is a circuit diagram of the water detection electrode circuit which is 2nd Embodiment of this invention. It is a circuit diagram of the water detection electrode circuit which is 3rd Embodiment of this invention. It is a circuit diagram of the water detection electrode circuit which is 4th Embodiment of this invention.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. Each figure is only schematically shown so that the present invention can be fully understood. Therefore, the present invention is not limited to the illustrated example. Moreover, in each figure, the same code | symbol is attached | subjected about the common component and the same component, and those overlapping description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a circuit diagram of a water detection electrode circuit according to the first embodiment of the present invention.
The water detection electrode circuit 100 includes an electrode 10, two photocouplers 20 and 22, and four resistors 31, 33, 35, 37, and 39, and A / D conversion of the microcomputer 150 (FIG. 3). Connected to the AD input port of the device 156 and the output port of the I / O port 158.

  The photocouplers 20 and 22 include phototransistors 20a and 22a as switching elements and photodiodes 20b and 22b. If a photocoupler array is used, lot variations at the time of manufacture are eliminated and the characteristics are easily aligned. Note that the A / D converter 156 functions as a potential detection circuit.

  The electrode 10 includes two metal rods 10a and 10b, and the two metal rods 10a and 10b are immersed in water (detection target water). One end of the resistor 31 is connected to a DC power source (single power source) of 5V, and the other end is connected to the collector of the phototransistor 20a. The emitter of the phototransistor 20a is grounded. In the phototransistor 22a, the emitter is grounded, the collector is connected to one end of the resistor 35, and the other end of the resistor 35 is connected to a DC power source of 5V.

  One metal rod 10a of the electrode 10 is connected via a resistor 33 to a connection point (point A) between the other end of the resistor 31 and the collector of the phototransistor 20a. 3) is connected to the AD input port (A / D converter 156). The other metal rod 10b of the electrode 10 is connected via a resistor 34 to a connection point between one end of the resistor 35 and the collector of the phototransistor 22a. The resistors 33 and 34 are for noise countermeasures.

  In other words, the DC power supply includes a series circuit of the resistor 31, the resistor 33, the electrode 10, the resistor 34, and the phototransistor 22a, and the series of the resistor 35, the resistor 34, the electrode 10, the resistor 33, and the photocoupler 20a. The circuit is connected.

  The photodiode 20 b has an anode connected to a 5 V DC power supply via a resistor 39 and a cathode connected to the output port 2 of the microcomputer 150. The photodiode 22 b has an anode connected to a 5 V DC power supply via a resistor 37 and a cathode connected to the output port 1 of the microcomputer 150. The output ports 1 and 2 are open collectors that are pulled up.

  Hereinafter, specific resistance values of the resistors 31, 33, 34, 35, 37, and 39 will be exemplified as examples. The resistors 31 and 35 have a resistance value of 82 kΩ, the resistors 33 and 34 have a resistance value of 2.2 kΩ, and the resistors 37 and 39 have a resistance value of 1 kΩ.

(Operation)
The water detection electrode circuit 100 is configured such that the output port 1 and the output port 2 of the microcomputer 150 (FIG. 3) are alternately turned to the LOW level.
First, assume that the output port 1 is at a LOW level and the output port 2 is at a HIGH level. Thereby, in the photocoupler 22, the photodiode 22b emits light, and the phototransistor 22a is turned on. On the other hand, in the photocoupler 20, the photodiode 20b is turned off and the phototransistor 20a is turned off.

  The water detection electrode circuit 100 is connected to a series circuit of three resistors 31, 33, and 34 and the electrode 10 (water) with a 5 V DC power supply (single power supply), and from the resistor 31 to the phototransistor 22 a. DC current flows. At this time, the potential at the point A to which the AD input port of the microcomputer 150 is connected is a power supply voltage of + 5V if there is no water, and if there is water, it is lowered by the voltage drop of the resistor 31 from the power supply voltage. . For this reason, the microcomputer 150 can determine the presence or absence of water by detecting the potential at the point A.

