JP2004294208A - Water level - water temperature sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the level and the temperature of water using the difference between heat generation in water of a thermosensitive device and heat generation in air. <P>SOLUTION: A sensor has a first thermosensitive device 1, a second thermosensitive device 2, and a determination circuit 3. The first and second devices 1 and 2 are immersed in water inside a tank, and incorportated in the tank. The first device 1 generates heat by itself and is used for detecting the difference in temperature by heat generation in the water and in the air, and the second device 2 is set in the same environment as the first thermosensitive device and is used for measuring an environmental temperature. The determination circuit 3 uses a temperature detected by the second device 2 as a reference temperature, compares a temperature detected by the first device 1 with the reference temperature, and determines from its higher or lower, or the coincidence of both temperatures whether the water level in the tank is a specified level, higher, or lower. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to a water level-water temperature detection system for installing in a hot water or water tank of equipment such as a dishwasher, a water heater, a washing machine, a dryer, and a bathtub to detect a water level and a water temperature of a liquid filled in the tank. Related to sensors.
[0002]
[Prior art]
For equipment with a hot water tank attached, such as a dishwasher dryer, a water level-water temperature detection sensor is installed in the tank to detect the liquid filling amount of the tank or to detect the liquid temperature in the tank. Is done.
[0003]
As a sensor for detecting the water level-water temperature in the tank, the applicant has previously proposed Patent Documents 1 and 2 and proposed Patent Document 3 as a water level sensor and put it into practical use.
[0004]
[Patent Document 1] JP-A-2001-289699
[Patent Document 2] JP-A-2002-148098
[Patent Document 3] JP-A-2002-107203
[0005]
The water level-water temperature detection composite sensor described in Patent Document 1 has a built-in temperature sensor in at least one of the paired electrodes. The paired electrodes are immersed in water in a tank from above, and the water temperature is passed through the electrodes. At the same time as detecting the water level based on the change in the resistance value between the electrodes.
[0006]
Further, the water level-water temperature detection sensor described in Patent Document 2 comprises a combination of a first electrode rod installed at an upper limit water level position in a tank and a second electrode rod installed below the water surface. The electrode rods are individually inserted into water in a tank, the water level is detected based on a change in electric resistance between the two electrode rods, and the water temperature is measured by a temperature sensor incorporated in the second electrode rod.
[0007]
Further, the water level detection sensor described in Patent Document 3 has a pair of rod-shaped electrodes, and the paired rod-shaped electrodes are immersed in water in a tank from above similarly to the sensor described in Patent Document 1. Although the water level is detected based on a change in the resistance between the rod-shaped electrodes, the sensor described in Patent Document 3 uses a rod-shaped electrode so that the resistance is not affected by water droplets remaining on a part of the sensor. The spaces are separated from each other by a shielding portion.
[0008]
As described above, the sensors described in Patent Documents 1, 2, and 3 measure the resistance between electrodes by immersing two electrodes in water, and measure the resistance between the electrodes when water is filled between the electrodes and the resistance between the electrodes. When the resistance value when the water runs out is detected and the resistance value when the water runs out between the electrodes is indicated, it is common that the water level falls below the position of the electrode.
[0009]
In the sensors described in Patent Literatures 1 and 3, the two electrodes are inserted at the same height into the water in the tank from above, and when the water level falls below the positions of the two electrodes at the same time, it is determined that the water level has dropped. However, in the cited document 2, even when the second electrode rod is immersed in water, it is determined that the water level has dropped when the position is lower than the position of the first electrode rod installed at the upper limit water level position in the tank. You. In the sensors described in Patent Documents 1 and 3, two electrodes can be inserted upward from the bottom of the tank. At this time, when the upper ends of both electrodes are exposed to the water surface, a decrease in the water level is detected. You.
[0010]
In the sensor described in Patent Literature 2, the distance between the electrodes does not matter, but when the electrodes are arranged in parallel as in Patent Literature 1, the distance between the electrodes is short, as pointed out in Patent Literature 3. A problem arises and measures need to be taken.
An object of the present invention is to provide a water level-water temperature sensor that measures a water level and a water temperature by utilizing a difference between heat generation of a thermosensitive element in water and heat generation in air.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, when using the water level-water temperature sensor according to the present invention, a water level-water temperature sensor having a first temperature-sensitive element, a second temperature-sensitive element, and a determination circuit,
The first temperature sensing element and the second temperature sensing element are immersed in water in a tank, and are built in a case,
The first temperature-sensitive element is for causing a self-heating to detect a difference in a heating temperature between water and air.
