JPS6234398Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a photoelectric smoke detector that detects smoke generated by a fire and issues an alarm.

Conventionally, in this type of photoelectric smoke detector, as shown in FIG. 1, for example, a light emitting element 2 such as a light emitting diode is driven to emit light intermittently by a transistor Tr1 that is turned on and off by an output pulse from an oscillation circuit 1. to generate pulsed light, and the scattered light or attenuated light of this pulsed light due to smoke is detected by a light receiving element 3 such as a photodiode.The output of the light receiving element 3 is amplified by an amplifier 4, and a capacitor _C0 for DC component removal is detected. through a voltage divider circuit consisting of a variable resistor VR and a resistor _R2 ,
When the output from the amplifier 4 obtained through this voltage dividing circuit reaches a set voltage, the transistor Tr2 is switched to cause the alarm circuit 5 to send out a fire alarm or alarm signal.

In this way, photoelectric smoke detectors detect fire by converting the amount of change in light caused by smoke into an electrical signal, so their detection characteristics are largely dependent on the characteristics of the light-emitting and light-receiving elements used. .

Incidentally, commercially available light emitting elements and light receiving elements have variations in characteristics due to their structures. Therefore, when used in a photoelectric smoke detector such as the one described above, the output characteristics of the amplifier will vary with respect to smoke concentration, as shown in FIG. 2, for example.

Here, if the operating point for transistor Tr2 to perform switching operation is 0.7 volts, then the 5 to 15% /
To set the alarm to be triggered at a smoke density of m, set the second
Regarding the characteristic curves A and B in the figure, the transistor
This can be set by adjusting the variable resistor VR that provides the base voltage of Tr2, but in cases such as characteristic curves C and D, it is not possible to adjust the alarm to be issued at a smoke density of 5 to 15%. Therefore, it is possible to select and use light-emitting elements and light-receiving elements that can obtain characteristic curves A and B, but it is difficult to select only usable elements from among a large number of elements. If you request something with a high price tag, there is a problem that it will be a custom-made product and will be expensive.

On the other hand, if the resulting characteristic curves are C or D, it may be possible to increase the output voltage by increasing the gain of the amplifier 4, but this would also amplify the noise components contained in the output voltage. , the S/N ratio decreases, making malfunctions more likely to occur.Also, as the gain is increased, the rate of change due to temperature characteristics also increases, and if installed in a place with rapid temperature changes, there is a risk that non-fire alarms may be more likely to be issued. be.

Another possible method is to increase the brightness of the light emitting diode, but this method increases current consumption, making it unsuitable for battery-powered fire detectors in particular, and shortening the life of the light emitting diode.

Furthermore, the switching transistor Tr
Although a comparator can be used instead of 2, this makes the circuit complicated and expensive.

In addition to these electrical measures, it is also possible to increase the amount of light that enters the light receiving element by installing an adjustment pin in the smoke detection section, but the adjustment pin may be contaminated with dew drops, insects, etc. It is easy to malfunction, it is difficult to make fine adjustments, and the design of the smoke detection part is also difficult.

The present invention was developed in view of the above, and when the oscillation circuit for driving the light emitting element generates an output, the capacitor installed at the output end of the amplifier that amplifies the detection output of the light receiving element oscillates. By charging by the output and extracting this charging voltage by superimposing it on the output of the amplifier, the transistor can be operated at a predetermined smoke concentration regardless of variations in the characteristics of the light emitting element and the light receiving element. It is an object of the present invention to provide a photoelectric smoke detector which is adjustable for switching operation.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the present invention. First, the configuration will be described. The circuit configuration consisting of an oscillation circuit 1, a light emitting element 2, a light receiving element 3, an amplifier 4, an alarm circuit 5, and transistors Tr1 and Tr2 is the same as the conventional example shown in FIG.

In addition to this configuration, in the present invention, the output of the oscillation circuit 1 is connected between the variable resistor VR and the resistor _R2 via the resistor _R3 , and the output of the oscillation circuit 2 is connected to the output terminal of the amplifier 4. Allows capacitor C ₀ to be charged. Also, in parallel with the capacitor C ₀ , there is a resistor for discharging the charge of the charged capacitor C ₀ .
R ₀ is connected.

Next, the operation of the above embodiment will be explained.

The oscillation circuit 1 oscillates an output pulse e _P of a predetermined pulse width at each predetermined period. When the output pulse e _P is generated, the transistor Tr1 is turned on and a driving current flows through the light emitting diode 2, and the light emitting diode 2 emits pulsed light. irradiate. The light from the light emitting diode 2 enters the light receiving element 3 as scattered light or attenuated light depending on the concentration of smoke flowing into the smoke detection section, is converted into an electrical signal, and is amplified and output by an amplifier 4.

It should be noted that the amplifier 4 in the embodiment shown in FIG. 3 uses one with low responsiveness, and there is a slight time delay before the detection signal of the light receiving element 3 is amplified and output.

On the other hand, when the oscillation circuit 1 generates an output pulse e _P , this output is applied to the capacitor C 0 via the resistor R ₃ and _{the variable resistor VR to charge the capacitor C 0 .}

To explain in detail the charging operation of the capacitor _C0 by this output pulse _eP , the circuit configuration of the output stage of the amplifier 4 is as shown in FIG.
3 (PNP) and transistor Tr4 (NPN), and at the time when the output pulse _eP is applied to the capacitor _C0 , the amplified output is not yet obtained and the transistor Tr4 is on and Tr3 is off. Therefore, as shown in the equivalent circuit in Figure 5, a capacitor whose power source is the output pulse e _P
A charging path for C ₀ is formed, and the capacitor C ₀ is charged by this charging path.

