JPS6324248B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a water level detection device.

The conventional water level detection device, as shown in Figure 1,
The primary winding of a step-down transformer T is connected to an alternating current power supply AC, and the first secondary winding T ₁ of this step-down transformer T is connected to a first winding consisting of a diode D ₁ and a capacitor C ₁ .
A rectifying and smoothing circuit CD ₁ is connected to the output terminal of the first rectifying and smoothing circuit CD ₁ , and a series circuit of an abnormality notification relay RY ₁ and a switching transistor Q ₁ is connected to the output terminal of the first rectifying and smoothing circuit CD 1. A second winding consisting of a diode D ₂ and a capacitor C ₂ in the secondary winding T ₂
A rectifying and smoothing circuit CD ₂ is connected to the output terminal of the second rectifying and smoothing circuit CD ₂ , and a series circuit of a control relay RY ₂ and a switching transistor Q ₂ is connected to the output terminal of the second rectifying and smoothing circuit CD 2. Connect one AC input end of each of diode bridges DB ₁ and DB ₂ to one end of the next winding T ₃ , and
The other AC input end of DB ₁ is connected to the first water level detection electrode E ₁ in the water tank K via the signal line L ₁ , and the other AC input end of the diode bridge DB ₂ is connected to the signal line L ₂ .
is connected to the second water level detection electrode E ₂ in the water tank K via the normally open contact RY _2a of the relay RY ₂ and connected to the third water level detection electrode E ₃ in the water tank K via the signal line L ₃ . The other end of the third secondary winding of the step-down transformer T is connected to the common electrode _E0 in the water tank K via the signal line _L0 , and the pair of DC output ends of the diode bridge _DB1 are connected to the resistor R. ₁ , the base of the switching transistor _Q1 via _R2 and capacitor _C3 .
A pair of DC output ends of the diode bridge DB ₂ are connected between the base and emitter of the switching transistor Q ₂ via resistors R ₃ and R ₄ and a capacitor C ₄ .
Power is supplied to the abnormality notification lamp LP through the normally open contact ry _1a of the relay RY ₁ , and to the motor M that drives the drainage pump through the normally open contact _{ry 2b of} the relay RY 2.

This water level detection device has _{a common electrode E 0 and} water level detection electrodes E ₁ , E ₂ ,
E ₃ is in an open state, and no base current is supplied from the third secondary winding T ₃ of the step-down transformer T to the switching transistors Q ₁ and Q ₂ .
Switching transistors Q ₁ and Q ₂ are both off, relays RY ₁ and RY ₂ are each in a de-energized state, normally open contacts ry _1a , ry _2a , and ry _2b are each in an open state, and the abnormality notification lamp is LP goes out,
The motor M has stopped and the drainage operation has stopped.

When the water level in tank K rises to more than X ₁ ,
The common electrode E ₀ and the water level detection electrode E ₃ are electrically connected through the water, but the signal line is connected by the normally open contact ry _2a.
Since _L3 is disconnected from the diode bridge _DB2 , the states of relays _RY1 and _RY2 do not change.

When the water level in the water tank K further rises to _X2 or higher, conduction occurs between the common electrode _E0 and the water level detection electrode _E2 through the water, and the third
A base current is supplied from the secondary winding T ₃ to the switching transistor Q ₂ via the diode bridge DB ₂ , resistors R ₃ , R ₄ and capacitor C ₄ ,
Switching transistor Q ₂ turns on and relay RY ₂ becomes energized, normally open contacts ry _2a and ry _2b.
is closed, the signal line _L3 is connected to the diode bridge _DB2 , the motor M is activated, and the drain pump drains water from the water tank K.

Due to the operation of the drainage pump, the water level in the water tank K increases to X ₂
When the voltage is less than 2, the connection between the common electrode E ₀ and the water level detection electrode E ₂ becomes open, but the signal line L ₃ is connected to the diode bridge DB ₂ and connected to the common electrode E ₀ by closing the normally open contact ry _2a . Since water is electrically connected to the water level detection electrode E ₃ , the state of the relays RY ₁ and RY ₂ does not change and the drainage operation continues.

