JPH0435766B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a liquid level detection device used in a liquid supply control system using a liquid level detector in boilers, water treatment equipment, and other liquid equipment. This relates to relay circuits.

[Conventional technology]

The liquid level detection relay used in conventional liquid level detection involves placing a long electrode rod and a short electrode rod in the liquid, and detecting the liquid level by the current flowing through the liquid between the electrode rods. A predetermined signal is generated by

In such a relay, the liquid level begins to rise from below the bottom of the long electrode, reaches the bottom of the long electrode, and then the signal changes from ON to OFF when it reaches the bottom of the short electrode. So, if the liquid level starts to fall in the opposite direction, the signal will remain OFF when it is in a position where only the long electrode is in contact, and the signal will be ON when it is in a position where it is not touching the long electrode.

[Problem that the invention seeks to solve]

However, in such a conventional relay circuit, when the liquid level drops from the lower end of the short electrode to the lower end of the long electrode, a DC current flows through the operating point improvement resistor to the long electrode for liquid level detection. Depending on the situation, the long electrode may easily corrode due to the unbalanced current between the long and short electrodes, making it impossible to accurately detect the liquid level, and as this corrosion progresses, the electrode itself may fall off. However, there were drawbacks such as the fact that it sometimes became impossible to detect the liquid level.

The present invention eliminates these conventional drawbacks and provides a safe liquid level detection relay that does not allow direct current to flow through the electrode rod itself, prevents corrosion of the electrode rod, and allows accurate liquid level detection over a long period of time. The purpose is to

[Means for solving problems]

In the present invention, a long electrode rod and a short electrode rod are placed in a liquid,
In a liquid level detection relay circuit that detects the liquid level by a current flowing through the liquid between the electrode rods and generates a predetermined signal to operate a pump, etc., the base of the electrode current detection transistor of the relay drive circuit and , is characterized in that a diode for DC protection is inserted in series with a resistor for improving the operating point between the collector of the relay driving transistor, and a diode for reverse potential protection is inserted for the base power supply of the electrode current detection transistor. This is a relay circuit for liquid level detection.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 and 2.
Changes in the liquid level are detected by the short electrode 1, long electrode 2, and common electrode 3 of the liquid level detector 6.The relay drive circuit 4 of the liquid level detection relay 7 detects the change in the liquid level using the relay circuit including the Zener diode 24 for noise prevention. When the relay 5 is closed, the pump is set to 0N, and when the relay 5 is open, the pump is turned off.
It is wired to a power transformer 23 which is connected to an AC power source 8 via a power source 7 .

As shown in FIG. 2, a resistor 3 for improving the operating point is connected between the base of the electrode current detection transistor 9 of the relay drive circuit 4 equipped with the liquid level detection relay circuit and the collector of the relay drive transistor 11.
A direct current prevention diode 22 is inserted in series with the relay drive circuit 4, and a reverse potential protection diode 26 is inserted between the base power supply of the electrode current detection transistor 9. be.

In the figure, 21 is a terminal, 23 is a power transformer, 24
is a Zener diode for noise prevention, 25 is a diode for charging current rectification, 26 is a reverse potential protection diode, 27, 28, 29 is a Zener diode for input overvoltage protection, 30 is a voltage dividing resistor, 31 is a manual reset switch, 32 33 is a resistor for overcurrent prevention, 34 is a charging current limiting resistor, 35 is a resistor for improving the operating point, 36 is a base current limiting resistor, and 37 is a unipolar phonograph.

[Effect]

When the liquid level does not reach the long electrode 2, the power supply 8
is turned on, the electrode current detection transistor 9
A base current flows to turn on the transistor 9, and the collector current of the transistor 9 flows to the unipolar capacitor 10 through the charging current limiting resistor 34, and the capacitor 10 is charged and the voltage across it increases. The relay driving transistor 11 is turned on, the electromagnetic coil 12 is excited, and the relay 5 is closed.

Next, when the liquid level reaches the long electrode rod 2 from this state, the alternating current flows from the power transformer 23 through the electrode rod terminal 13 to the common electrode rod 3, and the long electrode rod 2
from the electrode terminal 14 to the overcurrent prevention resistor 1.
5 and flows from the light receiving element resistor 16 to the resistor 36, but since the light receiving element resistor 16 has a high resistance and the current flowing through the light receiving element resistor 16 is minute, the base current of the electrode current detection transistor 9 is almost It does not change. Therefore, transistor 9 remains ON, electromagnetic coil 12 remains energized, and relay 5 remains closed.

