JP2502196Y2 - Liquid amount detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a liquid amount detecting device particularly applied to an electric pot.

(Prior Art) Conventionally, in a liquid amount detection device for a container such as an electric pot, as shown in Japanese Patent Application Laid-Open No. 59-162417, a static conductive material that is vertically connected to the outer surface of a non-conductive communication pipe communicating with the container is used. An electric electrode is provided, and the liquid amount is detected in an analog manner based on the continuous change of the electrostatic capacitance depending on the liquid level between the inner solution and the electrode in contact.

(Problems to be Solved by the Invention) An electrostatic capacity C between an electrostatic electrode and a content liquid to be the other electrode in the electrostatic capacity type liquid amount detecting device of this type is represented by the following formula. .

C = εS / d Here, ε is the inductivity of the communication tube, S is the facing area between the electrostatic electrode and the inner solution, and d is the wall thickness of the communication tube. Therefore, the capacitance varies depending on the diameter and wall thickness of the communication tube, the positional accuracy of the electrostatic electrode, the thickness of the adhesive agent for sticking the electrostatic electrode, and the like.

Therefore, if these factors vary for each product container, the capacitance will be different even for the same liquid amount,
There is a problem in that the amount of detected liquid varies and the accuracy decreases.

In particular, at the lowest level, the capacitance has a small absolute value and shows a value that is almost the same as the empty state, so that the degree of variation in the above factors affecting the detection value becomes large,
The accuracy becomes worse. Since detection at the lowest level has the most important meaning of preventing empty cooking in liquid amount detection, accuracy and reliability are required. Therefore, it was necessary to adjust the capacitance and the oscillation circuit for each product so that the accurate lowest level could be detected, but the increase in cost and the decrease in productivity accompanying this were problems. Was there.

Further, generally, the pumping pipe to which the electrostatic electrode is attached is connected to the bottom of the container via the connecting tube (see FIG. 1), and therefore the electrostatic electrode must be provided avoiding the connecting tube. Therefore, there is a problem that the lowest level is structurally high and reliability is deteriorated.
Therefore, it is conceivable to provide a connection port at the bottom of the container to lower the position of the connection tube, but this is not preferable because the structure becomes complicated and wasteful space is generated.

Furthermore, in the conventional liquid amount detection device, there is no choice but to take a different configuration depending on the size and model of the container, which makes it difficult to develop a series of products and is inferior in mass productivity.

The present invention has been made in view of the above problems, and has a high detection accuracy, and in particular, it can perform accurate and reliable detection at the lowest level, and it can also be used for containers of different sizes and models. The purpose is to provide.

(Means for Solving the Problem) In order to achieve the above-mentioned object, a first invention is to provide a plurality of electrostatic electrodes that are externally mounted in the liquid height direction on the outer surface of a non-conductive communication tube that communicates with a conductive metal container. A contact electrode provided below the lowest electrostatic electrode so that the liquid can come into contact with the liquid; and a liquid amount determining means for determining the liquid amount based on a change in electrostatic capacitance between the contact electrode and each of the electrostatic electrodes. A lowest level detecting means for detecting the lowest level based on the presence or absence of electrical conduction between the contact electrode and the conductive metal container.

In the second invention, a plurality of electrostatic electrodes are provided on the outer surface of the non-conductive communication tube that communicates with the conductive metal container in the liquid height direction, and the electrostatic electrodes are provided below the lowest electrostatic electrode so that they can come into contact with the liquid. Contact electrodes, individual oscillating means provided corresponding to each of the electrostatic electrodes, and oscillating a frequency corresponding to a change in capacitance between the electrostatic electrodes and the contact electrodes, and each of the individual oscillating means. It is provided with selection means for selectively suspending or operating the means, and determination means for determining the presence or absence of liquid at the position of the electrostatic electrode based on the frequency from each of the individual oscillating means.

(Operation) According to the configuration of the first aspect of the invention, the air and the wall of the communication pipe exist between the content liquid electrically conducting with the contact electrode and the electrostatic electrode above the liquid level. No substantial capacitor is formed. Therefore, the capacitance in this case is
There is only stray capacitance that exists between the electrostatic electrode or lead wire and the grounding part.

On the other hand, the content liquid that conducts with the contact electrode and the electrostatic electrode below the liquid level serve as opposing electrodes, forming a capacitor having the wall of the communication tube as a dielectric. In addition to the stray capacitance, the capacitor has a substantial capacitance determined by the material thickness of the communication tube and the facing area between the content liquid and the electrostatic electrode.

Therefore, the capacitance of the capacitor formed by each electrostatic electrode and the contact electrode changes depending on whether or not there is a liquid level at the position of each electrostatic electrode.

