JPH09184771A - Sensor for detecting overheat of hot-water supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably detect the overheating state of a heat exchanger in wide area by connecting a conductor to a thick-film PTC (positive temperature coefficient) resistor provided to the surface of a substrate and placing the substrate between the heat exchanger and a casing. SOLUTION: A casing 1 includes a heat exchanger 2 and a control part 8 therein, and a substrate 4 made of ceramic or resin film is adhered to a rear panel 3. The substrate 4 is provided with a thick-film PTC resistor body 5 thereon. The body 5 is formed by baking several kinds of metallic oxides, and its resistance value is sharply increased when the temperature exceeds the specified value. The body 5 is also formed zigzaged at a small width on the substrate 4. Then, when the device 2 is in an overheating condition, the body 5 becomes highly resistant, which is detected by the control part 8, and a solenoid valve is shut off as a result. Thus, the overheating condition can be detected quickly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for a water heater, and more particularly to an overheat detecting sensor for detecting abnormal overheating of the water heater and stopping the combustion device.

[0002]

2. Description of the Related Art Conventionally, in order to prevent abnormal overheat from occurring in a water heater due to a failure, it is safe to detect an overheat condition near the heat exchanger and stop the supply of gas to the water heater when there is abnormal overheat A device is provided. FIG. 7 shows a conventional example of a sensor for detecting overheat which detects such abnormal overheat.
A heat exchanger 2 and a controller 8 shown by a dotted line are housed in a casing 1 shown in the figure. Note that the front cover of the casing 1 is not shown. The heat exchanger 2 burns the gas to heat the water flowing through the water pipe. The control unit 8 is the heat exchanger 2
Control the amount of gas supplied to the.

A rear panel 3 for shielding the heat from the heat exchanger 2 is mounted inside the rear surface of the casing 1. The temperature fuses 13, 13, ... Connected in series by the lead wire 7 are attached to the rear panel 3. When any of the temperature fuses 13 is overheated and melted, the conduction between the lead wires 7 and 7 is cut off, and the heat exchanger 2 is detected by detecting this.
The gas supply to the is to be stopped.

If the heat exchanger of the water heater fails, it may locally overheat, and in the above safety device, detection by the temperature fuse can be sent if the portion of the heat exchanger away from the temperature fuse abnormally overheats. There was a problem. Also,
Since the thermal fuses are connected to each other by the lead wires, the wires are cluttered and there is a problem that it is difficult to assemble.

Further, in order to keep the thermal state of the thermal fuse constant, the distance between the rear panel and the thermal fuse has to be constant, which makes mounting the thermal fuse more troublesome. For example, Japanese Patent Laid-Open No. 4-93555 proposes a method of attaching a thermal fuse to a heat exchanger, but this method is not easy to attach the thermal fuse. Then, it is troublesome to replace the thermal fuse after the thermal fuse is blown.

In the safety device for a water heater proposed in Japanese Patent Laid-Open No. 4-174252, a synthetic resin light transmission line is arranged in a meandering manner at a position facing a back surface of a heat exchanger of a heat shield plate to transmit light. The amount of light transmitted through the line is detected. The light transmission line made of synthetic resin blocks light when the temperature exceeds a predetermined temperature, and overheat of the water heater is detected.

As described above, the sensor using the light transmission line as the overheat detecting sensor has a problem that it takes time to arrange the light transmission line in a meandering manner on the surface of the heat shield plate. Further, there is a problem that the light transmission line and the optical connector for connecting the light transmission line to the light source or the light receiving element are expensive and the manufacturing cost is increased. Further, there is a problem that it is difficult to keep the characteristics of the light source and the light receiving element constant and the overheated state cannot be detected with high accuracy.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to make it easy to manufacture and assemble and to cover a wide range of heat exchangers. An object of the present invention is to provide a sensor for detecting overheat of a water heater which can stably detect an overheat state.

