JPH0793677A - Photoelectric type smoke sensor - Google Patents

Abstract

PURPOSE:To prevent a smoke sensing function by the light emission efficiency of a light emitting element from stopping. CONSTITUTION:This photoelectric smoke sensor which is equipped with the light emitting element L and a light receiving element PD and which detects smoke by utilizing the scattering of light radiated from the light emitting element L by light intruding in the cabinet of the photoelectric smoke sensor and the change of received light quantity of the light receiving element PD is provided with a sensitivity deterioration recovering circuit 13 which increases a current on the light emitting element L when the light emission efficiency of the light emitting element L is decreased lower than a prescribed value. Therefore, it is possible to recover the smoke sensing function without exchanging the light emitting element L even when the light emission efficiency of the light emitting element L is deteriorated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric smoke detector that senses smoke by detecting scattered light from the smoke.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit diagram of a conventional photoelectric smoke detector. In the figure, the photoelectric smoke detector is a light emitting circuit 1 including a light emitting element L that emits light in the photoelectric smoke detector housing.
And a light emission control circuit 6 for driving the light emission circuit 1 intermittently.
A photoelectric conversion circuit 2 for receiving scattered light generated by scattering light emitted from the light emitting circuit 1 by smoke and converting it into an electric signal, and a sample for holding an output signal of the photoelectric conversion circuit 2 by sampling A hold circuit 3, a analog output circuit 4 for converting the signal held by the sample hold circuit 3 into an analog output signal, and a sensitivity deterioration determination circuit for determining a decrease in light emission efficiency of the light emitting element L 2 by the output of the photoelectric conversion circuit 2. 5 and.

The light emitting circuit 1 includes a light emitting element L such as a light emitting diode, a switching element (NPN transistor Q1) for driving the light emitting element L, and a light emitting drive circuit 7 for giving a drive signal to the NPN transistor Q1. It consists of a current limiting resistor R1. In order to intermittently drive the light emitting circuit 1, the light emission control circuit 6 divides the signal output from the oscillation circuit 8 by the frequency dividing circuit 9 to create an intermittent drive signal. The light emitting element L is configured to emit light intermittently by the intermittent drive signal.

When smoke enters the photoelectric smoke detector housing,
The light emitted from the light emitting element L 1 is scattered by the smoke and is received by the light receiving element PD included in the photoelectric conversion circuit 2. The photoelectric conversion circuit 2 is a light receiving element PD such as a photodiode.
And a reference voltage source 10 and an amplifier circuit including operational amplifiers A1, A2, A3, A4, resistors R2 to R6, and capacitors C1, C2. When the light receiving element PD is irradiated with light, a weak photocurrent flows. This photocurrent is DC-amplified by the amplifier circuit of the photoelectric conversion circuit 2, and its DC component is cut by the capacitor C2.
It is output to the sample hold circuit 3 which is composed of 7, a capacitor C3, and an electronic switch S which opens and closes according to a control signal. The sample-hold circuit 3 samples the voltage output of the photoelectric conversion circuit 2 when the electronic switch S is in the open state, and when the electronic switch S is in the closed state, the voltage output of the photoelectric conversion circuit 2 in the immediately previous open state. Is a circuit for holding as a voltage across the capacitor C3. The opening / closing timing of the electronic switch S is controlled by the light emission control circuit 6 in accordance with the light emission timing of the light emitting element L, but a detailed description thereof will be omitted here.

The analog output circuit 4 is composed of an operational amplifier A6, resistors R8 to R12, an NPN transistor Q2 and an n-channel MOS transistor Q3, and is a circuit for converting the output of the sample hold circuit 3 into a predetermined output signal.

The sensitivity deterioration determination circuit 5 is composed of a comparison circuit 11 and a counter circuit 12. Comparison circuit 11
Compares the output voltage of the operational amplifier A4 with a certain voltage level and outputs a high level to the counter circuit 12 if the output voltage of the operational amplifier A4 is equal to or lower than the voltage level. The counter circuit 12 is configured to count the number of times a high-level signal is generated and output a high-level signal when the number of times reaches a predetermined number. The switching element (n-channel MOS transistor Q3) is turned on by the high-level output signal of the counter circuit 12, the offset voltage becomes 0V, and the output of the analog output circuit 4 becomes 0V. By monitoring the output of the analog output circuit 4 with a receiver (not shown), a decrease in the luminous efficiency of the light emitting element L due to deterioration is detected.