  Next, it is assumed that the output port 2 of the microcomputer 150 changes to the LOW level and the output port 1 changes to the HIGH level. Thereby, in the photocoupler 20, the photodiode 20b emits light, and the phototransistor 20a is turned on. On the other hand, in the photocoupler 22, the photodiode 22b is turned off, and the phototransistor 22a is turned off.

  In the water detection electrode circuit 100, a series circuit of three resistors 35, 34, and 31 and an electrode 10 (water) is connected to a 5V DC power source, and a DC current flows from the resistor 35 to the phototransistor 20a. . At this time, the potential at the point A to which the AD input port of the microcomputer 150 is connected is the ground potential whether or not water is present. For this reason, in this state, the microcomputer 150 cannot determine the presence or absence of water. However, the microcomputer 150 can determine the presence or absence of water if the AD input port measures the potential at the connection point (point B) between the resistor 34 and the resistor 35.

  Furthermore, it is assumed that both the output ports 1 and 2 of the microcomputer 150 are at the HIGH level. In this case, both the phototransistors 20a and 22a are in the OFF state, and the potential at the point A becomes the power supply potential regardless of whether water is present or absent. Moreover, even if there is water, no current flows.

  When the output port 1 and the output port 2 of the microcomputer 150 are alternately set to the LOW level, the water detection electrode circuit 100 causes a direct current to flow from the resistor 31 to the phototransistor 22a or from the resistor 35 to the phototransistor. A direct current flows in the direction of 20a. Accordingly, reverse current flows through the electrodes 10 alternately.

  In addition, if the microcomputer 150 performs control so that the time when the output port 1 becomes the LOW level is equal to the time when the output port 2 becomes the LOW level, the electrode 10 causes a square-wave AC current to flow in water. Further, the microcomputer 150 provides a time for setting both the output ports 1 and 2 to the HIGH level between the time for setting the output port 1 to the LOW level and the time for setting the output port 2 to the LOW level. Causes a rectangular wave (odd function waveform) alternating current having a predetermined period to flow in water (see FIG. 4D).

FIG. 2 is a configuration diagram of a water heater provided with a water electrode detection circuit according to the first embodiment of the present invention.
The water heater 200 includes a primary heat exchanger 210, a secondary heat exchanger 220, a burner 230, and a neutralizer 250. The water heater 200 is provided with a water supply pipe so that the supplied water flows through the secondary heat exchanger 220 and the primary heat exchanger 210 to supply hot water, and the combustion exhaust gas generated by the burner 230 is provided. Is configured to heat feed water in such a manner that heat is exchanged in the primary heat exchanger 210 and sensible heat is taken away, and latent heat is taken away in the secondary heat exchanger 220.

  That is, the water heater 200 is configured to preheat the supplied water with the secondary heat exchanger 220 and reheat the preheated hot water with the primary heat exchanger 210. As a result, the secondary heat exchanger 220 reuses (recovers latent heat) the exhaust heat of about 200 ° C. of the primary heat exchanger 210 until it reaches about 60 ° C., thereby improving the overall thermal efficiency.

  In addition, when the secondary heat exchanger 220 recovers latent heat, a minute amount of components in the combustion exhaust gas is dissolved in the generated condensed water, so that the condensed water (drain water) becomes acidic. The neutralizer 250 includes a barrier 255 and the electrode 10 described above, stores condensed water, and neutralizes the condensed water flowing down from the secondary heat exchanger 220 with a neutralizing agent such as calcium carbonate.

  The barrier 255 blocks the flow of the combustion gas, and makes the neutralizer 250 also function as a water seal device. Here, the lower end portion of the electrode 10 is disposed above the lower end portion of the barrier 255, and if the water detection electrode circuit 100 detects water, the water heater 200 is surely sealed with water. . That is, the electrode 10 has a function as a water seal detection electrode.

  By the way, since the neutralizer 250 is filled with the neutralizing agent, clogging may occur and the water may be filled. It is preferable that the neutralizer 250 includes another electrode 10 (not shown) at a position higher than the electrode 10, and the other electrode 10 detects the filling of water.