The liquid amount determination means applies a voltage to each individual electrostatic electrode,
The voltage at the time of charging / discharging the capacitor formed between the electrostatic electrode and the contact electrode is detected. At this time, since the time constant during charging / discharging varies depending on the magnitude of the electrostatic capacitance, that is, the presence or absence of the liquid level at the position of the electrostatic electrode, the presence or absence of the liquid can be determined by the magnitude of the detected voltage. By determining the presence or absence of the liquid for each electrostatic electrode, the liquid amount can be digitally detected.

In addition, in the range from the time when the water level reaches the lower end of each electrostatic electrode to the upper end, the electrostatic capacitance changes in an analog manner,
By setting this median value as the threshold value, a slight variation can be ignored.

On the other hand, the lowest level detection means detects the presence or absence of electrical conduction between the contact electrode and the conductive metal container. If there is a liquid level at the position of the contact electrode, there will be conduction between both electrodes via the content liquid,
If there is no liquid level, it becomes non-conductive, so that the position of the contact electrode, that is, the lowest level can be detected.

Even if there is a connection tube as described above between the communication tube and the container, this contact electrode can be provided with a hole for mounting the contact electrode in advance when the connection tube is molded. Error does not occur. By providing the contact electrode on the connection tube in this manner, the lowest detection level can be lowered to almost an empty state. Therefore, the lowest level can be detected accurately and reliably.

Further, even if the size or model of the container is changed, it can be dealt with by changing the position of the electrostatic electrode of the communication tube, and it is possible to easily expand from a large size to a small size or another model.

Next, according to the configuration of the second aspect, each electrostatic electrode and the contact electrode form a capacitor as in the first aspect.

Then, the selecting means sequentially selects the levels to be detected. The individual oscillating means selected by the selecting means oscillates a frequency corresponding to the capacitance of the capacitor formed between the electrostatic electrode and the contact electrode. The determination means determines the magnitude of the electrostatic capacitance based on the frequency of this frequency signal, and determines whether or not liquid is present at the position of the electrostatic electrode. After this,
Since the selection means selects the level to be detected next, the same determination as to the presence or absence of the liquid is performed and the liquid amount is digitally detected.

Therefore, according to the second aspect, the selecting means and the determining means can be configured and controlled by the microcomputer. In this case, since the selecting means sequentially suspends / operates the individual oscillating means, it is not necessary to provide the discriminating means corresponding to each individual oscillating means, and a single configuration is sufficient.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings. This embodiment includes both the first device and the second device.

FIG. 1 is a circuit diagram of a liquid amount detecting device for an electric pot.
In the figure, reference numeral 1 denotes an inner container of an electric pot, which is made of a conductive metal material and has a heater 2 at the bottom. Reference numeral 3 denotes a pumping pipe, which is made of a synthetic resin and is connected to a connection port 4 provided on the lower end side surface of the inner container 1 via a connecting tube 5 and is erected.

A contact electrode 6 is attached to the connection tube 5 so as to penetrate the wall thereof and come into contact with water inside, and four annular electrostatic electrodes 7a to 7a are attached to the outer surface of the pumping pipe 3 at predetermined intervals in the water level direction. 7d is inserted. The contact electrode 6 has a resistance R
It is connected to the power supply line through ₁ , R ₂ and the transistor Q, and also the output port S _{01 of the} microcomputer 10.
It is connected to, each of the electrostatic electrode 7a~7d are connected to a power supply line via a resistor _{R 3, R 4, R 5} . A lead wire 8 is connected to the bottom of the inner container 1 and is grounded via a resistor R ₆ .

The liquid amount detection circuit is generally a microcomputer 10, a minimum level detection circuit 11, an individual oscillation circuit 12, and a display circuit 13.
It is composed of

The microcomputer 10 includes a lowest level detection circuit 11
Together with this, it constitutes the lowest level detecting means according to the first invention. Therefore, it has an output port S ₀₀ and an input port I ₀ for exchanging signals with the lowest level detection circuit 11.

Further, the microcomputer 10 constitutes a liquid amount discriminating means together with the individual oscillating circuit 12, and functions as a selecting means and a discriminating means according to the second invention. For this reason,
From the output port S ₀₁ to the contact electrode 6, the number of output ports S _{1 to} S ₄ corresponding to the electrostatic electrodes 7a to 7d, the output ports L _{1 to} L ₅ to the display circuit 13, and the individual oscillation means 12 And an input port I ₁ for receiving the signal input of.

