JPS6141040B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a detection signal processing circuit for a photoelectric smoke detector, in which the photoelectric smoke detector detects sudden and high-energy noise among disturbance noises caused by light, electricity, etc. and respond to this with
This can cause false alarms, so it is necessary to perform a delayed response operation in response to the input signal, or in other words, provide a certain amount of judgment period for the input signal to detect only the original signal caused by smoke during a fire. The purpose is to generate alarms with low power consumption.

Conventionally, in the detection signal processing circuit of this type of photoelectric smoke detector, the output pulse is determined only by the threshold level, but if even one noise exceeds this threshold level, a false alarm will occur. In addition, the sensor body has a structure that completely shields the ambient light, so the inflow of smoke becomes poor.

In view of these problems, this invention does not operate with a single pulse, but outputs only after several pulses, and smoke is generated from the light source driven by the light emitting pulse circuit. In photoelectric smoke detectors, a light-receiving element receives scattered light from particles, and a switching circuit detects an increase in current as the electrical resistance of the light-receiving element decreases. Level detection circuits, one-shot circuits, and CR time constant circuits are used. The present invention relates to a detection signal processing circuit for a photoelectric smoke detector, which includes an output circuit, a switching circuit, a switching reset circuit, and a discharge circuit.

Specific embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 will be explained. X, Y are the light emitting part and light receiving part of the photoelectric smoke detector, 1 is the level detection circuit,
2 is one shot circuit, 3 is CR time constant circuit, 4
5 is an output circuit, 5 is a discharge circuit, 6 is a switching circuit, and 7 is a switching reset circuit. The one-shot circuit 2 operates in the same way as a monostable multivibrator, and outputs only one pulse for a fixed period of time in response to a single trigger signal. The switching circuit 6 and the switching reset circuit 7 operate as RS flip-flops using transistors Q6 and Q7, and a set signal is generated by turning on the transistor Q2, and a reset signal is generated by turning on the transistor Q4. The output of the switching circuit 6 is the collector of the transistor Q5, and becomes L when the transistor Q2 is on, and becomes H when the transistor Q4 is on. This output controls the transistor Q3 of the discharge circuit using diodes d3 and d2. First, when the output is L, the diode d3 is turned on, so the voltage at point B is 0.7 [V], which divides the voltage between the diode d2 and the VBE of the transistor Q3, so the transistor Q3 is turned off, and the output is high. Since diode d3 is off when , diode d2 is turned on and transistor Q3 is turned on. The capacitor C1 is discharged when the transistor Q3 is turned on.

Next, the operating state of this invention will be described.

[] Normal state The input A of the level detection circuit 1 is at a low level and the one-shot circuit 2 is on standby. Also, when the output of the one-shot circuit 2 is off, the discharge circuit 5 is normally on, and the CR time constant circuit The charge in the capacitor _C1 of No. 3 is always discharged with low resistance, and the output of the output circuit 4 has not yet reached the alarm level. During this time, the switching reset circuit 7 operates in synchronization with the light emission pulse, and the reset state is repeated. Even if the switching circuit 6 is set due to noise, it will be reset by the next light emission pulse.

[] Smoke generation Since the input A of the level detection circuit 1 is at a high level, the output of the one-shot circuit 2 is turned on by the input signal of the first pulse, and the output remains unchanged until the next cycle of pulses arrives. The time constant of the CR time constant circuit 3 is set so that it can be extended, and if the next pulse following the above pulse is also at a high level,
Due to this pulse, the output of the one-shot circuit 2 continues to remain on.

Input A is the transistor of level detection circuit 1
If Q ₁ and Q ₂ are at a level that allows them to be turned on in a pulsed manner, the one-shot circuit 2 operates to shape and widen the pulse, and then, during the one-shot pulse period, the CR time constant circuit 3 operates, Charge is stored in capacitor _C1 and reaches the alarm output level. Since the stored charge has a high impedance when looking at the output, the potential is maintained without being almost discharged. At this time, the transistor Q3 is off, the CR time constant circuit 3 includes a diode d1, and is connected with the opposite polarity to the discharge, and the output circuit 4 has a high impedance (hfel× hfe2×
(output resistance value), there is almost no discharge. Also, before the alarm level is reached, input A cannot turn on transistors Q ₁ and Q ₂ and one-shot circuit 2 does not work, so it is of course impossible to charge any further, but switching circuit 6 cannot also be set, causing repeated is reset by the switching reset circuit 7,
The discharge circuit 5 operates and instantly discharges the capacitor.
The charge on C ₁ becomes zero.

[] Noise generation The output of the one-shot circuit 2 will remain on for the time period that is set to a level where the input A of the level detection circuit 1 does not reach the alarm level with just one pulse, and then After the elapsed time,
The output of the one-shot circuit 2 is turned off. When the output of the one shot circuit 2 is turned off, the discharge circuit 5 comes into operation and the output of the output circuit 4 does not reach the alarm level.

Fig. 2 shows the operation chart of the signal processing circuit of the present invention, in which [] is the normal state, [] is when smoke is generated, and [] is when noise is generated, respectively. It represents the potential of capacitor _C1 of circuit 5 and CR time constant circuit 3.

The detection signal processing circuit for a photoelectric smoke detector according to the present invention eliminates power consumption during standby mode by using a level detection circuit using only the VBE of a transistor, and eliminates power consumption during standby mode by using a one-shot circuit to generate signal pulses and pulses. By widening the width and shaping it, a stable signal can be obtained, and the CR time constant circuit saves time and the reliability can be increased by checking the signal level several times.

[Brief explanation of the drawing]

The drawings show an embodiment of a detection signal processing circuit for a photoelectric smoke detector according to the present invention.
The figure shows an electric circuit diagram, and FIG. 2 shows an operation chart of the signal processing circuit. X and Y are the light emitting part and light receiving part of the photoelectric smoke detector,
1 is a level detection circuit, 2 is a one shot circuit, 3
is a CR time constant circuit, 4 is an output circuit, 5 is a discharge circuit, 6 is a switching circuit, and 7 is a switching reset circuit.

Claims (1)

[Claims] 1. A photoelectric smoke detector that uses a light-receiving element to receive scattered light from smoke particles among the light from a light source driven by a light-emitting pulse circuit, and detects an increase in current due to a decrease in the electrical resistance of the light-receiving element. , a level detection circuit having a switching element that operates when the smoke concentration exceeds a certain level; a one-shot circuit that outputs a waveform-shaped pulse having a certain width in response to the operation of the switching element of the level detection circuit; A CR time constant circuit having a capacitor that is charged by the output, a switching circuit that responds to the output of the level detection circuit, a switching reset circuit that prevents operation of the switching circuit in synchronization with the light emission pulse circuit, and a switching circuit. In response to the output of
A photoelectric smoke detector characterized by being provided with a discharge circuit that discharges a capacitor of a CR time constant circuit, and an output circuit that operates at a predetermined level of the capacitor by continuous output of a one-shot circuit.