JPS62201323A - Liquid level detector - Google Patents

Abstract

PURPOSE:To automatically detect a proper liquid level without performing manual reset operation by carrying out a one-shot action at the time of charging a power source and driving a relay for a prescribed time. CONSTITUTION:The titled detector consists of the 1st and the 2nd probes E1 and E2 having upper and lower detection levels with the different lower ends respectively, the 3rd probe E3 to detect conduction with these probes and the relay X to short-circuit the 1st and the 2nd probes E1 and E2. Then, output corresponding to a liquid level is given after the power source is charged by driving the relay X once by an one-shot pulse from a one-shot circuit 12 to act for a prescribed time and drive the relay X after the power source is charged. Accordingly, the relay X is driven for a prescribed time and the 1st and the 2nd probes E1 and E2 are short-circuited even in case the power source is cut off and afterward, restored in an acting state. In this way, the proper detection output in accordance with the liquid level can be restored and the liquid level can be automatically detected without performing the reset operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a liquid level detection device that operates by detecting a liquid level, and particularly relates to a liquid level detection device that is characterized in its operation when the power is turned on.

[Summary of the invention]

The liquid level detection device according to the present invention has a first detection level having upper and lower detection levels, each having a different lower end. a second probe, a third probe that detects continuity with these probes, and a first probe. Due to the conduction of the third probe, the first. a relay for shorting the second probe; A liquid level detection device that detects the liquid level between the second probe performs a one-shot operation when the power is turned on, drives a relay for a predetermined period of time, and automatically obtains an appropriate output signal without having to perform a manual reset operation. This is what I did.

[Prior art and its problems]

Among conventional liquid level detection devices in which a probe is inserted into the liquid to detect the liquid level, there is a device that operates a relay depending on the liquid level to change the detection level. There is. FIG. 2 is a circuit diagram showing an example of such a conventional liquid level detection device 1. In this figure, terminal la.

A power transformer 2 is connected to 1b, and a detection circuit 3 is connected to its secondary side. Terminals IC to 1e are probe terminals for liquid level detection, and are connected to the power transformer 2 and the detection circuit 3. These terminals IC to 1e are connected to the first and second terminals, respectively, which determine the upper and lower detection liquid levels of a water tank, etc. Second probe El.

A probe E3 that detects continuity between E2 and these probes is connected. The detection circuit 3 receives a signal input when these probes are electrically connected and drives the relay X. relay This is to short-circuit between c and ld.

In this liquid level detection device, if the liquid level exceeds the detection level of the probe El, the terminal 1c,
conduction between le and a signal is applied to the detection circuit 3, the relay X is driven, and a signal indicating that the upper level has been reached is provided to the external device. At the same time, terminals 1c and ld are short-circuited, so even if the liquid level drops below the detection level of probe E1, relay X continues to operate, and probe E2
When the detection level falls below the lower detection level, relay X is deenergized and a signal indicating that the detection level has fallen below the lower detection level is transmitted to the outside.

However, after the liquid level exceeds the detection level of probe E1 and relay
is deenergized and its normally closed contact Xa opens. Therefore, even if power is supplied to the detection circuit 3 via the power transformer 2 after the power outage is restored or the power is turned on again, there is no continuity between the terminals 1c and ld, so the relay There was a problem that detection output could not be obtained. Therefore, in conventional liquid level detection devices, terminal 1 is
A reset switch 4 is provided to short-circuit C and LD, and after the power is turned on, the relay X is manually short-circuited to drive the relay X, but this has the disadvantage that it takes time and effort to operate.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional liquid level detection devices, and is capable of automatically restoring its output without having to operate a reset switch every time after a power outage is restored or the power is turned on again. It is an object of the present invention to provide a liquid level detection device that can

[Structure and effects of the invention]

The present invention provides a first sensor for detecting upper and lower levels inserted into the liquid, each having a different detection level at the lower end. a second probe, and a third probe having a lower detection level than the second probe; A detection circuit that detects continuity between the second probe and the third probe and provides a liquid level detection output; The first probe is driven by the conduction between the third probe. 979371 - A liquid level detection device having a relay that short-circuits between the second probes, and a circuit that operates for a predetermined period of time after power is turned on to drive the relay, and once the relay is driven by the one-shot pulse. The device is characterized in that it provides an output corresponding to the liquid level after the power is turned on.

As described above, according to the present invention, the relay is driven by one-shot operation for a predetermined period of time after power is turned on. Therefore, even if the power is cut off in the operating state and then restored, the relay is activated for a predetermined period of time and the first. The second probes are shorted. Therefore, by providing a reset switch, it is possible to return to an appropriate detection output according to the liquid level at that time without performing a reset operation.