[0007]

However, in the circuit shown above, when the luminous efficiency of the light emitting element L decreases,
Until the light emitting element L is replaced, the output from the photoelectric smoke detector to the receiver remains at 0V, so the smoke sensing function stops.

The present invention has been made in view of the above problems, and an object thereof is to provide a photoelectric sensor capable of recovering the smoke sensing function without replacing the light emitting element when the light emitting efficiency of the light emitting element is lowered. The purpose is to provide a structure for a smoke detector.

[0009]

In order to solve the above problems, the photoelectric smoke detector according to claim 1 comprises a light emitting element and a light receiving element, and the light emitted from the light emitting element is photoelectric smoke. In a photoelectric smoke detector that detects smoke by utilizing the fact that the amount of light received by the light receiving element changes due to scattering by light that has entered the housing of the sensor, the luminous efficiency of the light emitting element has dropped below a predetermined value. In this case, a sensitivity deterioration repair circuit for increasing the amount of current flowing through the light emitting element is provided.

According to another aspect of the photoelectric smoke detector of the present invention, a light emitting circuit having a light emitting element for emitting light in a photoelectric smoke detector housing, and a light emission control circuit for intermittently driving the light emitting circuit. , A photoelectric conversion circuit for receiving scattered light of smoke emitted from the light emitting circuit and converting it into an electric signal, a sample hold circuit for sampling and holding an output signal of the photoelectric conversion circuit, and a sample hold circuit In a photoelectric smoke detector including an analog output circuit for converting the held signal into an analog output signal, and a sensitivity deterioration determination circuit for monitoring the output of the photoelectric conversion circuit and determining a decrease in light emission efficiency of the light emitting element A sensitivity deterioration repair circuit for monitoring the output of the sensitivity deterioration determination circuit and increasing the amount of current flowing through the light emitting element when the light emission efficiency falls below a predetermined value is provided. And it is characterized in and.

[0011]

In the photoelectric smoke detector of the present invention, the sensitivity deterioration repair circuit 13 is a resistor provided in parallel with the resistor R1 of the light emitting circuit 1.
It is composed of a series circuit of R13 and n-channel MOS transistor Q4. When the light emitting element L deteriorates and the luminous efficiency decreases, the counter circuit 12 outputs a high level to the gate of the n channel MOS transistor Q4 of the sensitivity deterioration repair circuit 13, so that the n channel MOS transistor Q4 is turned on. As a result, assuming that the resistance values of the resistors R1 and R13 are equal, the resistance value between the emitter and the ground of the NPN transistor Q1 is reduced to about 1/2, and the current flowing through the light emitting element L is increased. It is possible to prevent a decrease in the amount of emitted light.

[0012]

1 is a circuit diagram of an embodiment of the photoelectric smoke detector of the present invention. The same components as those of the conventional circuit will be denoted by the same reference numerals and detailed description thereof will be omitted. Below, only different parts from the conventional circuit will be described.

The light emitting circuit 1 includes a resistor R13 and an n channel M.
The series circuit of the OS transistor Q4 is the sensitivity deterioration repair circuit 1
3 is provided in parallel with the resistor R1. Here, it is assumed that the resistors R1 and R13 are both resistors having a resistance value R. The gate of the n-channel MOS transistor Q4 is connected to the output of the counter circuit 12 provided in the sensitivity deterioration determination circuit 5. When the light emitting element L has not deteriorated and the count value of the counter circuit 12 has not reached the predetermined value, the gate of the n-channel MOS transistor Q4 has L
An ow level signal is given. Therefore, n channel M
The OS transistor Q4 remains off, and the resistance value between the emitter of the NPN transistor Q1 and the ground is R. At this time, the base voltage of NPN transistor Q1 is Vb,
If the emitter-to-emitter voltage is 0.7V, NPN transistor Q1
The collector current Ic of, that is, the drive current of the light emitting element L is
Ic = (Vb-0.7) / R.