  The water heater 200 includes the water detection electrode circuit 100 described above inside the neutralizer 250. Since the water detection electrode circuit 100 allows an alternating current to flow through water, corrosion of the electrode due to electrolysis and precipitation of impurities dissolved in water are unlikely to occur. In particular, since water in the neutralizer 250 is dissolved with calcium carbonate or the like as a neutralizing agent, calcium is likely to precipitate, but since the water detection electrode circuit 100 allows an alternating current to flow, this calcium precipitation occurs. Hard to do.

FIG. 3 is a block diagram of a water heater according to the first embodiment of the present invention.
The water heater 200 includes the water detection electrode circuit 100, the microcomputer 150, the burner ignition circuit 235, and the operation unit 240. The microcomputer 150 includes a control unit 152, a storage unit 154, and an A / D converter 156. I / O port 158. The A / D converter 156 includes the above-described AD input port, and the I / O port 158 includes the above-described output ports 1 and 2.

  The storage unit 154 includes a flash read only memory (FROM) and a random access memory (RAM). The control unit 152 is a CPU (Central Processing Unit) and controls the A / D converter 156 and the I / O port 158 by executing a program stored in the FROM, The burner ignition circuit 235 is caused to function.

  The burner ignition circuit 235 ignites the burner 230 (FIG. 2), and the control unit 152 causes the water detection electrode circuit 100 to function and confirms that water is stored in the neutralizer 250. Then, the burner ignition circuit 235 is operated to ignite the burner 230 (FIG. 2).

  The operation unit 240 includes a display unit 245, for example, displays that the water is insufficient in the neutralizer 250 (FIG. 2), and notifies the user of the abnormality.

FIG. 4 is a timing chart showing the operation of the water electrode detection circuit. The time change of the output ports 1 and 2 of the microcomputer 150, the potential change at the point A (FIG. 1) connected to the AD input port, and the electrode 10 Current.
The output port 1 and the output port 2 of the microcomputer 150 are alternately at the LOW level, and the width of the LOW level is time T1 (see FIGS. 4A and 4B). The potential at the point A is the voltage V1 when the output port 1 is in the LOW level time zone, the output port 2 is the ground potential during the LOW level time zone, and the power supply potential is 5 V in the other time zones. (See FIG. 4 (c)). The current flowing through the electrode 10 is a rectangular wave current (odd function waveform) in which the current flows only during the time period when the output ports 1 and 2 are at the LOW level (see FIG. 4D).

(Comparative example)
5A and 5B are circuit diagrams of a water electrode detection circuit as a comparative example of the present invention, in which FIG. 5A shows a direct current energization method and FIG. 5B shows an alternating current energization method.
In the DC energization method of FIG. 5A, the electrode 10 has one metal rod 10a connected to the power source Vcc via the resistor 31, and the other metal rod 10b grounded. Further, the connection point between the resistor 31 and one metal rod 10a is connected to the AD input port (potential detection circuit) of the microcomputer 150 (FIG. 3).

  In the direct current energization method, the current flowing to the water (detection target water) through the electrode 10 is always in a certain direction, so that corrosion of the metal rods 10a and 10b due to electrolysis and precipitation of impurities dissolved in water occur. Cheap.

  In the AC energization method of FIG. 5B, the electrode 10 has one metal rod 10a connected to one end of the secondary winding of the transformer 65 via the resistor 31, and the other metal rod 10b grounded. Has been. The connection point between the resistor 31 and one metal rod 10a is connected to the AD input port of the microcomputer 150. In the transformer 65, the other end of the secondary side winding is grounded, and an AC power source (for example, a commercial power source) is connected to both ends of the primary side winding.

  In the AC energization method, since the current flowing in the water through the electrode 10 is reversed every predetermined time, the corrosion of the metal rods 10a and 10b due to electrolysis and the impurities dissolved in the water are less than in the DC energization method. Malfunction due to precipitation is unlikely to occur. However, since the AC energization method uses the transformer 65, the component parts become expensive and the area occupied by the parts on the board increases.