When the water level in the water tank K further decreases to less than _X1 , the common electrode _E0 and the water level detection electrode _E3 become open, and the third secondary winding of the step-down transformer T
The supply of base current from T ₃ to switching transistor Q ₂ is stopped, switching transistor Q ₂ is turned off, relay RY ₂ is in a de-energized state, and normally open contacts RY _{2 a} and RY _{2 b} are opened. When the signal line _L3 is disconnected from the diode bridge _DB2 , the motor M is stopped and the draining operation is stopped.

Thereafter, the above operation is repeated.

If drainage is not performed due to a malfunction of the drainage pump, etc., and the water level in the water tank K exceeds _X3 , the common electrode _E0 and the water level detection electrode _E1 become electrically connected through the water, and the step-down transformer T 3 secondary winding T ₃
A base current is supplied from the diode bridge DB ₁ to the switching transistor Q 1 through the resistors R ₁ , R ₂ and the capacitor C ₃ , the switching transistor _{Q 1 is} turned on, and the relay RY ₁ is energized. Full water notification is performed by closing the normally open contact ry _1a and lighting the abnormality notification lamp LP.

In addition, when performing water supply control, power may be supplied to the motor M via the normally closed contact of the relay RY ₂ , and the water supply pump may be driven by this motor M.

However, in such a conventional water level detection device, each of the water level detection electrodes E ₁ , E ₂ , and E ₃ has a
When performing multi-stage water level detection that requires real signal lines L ₁ , L ₂ , and L ₃ , the detection device body Y and the water tank K are usually installed in different locations, which can lead to incorrect wiring during construction. Moreover, the wiring cost for long-distance detection was also excessive. In addition, when performing long-distance detection, ground capacitance (equivalent line capacitance) occurs between the signal line L ₀ and the signal lines L ₁ to _{L 3} , and this ground capacitance _is ~ _L3 becomes larger as it gets longer, so if the length of the signal line _L0 ~ _L3 exceeds a certain level, it will be as if the common electrode _E0 and the water level detection electrode are connected due to leakage current due to ground capacitance.
E ₁ to E ₃ operate as if they were electrically connected through water, turning on switching transistors Q ₁ and Q ₂ and energizing relays RY ₁ and RY ₂ (malfunction). Furthermore, since the interelectrode voltage _V1 is naturally limited, the lengths of the signal lines _L0 to _L4 are limited to prevent malfunctions, making it impossible to perform long-distance detection.

Therefore, an object of the present invention is to provide a water level detection device that can reduce the number of signal lines and perform long-distance detection without malfunction.