[0009]

A sensor for detecting overheat of a water heater according to the present invention is a hot water heater in which a heat exchanger is arranged in a casing, and a conductor is provided in a thick film PTC resistor attached to a surface of a substrate. And the substrate is arranged between the casing and the heat exchanger. What is the PTC resistor?
It means a resistor having a positive temperature coefficient, and is generally known as one obtained by firing several kinds of metal oxides or a resin / carbon-based resistance film.

When such a thick film PTC resistor is made to meander in a narrow width and is attached so as to cover a substrate arranged between the casing and the heat exchanger over a wide area, the local heat exchanger is Overheat can be detected. That is, the resistance value of the PTC resistor rapidly increases when the temperature exceeds a predetermined value, and the overheat of the heat exchanger is detected by detecting the resistance value of the entire PTC resistor linearly connected.

When a plurality of thick film PTC resistors are attached to the surface of the substrate and they are connected in series by conductors,
Local overheating of the heat exchanger is detected by detecting the resistance value of the series circuit of the conductor and the PTC resistor.

The thick film PTC resistor can be formed on the substrate by printing, and an overheat detecting sensor having stable characteristics can be manufactured at low cost.

If the thick film PTC resistor is made of a flexible resin material, it can be attached to the surface of the heat exchanger having irregularities.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An overheat detecting sensor for a water heater according to the present invention will be described below with reference to the drawings. FIG.
1A is a front view showing a water heater to which the present invention is applied, FIG.
(B) is a side sectional view showing the water heater. In the figure, the heat exchanger 2 and the control unit 8 are indicated by dotted lines, and members hidden behind them are displayed. Further, the lid provided on the front surface of the casing 1 is omitted.

A heat exchanger 2 and a controller 8 are housed in a casing 1 shown in the figure. The heat exchanger 2 burns the gas to heat the water flowing through the water pipe. The control unit 8 controls the amount of gas supplied to the heat exchanger 2 and the like. A back panel 3 that blocks heat from the heat exchanger 2 is fastened to the back surface of the casing 1. A substrate 4 made of ceramic or resin film is attached to the back panel 3. Substrate 4
A thick film of the PCT resistor 5 is formed on the substrate by a printing method or a vapor deposition method. The PCT resistor 5 is obtained by firing several kinds of metal oxides and has a temperature resistance characteristic as shown in FIG.
That is, as shown in the figure, when the temperature exceeds a predetermined value, the resistance value rapidly increases. Instead of the metal oxide as the PCT resistor 5, other PCT such as resin / carbon type resistor is used.
It is also possible to utilize a material having characteristics.

The PCT resistor 5 is formed on the substrate 4 so as to meander in a narrow width, and covers the substrate 4 as a whole as a plane. The terminals 6 and 6 are provided so as to be connected to both ends of the PCT resistor 5, and the terminals 6 and 6 are connected to the control unit 8 via lead wires 7 and 7. The substrate 4 on which the PCT resistor 5 is formed may be covered with a protective film depending on the usage conditions.

FIG. 2 shows a control system of the water heater. As shown in the figure, a temperature sensor 9 is provided on the water pipe outlet side of the heat exchanger 2, and a signal from the temperature sensor 9 is output to the control unit 8. The lead wires 7, 7 shown in FIG. 1 are connected to the control unit 8. A proportional solenoid valve 10 and a solenoid valve 14 are provided in a pipe for supplying gas to the gas burner of the heat exchanger 2. Further, the signal from the operation unit 11 is output to the control unit 8. The ignition device of the gas burner of the heat exchanger 2 is not shown.

Ignition, fire extinguishing, and hot water temperature are set by the operation unit 11. The control unit 8 operates the ignition device based on the signal from the operation unit 11, and also sets the temperature set value and the temperature sensor 9
The signals from are compared and the proportional solenoid valve 10 is operated to control the hot water at the outlet of the water pipe to a set temperature. At this time, the solenoid valve 14 is fully opened. When the heat exchanger 2 becomes abnormally overheated, the PTC resistor 5 becomes high in resistance, and the control unit 8 detects it and closes the solenoid valve 14. The solenoid valve 14 operates on the fail-safe side.

