JPS6217641A - Smoke sensor - Google Patents

Abstract

PURPOSE:To perform the stable detection of smoke with high accuracy, by controlling light emitting quantity by feeding back the detection level by a light receiving element directly receiving the light emitted from a light emitting element provided to the outside of a light receiving element receiving reflected light due to smoke. CONSTITUTION:A phototransistor (PTR)2 arranged at a position always directly receiving the light emitted from a light emitting diode (LED)1 and a PTR3 arranged at a position where the light emitted from LED1 is hardly incident under normal state but light reflected by smoke at the time of the generation of smoke is incident are incorporated in a circuit and the signal by PTR3 is inputted to a comparator 71 to be compared with reference voltage 72 and outputted as a smoke sensing signal. The signal by PTR2 is inputted to an OP amplifier 81 to be fed back to LED1 and the light emitting quantity of LED1 is automatically regulated so as to make the signal by PTR3 constant. By this method, the stable sensing of smoke can be performed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a smoke detection sensor formed by a combination of a light emitting element and a light receiving element.

<Summary of the Invention> In order to eliminate the influence of temperature fluctuations on the light-receiving element of a smoke detection sensor and the influence of output deterioration of the smoke detection sensor, the present invention separately provides a light-receiving element that directly receives the light emitted from the light-emitting element. The amount of light emitted from the light emitting element is automatically adjusted by feeding back the signal from the light receiving element.

<Prior Art> The structure of a conventional smoke detection sensor is shown in FIG. 4. A light emitting diode 1 and a phototransistor 2 for detecting light emitted from the light emitting diode 1 reflected by smoke are connected to a light shielding plate 3.
is located through.

The signal detected by the phototransistor is converted into a current and a voltage as shown in the circuit diagram of FIG.
becomes. This signal v1 and the reference voltage E are connected to a comparator 4.
An output signal v□ is obtained by comparing the values. The presence or absence of smoke is detected based on the state of this output signal V(,. The amount of light reflected by the smoke and the amount of smoke are proportional to each other. Therefore, the signal 1 and the reference voltage E are compared as described above. It is also possible to detect the amount of smoke.

However, the output of the phototransistor 2 was affected by fluctuations in ambient temperature and deterioration of the light emitting diode 1, and varied as shown in the following equation.

V/, -α・β・■1...(1) However, v'1: Phototransistor output voltage when there is a change in ambient temperature or deterioration of the light emitting diode.

■l: Phototransistor output voltage when there is no fluctuation in ambient temperature or deterioration of the light emitting diode.

α: Coefficient of variation of output value due to temperature fluctuation β: Coefficient of variation of output value due to deterioration of light emitting diode (problem to be solved by the invention) In the above conventional configuration, as shown in the signal waveform diagram of FIG. When fluctuations occur or deterioration of the light emitting diode occurs, the voltage level of the output voltage Vl changes as shown by the broken line due to fluctuations in the optical output current of the phototransistor 2, and the relative relationship with the reference voltage E shifts. The output voltage ■o also changed as shown by the broken line. That is, the smoke detection standard fluctuates by A, and in the worst case, the output voltage V□ remains at the H level or L level without being inverted, resulting in cases in which the presence or absence of smoke cannot be detected at all.

On the other hand, as shown in FIG. 7, two photodiodes PDI receive the light from the light emitting diode 1 in the same way.

In a smoke detection sensor incorporating PO2, the output voltage (1) of the OP amplifier 5 is expressed by the following equation.

However, I1: Current flowing through the phototransistor PDI I2: Current flowing through the photodiode PD2The output voltage V1 of the OP amplifier 5 is affected by fluctuations in the ambient temperature and deterioration of the light emitting diode 1, and changes as shown in the following equation. .

× (α・β・II −α・β・j2)R+X
(1+-12)R+ -α・β・■1 However, ■!
= Output of OP amplifier 5 when ambient temperature fluctuates or light emitting diode deteriorates A smoke detection sensor incorporating two photodiodes PDI and PD2 that receive light in the same manner was also affected by fluctuations in ambient temperature and deterioration of the light emitting diodes.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a light emitting element,
A first light receiving element is arranged at a position where the light emitted from the light emitting element always enters, and a first light receiving element is arranged at a position where the light emitted from the light emitting element always enters. a second light-receiving element disposed at a position where the light enters; a signal comparison circuit that compares a signal obtained by light reception by the second light-receiving element with a reference signal to obtain a smoke detection signal; The smoke detection sensor is equipped with a light emission amount correction circuit that feeds back a signal obtained by light reception by the light receiving element to the light emitting element to automatically adjust the light emission amount of the light emitting element.