  In contrast to these comparative examples, the water detection electrode circuit 100 of the first embodiment uses only a single power source without using a transformer (transformer 65), and AC current in water (a square wave current not including a DC component). The AC energization method that flows is realized. In other words, the water detection electrode circuit 100 is less likely to malfunction due to corrosion of the metal bars 10a and 10b due to electrolysis or precipitation of impurities dissolved in water. In addition, since the water detection electrode circuit 100 is configured using the photocouplers 20 and 22, the components are inexpensive and the area occupied by the components on the substrate is small.

(Second Embodiment)
Although the water detection electrode circuit 100 of the first embodiment is connected to the electrode 10 via the resistors 33 and 34, the resistors 33 and 34 can be omitted.
FIG. 6 is a circuit diagram of a water detection electrode circuit according to the second embodiment of the present invention.
The water detection electrode circuit 102 is different from the water detection electrode circuit 100 (FIG. 1) in that the resistors 33 and 34 are short-circuited by setting their resistance values to substantially zero. In other words, in the water detection electrode circuit 100, the resistor 33 is inserted between the electrode 10, the resistor 31, and the phototransistor 20a with respect to the water detection electrode circuit 102, and the electrode 10, the resistor 35, and the photo A resistor 34 is inserted between the transistor 22a.

  Thereby, when the phototransistor 20a or the phototransistor 22a is short-circuited, the water detection electrode circuit 102 has a potential at the point A different from the potential of the water detection electrode circuit 100, but the A / D converter 156 reduces the potential at the point A. It is the same as that of the water detection electrode circuit 100 that the presence or absence of water can be determined by measuring, and that an alternating current (a square wave current not including a direct current component) flows in the water.

(Third embodiment)
Although the water detection electrode circuit 100 according to the first embodiment and the water detection electrode circuit 102 according to the second embodiment use the photocouplers 20 and 22, they can be configured using a relay instead. The relay may be a mechanical relay or a semiconductor relay.

FIG. 7 is a circuit diagram of a water detection electrode circuit according to the third embodiment of the present invention.
The water detection electrode circuit 104 includes an electrode 10, a two-circuit two-contact relay 51 (two-contact switches 51a and 51b, a coil 51c), a resistor 41, a grounded DC power source (DC power source), a digital transistor 60, And is connected to an AD input port and an output port of the microcomputer 150 (FIG. 3).

  The two-circuit two-contact relay 51 includes a two-contact switch 51a including a first fixed contact, a second fixed contact, and a first movable contact, and two contacts including a third fixed contact, a fourth fixed contact, and a second movable contact. A switch 51b and a coil 51c that simultaneously switches the contacts of the two-contact switches 51a and 51b are provided. In FIG. 7, reference numeral 1 is assigned to the first fixed contact, reference numeral 2 is assigned to the second fixed contact, reference numeral 3 is assigned to the third fixed contact, and reference numeral 4 is assigned to the fourth fixed contact. ing.

  The two-circuit two-contact relay 51 is configured such that when the first movable contact is connected to the first fixed contact, the second movable contact is connected to the third fixed contact according to the energization state / non-energization state of the coil 51c. When one movable contact is connected to the second fixed contact, the second movable contact is connected to the fourth fixed contact.

  In the present embodiment, although it is not necessary to distinguish between them, in the two-circuit two-contact relay 51, a fixed contact that is closed when no current flows through the coil 51c is referred to as a normally closed contact (NC). A fixed contact that is open when no current flows through the coil 51c is referred to as a normally open contact (NO).

  The digital transistor 60 includes two internal resistors in addition to the transistor, and is configured to allow digital input. The digital transistor 60 is configured such that an internal resistor is connected between the base and emitter of the internal transistor, and is connected to the outside from the base via another internal resistor.

  One metal rod 10a of the electrode 10 is connected to the first movable contact, the first fixed contact is connected to one end of the resistor 41, and the other end of the resistor 41 is connected to a DC power source. The other metal rod 10b of the electrode 10 is connected to the second movable contact, and the third fixed contact is grounded. The first fixed contact and the fourth fixed contact are connected, and the second fixed contact and the third fixed contact are connected.

  One end of the coil 51 c is connected to the DC power supply, and the other end is connected to the collector of the digital transistor 60. The emitter of the digital transistor 60 is grounded, and the base is connected to the output port 1 of the microcomputer 150 (FIG. 3) via an internal resistor.

