JPS6331728B2 - - 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 a rectifying and smoothing circuit CD consisting of a diode D ₁ and a capacitor C ₁ is connected to the first secondary winding T ₁ of this step-down transformer T. A series circuit of a control relay RY ₁ and a switching transistor Q ₁ is connected to the output end of the smoothing circuit CD, while a diode bridge DB ₁ is connected to one end of the second secondary winding T ₂ of the step-down transformer T. Connect one AC input end,
Connect the other AC input end of the diode bridge DB ₁ to one electrode E ₁ in the water tank K via one signal line L ₁
and the second secondary winding T ₂ of the step-down transformer T
The other end is connected to the other electrode E ₂ in the water tank K via the other signal line L ₂ , and the pair of DC output ends of the diode bridge DB ₁ is connected via the resistors R ₁ and R ₂ and the capacitor C ₂ . It is connected between the base and emitter of switching transistor _Q1 .

In this water level detection device, when the water level in the water tank K is _X1 , the electrodes _E1 and _E2 are in an open state, and the switching transistor _{Q1 is} connected from the second secondary winding T2 of the step-down transformer T. No base current is supplied to
Switching transistor _Q1 is in the off state,
Relay RY ₁ is in a de-energized state.

When the water level in tank K rises to more than X ₂ ,
Conductivity is established between the electrodes E ₁ and E ₂ via a water resistance, and a switch is established from the second secondary winding T ₂ of the step-down transformer T via the diode bridge DB ₁ , resistors R ₁ , R ₂ and capacitor C ₂ . The base current is supplied to the switching transistor _Q1 , the switching transistor _Q1 is turned on, and the relay _RY1 becomes energized.

The water level in the water tank K can be controlled by rotating the motor to operate the water supply pump when the normally closed contact of relay RY ₁ is on, or by rotating the motor to operate the drain pump when the normally open contact is on.

However, in such a conventional water level detection device, when the detection device main body Y and the water tank K are separated, the signal lines L ₁ and L ₂ become long, and the ground capacitance increases between the signal lines L ₁ and L _2. (equivalent line-to-line capacitance C ₀ ) occurs, and this ground capacitance increases as the signal lines L ₁ and L ₂ become longer. Therefore, when the signal lines L ₁ and L ₂ are longer than a certain length, Due to the leakage current due to the capacitance, the switching transistor operates as if conduction was established between the electrodes E ₁ and E ₂ through water.
When Q ₁ turns on, RY ₁ is excited (malfunctioning), and the interelectrode voltage V ₁ is naturally limited, so to prevent this malfunction, the signal line is
The lengths of L ₁ and L ₂ were limited, 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 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, the first secondary winding _T1 of this step-down transformer T is connected to a rectifier and smoothing circuit CD, and a multiplication circuit MP and a level comparator are connected from this rectifier and smoothing circuit CD. LC and a voltage detection circuit to the second secondary winding _T2 of the step-down transformer T.
Connect VD to the third secondary winding of the step-down transformer T.
One end of T ₃ is connected to the electrode E ₁ in the water tank K via the primary winding of the current transformer CT and the signal line L ₁ , and the third secondary winding of the step-down transformer T
The other end of T ₃ is connected to the electrode E ₂ in the water tank K via the current limiting resistor R ₃ and the signal line L ₂ , and the output of the voltage detection circuit VD and the secondary winding output of the current transformer CT are multiplied by a circuit. Multiply by MP, average the output of this multiplier circuit MP with a low-pass filter F, and use the level comparator.
In addition to LC, the output of this level comparator LC is used as a relay.
It is designed to control pumps etc. by controlling RY ₁ . In this case, the low-pass filter F is a resistor
It consists of R ₄ , R ₅ and capacitor C ₃ .
The level comparator LC is composed of resistors R ₆ and R ₇ that divide the voltage of the rectifier and smoothing circuit CD, and a comparator CP that compares the output voltage of the low-pass filter F and the reference voltage given by the resistors R ₆ and R ₇ . has been done.
The voltage detection circuit VD also has low resistors R ₈ and R ₉ that divide the voltage V ₂ of the second secondary winding T ₂ of the step-down transformer T.
It consists of

Note that R ₀ is the load resistance of the current transformer CT,
Z is a varistor, and _C4 is a capacitor for phase correction.

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

When the water level in the water tank K is X ₁ and the electrodes E ₁ and E ₂ are not immersed in water, the third secondary winding T ₃ of the step-down transformer T - the primary winding of the current transformer CT -
Signal line L ₁ - Equivalent line capacitance C ₀ - Signal line L ₂ - Current limiting resistor R ₃ - Current i ₀ flows in the path of the third secondary winding T ₃ of the step-down transformer, and The current i ₁ flowing out from the secondary winding T ₃ becomes i ₀ . This current i ₀
is the leakage current flowing through the equivalent line capacitance C ₀ and has a waveform as shown in FIG _. The waveform of the voltage divided by _the voltage resistors R ₈ and R ₉ is also shown in FIG. 4.

