JP2574754B2 - Liquid level detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting device which operates by detecting a liquid level, and more particularly to a liquid level detecting device which is characterized by an operation at power-on.

[Summary of the Invention]

The liquid level detecting device according to the present invention comprises first and second probes having different lower ends and having upper and lower detection levels, and a third probe and a third probe for detecting continuity with these probes.
1, a relay for short-circuiting the first and second probes due to conduction of the third probe, and a one-shot operation at power-on in a liquid level detection device for detecting a liquid level between the first and second probes. Then, the relay is driven for a predetermined time to automatically obtain an appropriate output signal without manually performing a reset operation.

[Conventional technology and its problems]

Conventionally, as a liquid level detecting device, there is known a liquid level detecting device in which a probe for detecting a liquid level in a liquid is inserted so as to change a detection level by operating a relay according to the liquid level. I have. FIG. 2 is a circuit diagram showing an example of such a conventional liquid level detecting device 1. In this figure, a power transformer 2 is connected to terminals 1a and 1b,
The detection circuit 3 is connected to the next side. Terminals 1c to 1e are liquid level detection probe terminals, which are connected to the power transformer 2 and the detection circuit 3. These terminals 1c to 1e respectively have upper and lower detection liquid levels, such as an aquarium, for determining the first and second detection liquid levels.
The probes E1 and E2 are connected to a probe E3 for detecting conduction between the probes E1 and E2. The detection circuit 3 drives the relay X in response to a signal input when the connection between the probes is conducted. Relay X is normally open and normally closed contact Xc
The start / stop signal is supplied to an external device to supply and drain water, and the terminals 1c and 1d are short-circuited by the normally open contact Xa.

In this liquid level detection device, if the liquid level exceeds the detection level of the probe E1, the terminals 1c and 1e conduct through the probes E1 and E3, and a signal is input to the detection circuit 3, and the relay X is driven and the external circuit is driven. The device is provided with a signal indicating that the upper level has been reached. At the same time, terminals 1c and 1d are short-circuited,
The relay X continues to operate even when the liquid level falls below the detection level of the probe E1, and when the level falls below the detection level of the probe E2, the relay X is deenergized and externally falls below the lower detection level. Is transmitted.

However, after the liquid level exceeds the detection level of the probe E1 and the relay X is driven, the liquid level drops, and if there is a power failure or the power is cut off at the liquid level shown in FIG.
Is deenergized and the normally open contact Xa is opened. Therefore, even if power is supplied to the detection circuit 3 via the power supply transformer 2 after restoration of a power failure or power supply is turned on again, since the terminals 1c and 1d are not electrically connected, the relay X is not driven again and an appropriate liquid level is not obtained. There is a problem that a detection output cannot be obtained. Therefore, in the conventional liquid level detecting device, a reset switch 4 for short-circuiting between the terminals 1c and 1d is provided as shown in the figure, and the relay X is driven by short-circuiting between the terminals manually after the power is turned on. However, there was a drawback that it took.

[Object of the invention]

The present invention has been made in view of such a problem of the conventional liquid level detecting device, and automatically restores its output without operating the reset switch every time even after restoration of a power failure or power-on. It is an object of the present invention to provide a liquid level detecting device capable of performing the above operation.

[Structure and effect of the invention]

The present invention relates to first and second probes for detecting upper and lower levels, each having a different lower detection level and inserted into a liquid, and a third probe having a lower detection level than the second probe; A detection circuit for detecting conduction between the second probe and the third probe and providing a liquid level detection output; and a detection circuit that exceeds the detection level of the first probe and is driven by conduction between the first and third probes to provide the first and second probes. A relay for short-circuiting between the probes, the detection circuit comprising: a first DC power supply unit; a resistance voltage dividing circuit connected to the first DC power supply unit; A time constant circuit having a capacitor connected in parallel to one of the resistors, a first switching element that operates by applying a voltage from the first DC power supply unit to drive the relay, and a control terminal connected to the time constant circuit For a certain period of time after the power is turned on. A second switching element that conducts to make the first switching element conductive and makes the first switching element non-conductive when conducting, and a closed circuit including between the first and third probes; A second DC power supply unit for applying a negative voltage to the midpoint of the voltage dividing resistor of the time constant circuit when current flows between the first and third probes, wherein the relay is provided by a first switching element. It is characterized by having a relay contact that is driven and outputs a control signal to the outside, and short-circuits between the first and second probes.

According to the present invention having such a feature, after the power is turned on, the second switching element is turned off for a certain period of time to drive the first switching element and to energize the relay. Therefore, even when the power supply is cut off in the operating state and the power supply is restored thereafter, the first switching element operates for a predetermined time determined by the time constant circuit. Therefore, the relay contact is closed and the first and second probes are short-circuited. Therefore, it is possible to provide a reset switch and to return to an appropriate detection output corresponding to the liquid level at that time without performing a reset operation.

[Explanation of Example]