An embodiment of this invention is shown in FIGS. 2 and 3. In other words, this water level detection device is
The primary winding of a step-down transformer T is connected to AC, and the first secondary winding T1 of this step-down transformer T is connected to _a rectifier and smoothing circuit _CD1 , and from this rectifier and smoothing circuit _CD1 , multiplier circuits MP and 2 are connected. Power is supplied to the multiplier circuit SQ, level comparator LC and control circuit CR, and the voltage detection circuit VD and rectifier smoothing circuit are connected to the secondary winding _T2 of the step-down transformer T.
CD ₃ is connected in parallel, and the third 2 of the step-down transformer T
Connect the primary winding of the current transformer CT to one end of the secondary winding _T3 , connect one end of the signal line _L1 to the other end of the primary winding of this current transformer CT, and connect the third winding of the step-down transformer T. Connect one end of the signal line _L0 to the other end of the secondary winding _T3 , and connect a resistor to the other end of the signal line _L1 .
The water level detection electrodes E ₁ , E ₂ , E ₃ installed in the water tank K are connected via _{r 1} , r ₂ , r ₃ , and the common electrode E ₀ installed in the water tank K is connected to the other end of the signal line L ₀ . Connect the secondary winding output of the voltage detection circuit VD and the current transformer.
Multiply the CT secondary winding output by the multiplication circuit MP,
The output of this multiplier circuit MP is averaged by a low-pass filter F, while the output voltage of the rectifying and smoothing circuit CD ₃ is squared by a squaring circuit SQ, and the output of the low-pass filter F is squared by a level comparator LC of the squaring circuit SQ. The control circuit CR controls the pump etc. in response to the output of the level comparator LC by comparing it with the first, second and third reference voltages which are obtained by dividing the output voltage and increasing in order. There is. In this case, the low-pass filter F is composed of resistors _R5 , _R6 and a capacitor _C5 . The level comparator LC divides the output voltage of the comparators CP ₁ , CP ₂ , CP ₃ to which the output of the low-pass filter F is commonly applied to one input terminal of each, and the squaring circuit SQ to generate three reference voltages. _A variable resistor VR and resistors R ₇ , R ₈ , and resistors R ₇ , R ₈ ,
It consists of a series circuit of _R9 . The rectifying and smoothing circuit CD ₃ is composed of a diode D ₃ , capacitors C ₆ and C ₇ , and resistors R ₁₀ and R ₁₁ . control circuit
CR is each comparator CP ₁ ~ of level comparator LC
A sequence controller SC such as a relay sequence circuit, logic sequence circuit, and P-ROM that responds to the output of CP ₃ , and relays RY ₁ and RY ₂ that respond to the output of this sequence controller SC.
It is made up of. The voltage detection circuit VD is composed of resistors R ₁₂ and R ₁₃ that divide the voltage V ₂ of the second secondary winding T ₂ of the step-down transformer T. Resistance r ₁ ,
r ₂ and r ₃ are set high enough to ignore water resistance. Note that R ₀ is a load resistance of the current transformer CT, Z is a varistor, and C ₈ is a capacitor for phase correction.

Next, the operation of this water level detection device will be explained.

When the water level in the tank K is less than X ₁ and the electrodes E ₁ to _{E 3}
is not immersed in water, the third secondary winding T ₃ of the step-down transformer T - the primary winding of the current transformer CT - the signal line L ₁ - the equivalent line capacitance C ₀ - the signal line L ₀ - Current I ₀ in the path of the third secondary winding T ₃ of the step-down transformer T
flows, and the current i ₁ flowing out from the third secondary winding T ₃ of the step-down transformer T becomes I ₀ . This current I ₀ is a leakage current flowing through the equivalent line capacitance C ₀ and has a waveform as shown in FIG.
The waveform of the voltage V ₀ divided by the resistors R ₁₂ and R ₁₃ of the voltage V ₂ of the next winding T ₂ is also shown in FIG.

This current I ₀ is detected by the current transformer CT,
The secondary winding voltage is input to one input terminal of the multiplication circuit MP. At this time, the current transformer
The phases of the current and voltage waveforms on the primary and secondary sides of the CT are corrected by capacitor _C8 so that they are in phase.

Furthermore, the divided voltage v ₀ is input to the other input terminal of the multiplication circuit MP. By matching the polarities of voltage v ₀ and voltage V ₁ at this time, the voltage V ₁ is made to function as if it were input to the multiplication circuit MP.

The multiplication circuit MP multiplies the above two inputs and calculates the voltage.
This voltage v ₁ ' has a waveform as shown in FIG. 5, indicating the equivalent instantaneous electric energy due to _the current I ₀ and the voltage v ₀ .

The voltage v ₁ ' output from this multiplier circuit MP is averaged by a low-pass filter F, but the voltage v ₂ ' output from this low-pass filter F becomes 0 as shown in FIG. 6, and this voltage v ₂ ′ is the current I ₀ and the voltage v ₀
is the equivalent active power amount, and the equivalent line capacitance is
This value is always 0 if C ₀ is a pure capacitance.