FIG. 3 shows a test state in this embodiment. A test was carried out by bringing a rod heated to about 160 ° C. close to a part of the substrate 4 shown in the figure. The resistance increased at all points, and the control unit detected an overheated state. In this way, PTC
Since the resistors 5 are arranged in a meandering manner so as to form a plane as a whole, the resistance of the PTC resistor 5 as a whole can be rapidly increased and overheat can be detected no matter which part of the plane is overheated. It was

FIG. 5 shows another embodiment of the present invention. In this example, the conductive paste 12 and the PTC resistor 5a are formed on the substrate 4 by printing. The conductive paste 12 has a plurality of PTC resistors 5a, 5a ... Connected to terminals 6 and 6 in series. Other configurations are the same as those described above. Since the conductive paste 12 and the PTC resistor 5a are formed by printing, they can be manufactured at low cost even if they have a complicated shape. With such a configuration, the degree of freedom in designing the resistance value of the resistor 5a, the location of the resistor 5a, and the like is increased, and a sensor that stably detects abnormal overheating can be obtained.

FIG. 6 shows still another embodiment of the present invention.
In this example, the planar sensor formed of the substrate 4 and the PTC resistor 5 shown in FIG. 1 is bonded to the surface of the heat exchanger 2 having irregularities. By making the substrate 4 a flexible resin material, it can be attached to a heat exchanger having irregularities.

[0022]

As described above, according to the overheat detecting sensor of the water heater of the present invention, since the resistor and the lead wire can be formed by printing, the manufacturing and assembling are simple, and moreover, The overheated state can be detected stably over a wide range of the heat exchanger.

Further, since the sensor is formed in a film shape, it has a small heat capacity, and an overheated state can be detected quickly. Further, since the substrate and the resistor forming the planar sensor can be matched with various shapes, it is possible to design an overheat detecting sensor most suitable for the type of water heater.

[Brief description of the drawings]

FIG. 1 (a) is a front view showing a water heater to which the present invention is applied, and FIG. 1 (b) is a side sectional view showing the water heater.

FIG. 2 is a block diagram showing a control system of the water heater.

FIG. 3 is a partial front view showing a test point of the water heater.

FIG. 4 is a graph showing temperature characteristics of a PTC resistor used in the water heater.

FIG. 5 is a front view showing a sensor for detecting overheat according to another embodiment of the present invention.

FIG. 6 is a side view showing an overheat detecting sensor according to still another embodiment of the present invention.

FIG. 7 (a) is a front view showing an example of a conventional water heater,
FIG. 7B is a side sectional view showing the water heater.

[Explanation of symbols]

 1 Casing 2 Heat Exchanger 3 Rear Panel 4 Substrate 5, 5a PTC Resistor 6 Terminal 7 Lead Wire 8 Control Section 9 Temperature Sensor 10 Proportional Solenoid Valve 11 Operating Section 12 Conductive Paste 13 Thermal Fuse 14 Solenoid Valve

Claims (5)

[Claims] 1. A water heater having a heat exchanger arranged in a casing, wherein a conductor is connected to a thick film PTC resistor attached to a surface of a substrate, and the substrate is placed between the casing and the heat exchanger. A sensor for overheat detection of a water heater characterized by being arranged. 2. The thick film PTC resistor meanders in a narrow width and is arranged so as to cover the substrate in a wide range.
Sensor for overheat detection of water heaters. 3. The thick film PTC resistor is provided on the surface of a substrate, and they are connected in series by a conductor.
Sensor for overheat detection of water heaters. 4. The overheat detecting sensor for a water heater according to claim 1, wherein the thick film PTC resistor is formed on a substrate by printing. 5. The overheat detecting sensor for a water heater according to claim 1, wherein the substrate is made of a flexible resin material.