JPH0418076Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention includes a light projecting means and a light receiving means, and the light receiving means is provided with light emitting means according to the presence or absence of smoke particles in a space irradiated with light from the light projecting means. The present invention relates to a photoelectric smoke sensor that detects the presence or absence of smoke particles based on changes in the amount of received light.

[Background Art] As this type of photoelectric smoke detector, one having a configuration as shown in FIG. 1 has been considered. The light projecting means 1 is configured to turn on and off the current flowing to the light emitting diode LED using a driving transistor _Q1 in order to project pulsed light P having a predetermined period. Smoke particles are introduced into the space into which the pulsed light P from the light projecting means 1 is projected, and the light receiving means 2 detects changes in the amount of light depending on the presence or absence of smoke particles to control the load. It's summery.

That is, the light receiving means 2 is a photodiode.
It is a PD that converts changes in light intensity into current output.
The output of the light receiving means 2 is constructed by adding resistors R ₄ to _{R 6} and capacitors C _{1 and C 2 to a three-stage directly connected negative feedback amplifier consisting of transistors Q 2 to Q 4} and resistors R ₁ to R ₃ . As a result, the pulse current i ₀ output from the photodiode PD is amplified as a direct current, and its alternating current component is the current value of the pulse current i ₀ multiplied by a predetermined constant. It is converted into a voltage signal V ₁ having a voltage value. That is, V ₁ =
(R ₅ × R ₆ / R ₄ ) × i becomes ₀ . This voltage signal is input to the amplifier 4. Amplifier 4 is a transistor
It is composed of _Q5 , _Q6 , resistors _R7 to _R9 , and capacitor _C3 . In the amplifier 4, the input signal is current-amplified by the emitter follower amplifier equipped with the transistor _Q5 , and the DC component of the output from the connection point between the emitter of the transistor _Q5 and the resistor _R7 is connected to the capacitor _C3 .
and input it to the base as the control terminal of transistor _Q6 , which is a switching element for load control. That is, due to the AC component Vs (≒V ₁ ) of the output of the emitter hollow amplifier, the transistor Q ₆
It turns on and off.

The signal waveforms of each part of the circuit in FIG. 1 are as shown in FIG. 2. Here, we assume a scattered light type photoelectric smoke detector in which the light receiving means 2 receives the light scattered by smoke particles from the light projecting means 1, and smoke is generated at time t ₀ . Then, from now on, the amplifier 4
It is now possible to obtain a large current voltage Vs (more than 0.6V) that can turn on transistor _Q6 .

By the way, this kind of photoelectric smoke detector requires the concentration of smoke particles when the transistor Q ₆ is turned on,
That is, it is necessary to provide means for adjusting the sensitivity. That is, a sensitivity adjustment means is required to adjust variations among products and adjust sensitivity depending on the purpose of use. In the configuration shown in FIG. 1, the light projecting means 1 includes a light emitting diode.
A sensitivity setting volume VR′ connected in series with the LED is used as a sensitivity adjustment means. That is, the sensitivity is adjusted by adjusting the luminance of light emitted from the light projecting means 1.

Here, in the above configuration, for the purpose of setting low sensitivity or suppressing power consumption, the luminance of the light emitting means 1 may be lowered, or the light emitting means 2 may be lowered due to the optical system of the light emitting means 1 or the light receiving means 2 When the amount of incident light is reduced, the output current i ₀ of the light receiving means 2 becomes smaller, and the constant (=R ₆ ×
R ₅ /R ₄ ) must be set to a large value. However, if this constant value is increased, there is a problem that the operation becomes unstable, and the degree of amplification of the internal noise of the current-voltage converter 3 increases, increasing the possibility of malfunction due to noise components. A problem arises. Furthermore, since a relatively large current flows through the light projecting means 1, the sensitivity setting volume
Adjusting VR′ changes the power consumption as a whole, and the power consumption varies from sensor to sensor. In addition, the sensitivity setting volume
VR' is required to have a relatively low resistance value (about 10 to 20 Ω), and there is also the problem that using such a special variable resistor leads to an increase in size.

[Purpose of invention]

The present invention has been developed in view of the above points, and its purpose is to calculate the constant value by which the current value is multiplied in the current-voltage converter even when the output current of the light receiving means is small. There is no need to set it too high, malfunctions due to noise components are less likely to occur, and the sensitivity can be adjusted without adjusting the current flowing to the light emitting means, thereby reducing the consumption when adjusting the sensitivity. Sensitivity can be adjusted without attenuating the signal by preventing large fluctuations in power and adjusting the negative feedback amount of the amplifier installed after the current-voltage converter. An object of the present invention is to provide a photoelectric smoke detector in which an increase in noise is prevented in this way.