Next, when the output of the amplifier 4 starts to rise, the transistor Tr3 in FIG. 4 turns on.
Tr4 is switched off, resulting in the formation of the equivalent circuit shown in FIG. That is, as is clear from FIG. 6, the charging voltage Vc of the capacitor C ₀ charged in the state shown in FIG. 5 is superimposed on the output of the transistor Tr3.

FIG. 7 shows the signal waveforms of each part in the embodiment shown in FIG. 3. The amplified output is generated after a predetermined time t _d delay from the output pulse e _P , and during this time the output pulse e _P generates an amplified output. When the capacitor _C0 is charged, the voltage applied to the variable resistor VR is first applied to the capacitor
When the charging voltage V _c of C ₀ is reached and a time t _d elapses, the amplifier output is superimposed on the charging voltage V _c and applied to the variable resistor VR.

Thus, according to the present invention, the capacitor C ₀
Since the light receiving output voltage is increased by the charging voltage V _c , it is possible to modify the characteristic curves C and D shown in FIG. Adjustment can be made using the variable resistor VR so that the transistor Tr2 performs a switching operation when the smoke density is 15%/m.

FIG. 8 shows another embodiment of the present invention.
In the embodiment shown in FIG. 3, an amplifier 4 with low response is used, but in this embodiment, an amplifier with good response is used. Therefore, since there is no time delay in the output of light received by the amplifier 4, the output pulse e _P of the oscillation circuit 1 is delayed to drive the light emitting element 2 with a delay.

That is, at the output end of the oscillation circuit 1, there is a resistor R ₁
A delay circuit 6 consisting of a capacitor C ₁ and a capacitor C 1 is provided, and the light emitting element 2 is connected to the output terminal of an inverter 7 that inverts the output of the delay circuit 6 . The other configurations are the same as the embodiment shown in FIG.

Next, the operation of the embodiment shown in FIG. 8 will be described with reference to FIG. 9 showing signal waveforms of each part.

When oscillator circuit 1 generates an output pulse, the resistor
Capacitor C ₀ is charged via R ₃ and variable resistor VR.

At the same time, the output pulse e _P is applied to the delay circuit 6, and after a delay time t _d , the input of the inverter 7 is brought to H level. Therefore, the output of the inverter 7 becomes L level, and a drive current flows to the light emitting element 2, which irradiates the light emitting element 2 with pulsed light. If smoke has entered the smoke detector, this pulsed light enters the light receiving element 3 and is detected as scattered light or attenuated light by the smoke, and the amplifier 4 produces an output. The voltage that superimposes the charging voltage V _c of C ₀ is the variable resistance VR
will be applied to

As explained above, according to the present invention, the configuration is such that a capacitor provided at the output end of the amplifier is charged by the oscillation output at the time of output from the oscillation circuit, and the charging voltage of this capacitor is superimposed on the output of the amplifier. Since the transistor is switched using the voltage obtained from the smoke, even if there are variations in the light emitting element and light receiving element, the light receiving output characteristics can be adjusted to the operating point for fire detection at a predetermined smoke density. All commercially available light-receiving and light-emitting elements can be used as is, and the circuit is simple, resulting in excellent reliability and cost reduction, which reduces the lifespan of the elements. etc. will not occur.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional photoelectric smoke detector, Fig. 2 is a graph showing the light reception output characteristics with respect to smoke density due to variations in light emitting and light receiving elements, and Fig. 3 is a diagram showing an example of a conventional photoelectric smoke detector. A circuit diagram showing an example,
Figure 4 is a circuit diagram showing the output stage of the amplifier in Figure 3, and Figure 5 is a capacitor using the oscillation output pulse.
A circuit diagram showing an equivalent circuit of the embodiment of Fig. 3 when charging C ₀ , Fig. 6 a circuit diagram showing an equivalent circuit when superimposing the charging voltage of the capacitor C ₀ on the amplified output, and Fig. 7 The figure is a time chart showing the signal waveforms of each part in the embodiment of Fig. 3, Fig. 8 is a circuit diagram showing another embodiment of the present invention, and Fig. 9 is a time chart showing the signal waveforms of each part in the embodiment of Fig. 8. FIG. 3 is a time chart showing signal waveforms. 1... Oscillation circuit, 2... Light emitting element (light emitting diode), 3... Light receiving element (photodiode), 4
...Amplifier, 5...Alarm circuit, 6...Delay circuit,
7... Inverter, Tr1 to Tr4... Transistor, R ₀ to R ₃ ... Resistor, VR... Variable resistor, C ₀ , C ₁
...Capacitor.

Claims (1)

[Claims for Utility Model Registration] An oscillation circuit, a light emitting element that emits light based on the output pulse of the oscillation circuit, a light receiving element that detects scattered light or attenuated light due to smoke of light sent from the light emitting element, and the light receiving element. an amplifier for amplifying the output signal of the
A photoelectric smoker comprising: a resistive voltage divider circuit connected to the output end of the amplifier via a capacitor; and a transistor that performs a switching operation when the output of the amplifier obtained via the resistor voltage divider circuit reaches a set voltage. In the sensor, the output end of the oscillation circuit is connected to the voltage divider circuit so that the capacitor is charged via the voltage divider circuit when the oscillation circuit outputs, and the charging voltage of the capacitor is superimposed on the output of the amplifier. A photoelectric smoke detector characterized by being connected to.