This voltage v ₂ ' is compared with the first, second and third reference voltages which are obtained by dividing the output voltage of the squaring circuit SQ and increase in order by the level comparator LC, but the voltage v ₂ ' is higher than the first, second and third reference voltages. 1 reference voltage, comparators CP ₁ to _{CP 3}
All outputs are at a low level, and the sequence controller SC controls the relays RY ₁ and RY ₂ in response to the outputs of the comparators CP ₁ to CP ₃ .

When the water level in the water tank K exceeds X ₁ and the water level detection electrode E ₃ is immersed in water, the third 2
Secondary winding T ₃ - Primary winding of current transformer CT - Signal line L ₁ - Water level detection electrode E ₃ - Resistor r ₃ - Water - Common electrode
E ₀ - Signal line L ₀ - Current I ₃ will flow through water in the path of the third secondary winding T ₃ of the step-down transformer T and will flow out of the third secondary winding T ₃ of the step-down transformer T The current i ₁ becomes I ₀ +I ₃ and has a waveform as shown in FIG. 4, and the resistance value between the signal lines L ₁ and L ₀ becomes r ₃ .

This current I ₀ + I ₃ is detected by the current transformer CT, its secondary winding voltage is input to one input terminal of the multiplication circuit MP, and the divided voltage v ₀ is input to the other input terminal of the multiplication circuit MP. , the multiplication circuit MP is the above 2
By multiplying the two inputs, a voltage v ₁ with a waveform as shown in Fig. 5 is output, and this voltage v ₁ is applied to the low-pass filter F.
The voltage v ₂ is averaged by the waveform shown in Figure 6.
This voltage v ₂ is the voltage between the water level detection electrode E ₃ and the common electrode.
This is the equivalent active power amount due to the current I ₃ flowing between the current I ₃ and the voltage v ₀ , and it means that only the electric power due to the current I ₃ is detected.

This voltage v ₂ is compared with the first, second and third reference voltages in the level comparator LC, but since the voltage v ₂ is higher than the first reference voltage and lower than the second reference voltage, the comparator CP ₁ At the same time, the output of comparators CP ₂ and CP ₃ becomes low level, and in response to the output of comparators CP ₁ to CP ₃ , the sequence controller SC activates relays RY 1 and RY ₁ , respectively.
Control RY ₂ .

When the water level in the water tank K exceeds _X2 and the water level detection electrode _E2 is immersed in water, the third electrode of the step-down transformer T
Secondary winding T ₃ - Primary winding of current transformer CT - Signal line L ₁ - Water level detection electrode E ₂ - Resistor r ₂ - Water - Common electrode
A current I ₂ will flow through the water in the path of E ₀ - signal line L ₀ - third secondary winding T ₃ of the step-down transformer T and flows out from the third secondary winding T ₃ of the step-down transformer T The current i ₁ becomes I ₀ + I ₂ + I ₃ , and the signal lines L ₁ , L ₀
The resistance value between them is 1/1/r ₂ +1/r ₃ .

This current I ₀ + I ₂ + I ₃ is detected by the current transformer CT, its secondary winding voltage is input to one input terminal of the multiplication circuit MP, and the divided voltage v ₀ is input to the multiplication circuit MP.
The multiplier circuit MP similarly outputs a voltage v ₁ , and this voltage v ₁ passes through a low-pass filter F to become a voltage v ₂ (corresponding to the electric power due to the current I ₂ + I ₃ ), _The comparator
The outputs of CP ₁ and CP ₂ become high level, and the output of comparator CP ₃ becomes low level.

When the water level in the water tank K exceeds X ₃ and the water level detection electrode E ₁ is immersed in water, the third 2
Secondary winding T ₃ - Primary winding of current transformer CT - Signal line L ₁ - Water level detection electrode E ₁ - Resistor r ₁ - Water - Common electrode
A current I ₁ will flow through the water in the path of E ₀ - signal line L ₀ - third secondary winding T ₃ of the step-down transformer T and will flow out of the third secondary winding T ₃ of the step-down transformer T The current i ₁ becomes I ₀ +I ₁ +I ₂ +I ₃ , and the signal line L ₁ ,
The resistance value between L ₀ is 1/1/r ₁ +1/r ₂ +1/r ₃ .

