KR890004951B1 - Water level detective circuit - Google Patents

Abstract

The circuit utilizing electrode (1) for detecting water level measures capacitance of water. The circuit comprising registors (R1- R3, R5, VR), diodes (D1-D3), transistors (TR1,TR2) and a photo coupler (PC) is turned on at positive half cycle of AC input. A variable registor (VR) is utilized to adjust the reference voltage determined by the type of water.

Description

Water level detection circuit of electrode

1 is an overall block diagram of the water level detection circuit of the present invention.

2 is a detailed circuit diagram of the water level detection circuit of FIG.

3 is an output waveform diagram of the water level detection circuit of the present invention. FIG. 3 (a) is a waveform diagram of an AC power supply voltage, and FIG. 3 (b) is a waveform in a state in which the capacitor C is charged without detecting the water level. 3 (c) is a waveform diagram of the voltage discharged from the capacitor C when the water level is detected, and FIG. 3 (d) is a waveform diagram of the state output from the comparator.

* Description of the main parts of the drawings

1: water tank 2: electrode

3: water level detection circuit, R ₁ to R ₁₀ : resistance

C: capacitor VR: variable resistor

Ph-TR: Phototransistor TR ₁ , TR ₂ : Transistor

Conp: Comparator

The electrode level sensor circuit for automatically controlling the water level of the boiler of the present invention.

Conventionally, electrodes are used to automatically control the water level of water pipe boilers, perfusion boilers, water level tanks, etc. The electrode of this level detection is provided with high-quality technology, but water is used, namely tap water (10-15 kΩ / cm) and sea water (0.05 kΩ). / Cm), boiler dielectric (50-70kΩ / cm), distilled water (100kΩ or more), groundwater (5-20kΩ / cm), and dielectrics with various resistance values. This is the value of parallel connection of resistance and capacitance. Therefore, when the change in the detection resistance value of the electrode is detected by the DC method, the charge is charged or discharged to the capacitor due to the capacitance, and an error occurs due to the charge / discharge voltage. In addition, most of the water level control has a problem that the level circuit of the input and output unit is required by the application of a microprocessor.

In order to solve the above problems, the detection of the electrode rod as a detection of the capacitance by the AC method than the specific resistance of the water to offset the charging effect to enable high-level detection with high reliability and low error rate to the accompanying drawings. When explaining the present invention in detail as follows.

1 is a block diagram of a water level control unit in a boiler or the like of the present invention. The power input from the power supply voltage terminal AC drives a motor M and a pump by operating a switch unit SW. The water level is detected by the water level control system 4 composed of a plurality of electrode rods 2 and water level detection circuits 3 having different lengths, but the water level detection circuit 3 being made of water. 2, as shown in Fig while connected via the electrode (2) has a resistance (R ₅₎ a through the power supply voltage terminal (AC) and a variable resistor (VR) resistance (R ₁₎ through a reverse diode (D ₂₎ to the base terminal of the connection to the base terminal of the transistor (TR ₁₎ and the power supply voltage terminal (AC) is an emitter terminal and a transistor (TR ₂₎ to the transistor (TR ₁₎ through the diode (D ₁₎ resistance (R ₃₎ In addition to the transistor (TR ₂ ) through the light emitting diode (LED) of the resistor (R ₂ ) and photocoupler (PC) Is connected to the emitter terminal of the transistor (TR ₁ ), the collector terminal of the transistor (TR ₂ ) is connected to the water tank (l) and the power supply voltage terminal (AC) through the reverse diode (D ₃ ), the photocoupler ( The collector terminal of the photo transistor PH-TR of the PC) is connected to the inverting terminal of the comparator OP through the resistor R ₆ while being connected through the power supply voltage terminal Vcc, the resistor R ₄ and the capacitor C. connection and connected to the comparator (OP) a non-inverting terminal of the power supply voltage terminal (Vcc) to the resistance (R ₇₎ (R ₈₎ connected through a (R _9), and its output the power supply voltage terminal (Vcc) of the resistor (R ₁₀ ) Is output through

Referring to the effects of the present invention configured as described above are as follows.