FIG. 1 is a circuit diagram showing an embodiment of a liquid level detecting device according to the present invention. In this figure, the same parts as those of the conventional example are denoted by the same reference numerals. The power transformer 2 is connected between the terminals 1a and 1b.
Is provided, and one of the secondary windings is provided to the detection circuit 10 side and one end of the other winding is provided to the probe side, as in the above-described conventional example. In the present embodiment, the power transformer 2 having one secondary output connected to a rectifier circuit including a diode bridge 11 and a smoothing capacitor C1 and this rectifier circuit constitute a first DC power supply unit. A voltage dividing circuit composed of resistors R1 and R2 is connected between the DC power supply terminal a and the ground terminal e, and a capacitor C2 is connected between the connection point b and the ground. The resistors R1 and R2 and the capacitor C2 constitute a time constant circuit, and the transistor TR1 is a second switching element that is turned off for a certain period of time after power is turned on by the time constant circuit. The time constant circuit and the transistor TR1 are one-shot circuits that operate the relay X for a predetermined time after the power is turned on.
Make up 12. The transistor TR1 has a base connected to the connection point b, a collector and an emitter connected to a power supply via resistors R3 and R4, and a collector connected to the base of the transistor TR2. A relay X is connected in series to the collector of the transistor TR2, and the emitter is an emitter resistor.
Connected to resistor R4 via R5. The transistor TR2 is a first switching unit that drives the relay X based on the output of the transistor TR1. On the other hand, a second diode bridge 13 and a smoothing capacitor C3 are connected between the terminals 1c and 1e via a secondary output of the power transformer 2. The power transformer 2, the diode bridge 13, and the smoothing capacitor C3
It constitutes a second DC power supply unit. Diode bridge
The output of the positive electrode 13 is connected to the ground terminal e of the detection circuit 10, and the negative output terminal c is connected to the connection point b of the resistors R1 and R2 via the resistor R6. The probe terminals 1c to 1e for detecting the liquid level are provided with first and second probes E1 and E2 for determining the upper and lower detection liquid level of a water tank and the like, respectively, and a probe E3 for detecting continuity with these probes. The connection is the same as in the above-described conventional example.

(Operation of Embodiment) When the power is turned on, a DC voltage is generated between the power supply terminal a and the ground terminal e of the detection circuit 10 by the diode bridge 11, and the resistance is reduced.
The voltage is divided by R1 and R2, but until the one-shot circuit 12 operates and the capacitor C2 is charged, the potential of the connection point b of the resistors R1 and R2 is low, and the transistor TR1 is turned off.
Therefore, the transistor TR2 is turned on, the relay X is driven, and the normally open contact Xa is also closed. When the capacitor C2 is charged after a predetermined time, the potential of the connection point b rises and the transistor TR1 is turned on, and at the same time, the transistor TR2
Is turned off and the relay X is deenergized. Therefore, after returning to the normal operation, a predetermined output is given according to the liquid level detected by the probes E1 to E3. That is, the liquid level is probe E1
Is exceeded, the connection between the terminals 1c and 1e is closed, so that a negative voltage is generated from the output terminal c of the diode bridge 13 and the potential at the connection point b decreases. Therefore the transistor TR
1 is turned off and the relay X is driven. The liquid level detection signal is transmitted to the outside through the normally open and normally closed contacts Xc of the relay X, and at the same time, the normally open contacts Xa are closed and the probes E1 and E2 are closed.
Has the same potential, and even if the liquid level drops below the detection level of probe E1
Relay X continues to operate as long as it is between the detection levels of E1 and E2. When the liquid level falls below the detection level of the probe E2, the terminals 1d and 1e become non-conductive, so that no negative voltage is generated at the output terminal c of the diode bridge 13 and the potential of the connection point b of the resistors R1 and R2 is reduced. The fact that the transistor TR1 is driven by the rise to deactivate the relay X is the same as in the above-described conventional example.

When the liquid level is between the detection levels of the probes E1 and E2 and the power is cut or the power is cut off, the relay X is deenergized and the electric charge of the capacitor C2 is discharged through the resistor R2. And if the power outage is restored after that, the capacitor
The transistor TR1 is turned off and the transistor TR2 is turned on to drive the relay X for a predetermined time until the charging of C2 is started and the charging is almost completed. Therefore, normally open contact of relay X
Xa is closed, and the probes E1 and E2 have the same potential. Thereafter, the capacitor C2 is charged, but a negative voltage is generated at the output terminal c of the diode bridge 13, so that the relay X is not deenergized, and the relay X continues to be driven until the liquid level falls below the detection level of the probe E2. Therefore, a normal liquid level detection output can be obtained without using the reset switch every time the power is turned on.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a liquid level detecting device according to the present invention, and FIG. 2 is a block diagram showing an example of a conventional liquid level detecting device. 1a to 1e Terminal, E1, E2, E3 Probe, 2 Power transformer, 3, 10 Detection circuit, 11, 13 Diode bridge, 12 One-shot circuit, X Relay

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tsunetori Furusawa Ichinomiya-cho, Ichinomiya-cho, Aso-gun, Kumamoto 4429 Minamiyucho, Aso-Tateishi Electric Co., Ltd. 4429, Minamiyu-cho, Miyaji-sha Aso Tateishi Electric Co., Ltd. (56) References: Japanese Utility Model Sho 59-189121 (JP, U) Japanese Utility Model Sho 50-7819 (JP, Y1) )

Claims (1)

(57) [Claims] 1. A first and a second probe for detecting upper and lower levels inserted in a liquid, each having a different lower detection level.
And a third probe having a lower detection level than the second probe, a detection circuit for detecting conduction between the first and second probes and the third probe and providing a liquid level detection output, and a detection level of the first probe. A relay driven by conduction between the first and third probes to short-circuit the first and second probes, wherein the detection circuit comprises: a first DC power supply; A time constant circuit having a resistor voltage dividing circuit connected to the first DC power supply unit and a capacitor connected in parallel with one of the voltage dividing resistors; and applying a voltage from the first DC power supply unit. A first switching element that operates and drives the relay, a control terminal is connected to the time constant circuit, and is non-conductive for a certain period of time after power is turned on to make the first switching element conductive; First A second switching element that makes the switching element non-conductive; and a closed circuit including the first and third probes, wherein the time constant circuit is formed when the first and third probes are energized. A second direct-current power supply unit that applies a negative voltage to the midpoint of the voltage-dividing resistor. The relay is driven by the first switching element, outputs a control signal to the outside, A liquid level detecting device having a relay contact for short-circuiting between the first and second probes.