Next, when the light emitting efficiency of the light emitting element L decreases and the counter circuit 12 counts a predetermined count number, a high level signal is output to the gate of the n channel MOS transistor Q4. This allows n-channel MO
S-transistor Q4 turns on and NPN transistor
The resistance value between the emitter of Q1 and ground changes to about 1 / 2R. The collector current Ic at this time is Ic = (Vb-0.7) / (1 / 2R) = 2
It becomes (Vb-0.7) R, which is twice as high as that before the light emitting efficiency of the light emitting element L is lowered. Here, the comparison circuit 11 is set to High when the light emission amount of the light emitting element L is reduced to 1/2 of the initial state.
When the level signal is set to be output, after the luminous efficiency of the light emitting element L is lowered, the amount of current for driving the light emitting element L is almost double that before deterioration, so that the light emitting amount of the light emitting element L is It is almost doubled, and it is possible to repair the decrease in the light emission amount due to the decrease in the light emission efficiency of the light emitting element L 1.

Since the smoke detection function can be restored by constructing the light emitting circuit 1 as described above, FIG.
The analog output circuit 4 of the conventional circuit shown in
An n-channel M that was connected between the non-inverting input of A6 and ground and had its gate connected to the output of the counter circuit 12.
Except for the OS transistor Q3, the analog output signal from the photoelectric smoke detector to the receiver does not become 0V when the light emitting element L deteriorates.

The circuit configurations of the amplifier circuit of the photoelectric conversion circuit 2, the sample hold circuit 3, and the analog output circuit 4 are not limited to the circuits shown in the embodiments. The switching elements such as the n-channel MOS transistor and NPN transistor are not limited to those shown in the embodiments.

[0017]

As described above, according to the photoelectric smoke detector of the present invention, the luminous efficiency of the light emitting element is lowered by providing the sensitivity deterioration repair circuit for increasing the amount of current flowing through the light emitting element. Even in this case, it is possible to automatically prevent a decrease in the amount of emitted light and restore the smoke sensing function.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a photoelectric smoke detector according to the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional photoelectric smoke detector.

[Explanation of symbols]

 1 Light emitting circuit 2 Photoelectric conversion circuit 3 Sample hold circuit 4 Analog output circuit 5 Sensitivity deterioration determination circuit 6 Light emission control circuit 7 Light emission drive circuit 8 Oscillation circuit 9 Dividing circuit 10 Reference voltage source 11 Comparison circuit 12 Counter circuit 13 Sensitivity deterioration repair circuit

Claims (2)

[Claims] 1. A light emitting device and a light receiving device are provided, wherein light emitted from the light emitting device is scattered by light that has entered the photoelectric smoke detector housing, and the amount of light received by the light receiving device is changed. In a photoelectric smoke detector that detects smoke by utilizing smoke, a sensitivity deterioration repair circuit that increases the amount of current flowing through the light emitting element when the light emitting efficiency of the light emitting element is lower than a predetermined value is provided. Photoelectric smoke detector that does. 2. A light emitting circuit having a light emitting element for emitting light, a light emission control circuit for intermittently driving the light emitting circuit, and a light emitted from the light emitting circuit in a photoelectric smoke detector housing. A photoelectric conversion circuit that receives scattered light from smoke and converts it into an electrical signal, a sample hold circuit that samples and holds the output signal of the photoelectric conversion circuit, and converts the signal held by the sample hold circuit into an analog output signal In the photoelectric smoke detector, the output of the sensitivity deterioration determination circuit is monitored in a photoelectric smoke detector including an analog output circuit for monitoring the output of the photoelectric conversion circuit and a sensitivity deterioration determination circuit for determining a decrease in luminous efficiency of the light emitting element. Then, the photoelectric smoke detector is provided with a sensitivity deterioration repair circuit for increasing the amount of current flowing through the light emitting element when the light emission efficiency falls below a predetermined value.