First, power is applied from the power supply voltage terminal (AC) to drive the motor (M) pump (Pump) to fill the water tank (l). The resistance value caused by water is generated between

×AC의 수위 검지 수준전압이 발생하게 되고, 여기서 Zeq는 물의 고유 전항과 정전 용량에 의한 고유등가 임피던스이다.Since the resistance value of water is determined according to the type of water, if the resistance value exceeds a certain value, it cannot be detected. Therefore, if the water in the tank l does not rise to the level of the water level electrode 2, the resistance of the air becomes the same as the result of being cut off to infinity, and the present invention operated in this way will be described in detail with reference to FIG. As the power supplied from the power supply voltage terminal AC does not flow through the water tank 1 and the electrode 2, the two transistors TR ₁ TR ₂ and the photo coupler PC cannot be turned on. Only the signal of "L" is output to the output terminal of OP). Then, the water level of the tank 1 rises, and the instantaneous resistance value at which the water reaches the electrode 2 changes from infinity to the intrinsic resistance value determined according to the type of water, and at this time, in (A) of the power supply voltage terminal AC, variable resistor (VR), a resistance (R ₁₎ (R _5), electrodes (2), as a closed circuit fed back to through the tank (l) (B) forming a diode on the (a) (D _1), transistor Through the emitter-base of (TR ₁ ), diode (D ₂ ), resistor (R ₅ ), electrode (2), and tank (l), a closed circuit is returned to (B) to form a power supply during the half cycle of AC power. The transistor TR ₁ is turned on as it flows. Therefore, the diode (D _1), the resistance (R _2), photo coupler (PC) light emitting diode (LED), the emitter of the transistor (TR ₂₎ in (A) - the emitter of the base, a transistor (TR ₁₎ - collector When a closed circuit is fed back to (B) via the diode (D ₃ ), the resistance (R ₅ ) during the half cycle in which the AC power supply voltage of the waveform as shown in FIG. Between V and diode D ₂

A level detection level voltage of AC occurs, where Zeq is the intrinsic equivalent impedance due to the intrinsic potential of the water and the capacitance.

During the half cycle in which the AC power supply voltage is negative, the discharge voltage charged to the water capacitance is higher than the AC power supply voltage, so that the water level detection reference voltage Vref has a negative value. ₁ ) is biased in the reverse direction to turn off the transistors TR ₁ (TR ₂ ), and this charged voltage is discharged in a half cycle by the diode D ₂ (D ₃ ) and disappears in half cycle, thus detecting the water level. The phenomenon that causes an error in operation is prevented. The on / off square wave output signal detects the water level. The water level is detected by the on / off pulse clock by directly connecting the collector terminal of the photo transistor (PH-TR) to the input port of the microprocessor (not shown). This affects the microprocessor (not shown), so it is desirable to input at low or high TTL levels. Therefore, when the square wave signal output from the collector terminal of the photo transistor PH-TR is output through the resistors R ₄ , R ₆ , and the capacitor C, the applied power supply Vcc is not detected while the water level is not detected. ) Is charged to the capacitor C as shown in FIG. 3 (b), and the photo transistor PH-TR is turned on during the positive (+) period for detecting the water level. The voltage is discharged as in FIG. 3 (c). The voltage and time charged and discharged in the capacitor C are arbitrarily adjusted by the values of the resistor R ₄ and the capacitor C.

The voltage discharged from the capacitor C is applied to the inverting input terminal (-) of the comparator OP through the resistor R ₆ , while the applied power supply Vcc is divided by the split resistor R ₇ (R ₈ ). When the voltage is smaller than the reference voltage compared to the reference voltage applied to the non-inverting input terminal (+), that is, while “H” is output only while charging the capacitor C, the output terminal of the comparator OP is shown in FIG. The TTL level as shown is output. Therefore, when the water level of the water tank (1) is detected, the level is high and when the level is not detected, the level is low. On the other hand, since the detection resistance value varies depending on the kind of water used in the water tank 1, the detection adjustment may be adjusted by the variable resistor VR. In other words, if the value of the variable resistor VR is varied, the AC input bias distribution of the voltage flowing through the resistor R ₁ and the diode D ₁ becomes the same, so that the range of the detection abnormal value can be varied. Even good water quality can detect a good thing. In addition, the resistance (R ₅ ) of the input of the electrode 2 is to prevent a lot of current flows when the electrode 2 and the tank (l) is connected.

As described above, in order to detect the water level of the boiler or the like, the present invention can detect the water level with the capacitance by the AC method rather than the resistivity of the water, so that the water level can be detected with high reliability and low error rate. In addition, it can also provide the advantage of good detection in any kind of water quality.

Claims (3)

In the water level detection circuit of the electrode which enables the water level detection circuit (3) to detect the water level by the electrode (1), the capacitance value of the water is detected by the AC input voltage, but the level is adjusted according to the detected output. The water level detection circuit of the electrode rod that can be detected. The resistor (R ₁ ~ R ₃ ), resistor (R ₅ ), variable resistor (VR), diode (D ₁ ~ D ₃ ), transistor (TR ₁ ) (TR) to be turned on during the half period of the AC input voltage. ₂ ) and a photocoupler (PC) to configure the water level detection circuit of the electrode, characterized in that to detect the capacitance of the water. The water level detection circuit of an electrode bar according to claim 1, comprising a resistor (R ₄ ), a capacitor (C) resistors (R ₆ to R ₁₀ ), and a comparator (OP) to detect the level.

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