JPH0297786A - Gas cutoff device - Google Patents

Abstract

PURPOSE:To contrive the reduction of consumption power in a reset detecting circuit by allowing an electric current to flow in a collector circuit changing its potential and feeding a reset signal to a control circuit, when the electric current is allowed to flow in a base of the second transistor being turned on in manual resetting. CONSTITUTION:When manual resetting operation is performed, a short time coil 3C generates electromotive force allowing a base current to pass through an analog switch 4E and a resistor 4D and to flow in a base-emitter circuit of the first transistor 4C, and it is turned on. Here the base current is allowed to flow also in the second transistor 4F, and it is also turned on. The collector voltage of the transistor 4C decreases to about -0.7 to -0.8V for potential of a negative pole of a battery 5, but voltage of an input i2 of a microcomputer 2B obtains a range of 0V through voltage of the battery 5, and a negative voltage input to the computer 2B is prevented. While an input rated value to the computer 2B is normally limited, and the computer is protected in is element by limiting the input to within the rated value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas cutoff device for measuring the flow rate of gas to prevent gas explosions caused by various causes.

[Prior art]

This type of gas cutoff device is equipped with a return detection circuit that detects the electromotive force generated when the self-holding manual return type solenoid valve that shuts off the gas flow path is manually returned, and outputs a return signal to the control circuit. There are some circuits that use FETs (field effect transistors) in the return detection circuit (for example, Japanese Patent Laid-Open No. 59
-1883 Publication).

This type of gas cutoff device includes one having the configuration shown in FIG. In FIG. 2, reference numeral 1 denotes a flow rate sensor that is attached to the gas meter 7 and detects the flow rate of gas. This sensor is
For example, there is a gas meter that combines a magnet provided in a diaphragm constituting a gas meter or a part of a link mechanism that transmits the reciprocating motion of the diaphragm to an indicator, and a reed switch that detects the position of this magnet. The gas flow rate can be determined by measuring the time from when the reed switch is turned on to when it is turned on again. Reference numeral 3 denotes a self-holding manual return type solenoid valve that combines a magnet and an electromagnetic coil provided in the gas flow path, and shuts off the gas flow path in response to a cutoff signal from the control unit 6. This electromagnetic valve is designed to self-maintain in an open state by the force of a magnet, reducing consumption of the battery that serves as the device's power source. Further, the shutoff operation is performed when the self-holding state is released as the electromagnetic force generated by passing a current through the electromagnetic coil overcomes the force of the magnet holding the valve in the open state.
Once it is in the closed state in this way, it will no longer be brought into the open state by the force of the magnet alone, and there is no longer any need for current to flow. To open the valve, open it manually and use the magnet to hold it in place. The control unit 6 is the flow rate sensor 1
It processes this signal according to a predetermined processing procedure, determines whether or not to shut off, and if the shut-off conditions are satisfied, outputs a shut-off signal to the solenoid valve 3. As a processing procedure, for example, it is determined whether the flow rate detected by the flow rate sensor 1 continues to flow at a constant value for a predetermined time period.

If it exceeds the flow rate, it means that the equipment corresponding to the flow rate has been used for a longer period of time than the normal usage time, and such a state indicates some kind of abnormality and a shutoff signal is output.

Since this type of device uses a self-holding manual return type solenoid valve, it is necessary for the control section to recognize whether or not the valve is in the cutoff state after the control section outputs a cutoff signal.

For this reason, a return detection circuit was provided that detects the electromotive force generated in the coil of the solenoid valve when the solenoid valve is manually reset and outputs a return signal. Let me explain this in a little more detail.

In Fig. 3, 2 is a control circuit that turns on and off the reed switch of the flow rate sensor 1 using a 2A resistor and a voltage of "Old" and "Old".
The microcomputer 2B receives this signal and processes it according to a predetermined processing procedure stored as a program.If the cutoff condition is satisfied, the microcomputer 2B outputs a cutoff signal.
This turns on the transistor 2C, current flows through the electromagnetic coil 3C of the electromagnetic valve 3, and the gas flow path is cut off.