(Operation)
First, it is assumed that the output port 1 of the microcomputer 150 outputs a LOW level.
The digital transistor 60 is turned off and no current flows through the coil 51c. In the present embodiment, in the two-circuit two-contact relay 51, when the coil 51c is in a non-energized state, the first fixed contact and the first movable contact are connected, and the third fixed contact and the second movable contact are connected. Suppose you connect.

  In the water detection electrode circuit 104, a direct current power source supplies a current in this direction via the resistor 41, the first fixed contact, the first movable contact, the electrode 10 (water to be detected), the second movable contact, and the third fixed contact. Shed. That is, if water is immersed in the electrode 10, the AD input port (point A) has a potential obtained by subtracting the voltage drop of the resistor 41 from the power supply voltage. On the other hand, when water is not immersed in the electrode 10, the AD input port (point A) becomes the power supply voltage.

Next, it is assumed that the output port 1 has changed to a HIGH level.
The digital transistor 60 is turned on, and a current flows through the coil 51c. At this time, in the two-circuit two-contact relay 51, when the coil 51c is energized, the second fixed contact and the first movable contact are connected, and the fourth fixed contact and the second movable contact are connected.

  In the water detection electrode circuit 104, a direct current power source passes a current in this direction through the resistor 41, the fourth fixed contact, the second movable contact, the electrode 10, the first movable contact, and the second fixed contact. That is, the current flowing through the electrode 10 is in the opposite direction to that when the output port 1 of the microcomputer 150 outputs a LOW level. Therefore, if the output port 1 alternately outputs a HIGH level and a LOW level, the current flowing in the water soaking the electrode 10 becomes a rectangular wave current having a direct current component. Also, if the HIGH level time output from the output port 1 is the same as the LOW level time, it becomes a square wave current (AC current that does not include a DC component), which dissolves in electrode corrosion or water due to electrolysis. It becomes difficult to cause malfunction due to precipitation of impurities.

  When the electrode 10 is immersed in water, the AD input port (point A) has a potential obtained by subtracting the voltage drop of the resistor 41 from the power supply voltage, while the electrode 10 is not immersed in water. In this case, the AD input port (point A) becomes the power supply potential.

  According to the water detection electrode circuit 104 of the present embodiment, since a square wave current (an AC current not including a DC component) flows in water, malfunction due to electrode corrosion caused by electrolysis or precipitation of impurities dissolved in water. Is unlikely to occur. Further, since the transformer (transformer 65 (FIG. 5B)) is not provided, the transformer is inexpensive and the area occupied by the components is small. The mechanical relay has one coil, but the transformer has two windings. A line is necessary.

(Fourth embodiment)
In the water detection electrode circuit 104 of the third embodiment, a square wave current always flows in the water, and the current flowing in the water cannot be turned off. For this reason, the water heater 200 (FIG. 2) has a square wave current in the water as long as the DC power supply supplies DC power even after the presence of water is confirmed before the ignition of the burner 230 (FIG. 2). It continued to flow.

FIG. 8 is a circuit diagram of a water electrode detection circuit according to the fourth embodiment of the present invention.
The water detection electrode circuit 106 is obtained by adding a photocoupler 24 (phototransistor 24a and photodiode 24b) and a resistor 45 to the water detection electrode circuit 104 of the third embodiment.

  The water detection electrode circuit 106 includes an electrode 10, a two-circuit two-contact relay 53 (53a, 53b, 53c), a resistor 43, a grounded DC power source (DC power source), and a photocoupler 24 (24a, 24b). Are connected to the AD input port and the output ports 1 and 2 of the microcomputer.

  The two-circuit two-contact relay 53 includes a two-contact switch 53a including a first fixed contact, a second fixed contact, and a first movable contact, and two contacts including a third fixed contact, a fourth fixed contact, and a second movable contact. A switch 53b and a coil 53c that simultaneously moves the movable contacts of the two-contact switches 53a and 53b are provided.