The second temperature sensing element is installed in the same environment as the first temperature sensing element and measures the environmental temperature.
The determination circuit sets the temperature detected by the second temperature-sensitive element as a reference temperature, compares the temperature detected by the first temperature-sensitive element with the reference temperature, and determines whether the water level in the tank is equal to or greater than a specified level based on the level of the temperature or a match between the two temperatures. It is a circuit that determines whether the value is less than or equal to.
[0012]
Further, the first temperature-sensitive element and the second temperature-sensitive element are installed in a tank of equipment at a predetermined water level at a certain distance or more so as not to cause thermal interference with each other. Is what it is.
[0013]
In addition, the first thermosensitive element that has self-heated generates a “high” or “low” water level of the liquid filled in the tank from the installation position of the first thermosensitive element depending on the level of the heat generation temperature. The water temperature is detected from the measured temperature when it is determined that the water level is equal to or higher than a specified water level.
[0014]
Further, the second temperature sensing element is for detecting the temperature of the environment in which the second temperature sensing element is installed, regardless of whether it is in water or in the air,
The temperature detected by the second temperature-sensitive element determines a temperature that is used as a criterion for determining whether the heat generation temperature of the first temperature-sensitive element is high or low.
[0015]
The determination circuit compares the output of the first output circuit with the output of the second output circuit,
The first output circuit is a circuit that outputs a voltage corresponding to a detected temperature of the first thermosensitive element,
The second output circuit is a circuit that outputs a voltage corresponding to a detected temperature of the second temperature sensing element as a reference voltage.
[0016]
The reference voltage is a criterion for determining whether the output voltage of the first thermosensitive element indicates a relatively high voltage in water or a relatively low voltage in air. It is shown.
[0017]
Further, the reference voltage is set as an intermediate voltage value between the output voltage of the first thermosensitive element in water and the output voltage in air.
[0018]
Further, the reference voltage is set to a voltage value close to the output voltage of the first thermosensitive element in water or the output voltage in air.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment according to the present invention will be described below with reference to the drawings. In FIG. 1, the water level sensor according to the present invention includes a combination of a first temperature sensing element 1, a second temperature sensing element 2, and a determination circuit 3.
[0020]
The first temperature sensing element 1 and the second temperature sensing element 2 are specifically thermistors. As shown in FIG. 2A, the first temperature-sensitive element 1 (the same applies to the second temperature-sensitive element 2) is built in a metal case 4, and from the metal case 4, a pair of respective elements is provided. , And a connector 6 is attached to an end of the lead wire 5. In this embodiment, the first temperature sensing element 1 and the second temperature sensing element 2 are spaced at a certain interval (at least 10 mm or more) so that thermal interference does not occur as shown in FIG. It is held by the holder 7 in a parallel posture.
[0021]
The holder 7 integrally has a circular flange 8 as shown in FIG. 2C, and the first temperature-sensitive element 1 and the second temperature-sensitive element 2 project upward from the flange 8. . When the first temperature-sensitive element 1 and the second temperature-sensitive element 2 are installed in the tank 9 of equipment such as a dishwasher, they are opened at the bottom of the tank 9 as shown in FIG. The holder 7 is inserted from above into the hole, the flange 8 is supported on the opening edge of the tank 9, the packing 10 is provided on the holder 7, the packing 10 is applied to the lower bottom surface of the tank 9, and the outer periphery of the holder 7 is further engraved. A nut 12 is screwed into the screw 11 and the packing 10 is tightened to fix the holder 7 to the tank 9. The first temperature-sensitive element 1 and the second temperature-sensitive element 2 are fixed to a predetermined height in the tank 9. It is installed in the position.
[0022]
The first temperature sensing element 1 is configured to generate heat by itself and detect a difference in heat generation temperature between water and air. The thermistor self-heated in water has a much larger heat dissipation constant than self-heated in air.