The lowest level detection circuit 11 is composed of a transistor Q and a comparator CM ₀ . The emitter of the transistor Q is connected to the power supply line, the collector is connected to the contact electrode 6 via the current control resistors R ₁ and R ₂ , and the base is connected to the power supply line via the resistor R ₇ , and
It is connected to the output port S ₀₀ of the microcomputer 10 via the resistor R ₈ . Comparator CM ₀ - input terminal is connected between the resistor R _9, R ₁₀ lines are grounded via a resistor R _9, R ₁₀ from the collector terminal of the transistor Q,
The + input terminal is connected to the contact electrode 6 side of the current limiting resistor R ₁ . It should be noted that D ₁ and D ₂ are diodes for noise prevention.

Individual oscillator circuit 12 has four consists comparator CM ₁ ~CM _4, of the comparators CM ₁ ~CM ₄ - input terminal is connected to the electrostatic electrode 7a to 7d, + input terminal resistor from the power supply line R ₁₁ , R ₁₂ is connected between the resistors R ₁₁ and R _{12 of} the grounded line, and the output terminal is connected to the common input terminal I ₁ of the microcomputer 10. Midpoint between the resistors R _4, R ₅ of each voltage supply line to the electrostatic electrode 7a~7d is connected to the output terminal S ₁ to S ₄ of the microcomputer 10.
R ₁₃ is a resistor for changing the comparator CM ₁ to the reference voltage of CM ₄ .

Display circuit 13 consists of five LED14,15a～15d, the output terminal L ₁ ~L ₅ of one side microcomputer 10
, And the + side is connected to the power supply line via the resistor R ₁₄ .

By the way, the output terminal S of the microcomputer 10
_As shown in FIG. 1, ₀₀ is normally fixed to Z (high impedance), output terminals S _{1 to} S ₄ are normally fixed to L (low level), and output terminals L _{1 to} L ₅ are normally Z. It is fixed. Further, the microcomputer 10 has an event counter 16 therein and counts the frequency signal input to the input port I ₁ .

As shown in FIG. 2, when the power is turned on, the CPU of the microcomputer 10 first detects the lowest level in step S101, starts a t-time timer (normally 2 to 3 seconds) in step S102, After sequentially detecting the liquid amounts in steps S103 to 106, if the time is not up in step S107, the liquid amount detection is continued, and if the time is up, the process returns to step S101 to similarly detect the lowest level and the liquid amount. Perform detection.

i) Lowest level detection The microcomputer 10 outputs the output port S for about 1 ms.
_The L signal is output from ₀₀ and the output port S ₀₁ is fixed to Z. As a result, the transistor Q is turned on, and H (high level) voltage is applied to the contact electrode 6.

At this time, when the water level in the inner container 1 is less than L _0, that is, in an empty state, the applied voltage cuts off the current path and no voltage drop occurs. Therefore, the + input terminal of the comparator CM ₀ is set to H level. A signal is input. On the other hand, the comparator CM ₀ - since the input terminal partial pressure 1 / 2Vcc by the resistors R _9, R ₁₀ are applied, + who input terminal becomes high potential, the comparator CM ₀ microcomputer signal of an H Output to 10 input ports I ₀ .

As a result, the microcomputer 10 outputs the output port L
A pulse signal is output from ₁ to blink the LED 14, and a current cutoff signal to the heater 2 is output from an output port (not shown). As a result, there is no water in the inner container 1,
A warning is displayed to indicate that the heater 2 is in an empty state, and the heater 2 is de-energized. Note that a buzzer or the like can give an alarm if necessary.

Further, when the water level in the inner container 1 is L ₁ or more, the contact electrode 6 is in contact with water, so that the applied voltage flows through the water to the ground of the circuit. Thus, a voltage drop occurs in the current limiting resistor R _1, to the positive input terminal of the comparator CM ₀ results signal L is input, the comparator CM ₀ outputs an L signal. In this case, the microcomputer 10
Outputs an L signal from the output port L ₁ to light the LED 14. As a result, it is displayed that the water level is above the L ₁ level.

After the above detection, the output ports S ₀₀ and S ₀₁ are fixed to Z and L, respectively.

ii) liquid amount detection microcomputer 10 first to the water level to perform a first level detection display Kano L ₁ or L _2, select only the output port S ₁ output Z signal from the output port S ₁ To do.

Thus the voltage to the electrostatic electrode 7a via a resistor R _4, R ₅ from the power supply line is applied. On the other hand, since the contact electrode 6 is dropped to L via the output port S ₀₁ , the capacitor Cs ₁ is formed between the contact electrode 6 and the electrostatic electrode 7a.

The + input terminal of the comparator CM ₁ partial pressure 1 / 2Vcc by the resistor R _11, R ₁₂ are inputted, - charging of the computer Cs ₁ to the input terminal, the discharge voltage is input. Therefore, the capacitor CM ₁ alternately outputs the H and L signals with the predetermined threshold value of the voltage at the time of charging and discharging the capacitor Cs ₁ as the boundary to perform the oscillating operation.