When the liquid level rises further and reaches the short electrode 1,
The alternating current flows from the electrode terminal 13 through the common electrode 3 and the liquid to the short electrode 1, and further flows through the electrode terminal 17 and the overcurrent prevention resistor 18, and the base voltage of the electrode current detection transistor 9 increases. is divided, transistor 9 is turned off, current no longer flows through charging current rectifying diode 25 and charging current limiting resistor 34, unipolar capacitor 10 is discharged, and relay driving transistor 11 is turned off. At this time, the potential of the terminal 21 rises, the light emitting diode lighting transistor 19 turns on, the light emitting diode 20 emits light, and the resistance value of the light receiving element resistor 16 connected to it decreases, so that the liquid level falls below the long electrode rod 2. Relay 5 remains open until lowered.

Furthermore, the liquid level drops from the long electrode rod 2 and the long electrode rod 2
When there is no contact, the electrode bar terminals 13 and 14 are released, so the base voltage of the electrode current detection transistor 9 is released from the divided voltage state, the transistor 9 is turned on, and at the same time the relay 5 is closed.

At this time, the relay driving transistor 11 is OFF during the period from when the liquid level is above the lower end of the single electrode rod 1 to below the lower end of the long electrode rod 2.
Since the terminal 21 has a positive DC potential, the DC current prevention diode 22 prevents DC current from flowing from the operating point improvement resistor 35 to the long electrode rod 2 or the single electrode rod 1 through the base current limiting resistor 36. prevent.

By providing the DC component prevention diode 22 in the relay drive circuit 4 in this way, when the liquid level decreases from the lower end of the short electrode rod 1 to the lower end of the long electrode rod 2, a DC component flows into the long electrode rod itself. prevent
The progress of corrosion is extremely suppressed, and the inability to detect the liquid level due to the electrode rod itself falling off due to corrosion is prevented.

〔Effect of the invention〕

In the present invention, a diode for preventing direct current is inserted in series with a resistor for improving the operating point between the base of the electrode current detection transistor of the relay drive circuit and the collector of the relay drive transistor, and a diode for reverse potential protection is inserted. By inserting it between the base power supply of the electrode current detection transistor, it prevents direct current from flowing through the long electrode rod that is submerged in the liquid for a long time, suppresses the progress of corrosion of the electrode rod, and allows accurate liquid level detection for a long time. It is possible to control the liquid level safely without being unable to detect the liquid level due to the electrode rod falling off due to corrosion, etc., and has a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit diagram of a liquid level detection relay according to an embodiment of the present invention, and FIG. 2 is a relay drive circuit diagram. 1...Short electrode, 2...Long electrode, 3...Common electrode, 4...Relay drive circuit, 5...Relay,
7... Relay for liquid level detection, 8... AC power supply, 9...
... Transistor for electrode current detection, 10 ... Unipolar capacitor, 11 ... Transistor for driving relay, 12 ... Electromagnetic coil, 13 ... Electrode terminal,
14... Electrode bar terminal, 15... Resistor for overcurrent prevention, 16... Light receiving element resistance, 17... Electrode bar terminal, 18... Resistor for overcurrent prevention, 19... Transistor for lighting the light emitting diode, 20... ...Light emitting diode, 21...Terminal, 22...Direct current prevention diode, 23...Power supply transformer, 24...Zener diode for noise prevention, 25...Charging current rectification diode, 26...For reverse potential protection Diode, 27, 28, 29... Zener diode for input overvoltage protection, 30... Voltage dividing resistor, 31...
...Manual return switch, 32...Direct current power supply diode, 34...Charging current limiting resistor, 35...
Resistor for improving operating point, 36... Resistor for limiting base current.

Claims (1)

[Claims] 1 A liquid level detection relay that detects the liquid level by placing a long electrode rod and a short electrode rod in the liquid, and detects the liquid level by the current flowing through the liquid between the electrode rods, and generates a predetermined signal to operate a pump, etc. In the circuit, a diode for preventing direct current is inserted in series with a resistor for improving the operating point between the base of the electrode current detection transistor of the relay drive circuit and the collector of the relay drive transistor, and a diode for reverse potential protection is inserted between the electrode current detection transistor and the collector of the relay drive transistor. A relay circuit for liquid level detection, characterized in that it is inserted between the base power supply of a current detection transistor.