JPS5852491Y2 - Liquid level detection device - Google Patents

Description

[Detailed description of the invention] This invention relates to a liquid level detection device that detects the liquid level of batteries, etc., and stabilizes operation against power fluctuations etc.
This prevents fluctuations in the operating point of the detection element due to ambient temperature and improves detection accuracy.

A conventional liquid level detection device that detects a drop in the liquid level by installing an electrode in a liquid such as an electrolyte of a battery is constructed as shown in FIG. The voltage of the AC power source is stepped down or stepped up by a power transformer T, and is supplied to the respective terminals of a pair of electrodes provided in the liquid, that is, electrode terminals 3 and 4 via current limiting resistors R, , R2.

When both electrodes are immersed in the liquid, current flows through the liquid, and since the impedance between the two electrodes is small, almost no current flows through the rectifying bridge BR, and the relay Ry for outputting the detection signal is not driven, and a lamp etc. indicates that the liquid level is normal.

Next, when the liquid decreases and the liquid level drops and both electrodes are exposed from the liquid to above the liquid surface, the impedance between the two electrodes is large and no current flows between the electrode terminals 3 and 40. The current from the secondary side of the power transformer T is converted to direct current by the rectifier bridge BR, and after being smoothed by the smoothing capacitor C, it is supplied to the relay Ry, which drives the relay Ry and outputs a detection signal, which can be used as a lamp or alarm. This will notify you of a drop in the liquid level.

However, due to the circuit configuration, the current limiting resistors R1, R
If an electrode with a large resistance value is used for electrode 2, there is a risk of malfunction, so an electrode with a small resistance value is used, and a large current is passed through the liquid through both electrodes.

Therefore, for example, if gas is generated in the battery and the liquid is reduced and the electrodes are exposed above the liquid surface, there is a risk that the gas will explode.

In addition, a liquid level device has been devised in which the voltage between both electrodes turns on and off a detection element made of a semiconductor such as a thyristor to control the drive of a relay, but temperature drift occurs due to the temperature characteristics of the semiconductor, and the liquid level This causes the inconvenience that the operating point of the semiconductor that detects and operates changes.
The disadvantage is that the operating point changes due to power supply fluctuations.

This invention takes into account the above-mentioned conventional problems and provides a constant voltage circuit, a temperature compensation circuit for the detection element, etc. to stabilize the operation and improve detection accuracy.
Next, this invention will be explained in detail with reference to the drawings from FIG. 2 onwards showing one embodiment thereof.

In Fig. 2, a and b are a pair of AC power supply terminals at both ends of the secondary winding of a power transformer T with both ends of the primary winding connected to AC input terminals 1 and 2, and C It is a constant voltage circuit connected to one AC power supply terminal a through a first current limiting resistor r1, and the other end is connected to the other AC power supply terminal A, and includes two Zener diodes zD0 connected in anti-series,
Consists of zD2.

Ry and TH are detection elements such as relays and thyristors for outputting detection signals, and the input terminal or anode and the output terminal or cathode of the relay Ry and the detection element TH are connected in series between both AC power supply terminals a and b. The control terminal, ie, the gate G, of the detection element TH is connected to one electrode terminal 3.

DI and CI are a first diode and a first capacitor connected in parallel to the relay Ry, respectively, and a first capacitor for keeping the relay Ry in the on state; This is the connected second current limiting resistor, and a resistor with a large resistance value is used.

C2. D2. R is a second capacitor for surge absorption connected in parallel between the control terminal G and the cathode of the detection element TH, a second diode and a detection resistor for protection of the detection element TH, and A is the other electrode terminal 4. A temperature compensation circuit for the detection element TH connected between the cathode of the detection element TH, and one diode D3 having the same polarity as the diode D2 of the detection element TH between the gate G and the cathode, and the diode D3. The other diode D connected in antiparallel to D3
It consists of 4.

Next, the operation of the embodiment will be explained.