At this time, when the water level is at the L ₁ level and there is no water at the position of the electrostatic electrode 7a, the capacitance is small and the time constant during charging and discharging is small as described above.
₁ oscillates at a relatively high frequency (50 to 55 kHz).

Further, when the water level is at the L ₂ level and water is present at the position of the electrostatic electrode 7a, the capacitance is large and the time constant at the time of charging and discharging is large, so the comparator CM ₁ has a relatively low frequency ( 25kHz) oscillation.

Therefore, the microcomputer 10 uses the comparator CM
By counting the frequency of the signal input to the input port I ₁ from ₁ by the event counter 16 can determine the presence or absence of water at the position of the electrostatic electrode 7a. That is, the microcomputer 10 keeps the output port L ₁ at Z when the high frequency is detected to turn off the LED 15a, and outputs the L signal from the output port L ₂ to turn on the LED 15a when the low frequency is detected. As a result, the presence or absence of the water level at the position of the electrostatic electrode 7a is detected.

During the detection of the first level, another output port S
_{2 to} S ₄ are fixed to L, and electrostatic electrodes 7b to 7d corresponding to each are
Since no voltage is supplied to the capacitor, a capacitor is not formed and the comparators CM _{2 to} CM ₄ do not oscillate.

Next, in order to perform the microcomputer 10 water level L ₂ or L ₃ Kano second level detection, by selecting only the output port S _2, and outputs a Z signal from the output port S _2, following a similar level A determination is made and this operation is continuously performed. Therefore, as a result of the LEDs 15a to 15d displaying the presence or absence of the water level at the positions of the electrostatic electrodes 7a to 7d, the liquid amount in the inner container 1 is displayed as a whole.

(Effect of Device) As is apparent from the above description, according to the first device,
Since the presence or absence of the liquid level at the position of each electrostatic electrode is detected by a digital change in the electrostatic capacitance, even if there is some variation in the electrode mounting position, it can be detected with a certain accuracy. Therefore, it is not necessary to adjust each product, and the number of manufacturing steps and the cost can be reduced.

Also, since the lowest level is detected depending on the presence or absence of electrical conduction between the contact electrode provided below the electrostatic electrode and the container, the contact electrode should be attached to the connection tube that connects the communication tube and the container and should be close to the bottom. It is possible to detect the lowest level that is almost empty, and the accuracy and reliability are improved.

Furthermore, since the presence or absence of the liquid level at each electrostatic electrode position is detected by the plurality of electrostatic electrodes, the same device can be used even if the size or model changes, and a wide range of series development is possible.

On the other hand, according to the second aspect, as in the first aspect, it is possible to improve accuracy, develop a series of sizes and models, and use a single determination means for determining the presence or absence of the liquid level at each electrostatic electrode position. Therefore, the circuit configuration is simplified and the cost can be reduced.

[Brief description of drawings]

1 and 2 are a circuit diagram and a flow chart, respectively, of the liquid amount detecting device according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Inner container, 3 ... Pumping pipe (communication pipe), 6 ... Contact electrodes, 7a-7d ... Electrostatic electrodes, 10 ... Microcomputer (liquid amount determination means, selection means, determination means), 11 ...... Minimum level detection circuit, 12 …… Individual oscillator circuit.

Claims (2)

(57) [Scope of utility model registration request] 1. A plurality of electrostatic electrodes, which are mounted on the outer surface of a non-conductive communication tube communicating with a conductive metal container in the liquid height direction, and a contact provided below the lowest electrostatic electrode so as to be in contact with the liquid. Electrodes,
A liquid amount determination means for determining a liquid amount based on a change in electrostatic capacitance between the contact electrode and each of the electrostatic electrodes, and presence or absence of electrical conduction between the contact electrode and the conductive metal container. And a lowest level detection means for detecting the lowest level based on the liquid level detection apparatus. 2. A plurality of electrostatic electrodes externally mounted in the liquid height direction on the outer surface of a non-conductive communication tube communicating with a conductive metal container, and a contact provided below the lowest electrostatic electrode so as to be in contact with the liquid. Electrodes,
Individual oscillating means provided corresponding to each of the electrostatic electrodes and selectively oscillating each individual oscillating means for oscillating a frequency corresponding to a change in capacitance between the electrostatic electrodes and the contact electrode. A liquid amount detecting device comprising: a selection unit that is paused or operated, and a determination unit that determines the presence or absence of liquid at the position of the electrostatic electrode based on the frequency from each of the individual oscillation units.