JP2746078B2 - Photoelectric smoke detector - Google Patents

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 for detecting smoke by detecting light scattered by smoke.

[0002]

2. Description of the Related Art A photoelectric smoke detector according to the present invention includes a light emitting element and a light receiving element.
It is a type that outputs an analog signal. FIG. 2 shows an example of a circuit diagram of a conventional photoelectric smoke detector. In the figure,
Reference numeral 1 denotes a light emitting element driving circuit which is controlled by a control circuit 4 described later to cause the light emitting element L to emit light intermittently. The transistor Q is a switching element that is opened and closed by the light emitting element drive circuit 1, and the resistor R1 is a current limiting resistor.

[0003] Reference numeral 2 denotes a three-stage amplifier circuit which converts a photocurrent output from the light receiving element PD such as a photodiode according to the amount of received light into a voltage signal and amplifies the voltage signal. The DC component of the voltage signal output from the three-stage amplifier circuit 2 is cut by the capacitor C1 and input to the sample and hold circuit 3.

The sample hold circuit 3 is a circuit for temporarily holding a voltage signal output from the three-stage amplifier circuit 2,
An operational amplifier A1 as a first buffer circuit, an operational amplifier A2 as a second buffer circuit, a transistor switch S1 as a first transistor switch and a first resistor connected between the output of the operational amplifier A1 and the input of the operational amplifier A2. It comprises a series circuit of a resistor R2 and a capacitor C1 connected between the input of the operational amplifier A2 and ground. The open / close state of the transistor switch S1 is controlled by a control circuit described later. The sample hold circuit 3 samples the input voltage when the transistor switch S1 is in the closed state, and holds the sampled voltage signal as the voltage across the capacitor C2 when the transistor switch S1 is in the open state. The resistors R3 and R4 are circuits for adding an offset voltage to the voltage signal input to the sample and hold circuit 3, and the capacitor C3 is provided for stabilizing the offset voltage. The voltage signal held and output by the sample and hold circuit 3 is converted into a predetermined voltage signal by an analog output circuit 4 at the next stage, and is output to a receiver (not shown) of the disaster prevention system.
However, in order not to react to temporary smoke such as cigarette smoke,
The resistance value of the resistor R2 of the sampling and holding circuit 3 is set to a relatively large value so that it is possible to detect smoke several times and determine that smoke due to a fire has occurred. Are not charged sufficiently. By configuring the sampling and holding circuit 3 in this way, the smoke signal is detected several times, and the capacitor C2 is sufficiently charged. A signal can be output.

The control circuit 5 sends an intermittent drive signal to the light emitting element drive circuit 1 to cause the light emitting element L to emit light intermittently, and controls the transistor switch S1 provided in the sample and hold circuit 3 to control the sample and hold circuit. 3 is a circuit for switching operation.

Reference numeral 6 denotes a power supply circuit which generates a necessary voltage from an external power supply (not shown) connected to the power input terminals A and B and supplies it to each circuit.

[0007] The operation of the photoelectric smoke detector configured as described above will be described below. When smoke enters the inside of the photoelectric smoke detector, the radiated light of the light emitting element L which emits light intermittently is scattered by the smoke. The light receiving element PD outputs a photocurrent according to the amount of the scattered light. The photocurrent is a three-stage amplifier 2
The signal is converted into a voltage signal, held in the sample hold circuit 3, and output from the analog output circuit 4 to the receiver. The receiver is configured to determine the signal level output from the photoelectric smoke detector and detect the occurrence of a fire.

[0008]

The circuit shown above is:
The output of the three-stage amplifier 2 is sampled and held by the time constant of the resistor R2 and the capacitor C2, and an analog output is output from the analog output circuit 4. In this case, as described above, in order to prevent malfunction due to cigarette smoke or the like, the resistance value of the resistor R2 is set to a relatively large value, and the time constant of the capacitor C2 and the resistor R2 is set to a relatively large value. Therefore, when actually putting smoke into the photoelectric smoke detector and performing an operation test of the photoelectric smoke detector, etc., the smoke must be kept on for a certain period of time, that is, the time required for several intermittent flashes. Therefore, the operation test takes a long time, and when the number of photoelectric smoke detectors is large, the operation test is very troublesome.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a structure of a photoelectric smoke detector which can easily perform an operation test of the photoelectric smoke detector.