The power AC from both AC power terminals a and b via the power transformer T is supplied to the parallel circuit of the relay Ry, the first diode D1, the first capacitor C, and the series circuit of the detection element TH. It is supplied to both ends of the constant voltage circuit Cv via the first current limiting resistor r□, and the power supply voltage is stabilized by the constant voltage circuit C■, and the stabilized output AC of the constant voltage circuit CV is supplied to the second current limiting circuit. resistor r2 and both electrode terminals 3,
4 and temperature compensation circuit A in series.

When the liquid level is high and in a normal state, both electrodes are immersed in the liquid and the impedance between the electrode terminals 3 and 40 is very small.

Therefore, during the positive half-cycle period of the output AC, that is, the positive half-cycle period of the power AC
A small current flows through the other end of the constant voltage circuit Cv, and at this time, almost no current flows through the gate G of the detection element TH, the detection element TH is not turned on, and the relay Ry is not driven. No detection signal is output, and the normal state of the liquid level is notified.

Next, when the liquid decreases and the electrode is exposed from the liquid to the liquid surface, resulting in an abnormal state, the impedance between both electrode terminals 3 and 4 increases, and therefore the voltage across the detection resistor R increases. growing.

Therefore, a current flows through the second current limiting resistor r2 to the gate G of the detection element TH during the positive half cycle period of the AC power supply, the detection element TH is turned on, and the relay Ry is driven and turned on.

At this time, the detection element TH is in the ON state only during the positive half cycle period of the power supply AC, and is in the OFF state during the negative half cycle period, but during the positive half cycle period, the first capacitor C1
is charged, and the charge in the first capacitor C0 is discharged through the relay Ry during the negative half cycle period, so the relay Ry maintains the on state and continues to output the detection signal to the outside, and the power supply The drop in liquid level continues to be reported during the negative half cycle of AC.

Even if the power supply voltage fluctuates, the power supply transformer T insulates the primary and secondary sides, and the power supply AC is stabilized by the constant voltage circuit C■, and the output AC of the constant voltage circuit Cv is stabilized. Since the voltage is applied to the electrode terminals 3 and 4, the operating point of the detection element TH does not vary.

Moreover, between the gate G and the cathode of the detection element TH,
During the positive half cycle of the power supply AC, both electrode terminals 3, 40
A superimposed voltage between the voltage between the two and the forward voltage of one diode D3 of the temperature compensation circuit A is applied, and at this time, the forward current of the diode D3 changes with temperature, and as shown in FIG. The forward voltage of diode D3 when turned on and forward current It flows becomes forward voltage vth when the temperature is high, and becomes forward voltage Vtt which is higher than forward voltage vth when the temperature is low.

On the other hand, the characteristics of the voltage between the gate G and the cathode, that is, the gate voltage, with respect to the input current, that is, the gate current, of the gate G of the detection element TH are as shown in FIG.

In addition, in FIG. 4, Igh. Each Igt is a gate current that becomes the minimum trigger current at high temperature and low temperature, and its value is larger at low temperature than at high temperature.

Furthermore, vgh and vgz are gate voltages that are the minimum trigger voltages at high and low temperatures, respectively, and their values are larger at low temperatures than at high temperatures.

That is, when the detection element TH becomes low temperature, a large gate voltage and gate current are required to turn on or trigger, and when the temperature becomes high, the gate voltage and gate current required for triggering become small.

When the temperature is high, the gate voltage for triggering the detection element TH becomes smaller, and the forward voltage that turns on one diode D30 of the temperature compensation circuit A also becomes lower.
Conversely, when the temperature is low, the gate voltage for triggering the detection element TH increases, and the forward voltage that turns on the diode D3 also increases, so that malfunctions of the detection element TH due to temperature changes are prevented.

Note that when the liquid level falls, the electrolyte adheres between the two exposed electrodes, and in reality the impedance between the two electrodes is not infinite. When the gate voltage becomes high, there is a risk that the detection element TH will not turn on if the diode D3 is turned off, but when the temperature is low, the forward voltage at which the diode D3 turns on also becomes high, so it is necessary to turn on the detection element TH reliably. I can do it.

In other words, fluctuations in the operating point of the sensing element TH due to changes in ambient temperature are compensated for by fluctuations in the operating point of one diode D3 of the temperature compensation circuit A, which fluctuates almost identically, and the sensing element TH remains constant regardless of the ambient temperature. Turns on and off at the operating point.