[Disclosure of invention]

In the light projecting means 1, the sensitivity setting volume VR' was connected in series to the light emitting diode LED in the configuration shown in FIG. 1, but in the configuration of this embodiment, it is replaced with a fixed resistor Ra as shown in FIG. . Therefore, the brightness of the pulsed light output from the light projecting means 1 when turned on is constant. On the other hand, the output current of the light receiving means 2 is converted into a voltage signal by a current-voltage converter 3 similar to the configuration shown in FIG. The amplification degree of the amplifier 4 can be adjusted at a relatively low amplification degree of about 2 to 5 times using a sensitivity setting volume VR. That is,
The emitter of transistor _Q5 is connected to the positive terminal of the power supply through a parallel circuit of resistor _R7 and capacitor _C4 , and a series circuit with a sensitivity setting volume VR, and the collector of transistor _Q5 is connected to the positive pole of the power supply through resistor _R10 . The voltage signal from the current-voltage converter 3 is input to the base of the transistor _Q5 . Collector and resistor of transistor Q ₅
The connection point with _R10 is the switching element transistor _Q6 via the DC blocking capacitor _C3 .
connected to the base of Also, transistor _Q6
A resistor _R9 is connected in parallel between the base and emitter of. Therefore, ignoring the impedance of capacitor _C3 , the amplification degree of amplifier 4 is _R9 .
R ₁₀ / (R ₉ + R ₁₀ )・VR. That is, by adjusting the sensitivity setting volume VR, the amount of negative feedback in the amplifier 4 changes, and the degree of amplification is adjusted.

According to this configuration, the luminance of the light emitting means 1 may be lowered for the purpose of setting low sensitivity or suppressing power consumption, or the light emitting brightness of the light emitting means 1 or the light receiving means 2 may be lowered due to the optical system of the light emitting means 1 or the light receiving means 2. Even if the output current i ₀ of the light receiving means 2 becomes small by reducing the amount of incident light, the amplifier 4 performs amplification even if the degree of amplification is low. As a whole, it is possible to secure an amplification degree sufficient to turn on transistor _Q6 . In other words, in the current-voltage converter 3, there is no need to set the constant (=R ₆ × R ₅ /R ₄ ) by which the current value is multiplied to a large value, and unstable operation can be prevented. - There is no increase in amplification for internal noise of the voltage converter 3, and malfunctions due to noise components can be prevented. Moreover, the sensitivity setting volume VR adjusts the degree of amplification by changing the amount of negative feedback in the amplifier 4, which is downstream of the current-voltage converter 3 and receives a relatively high voltage. Therefore, there is no input voltage attenuation element, and if the internal noise of the amplifier 4 is kept constant, a large signal-to-noise ratio can be achieved. In this way, by increasing the overall amplification degree on the light receiving side, the output current of the light receiving means 2 can be reduced, so the luminance of the light emitting means 1 can be lowered, and the consumption This leads to power consumption reduction. Furthermore, since the light projecting means 1 is not provided with a sensitivity setting volume, there is little change in power consumption due to sensitivity adjustment, and variations in power consumption from sensor to sensor can be suppressed.

[Effect of idea]

As described above, the present invention includes a relatively low amplification amplifier that amplifies the voltage after converting the current output of the light receiving means into a voltage signal by a current-voltage converter,
This amplifier has a transistor with a sensitivity setting volume inserted between the emitter and one pole of the power supply, a resistor inserted between the collector and the other pole of the power supply, and a DC current at the connection point between the collector and the resistor. Since it is equipped with a load control switching element whose control terminal is connected via a blocking capacitor, even if the output current of the light receiving means is small, the overall increase is sufficient to turn on the switching element. This makes it possible to ensure width. That is, the current-voltage converter can be used in a stable operating range, and the ratio of the output voltage signal to the internal noise can be increased. Furthermore, since the sensitivity is adjusted by adjusting the amount of negative feedback of the amplifier using the sensitivity setting volume, the sensitivity can be adjusted without including the attenuation element of the input voltage to the amplifier. If the internal noise of the amplifier is kept constant, the signal-to-noise ratio can be increased and malfunctions due to noise can be prevented. Furthermore, by increasing the amplification degree on the light receiving side,
Since the output current of the light receiving means can be reduced, the luminance of the light emitting means can be lowered, which leads to a reduction in power consumption. Further, since the light projecting means is not provided with a sensitivity setting volume, there is an advantage that there is little change in power consumption due to sensitivity adjustment, and variations in power consumption from sensor to sensor can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is an explanatory diagram of the same operation as above, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 1 is a light emitting means, 2 is a light receiving means, 3 is a current-voltage converter, 4 is an amplifier, C ₃ is a capacitor, Q ₅ , Q ₆
is a transistor, _R10 is a resistor, and VR is a sensitivity setting volume.

Claims (1)

[Scope of utility model registration request] A light projection means that emits pulsed light of a predetermined period with a fixed light intensity set when emitting light, and converts changes in light intensity depending on the presence or absence of smoke particles in the space where the pulsed light is projected into a current output. a current-voltage converter that converts the current output of the light receiving means into a voltage signal having a voltage value obtained by multiplying the current value by a predetermined constant;
It is a relatively low amplification amplifier that amplifies the voltage of the output of the current-voltage converter.The amplifier has a sensitivity setting volume inserted between the emitter and one pole of the power supply, and the collector and the amplifier. It comprises a transistor with a resistor inserted between it and the other pole of the power supply, and a switching element for load control whose control terminal is connected to the connection point between the collector and the resistor via a DC blocking capacitor. Photoelectric smoke detector.