  One metal rod 10 a of the electrode 10 is connected to the first movable contact, the first fixed contact is connected to the emitter of the phototransistor 24 a, and the collector is connected to one end of the resistor 43. The other end of the resistor 41 is connected to a DC power source. The other metal rod 10b of the electrode 10 is connected to the second movable contact, and the third fixed contact is grounded. The first fixed contact and the fourth fixed contact are connected, and the second fixed contact and the third fixed contact are connected.

  One end of the coil 53 c is connected to the DC power supply, and the other end is connected to the collector of the digital transistor 60. The emitter of the digital transistor 60 is grounded, and the base is connected to the output port 1 of the microcomputer 150 (FIG. 3) via an internal resistor. The photodiode 24b has an anode connected to one end of the resistor 45 and the other end connected to a DC power source. The cathode of the photodiode 24 b is connected to the output port 2 of the microcomputer 150.

(Operation)
First, assume that the output port 2 of the microcomputer is at the LOW level. In this case, since a current flows through the photodiode 24b and the phototransistor 24a is turned on, the operation of the water detection electrode circuit 106 is the same as the operation of the water detection electrode circuit 104 of the third embodiment.
Next, it is assumed that the output port 2 of the microcomputer 150 (FIG. 3) is at a HIGH level. In this case, no current flows through the photodiode 24b, the phototransistor 24a transitions to the OFF state, no current flows through the electrode 10 in any direction, and the AD input port of the microcomputer 150 becomes HIGH level.

  That is, unlike the water detection electrode circuit 104, the water detection electrode circuit 106 can block the current flowing through the electrode 10. If the water detection electrode circuit 106 confirms the presence or absence of water before the burner 230 is ignited and the current flowing through the electrode 10 is cut off after the confirmation, the water heater 200 (FIG. 2) However, it is difficult to cause malfunction due to electrode corrosion caused by electrolysis or precipitation of impurities dissolved in water.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications such as the following are possible.
(1) Although the water detection electrode circuit 100 (FIG. 1) of the first embodiment measures the potential at the connection point (point A) between the resistor 31 and the resistor 33, the resistor 35 and the resistor 34 are measured. The potential at the connection point may be measured. Similarly, the water detection electrode circuit 102 (FIG. 6) of the second embodiment measures the potential at the connection point (point A) between the resistor 31 and the electrode 10, but the connection between the resistor 35 and the electrode 10. You may measure the electric potential of a point (point B).

(2) The water detection electrode circuit 104 (FIG. 7) of the third embodiment applies a DC voltage to one end of the resistor 41 and grounds the third fixed contact of the two-contact switch 51b. One end of 41 may be grounded and a DC voltage may be applied to the third fixed contact of the two-contact switch 51b. That is, a DC power source may be connected between one end of the resistor 41 and the third fixed contact of the two-contact switch 51b.

(3) In the water detection electrode circuit 106 (FIG. 8) of the fourth embodiment, the phototransistor 24a is inserted between the first fixed contact of the two-contact switch 53a and the resistor 43. , Between the resistor 43 and the DC power source, between the first movable contact of the two-contact switch 53a and the electrode 10 or between the electrode 10 and the third fixed contact of the two-contact switch 53b. It may be between the second movable contact of the contact switch 53b. That is, the switch element (phototransistor) includes a connection line connecting the electrode 10 and the first movable contact, a connection line connecting the electrode 10 and the second movable contact, the first fixed contact, the third fixed contact, What is necessary is just to insert in any one or several connection line with the resistor and the several connection line which connects DC power supply in series.

(4) In the water detection electrode circuits 100 (FIG. 1) and 102 (FIG. 6), the resistor 31 and the electrode 10 are connected in series, and the photocoupler 22a that is a switch element, the resistor 35, and the photocoupler 20a. In combination constitutes a switch circuit that reverses the direction of the current flowing through the electrode 10. The water detection electrode circuits 104 (FIG. 7) and 106 (FIG. 8) constitute a switch circuit that reverses the direction of the current flowing through the electrode 10 by the two-contact switches 51a, 51b, 53a, and 53b.

(5) In each of the above embodiments, the potential of the electrode 10 is detected using the A / D converter 156. However, the potential may be compared with a predetermined set potential using a comparator or a hysteresis comparator.