The temperature compensation circuit A is composed of two diodes D3tD4 connected in anti-parallel. If it were composed of only one diode D3 facing the same direction as the detection element TH, it would not be possible to connect the electrolyte of the battery in one direction. This is to prevent polarization from occurring due to current flow.

As described above, according to the liquid level detection device of this invention, a pair of electrodes are provided which are exposed above the liquid surface from the liquid when the liquid in the battery etc. decreases, and the impedance between the pair of electrodes is reduced. In a liquid level detection device that detects the liquid level of the liquid by turning on and off a detection element TH such as a thyristor according to a change, and controlling the drive of a relay Ry for outputting a detection signal by the detection element TH, the relay Ry and the detection Element T
The input and output terminals of H are connected in series between a pair of AC power supply terminals a and b, and a capacitor C1 for maintaining the on state of the relay Ry is connected in parallel to the relay Ry. The power source alternating current of AC power source terminals a and b is stabilized and stabilized between one end C connected to the one AC power source terminal a via a first current limiting resistor r1 and the other AC power source terminal S. Constant voltage circuit C that supplies output AC
and a second current-limiting resistor r2 having a large resistance value provided between the one end C and the control terminal G of the detection element TH connected to the electrode terminal 3 of the one electrode, and the control terminal G.
and the other AC power supply terminal, and a detection resistor R provided between the electrode terminal 4 of the other electrode and the other AC power supply terminal, and the control terminal G and the other and a temperature compensation circuit A consisting of one diode D3 having the same polarity as the diode D2 of the detection element TH between the AC power supply terminal and the other diode D4 in antiparallel to the diode D3. The constant voltage circuit prevents the operating point of the detection element from changing due to power fluctuations, and the temperature compensation circuit allows the detection element to be turned on and off at a constant operating point regardless of the ambient temperature, resulting in significantly improved operation. In addition to being stable, it is possible to prevent false detection due to temperature and improve detection accuracy.

Furthermore, by providing a current limiting resistor with a large resistance value and passing a small current through the liquid, there is no danger of gas explosion, etc., and it is safe.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a conventional liquid level detection device, Fig. 2 is a wiring diagram of an embodiment of the liquid level detection device of this invention, and Fig. 3 is a forward voltage and forward current of the diode shown in Fig. 2. FIG. 4 is a diagram showing the relationship between the gate current and gate voltage of the detection element in FIG. 2. a, b... AC power supply terminal, C... one end, 3, 4... electrode terminal, CV... constant voltage circuit, TH... ...Detection element, G...Gate, R...Resistance for detection, r□...Resistance for first current limiting, r2...For second current limiting Resistance, A.
...Temperature compensation circuit, D2. D3. D4...
・Diode, Ry...Relay, C1...
...First capacitor.

Claims (1)

[Claims for Utility Model Registration] In addition to providing l pairs of electrodes that are exposed above the liquid surface from the liquid when the liquid in the battery decreases, and detecting elements such as thyristors by changing the impedance between the l pairs of electrodes. T.H.
In the liquid level detection device that detects the liquid level of the liquid by controlling the drive of a relay Ry for outputting a detection signal by the detection element TH, the input terminal and the output terminal of the relay Ry and the detection element TH A pair of AC power terminals a. 6 are connected in series, and a capacitor C□ for maintaining the ON state of the relay Ry is connected in parallel to the relay Ry, and the power AC of both the AC power supply terminals a and b is stabilized. The first current limiting resistor r is connected to the AC power supply terminal a.
a constant voltage circuit C■ supplying a stabilized output AC between one end C and the other AC power supply terminal connected via □; A second current limiting resistor r2 having a large resistance value is provided between the connected control terminal G of the detection element TH, and a detection device is provided between the control terminal G and the other AC power supply terminal. and a diode D2 of the detection element TH provided between the electrode terminal 4 of the other electrode and the other AC power supply terminal and between the control terminal G and the other AC power supply terminal. A liquid level detection device comprising a temperature compensation circuit A consisting of one diode D3 having the same polarity as the polarity of the diode D3, and the other diode D4 antiparallel to the diode D3.