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 the capacitor _C4 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, which indicates 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 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 reference voltage by the comparator CP, but since the voltage v ₂ ′ is smaller, the output of the comparator CP becomes a low level and the relay RY ₁
is energized and the water supply pump operates.

When the water level in the water tank K is _X2 higher, the electrodes E ₁ and E ₂
is immersed in water, the third secondary winding of the step-down transformer T
T ₃ - Primary winding of current transformer CT - Signal line L ₁
- Electrode E ₁ - Water - Electrode E ₂ - Signal line L ₂ - Current limiting resistor -
Current i ₂ will flow through the water in the path of the third secondary winding T ₃ of the step-down transformer T, and the current i ₁ flowing out from the third secondary winding T ₃ of the step-down transformer T will be i ₀
+i ₂ , resulting in a waveform as shown in FIG.

This current i ₀ + i ₂ 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 multiplies the above two inputs and generates a voltage with a waveform as shown in Figure 5.
v ₁ is output, and this voltage v ₁ is averaged by a low-pass filter F to become a voltage v ₂ with a waveform as shown in FIG. 6. This voltage v ₂ is a current i ₂ flowing between electrodes E ₁ and E ₂ .
It is the equivalent active energy due to the voltage v 0 and the voltage v ₀ , and has a constant value.

This voltage v ₂ is compared with the reference voltage in the comparator CP, and since the voltage v ₂ is larger, the comparator
The output of CP becomes high level, relay RY ₁ is deenergized, and the water pump is stopped.

Note that the reference voltage, that is, the inversion level of the comparator CP, is set to an arbitrary value in consideration of noise malfunctions and the like. Moreover, when draining water, the drain pump shown in FIGS. 2 and 3 may be controlled in the opposite manner to the relay _RY1 .

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 power amount is added to the comparator CP and compared with the reference voltage, it is completely unaffected by the equivalent line capacitance _C0 , and long-distance detection can be easily performed. In addition, step-down transformer T
A rectifying and smoothing circuit from the circuit loop from the third secondary winding T ₃ to the electrodes E ₁ and E ₂ through the signal lines L ₁ and L ₂
Since the CD, low-pass filter F, level comparator LC, multiplication circuit MP, and voltage detection circuit VD are insulated and separated by a current transformer CT and a 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, an amplifier AP may be inserted before or after the multiplication circuit MP, as shown in FIG. 7 or 8. be.

Another embodiment of the invention is shown in FIG. That is, this water level detection device uses a current detection resistor R ₁₀ instead of the current transformer CT shown in FIGS. 2 and 3.
The voltage drop across the current detection resistor R ₁₀ is applied to one input terminal of the multiplier circuit MP, and the voltage across the third secondary winding T ₃ of the step-down transformer is determined by the voltage detection resistors R ₈ and R ₉ . The voltage is divided and applied to the other input terminal of the multiplication circuit MP, and the other configurations are the same as those in FIGS. 2 and 3.

Although this embodiment cannot protect electronic components against surges, other effects are similar to those of the previous embodiment.

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 first electrode connected to the other end of the first signal line, a second electrode installed in the water tank and connected to the other end of the second signal line, and a current flowing out from the AC power source. a current detection circuit for detecting, a voltage detection circuit for detecting the voltage of the AC power supply, a multiplication circuit for multiplying the output of the current detection circuit and the output of the voltage detection circuit, and averaging the output of the multiplication circuit. Since it includes a low-pass filter and a level comparator that compares the output of the low-pass filter with a reference voltage, it has the advantage that 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 an embodiment of the present invention, Fig. 3 is a specific circuit diagram thereof, and Figs. 4, 5, and 6 are respective diagrams thereof. Voltage and current waveform diagrams of each part, Figures 7 and 8 are block diagrams of main parts of modified examples, respectively.
The figure is a block diagram of another embodiment of the invention. AC...Alternating current power supply, T...Step-down transformer, _E1 ,
E ₂ ... Electrode, K ... Water tank, L ₁ , L ₂ ... Signal line,
CT...Current transformer, VD...Voltage detection circuit, MP...Multiplication circuit, F...Low pass filter, LC...Level comparator.

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 first electrode installed in the water tank and connected to the other end of the first signal line, and a second electrode installed in the water tank and connected to the other end of the second signal line. an electrode, a current detection circuit that detects the current flowing out from the AC power source, a voltage detection circuit that detects the voltage of the AC power source, and a multiplier that multiplies the output of the current detection circuit and the output of the voltage detection circuit. circuit and
A water level detection device that includes a low-pass filter that averages the output of this multiplication circuit, and a level comparator that compares the output of this low-pass filter with a reference voltage. 2. The water level detection device according to claim 1, wherein the current detection circuit is constituted by a current transformer, and an isolation transformer is interposed between the voltage detection circuit and the power source.