[Explanation of Examples]

(Configuration of Embodiment) FIG. 1 is a circuit diagram showing an embodiment of a liquid level detection device according to the present invention. In this figure, the same parts as in the conventional example are given the same reference numerals. Now, a power transformer 2 is provided between the terminals ia and tb, and one of the secondary windings is connected to the detection circuit 10 side.
The fact that one end of the other winding is applied to the probe side is similar to the conventional example described above. In this embodiment, a rectifier circuit consisting of a diode bridge 11 and a smoothing capacitor CI is connected to one of the secondary outputs. And this DC power supply terminal a
A voltage dividing circuit consisting of resistors R1 and R2 is connected between the terminal e and the ground terminal e, and a capacitor C2 is connected between the connection point and the ground terminal e. Resistors R1, R2 and capacitor C2 form a one-shot circuit 1 that operates relay X for a predetermined time after power is turned on.
2. The base of the transistor Tfll is connected to the connection point, the collector and emitter ends are connected to the power supply via resistors R3 and R4, and the collector is further connected to the base of the transistor TR2. transistor TR
A relay X is connected in series to the collector of No. 2, and the emitter is connected to a resistor R4 via an emitter resistor R5. Transistor TR2 drives relay X based on the output of transistor TRI. On the other hand, a second diode bridge 13 and a smoothing capacitor C3 are connected between the terminals 1c and le via the secondary output of the power transformer 2.

The output of the positive side of the diode bridge 13 is sent to the detection circuit 10.
The negative output terminal C is connected to the ground terminal e of the resistor R6 via a resistor R6, and to the connection point of the resistors R1 and R2. The probe terminals 1c to 1e for liquid level detection have first and second terminals, respectively, which determine the upper and lower detection liquid level levels of a water tank or the like. Second probe El
, E2, and a probe E3 for detecting conduction between these probes is connected as in the conventional example described above.

(Operation of the embodiment) When the power is turned on, a DC voltage is generated between the power terminal a and the ground terminal e of the detection circuit 10 by the diode bridge 11, and is divided by the resistors R1 and R2, but the one-shot circuit 12 operates and the capacitor Resistor R until C2 is charged
The potential of the connection point between 1 and R2 is low (transistor 1゛R1
is in the off state. Therefore, transistor TR2 becomes conductive, driving relay X and closing its normally open contact Xa.

When the capacitor C2 is charged after a predetermined period of time has elapsed, the potential at the connection point S 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, normal operation is resumed thereafter, and a predetermined output is given by the liquid level rail detected by the probe El-E3. That is, if the liquid level exceeds the detection level of the probe El, the terminals 1c and 1e are closed, so a negative voltage is generated from the output terminal C of the diode bridge 13, and the potential at the connection point 1 decreases. Therefore, transistor TR1 is turned off and relay X is driven.

Then, a liquid level detection signal is transmitted to the outside through the normally open and normally closed contacts Xc of relay Even if the liquid level falls below the detection level of probe El, the liquid level will still be detected by probe El.

Relay X continues to operate as long as it is within the detection level of E2. When the liquid level falls below the detection level of the probe E2, the terminals 1d and le become non-conductive, and no negative voltage is generated at the output terminal C of the diode bridge 13, and the resistor R1
, R2, the transistor'
The fact that FR1 is driven and relay X is deenergized is similar to the conventional example described above.

When the liquid level is between the detection levels of the probes El and E2, if there is a power outage or the power is cut off, the relay X is deenergized and the charge in the capacitor C2 is discharged through the resistor R2. Afterwards, when the power outage is restored, charging of the capacitor C2 is started as described above, and the transistor TRI is turned off and the transistor TR2 is turned on for a predetermined period of time until the charging is almost completed, and the relay X is activated four times. Therefore, normally open contact Xa of relay X is closed, and probe El.

E2 has the same potential. After that, the capacitor C2 is charged, but since a negative voltage is generated at the output terminal C of the diode bridge 13, the relay X is not deenergized, and the liquid level reaches the probe E
Relay X continues to be driven until it becomes lower than the detection level of 2. Therefore, using the Senoto Sinch, it is possible to obtain a normal liquid level detection output without having to operate it every time the power is turned on.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional liquid level detection device.
FIG. 2 is a block diagram showing an example of a conventional liquid level detection device. la ~ le -- one terminal El, E2,
E3---Probe 2・Par-°-Power transformer 3, 10---Detection circuit 11.13-
・・・−・−Diode bridge 12−−−−−・One shot circuit Figure 1

Claims (2)

[Claims] (1) First and second probes for detecting upper and lower levels inserted into the liquid and having different detection levels at their lower ends, and a third probe having a lower detection level than the second probe; , a detection circuit that detects continuity between the second probe and the third probe and provides a liquid level detection output; and a detection circuit that exceeds the detection level of the first probe and is driven by the continuity between the first and third probes; A liquid level detection device having a relay that short-circuits between the second probes has a one-shot circuit that operates for a predetermined time after power is turned on and drives the relay, and once the relay is driven by the one-shot pulse, the power is supplied. A liquid level detection device characterized in that it provides an output corresponding to the liquid level after charging. (2) The liquid level detection device according to claim 1, wherein the detection circuit provides a liquid level detection output to the outside by using the relay output.