As this current I ₀ + I ₁ + I ₂ + I ₃ flows, the multiplier circuit MP similarly outputs the voltage v ₁ , and this voltage v ₁
is the voltage v ₂ (current I ₁ + I ₂
+ _I3 ) and is compared with the first, second, and third reference voltages, but since the voltage _v2 is higher than the third reference voltage, the comparators _CP1 to
All CP ₃ outputs are at high level.

Figure 7 shows signal lines for water level changes in tank K.
This is a characteristic diagram showing the change in resistance value between L ₁ and L _0. Figure 8 is a characteristic diagram showing the change in current i ₁ with respect to the change in water level in water tank K, and the resistance values of resistors r ₁ , r ₂ , r ₃ If the current i ₁ is made equal, the current i 1 changes in a stepwise manner with equal step heights as the water level changes.

Note that the first, second, and third reference voltages, that is, the inversion levels of the comparators CP ₁ to _{CP 3} are set to arbitrary values in consideration of noise malfunctions and the like.

In this way, the water level detection device of this embodiment calculates the equivalent active power amount based on the current i ₁ and the voltage v ₀ ,
Since this equivalent active energy is added to the level comparator LC and compared with the first, second, and third reference voltages, it is completely unaffected by the equivalent line capacitance _C0 , making long-distance detection easy. It can be carried out. Also, the third secondary winding T ₃ of the step-down transformer T
The water level detection electrodes E _{1 ,} E ₂ , E ₃ are connected to the signal line L ₁ via resistors r ₁ , r ₂ , r ₃ respectively,
The current _i1 flowing out from the third secondary winding _T3 of the step-down transformer T is changed in a stepwise manner according to the change in the water level within the step-down transformer T.
It is possible to detect only L ₁ and L ₀ , and this number does not increase even if the number of detection levels increases, making it possible to prevent incorrect connections during construction and to reduce wiring costs. In addition, the reference voltage to be applied to the level comparator LC is created by dividing the voltage obtained by rectifying and smoothing the voltage V ₂ of the second secondary winding T ₂ of the step-down transformer T and squared it to follow the secondary side power. Because this method is adopted, operation is stable against voltage fluctuations of the AC power supply. In addition, the water level detection electrode is connected from the third secondary winding T ₃ of the step-down transformer T through the signal lines L ₁ and L ₀ .
From the circuit loop leading to E ₁ to E ₃ and the common electrode E ₀ , rectifying and smoothing circuits CD ₁ , CD ₃ , multiplication circuit MP, low-pass filter F, level comparator LC, control circuit CR,
Since the squaring circuit SQ and the voltage detection circuit VD are insulated and separated by the current transformer CT and the step-down transformer T, it is possible to prevent these electronic circuit components from being destroyed by lightning surges, switching surges, etc.

Note that depending on the magnitude of the input signal to the multiplication circuit MP or the magnitude of the output signal of the multiplication circuit MP, the ninth
As shown in the figure or FIG. 10, an amplifier AP may be interposed before or after the multiplication circuit MP. Further, the number of water level detection levels is not limited to three.