<Example> Fig. 1 is a circuit diagram showing the principle of the device of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the device of the present invention, Fig. 3 (A),
(B) and (C) are diagrams showing examples of arrangement of a light emitting element and two light receiving elements, respectively.

In FIG. 1, there is a first phototransistor 2 arranged at a position where the light emitted from the light emitting diode 1 directly enters at all times, and a first phototransistor 2 which is placed at a position where the light emitted from the light emitting diode 1 is always directly incident, and a first phototransistor 2 which is placed at a position where the light emitted from the light emitting diode 1 is always directly incident. A second phototransistor 3 disposed at a position where light reflected by smoke enters is incorporated into the circuit, and the signal from the second phototransistor 3 is passed through a comparison circuit 7 with a reference signal. Output as smoke detection information. On the other hand, the signal from the first phototransistor 2 is fed back to the light emitting diode 1 via the light emission amount correction circuit 8, and the light emission amount of the light emitting diode 1 is automatically adjusted so that the signal from the first phototransistor 3 is constant. . That is, in the present invention, the first phototransistor 2 is used for adjusting the amount of light emitted from the light emitting diode l. By doing so, it is possible to eliminate changes in the amount of light emitted due to deterioration of the light emitting diode 1 or temperature fluctuations.

FIG. 2 shows an example of a circuit actually used. Assuming that the optical output current from the first phototransistor 2 is 1sc and the driving current of the light emitting diode 1 is IF, the optical output current 1sc from the first phototransistor 2 is converted into a voltage and becomes a voltage Vt (-Isc-VR). The voltage is input to the OP amplifier 81 as a signal, and is operationally amplified to become the base voltage of the transistor 82. Therefore, ■ When 10 becomes smaller, the drive current IF
increases inversely proportionally, and as V+ increases, IF decreases by inverse comparison. Therefore, the amount of light emitted from the light emitting diode 10 is always kept constant. The optical output current from the second phototransistor 3 is converted into a current voltage and passed through a comparator 71.
It is compared with a reference voltage 72 and output as a smoke detection signal.

Figure 3 shows a light emitting diode l and a first phototransistor 2.
, which shows an example of the arrangement of the second phototransistor 3. In the example of (A), the first phototransistor 2 is arranged at a position facing the light emitting diode 1, and the second phototransistor 3 is placed in a position facing the light emitting diode 1. It is placed in a shielded position where it cannot be directly accessed. When smoke S is generated, light reflected by the smoke S enters the second phototransistor 3. In example (B), the arrangement of the second phototransistor 3 is the same as in example (A), but the first phototransistor 2 is placed very close to the light emitting diode 1 to avoid the influence of smoke. What makes it so? In addition, in the example (C), the first
This is an example in which light from a light emitting diode l is made incident on a phototransistor 2.

Note that in the examples of FIGS. 1 and 2, 1. Instead of the second phototransistor 2.3, the first . A second photodiode can be used. In this case, since the photodiode has small variations in optical characteristics, the first. The influence between the second photodiodes can be reduced. Therefore, more accurate temperature compensation and output deterioration compensation can be performed.

Effects> The present invention has the above-described configuration, and includes a light receiving element that directly receives the light emitted from the light emitting element, and the detection level by the light receiving element is fed back to the light emitting element to automatically adjust the amount of light emitted. Therefore, it is possible to reliably compensate for output deterioration and temperature fluctuations of the light emitting element and maintain a constant amount of light emission at all times. Therefore, highly accurate and stable smoke detection can be performed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the principle of the device of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the device of the present invention, Fig. 3 (A),
(B) and (C) are diagrams each showing an example of the arrangement of a light emitting element and two light receiving elements, Figure 4 is a side view of a conventional smoke detection sensor, Figure 5 is its circuit configuration diagram, and Figure 6 is its The signal waveform diagram in FIG. 7 is a circuit configuration diagram of a conventional smoke detection sensor. l...Light emitting diode 2...First phototransistor 3...Second phototransistor 7...Comparison circuit 8...Emission amount correction circuit Patent applicant Sharp Corporation Agent Patent attorney Nishi 1) New Figure 3, Figure 4, Figure 5

Claims (1)

[Claims] A light emitting element, a first light receiving element disposed at a position where the light emitted from the light emitting element always enters, and a first light receiving element where the light emitted from the light emitting element is difficult to enter at all times, but is reflected by smoke when smoke is generated. a second light-receiving element disposed at a position where the received light enters; a signal comparison circuit that compares a signal obtained by the reception of light by the second light-receiving element with a reference signal to obtain a smoke detection signal; A smoke detection sensor comprising: a light emission amount correction circuit that feeds back a signal obtained by light reception by the first light receiving element to the light emitting element to automatically adjust the light emission amount of the light emitting element.