4' is a return detection circuit, which is composed of a FET 4A and a resistor 4B. The FET 4A has a gate-source voltage Vcs of zero V, and is in an on state between its drain and source. When the solenoid valve 3 is manually reset, an electromotive force is generated in the solenoid coil. The electromotive force is FET4
The gate and source of FET A will be reverse biased, and if it becomes higher than its cutoff voltage VOFF, FET4
A is turned off. The microcomputer 2B controls the power supply of the return detection circuit 4'. This will be explained using the timing chart of FIG. Before the microcomputer 2B outputs the cutoff signal tl, its output OL is "Lo", the transistor 2C is off, and its output 0. is "Lo" and does not supply power to the return detection circuit 4', so that the battery consumption of the return detection circuit 4' is almost zero. Since the cutoff condition is satisfied at time t,
The microcomputer 2B keeps the output OL at 1 until time tλ.
"Old", turn on transistor 2C, and turn on electromagnetic coil 3C.
A current is applied to the solenoid valve 3 to turn it off. Time 1z
, the transistor 2C transitions from on to off, but
At this time, a voltage is generated in the direction in which the current continues to flow through the coil 3C of the solenoid valve 3. That is, until the time point, a voltage in the opposite direction to the voltage up to time 11 is generated. Since this voltage has the same polarity as the voltage caused by the electromotive force generated when the solenoid valve 3 is manually reset, immediately after time tλ color, when the output O2 of the microcomputer 2B becomes "H", the power supply of the reset detection circuit 4 is activated. is supplied, the back electromotive force generated between time t2 and t9 is detected, and this is output to the microcomputer 2B as a recovery detection signal.In order to avoid such a problem, the back electromotive force is After the disappearance, that is, from time t after a predetermined period of time has elapsed from the cutoff signal output end time t, the microcomputer 2B sets its output 02 to H-bi. As a result, the power supply of the recovery detection circuit 4'' is turned on. Supplied. Until time I when manual return operation is performed,
Since the gate-source voltage Vcs of FET4A is zero, FET4A is turned on and the microcomputer 2B
The input i, becomes "Lo". Solenoid valve 3 at time t9
When the manual return operation is performed, an electromotive force is generated in the electromagnetic coil until time t6, so the FET 4A is turned off and "H Bi" is input as a return signal to the input iλ of the microcomputer 2B. recognizes the return operation and returns its output to 0 again at time t2.
1 to "Lo" to stop supplying power to the recovery detection circuit 4'.

[Problems to be solved by the present invention]

The demand for gas meters with safety functions as described in the above-mentioned prior art has increased recently, and it is essential that the gas meters require no maintenance until their certification period expires. Furthermore, since the control electronic circuit is battery-powered, reducing the current of the electronic circuit is highly effective in achieving maintenance-free operation.

However, in the above-mentioned prior art, while the power is being supplied to the return detection circuit 4'', immediately from time t to t in FIG.
Until F, strictly speaking, time 1. ) to the time when a back electromotive force is generated in the coil 3C of the solenoid valve 1=
Except for the period from ; to t6, the gate-source voltage VGS of the FET 4A is zero, and the drain-source is in the on state, so current continues to flow through the recovery detection circuit 4'.

After the solenoid valve 3 closes, power is supplied to the return detection circuit 4' at a certain time, and after that, it is uncertain when the solenoid valve 3 will be manually operated to return. If the manual reset operation is not performed and the device is turned off, the current will flow to FET4A,
There was a problem that the battery ran out quickly.

In view of the above-mentioned problems, the present invention provides a gas return detecting circuit that allows a current to flow only when a back electromotive force is generated in the coil 3C by manual return operation of the solenoid valve, and in which almost no current flows at other times. The purpose is to propose a blocking device.