Other embodiments of the invention are shown in FIGS. 11 to 14.
As shown in the figure. That is, this water level detection device connects water level detection electrodes E ₁ , E ₂ , E ₃ to signal line L ₁ and resistors r ₁ , r ₂ , r _{3 .}
Instead of connecting them through each, connect the water level detection electrodes E ₁ , E ₂ , and E ₃ sequentially in the depth direction, and connect the upper end of the uppermost water level detection electrode E ₁ to the other end of the signal line L _1. However, resistors _{r 1 ,} r ₂ , and r ₃ are interposed at the upper connection points of the water level detection electrodes E 1 , E ₂ , and E ₃ , respectively.
The other configurations are the same as those in FIGS. 2 and 3. In this case, the water level detection electrode E ₁ is the 12th
As shown in the figure, it is composed of a metal rod H, and a male threaded portion _H1 is provided at the lower end. In addition, as shown in FIGS. 13 and 14, the built-in resistor part J that has a built-in resistor _r1 has a female threaded part J that can be screwed into the male threaded part _H1 on the upper surface of the cylindrical body _J1 made of an insulator. ₂ , and electrically connect this electrode connection part J ₃ and one end of the resistor r ₁ , and electrically connect _the metal rod H and the other end of the resistor r ₁ . Connected. The same applies to the water level detection electrodes E ₂ and E ₃ .

The operation of this water level detection device will be explained.

When the water level in the water tank K is less than X ₁ , the third secondary winding T ₃ of the step-down transformer T - the primary winding of the current transformer CT - the signal line L ₁ - the equivalent line capacitance C ₀
- Signal line L ₀ - Third secondary winding of step-down transformer T
Current I ₀ flows through the path T ₃ , and current i ₁ becomes I ₀ .

When the water level in the water tank K is above _X1 , the third secondary winding _T3 of the step-down transformer T - the primary winding of the current transformer CT - the signal line _L1 - the water level detection electrode
A current I ₃ flows in the path of E ₁ , E ₂ , E ₃ - water - common electrode E ₀ - signal line L ₀ - third secondary winding T ₃ of the step-down transformer T, and the current i ₁ is I ₀ + I ₃ , and the resistance value between the signal lines L ₁ and L ₀ is r ₁ +r ₂ +r ₃ .

When the water level in the water tank K is above _X2 , the third secondary winding _T3 of the step-down transformer T - the primary winding of the current transformer CT - the signal line _L1 - the water level detection electrode
A current I 2 flows in the path of E ₁ , E ₂ - water - common electrode E ₀ - signal line L ₀ - third secondary winding T ₃ of the step-down transformer T, and the current _{i 1 becomes} I ₀ + I ₂ , The resistance value between the signal lines L ₁ and L ₀ is r ₁ + r ₂ .

When the water level in the water tank K is above _X3 , the third secondary winding _T3 of the step-down transformer T - the primary winding of the current transformer CT - the signal line _L1 - the water level detection electrode _E1
-Water-Common electrode E ₀ -Signal line L ₀ -Step-down transformer T
A current I ₁ flows in the path of the third secondary winding T ₃ of
i ₁ becomes I ₀ + I ₁ , and the resistance value between signal lines L ₁ and L ₀ is r ₁
becomes.

Changes in current i ₁ due to this change in water level will be detected in the same way as in FIGS. 2 and 3.

Figure 15 shows signal lines for water level changes in tank K.
This is a characteristic diagram showing the change in resistance value between L ₁ and L ₀ .
The figure is a characteristic diagram showing changes in current i ₁ with respect to changes in water level in water tank K. The ratio of the resistance values of resistors r ₁ , r ₂ , and r ₃ is set to
If the ratio is 3:1/6:1/2, the current i ₁ will change in a stepwise manner with equal step heights as the water level changes.

The effects of this embodiment are similar to those of the previous embodiment.

Still another embodiment of the invention is shown in FIG. In other words, this water level detection device uses a resistor for current detection instead of the current transformer CT shown in Figure 3.
R ₁₄ is used, the load resistor R ₀ , varistor Z and capacitor C ₈ are omitted, and the rectifier smoothing circuit CD ₂ and voltage detection circuit VD are connected to the third secondary winding T ₃ of the step-down transformer T. The second secondary winding _T2 of T is omitted, and the rest is the same as that of FIGS. 2 and 3.

Although this embodiment does not provide protection against surges, other effects are similar to those of FIGS. 2 and 3.