[0010]

In order to solve the above-mentioned problems, a photoelectric smoke detector according to the present invention detects scattered light due to smoke, converts the light signal into a voltage signal, and converts the voltage signal into a voltage signal.
A first buffer circuit (the operational amplifier A1), a second buffer circuit (the operational amplifier A2), and a first buffer circuit connected between the output of the first buffer circuit (the operational amplifier A1) and the input of the second buffer circuit (the operational amplifier A2). A sample-and-hold circuit 3 including a series circuit of a transistor switch (transistor switch S1) and a first resistor (resistance R2), and a capacitor (capacitor C2) connected between the input of the second buffer circuit (op-amp A2) and ground. And a second transistor switch (transistor switch S2) and a second resistor (resistance R) in parallel with the first resistor (resistance R2) of the sample and hold circuit 3.
It is characterized in that the series circuit of 5) is provided.

[0011]

[Operation] During the operation test, by closing the transistor switch S1 of the sample-and-hold circuit 3, the resistance between the transistor switch S1 and the non-inverting input of the operational amplifier A2 becomes the resistance of the parallel circuit of the resistors R2 and R5. Since the capacitor C2 is charged faster than in the normal operation,
The reaction operation of the photoelectric smoke detector can be accelerated.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the photoelectric smoke detector according to the present invention will be described with reference to FIG. The same components as those of the conventional circuit are denoted by the same reference numerals, and detailed description is omitted.

The photoelectric smoke detector of the present invention comprises a light emitting element L
A series circuit of a transistor Q as a switching element and a current limiting resistor R1 is driven by the light emitting element driving circuit 1 to cause the light emitting element L to emit light intermittently. When smoke enters the inside of the photoelectric smoke detector, the emitted light of the light emitting element L is scattered by the smoke. The light receiving element PD outputs a photocurrent according to the amount of the scattered light. The photocurrent is converted into a voltage signal by the three-stage amplifier 2 and amplified. Further, the DC component is cut by the capacitor C1, is held in the sample and hold circuit 3, is converted into a predetermined analog signal by the analog output circuit 4, and is output to a receiver (not shown). The receiver is configured to determine the signal level output from the photoelectric smoke detector and detect the occurrence of a fire.

As shown in the drawing, the photoelectric smoke detector according to the present invention is different from the conventional example in that the sample and hold circuit 3
, A transistor switch S2 as a second transistor switch and a resistor R5 in parallel with a resistor R2 as a first resistor.
This is the point that a series circuit is added.

During normal operation, the transistor switch S2 is set to an open state. In this state, the charging current of the capacitor C2 is limited by the resistor R2, and the capacitor C2 operates as in the conventional example. At the time of the operation test, the transistor switch S2 is set to the closed state, and a smoke test is conducted in which smoke is actually injected into the photoelectric smoke detector. By closing the transistor switch S2, the resistance between the transistor switch S2 and the non-inverting input of the operational amplifier A2 as the second buffer circuit becomes
Since the resistance is a parallel combined resistance value of the resistance R2 and the resistance R5, the capacitor C2 is charged faster than in the normal operation. Thus, the transistor switch of the sample and hold circuit 3
By switching S2, the time constant of the sample and hold circuit 3 can be reduced, the response to the signal level can be increased, the speed of smoke detection can be increased, and the time required for the operation test can be reduced.

[0016]

As described above, according to the photoelectric smoke sensor of the present invention, the time constant of the sample and hold circuit is made smaller than that in the normal operation during the operation test, and the response of the photoelectric smoke sensor is reduced. , The operation test time can be shortened and the test can be facilitated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one 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]

L Light emitting element PD Light receiving element A, B Power input terminal A1 Operational amplifier (first buffer circuit) A2 Operational amplifier (second buffer circuit) S1 transistor switch (first transistor switch) S2 transistor switch (second transistor switch) R2 resistor (second 1 resistor) R5 resistor (second resistor) C2 capacitor 1 light emitting element drive circuit 2 three-stage amplifier circuit 3 sample hold circuit 4 analog output circuit 5 control circuit 6 power supply circuit

Claims (1)

(57) [Claims] 1. A method for detecting light scattered by smoke, converting an optical signal into a voltage signal, and converting the voltage signal into a first buffer circuit, a second buffer circuit, an output of the first buffer circuit and a second buffer circuit. A sample and hold circuit including a series circuit of a first transistor switch and a first resistor connected between the inputs of the buffer circuit and a capacitor connected between the input of the second buffer circuit and the ground outputs the data. A photoelectric smoke sensor, wherein a series circuit of a second transistor switch and a second resistor is provided in parallel with the first resistor of the sample and hold circuit.