[Means to solve the problem]

In order to achieve the above object, the gas cutoff device of the present invention includes:
A flow rate sensor that detects the gas flow rate, a control circuit that outputs a cutoff signal when a signal from the flow rate sensor satisfies a predetermined condition, and a self-holding manual return type solenoid valve that cuts off the gas flow path in response to the cutoff signal. and a return detection circuit that detects an electromotive force generated when the solenoid valve is manually reset and outputs a return signal to the control circuit, and a battery that supplies power supply voltage to these control circuits and the return detection circuit. In the gas cutoff device in which one end of the coil of the electromagnetic valve is connected to one end of the battery, the return detection circuit includes a first transistor 4C, a second transistor 4F having a polarity different from that of the transistor, The first resistor 4G and the second resistor 4G
+1 and an analog switch 4E, the base and emitter of the first transistor 4C are connected to the coil 3 of the solenoid valve.
The polarity of the first transistor is such that the base-emitter PN junction is in the forward direction with respect to the direction of the electromotive force. The collector of the first transistor 4C is connected to the base of the second transistor 4F via the first resistor 4G, the collector of the second transistor is connected to the control circuit 2, and the collector of the first transistor 4C is connected to the base of the second transistor 4F via the first resistor 4G. and the emitter is connected to the other end of the battery 5 through the control circuit 2, and the control circuit 2 turns on the analog switch 4E for a predetermined period of time while outputting the cutoff signal and continuously thereafter. It is characterized by outputting an opening control signal.

[Effect]

As in the prior art, a current flows through the coil 3C of the solenoid valve in response to a cutoff signal from the control circuit, and the gas flow path is cut off.

The analog switch 4E outputs a control signal to open the analog switch 4E for a predetermined period of time while the control circuit 2 outputs the cutoff signal. The time when this control signal is output is, for example, from time t1 to t4 in FIG.
At time t, the analog switch 4E closes.

Next, when the solenoid valve is reset manually, an electromotive force is generated in the coil 3C, current flows through the analog switch 4E and the base-emitter circuit of the first transistor 4C, and while the electromotive force is generated, The first transistor 4C is turned on. Therefore, current flows through the base-emitter circuit of the first resistor 4G and the second transistor 4F. At this time, the first resistor 4G limits the base current of the second transistor 4F.

In this way, when a current flows through the base of the second transistor 4F and turns on the transistor, a current flows through its collector circuit, changing the potential of the collector and sending a return signal to the control circuit.

Analog switch 4 [! is opened and closed by a control signal from the control circuit 2, and prevents an excessive voltage from being applied between the base and emitter of the first transistor 4C, thereby protecting the transistor.

〔Example〕

In the embodiment shown in Fig. 1, ■ is a flow rate sensor, 2 is a control circuit, 2
A is a resistor, 2B is a microcomputer, 2C is a transistor, 3C is a solenoid valve coil, 4 is a return detection circuit, 5
is a battery, 4C is the first transistor of NPN type, 4G is the first resistor, 4H is the second resistor, and 4D is the resistor inserted in the base circuit of the first transistor, and they are connected as shown in the figure. ing.

Note that the first transistor 4C and the second transistor 4
Resistors 4I and 4J are connected between the base and emitter of F, respectively.

The output of microcomputer 2B is 0. When a cutoff signal is output from time t1 to time t), the transistor 2C is turned on during that time, current flows through the coil 3C of the solenoid valve, and the gas flow path is cut off. When the current is cut off at time tλ, an electromotive force is generated in the coil 3c of the solenoid valve from time tz to t3 in the direction of the 10- sign shown in the figure. At this time, since the analog switch 4E is open, the first No current flows through the base circuit of the transistor. At time t4, analog switch 4I! is activated by the control signal from output 03 of microcomputer 2B! closes. After that, when a manual return operation is performed at time t9, an electromotive force is generated in the coil 3c for a short time from time t5 to t&, which passes through the analog switch 4E and resistor 4D to the base-emitter circuit of the first transistor 4C. The base current flows through transistor 4.
C turns on. At this time, the second transistor 4F
A base current flows through the transistor 4F, and the transistor 4F is also turned on. At this time, the voltage at the collector of the first transistor 4C ranges from -0.7 to -0, with respect to the potential at the negative electrode of the battery 5.
However, the voltage at the input 12 of the microcomputer 2B decreases to about 8V due to the presence of the second transistor 4F.
The voltage range is from OV to the voltage of the battery 5, and negative voltage input to the microcomputer 2B is prevented. The rated value of the input of a microcomputer is usually limited to -0.5■ to the power supply voltage +0.5■, so the microcomputer's elements (
integrated circuits). In this way, the voltage generated in the coil 3C of the solenoid valve at the time of manual return is a minute voltage of about -0.6 to 0.8V, and the first transistor 4C
Even if the operating point of the second transistor 4F is in the non-saturation region, the second transistor 4F is in the saturation region and performs stable switching operation.