[0023]
Therefore, the self-heating temperature of the thermistor is higher in air than in water. Therefore, if the heat generation temperature of the first temperature-sensitive element 1 that has caused self-heating is measured, whether the first temperature-sensitive element 1 is in the air or in the water, in other words, depending on the magnitude of the temperature, It can be determined whether the water level of the liquid filled in 9 is “higher” or “lower” than the installation position of the first temperature sensing element 1. That is, the heat generation temperature is low as long as the first temperature sensing element 1 is immersed in water, but when the water level in the tank 9 drops to a position where the first temperature sensing element 1 is exposed to the air, The exothermic temperature rises sharply.
[0024]
Further, when the water in the tank 9 is at or above a prescribed water level and the first temperature-sensitive element 1 is immersed in the water, the temperature of the water in the tank 9 can be detected from the measured temperature. The second temperature sensing element 2 determines the temperature that is used as a reference for determining whether the heat generation temperature of the first temperature sensing element 1 is “high” or “low”. The second temperature sensing element 2 accurately detects the temperature of the environment in which the second temperature sensing element is installed, regardless of whether it is in water or in the air.
[0025]
The determination circuit 3 uses the temperature detected by the second temperature-sensitive element as a reference temperature, compares the temperature detected by the first temperature-sensitive element with the reference temperature, and determines whether the water level in the tank 9 is high or low or based on a match between the two temperatures. The determination circuit 3 determines whether the output is equal to or more than the specified value or less than the specified value. As will be described later, the determination circuit 3 is configured as a circuit that directly compares the output of the first output circuit 13 and the output of the second output circuit 14. You.
[0026]
FIG. 3 shows an example of an output circuit (referred to as a first output circuit) 13 of the first temperature sensing element 1. The first output circuit 13 is a circuit that outputs a voltage corresponding to a temperature detected by the first temperature-sensitive element 1, and a thermistor having a small heat dissipation constant is used as the first temperature-sensitive element 1. In this example, A glass-filled thermistor having a resistance value of 2 kΩ at 25 ° C. and B25 / 50 = 3500 K was used. The power supply was connected to DC 20V. In addition, since the resistance of the first temperature sensing element 1 decreases due to self-heating, a current limiting resistor R _S (= 500Ω) is connected in series with the first temperature sensing element 1 to prevent damage due to thermal runaway. However, the current flowing through the first temperature sensing element 1 is limited by the voltage drop caused by the resistor _RS . Although a resistance value of 500Ω was selected as the current limiting resistor _RS , the resistance value is determined from the output voltage, current, and power supply voltage of the thermistor at that time when the operating temperature is determined.
[0027]
FIG. 4 shows a case where the first temperature sensing element 1 is immersed in water (when a water level higher than a specified level is maintained in the tank 9) and a case where the first temperature sensing element 1 is exposed to air (in the tank 9). (When the water level falls below a specified level). In this embodiment, the heat dissipation constant in the air of the thermistor used for the first temperature sensing element 1 is 2.3 W / ° C., while in the water it is 5.7 W / ° C., which is about 2.5 times. There is a difference.
[0028]
In FIG. 4, Va-w indicates an output voltage in water, and Va-a indicates an output voltage in air. In this example, when the water temperature in the tank 9 is about 50 ° C., the output terminal voltage Va is about 7.5V. The output terminal voltage Va when the water temperature drops to 20 ° C. due to the addition of water into the tank 9 due to the drop in the water level rises to 12 V, but when the water level drops and the first temperature sensing element is exposed to the air. The self-heating temperature rises to a level of 80 to 90 ° C., and the output terminal voltage Va becomes 6V.
[0029]
As is clear from FIG. 4, the output voltage of the first temperature sensing element 1 is either immersed in water or exposed to air, regardless of whether it is in water or air. The output voltage Va-w when immersed in water is higher than the output voltage Va-a when immersed in air. Varies depending on the environmental temperature. Therefore, when used in a wide temperature range, it is necessary to perform temperature compensation. The second temperature sensing element 2 is used for temperature compensation.
[0030]
FIG. 5 shows an example of the output circuit (second output circuit) 14 of the second temperature sensing element 2. The second output circuit 14 is a circuit that outputs a voltage corresponding to a temperature detected by the second temperature-sensitive element 2 as a reference voltage, and the second temperature-sensitive element 2 accurately outputs a voltage over a wide range of at least 0 ° C. to 100 ° C. It is necessary that the thermistor be capable of detecting a change in temperature. In this embodiment, a chip type thermistor (Rth = 20 kΩ at 25 ° C., B25 / 50 = 3930 K) is used, and resistors Ra, Rb, and Rc are used in the second output circuit 14 so as not to generate heat. The resistor Rc is connected in parallel with the second temperature sensing element, and the resistors Ra and Rb are connected in series to form a resistor network.