DESCRIPTION OF SYMBOLS 10 Electrode 10a, 10b Metal rod 20, 22, 24 Photocoupler 20a, 22a, 24a Phototransistor (switch element)
20b, 22b, 24b Photodiode 31, 33, 34, 35, 37, 39, 41, 43, 45 Resistor 51, 53 Two-circuit two-contact relay 51a, 51b, 53a, 53b Two-contact switch 51c, 53c Coil 60 Digital Transistor 65 Transformer 100, 102, 104, 106 Water detection electrode circuit 150 Microcomputer 152 Control unit 154 Storage unit 156 A / D converter (potential detection circuit)
158 I / O port 200 Water heater 210 Primary heat exchanger 220 Secondary heat exchanger 230 Burner 235 Burner ignition circuit 240 Operation unit 245 Display unit 250 Neutralizer 255 Barrier

Claims (7)

A water detection electrode circuit that detects the presence or absence of the detection target water by passing an electric current through an electrode immersed in the detection target water,
A first series circuit in which a first resistor, a third resistor, the electrode, a fourth resistor, and a first switch element are connected in series in this order;
A second series circuit in which a second resistor, the fourth resistor, the electrode, the third resistor, and a second switch element are connected in series in this order;
A DC power source for applying a voltage to both ends of the first series circuit and to both ends of the second series circuit;
A potential detection circuit that detects a potential at one or both of a connection point between the first resistor and the third resistor and a connection point between the second resistor and the fourth resistor. When,
A water detection electrode circuit comprising: a control unit configured to substantially equalize a short circuit time of the first switch element and a short circuit time of the second switch element. The water sensing electrode circuit according to claim 1,
The water detection electrode circuit, wherein the third resistor and the fourth resistor are in a short circuit state. The water detection electrode circuit according to claim 1 or 2,
The first switch element and the second switch element are phototransistors inside a photocoupler,
The water detection electrode circuit, wherein the control circuit controls the short-circuiting time by causing a photodiode inside the photocoupler to emit light. A water detection electrode circuit that detects the presence or absence of the detection target water by passing an electric current through an electrode immersed in the detection target water,
When the first movable contact is connected to the first fixed contact, the second movable contact is connected to the third fixed contact, and when the first movable contact is connected to the second fixed contact, the second movable contact is A two-circuit two-contact relay connected to the fourth fixed contact;
A resistor having one end connected to the first fixed contact and the fourth fixed contact;
A DC power source for applying a DC voltage between the other end of the resistor and the second fixed contact and the third fixed contact;
A potential detection circuit for detecting a potential at a connection point between the resistor and the first fixed contact;
A control unit for making the energization time and non-energization time of the coil of the two-circuit two-contact relay substantially equal,
The water detection electrode circuit, wherein the electrode is connected to the first movable contact and the second movable contact. The water detection electrode circuit according to claim 4,
A connection line connecting the electrode and the first movable contact; a connection line connecting the electrode and the second movable contact; the first fixed contact; the third fixed contact; the resistor; A water detection electrode circuit, further comprising a switch element inserted into any one or a plurality of connection lines of a plurality of connection lines connecting DC power supplies in series. A primary heat exchanger that directly heats with a burner, a secondary heat exchanger that preheats water with the exhaust gas of the primary heat exchanger, and supplies the preheated water to the primary heat exchanger; and the secondary heat exchanger A water heater comprising a neutralizer for neutralizing condensed water condensed in a heat exchanger,
The water detection electrode circuit according to any one of claims 1 to 5, further comprising:
The water heater is characterized in that the electrode is provided inside the neutralizer. A water detection electrode circuit that detects the presence or absence of the detection target water by passing an electric current through an electrode immersed in the detection target water,
A series circuit in which a resistor and the electrode are connected in series;
A switch circuit that reverses the direction of the current flowing through the electrode;
A DC power supply for applying a voltage to one end of the resistor;
A potential detection circuit for detecting the potential of the other end of the resistor;
The water detection electrode circuit, wherein the switch circuit includes a control unit that substantially equalizes a time during which a current flows through the electrode in a positive direction and a time during which a reverse current flows.

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