Note that the circuit shown in FIG. 11 can also be modified in the same manner as shown in FIG. 17.

As described above, the water level detection device of the present invention includes an AC power source, first and second signal lines each having one end connected to one end of the AC power source and the other end thereof, and the water level detecting device installed in an aquarium. a group of water level detection electrodes connected to the other end of the first signal line, a common electrode installed within the water level and connected to the other end of the second signal line, the first signal line and the water level detection a resistor group that is connected between the electrode group and changes the composite resistance value stepwise in response to changes in the water level in the water tank; a current detection circuit that detects the current flowing out from the AC power source; and the AC power source. a voltage detection circuit that detects the voltage of the current detection circuit; a multiplication circuit that multiplies the output of the current detection circuit by the output of the voltage detection circuit; a low-pass filter that averages the output of the multiplication circuit; Since it is provided with a level comparator for comparison with a reference voltage group, the number of signal lines can be reduced, and long-distance detection can be performed without malfunction.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional water level detection device, Fig. 2 is a block diagram of a water level detection device according to an embodiment of the present invention, Fig. 3 is a specific circuit diagram thereof, and Figs. 4 to 6
The figures are voltage and current waveform diagrams of each part, Figure 7 is a characteristic diagram showing the change in resistance between signal lines in response to changes in water level, Figure 8 is a characteristic diagram showing changes in current in response to changes in water level, and Figure 9 is a characteristic diagram showing changes in resistance between signal lines in response to changes in water level. 10 and 10 are block diagrams of main parts of a modified example, FIG. 11 is a circuit diagram of a water level detection device according to another embodiment of the present invention, FIG. 12 is a front view of a water level detection electrode, and FIG. 13 is its main part. FIG. 14 is a cutaway front view of the main part, FIG. 15 is a characteristic diagram showing changes in resistance between signal lines with respect to changes in water level in another embodiment, and FIG.
The figure is a characteristic diagram showing the current change with respect to the water level change, and FIG. 17 is a main part circuit diagram of still another embodiment of the present invention. AC: AC power supply, CD ₁ , CD ₃ : Rectifying and smoothing circuit, VD: voltage detection circuit, CT: current transformer, MP: multiplication circuit, F: low-pass filter, SQ: square circuit, LC ...Level comparator,
K...Water tank, _E1 , _E2 , _E3 ...Water level detection electrode, _E0
... Common electrode, L ₀ , L ₁ ... Signal line, T ... Step-down transformer, r ₁ , r ₂ , r ₃ ... Resistor.

Claims (1)

[Claims] 1. An alternating current power supply, and a first and a second power supply having one end connected to one end and the other end of the alternating current power supply, respectively.
a signal line, a group of water level detection electrodes installed in the aquarium and connected to the other end of the first signal line, and a common electrode installed in the aquarium and connected to the other end of the second signal line. and a resistor group connected between the first signal line and the water level detection electrode group to change the composite resistance value in stages in response to changes in the water level in the aquarium;
a current detection circuit that detects the current flowing out from the AC power supply; a voltage detection circuit that detects the voltage of the AC power supply; a multiplication circuit that multiplies the output of the current detection circuit and the output of the voltage detection circuit; A water level detection device comprising a low-pass filter that averages the output of a multiplication circuit, and a level comparator that compares the output of the low-pass filter with a reference voltage group. 2. The water level detection device according to claim 1, wherein the current detection circuit is constituted by a current transformer, and an insulation transformer is interposed between the voltage detection circuit and the AC power source. 3. The water level detection device according to claim 1, wherein each of the water level detection electrode groups has an upper end connected to the other end of the first signal line through a corresponding one of the resistance groups. 4. Each of the water level detection electrode groups is connected sequentially in the depth direction, and the upper end of the uppermost one is connected to the other end of the first signal line, and the resistor group is connected to the upper connection point of each of the water level detection electrode groups. A water level detection device according to claim 1, wherein a corresponding one of the following is interposed.