[0031]
The output voltage Vc output from the second output circuit 14 distinguishes between the output voltage Va-w of the first thermosensitive element 1 shown in FIG. 4 in water and the output voltage Va-a in air. This is for setting a reference voltage. The second temperature-sensitive element 2 is always placed in the same environment as the first temperature-sensitive element 1, and measures the temperature of the environment. Does not make a difference.
[0032]
FIG. 6 shows output voltages (reference voltage Vc1, reference voltage Vc2) at an environmental temperature determined by the values of the resistors Ra, Rb, and Rc. As is clear from FIG. 6, the reference voltage Vc1 is an intermediate voltage value between the output voltage Va-w of the first temperature sensing element 1 in water and the output voltage Va-a in air, and the reference voltage Vc2 Indicates a voltage value close to the output voltage Va-a in the air. Although not illustrated, the reference voltage may be set to a voltage value close to the underwater output voltage Va-w.
[0033]
When the reference voltage Vc1 is selected, when the output voltage of the first temperature sensing element 1 is higher than the reference voltage Vc1, it is determined that the water level in the tank 9 is higher than the specified level. It is judged that the water level inside is below the regulation. Further, when the reference voltage Vc2 is selected, when the output voltage of the first temperature sensing element is higher than the reference voltage Vc1, it is determined that the water level in the tank 9 is higher than the specified level. Is the same as the case where is selected, but when the water level in the tank 9 falls below the specified value, the output voltage of the first thermosensitive element 1 indicates a voltage close to the reference voltage Vc2.
[0034]
In any case, the reference voltage indicates whether the output voltage of the first temperature sensing element 1 indicates a relatively high voltage in water or a relatively low voltage in air. It shows a criterion for judgment, and where to put the criterion can be arbitrarily selected.
[0035]
In the present invention, the measured temperature of the first temperature sensing element 1 is indicated as an output voltage of the first output circuit 13, and whether the measured temperature is the temperature of water or the temperature of the air is determined by the second output circuit 14. Of the output voltage.
[0036]
The output Va of the first output circuit 13 and the output Vc of the second output circuit 14 are directly compared by the determination circuit 3. 7, the determination circuit 3 connects a first output circuit 13 and a second output circuit 14 to a DC power supply 16 in parallel, and outputs an output terminal Va of the first output circuit 13 and a second output A voltmeter 15 is connected to the output terminal Vc of the circuit 14. Note that the reference voltage Vc1 shown in FIG. 6 was selected for the resistance network of the second output circuit.
[0037]
In this example, as shown in the conceptual diagram of FIG. 8, if the measured value of the temperature by the first thermosensitive element 1 is larger than the reference value Vc1, the voltmeter 15 of the determination circuit 3 swings to the plus side and the water level rises. It indicates that the water level is equal to or higher than the specified value, and if it is smaller than the reference value Vc1, it indicates that the water level is below the specified value by swinging to the negative side. The voltmeter 15 is, of course, not limited to reading the change in the water level according to the direction of the movement of the needle, but can also output a digital signal. The water temperature is indicated by the detected temperature of the second temperature-sensitive element 2 that detects the environmental temperature under the condition that the first temperature-sensitive element 1 detects that the element is in water.
[0038]
As described above, in the embodiment, the example in which the first temperature sensing element 1 and the second temperature sensing element 2 are inserted into the tank 9 from below to detect the water level in the tank 9 has been described. Thereby, when the water level falls below the installation height of the first temperature sensing element 1 and the second temperature sensing element 2, it is determined that the tank is empty, and a signal output from the determination circuit 3 For example, a water supply command to the inside of the tank 9 is issued, or the power of a heater (not shown) for heating the tank 9 is turned off to prevent the tank 9 from being idle. When measuring the water level by inserting the temperature sensing elements 1 and 2 into the tank 9 from above, the measuring procedure is exactly the same.
[0039]
【The invention's effect】
As described above, the present invention detects the change in the water level in the tank by utilizing the fact that the heat generation temperature of the self-generated first temperature sensing element is different between water and air. Can be easily determined by comparing with the reference ambient temperature, and at the same time, the temperature of the water filled in the tank can be detected.