The reason why the analog switch 4E is opened by a signal from the control circuit is that even if a cutoff current flows through the coil 3C of the solenoid valve and the terminal voltage of the coil 3C reaches 3V, which is the battery voltage, that voltage is connected to the base of the first transistor. This is to protect the first transistor by preventing it from being applied in the opposite direction to the emitter junction, and to prevent malfunction due to the electromotive force generated in the coil when the cutoff current is cut off. 4E may be controlled by the output O of the microcomputer 2B.

Note that the analog switch 4E uses an analog switch integrated circuit that can control opening and closing with a low voltage of 0 to 3 cm and requires very small current for control.

Also, the diode 2D connected in parallel to the coil 3C is
The terminal voltage of the coil 3C due to the electromotive force generated when manually returning the cutoff valve is limited to about -0.8V. Note that the analog switch 4E may be inserted between the emitter of the first transistor 4C and one end of the coil 3C;
If this is done, a voltage exceeding the rated value will be applied to both ends of the analog switch at the time of return, which is unfavorable in terms of reliability.

〔Effect of the invention〕

According to this invention, the current consumed by the return detection circuit is substantially only for a short time when the solenoid valve is manually operated to return, so that the current consumption of the return detection circuit can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit according to an embodiment of the present invention, FIG. 2 is a schematic diagram of a gas cutoff device, FIG. 3 is an electric circuit of a conventional technique, and FIG. 4 is a timing chart explaining the operation of the conventional technique. DESCRIPTION OF SYMBOLS 1... Flow rate sensor, 2... Control circuit, 3... Solenoid valve, 3C... Coil of electromagnetic valve 3, 4... Return detection circuit, 4C... First transistor, 4B... ...Analog switch, 4F...Second transistor, 4G...
・First resistor, 411... Second resistor, 5... Battery

Claims (1)

[Claims] A flow rate sensor that detects the gas flow rate, a control circuit that outputs a cutoff signal when a signal from the flow rate sensor satisfies a predetermined condition, and a self-holding manual return type solenoid valve that cuts off the gas flow path in response to the cutoff signal. and a return detection circuit that detects an electromotive force generated when the solenoid valve is manually reset and outputs a return signal to the control circuit, and a battery that supplies power supply voltage to these control circuits and the return detection circuit. In the gas cutoff device in which one end of the coil of the electromagnetic valve is connected to one end of the battery, the return detection circuit includes a first transistor (4C) and a second transistor (4C) having a polarity different from that of the transistor. 4F), a first resistor (4G),
A second resistor (4H) and an analog switch (4E) are provided, and the base and emitter of the first transistor (4C) are connected to the one end and the other end of the coil (3C) of the solenoid valve,
One of them is connected to each other via an analog switch (4E), and the polarity of the first transistor is selected so that the base-emitter PN junction is in the forward direction with respect to the direction of the electromotive force. The collector of the transistor (4C) is connected to the base of the second transistor (4F) via the first resistor (4G), the collector of the second transistor is connected to the control circuit (2), and the collector of the second transistor (4F) is connected to the control circuit (2). 4
H) is connected to the one end of the battery (5), and the emitter is connected to the other end of the battery (5), and the control circuit (2) is connected to a predetermined value while outputting the cutoff signal and continuously thereafter. A gas cutoff device, characterized in that it outputs a control signal that opens the analog switch (4E) for a period of time.