[0040]
According to the present invention, a first temperature-sensitive element for detecting a difference between heat generation temperatures in water and air by causing self-heating, a second temperature-sensitive element for measuring an environmental temperature, and a second temperature-sensitive element The temperature detected by the first temperature sensing element is compared with the reference temperature, and it is determined whether the water level in the tank is equal to or higher than a specified level based on the level of the detected temperature or the coincidence of the two temperatures. Alternatively, the presence or absence of water in the tank can be accurately detected.
[0041]
Further, according to the present invention, two temperature sensing elements are inserted into the tank, but are not electrode rods as in Patent Documents 1 to 3 cited as prior examples, so that the first and second temperature sensing elements are used. The first and second temperature sensing elements are placed in the same environment without being affected by the water droplets attached to the bridge between them and the resistance value of the liquid. It is possible to accurately judge whether it is in the middle. The present invention can provide excellent effects when installed in warm water or a water tank of equipment such as a dishwasher, a water heater, a washing machine, a dryer, and a bathtub.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an installation example of a water level sensor according to the present invention.
2A is a view showing a first temperature sensing element built in a case, FIG. 2B is a front view of a water level sensor, and FIG. 2C is a plan view of the same.
FIG. 3 is a first output circuit diagram.
FIG. 4 is a diagram showing voltage waveforms in water and in air output from a first output circuit.
FIG. 5 is a second output circuit diagram.
FIG. 6 is a reference waveform diagram output from a second output circuit.
FIG. 7 is a diagram of a determination circuit.
FIG. 8 is a diagram illustrating a direction of a swing of a voltmeter of a determination circuit and a determination procedure in water and in air.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st temperature sensing element 2 2nd temperature sensing element 3 Judgment circuit 4 Metal case 5 Lead wire 6 Connector 7 Holder 8 Flange 9 Tank 10 Packing 11 Screw 12 Nut 13 First output circuit 14 Second output circuit 15 Voltmeter 16 DC power supply

Claims (8)

A water level-water temperature sensor having a first temperature sensing element, a second temperature sensing element, and a determination circuit,
The first temperature sensing element and the second temperature sensing element are immersed in water in a tank, and are built in a case,
The first temperature-sensitive element is for causing a self-heating to detect a difference in a heating temperature between water and air.
The second temperature sensing element is installed in the same environment as the first temperature sensing element and measures the environmental temperature.
The determination circuit sets the temperature detected by the second temperature-sensitive element as a reference temperature, compares the temperature detected by the first temperature-sensitive element with the reference temperature, and determines whether the water level in the tank is equal to or greater than a specified level based on the level of the temperature or a match between the two temperatures. A water level sensor, which is a circuit for determining whether the water level is below or not. The first temperature sensing element and the second temperature sensing element are installed in a tank of equipment at a specified water level at a certain interval that does not cause thermal interference with each other. The water level sensor according to claim 1, wherein The first temperature-sensing element that has caused self-heating determines whether the level of the liquid filled in the tank is “high” or “low” from the installation position of the first temperature-sensing element depending on the level of the heat generation temperature. The water level sensor according to claim 1, wherein the water temperature is detected from the measured temperature when the water temperature is determined to be equal to or higher than a specified water level. The second temperature sensing element detects the temperature of the environment in which the second temperature sensing element is installed, regardless of whether it is in water or in the air.
2. The water level sensor according to claim 1, wherein the detection temperature of the second temperature sensing element determines a temperature that is used as a reference for determining whether the heat generation temperature of the first temperature sensing element is high or low. 3. The determination circuit compares an output of the first output circuit with an output of the second output circuit,
The first output circuit is a circuit that outputs a voltage corresponding to a detected temperature of the first thermosensitive element,
The water level sensor according to claim 1, wherein the second output circuit is a circuit that outputs a voltage corresponding to a temperature detected by the second temperature sensing element as a reference voltage. The reference voltage indicates a criterion for determining whether the output voltage of the first temperature sensing element indicates a relatively high voltage in water or a relatively low voltage in air. The water level sensor according to claim 5, wherein The water level sensor according to claim 5, wherein the reference voltage is set as an intermediate voltage value between an output voltage of the first temperature sensing element in water and an output voltage in air. The water level sensor according to claim 5, wherein the reference voltage is set to a voltage value close to an output voltage of the first temperature sensing element in water or an output voltage in air.

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