JPH0573786A - Photoelectric smoke sensor - Google Patents

Abstract

PURPOSE:To prevent the occurrence of erroneous report based on the abnormality of a photoelectric conversion element by providing a means which detects the abnormality of the photoelectric conversion element which detects scattered light due to smoke. CONSTITUTION:When a control signal Vc from a control circuit 10 is in the low level, a PMOS transistor TR Q1 is turned on, and an NMOS TR Q2 is turned on. Consequently, the drain (d) of the TR Q2 goes to the low level to operate an amplifying and operating circuit 20. If leak occurs in a photoelectric conversion element 2, a potential Vs of the source (s) of the TR Q2 rises. Therefore, the TR Q2 cannot be turned on. At this time, a potential Vd of the drain (d) of the TR Q2 is always in the high level independently of the control signal Vc, and the amplifying and operating circuit 20 is not operated. Thus, the occurrence of erroneous report due to the abnormal current of leak in the photoelectric conversion element 2 is prevented.

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 detects a fire by detecting scattered light of smoke with a photoelectric conversion element.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional photoelectric smoke detector. The configuration and operation will be described below.
The light emitting element 1 intermittently generates an optical signal by the control circuit 10. Unlike the light emitting direction of the light emitting element 1 and the light receiving direction of the photoelectric conversion element 2, the photoelectric conversion element 2 receives almost no light when smoke is not present in the smoke sensor. On the other hand, when smoke is present in the smoke sensor, the light from the light emitting element 1 is scattered by the smoke, so the photoelectric conversion element 2 receives the scattered light by the smoke. Since the scattered light is extremely weak, it is amplified by the light receiving amplifier 21 and then compared with a predetermined reference level by the comparison circuit 22. The output of the comparison circuit 22 is counted by the count circuit 23, and when a light reception detection signal exceeding the reference level is obtained a predetermined number of times or more, the alarm circuit 30 issues a smoke detection signal. The comparison circuit 22 determines whether or not the smoke density is equal to or higher than a predetermined density, and the count circuit 23 performs a counting process in order to prevent malfunction due to electromagnetic noise or the like.

[0003]

In the above-mentioned conventional example, the light receiving amplifier 21, the comparing circuit 22, and the counting circuit 23 are provided.
The amplification / arithmetic circuit 20 including is detecting scattered light due to smoke in synchronization with the control signal from the control circuit 10. The photoelectric conversion element 2 is composed of a photodiode and is applied with a reverse bias voltage. Then, when the light from the light emitting element 1 is scattered by smoke and is received by the photoelectric conversion element 2, a weak photocurrent flows in the photoelectric conversion element 2 in the opposite direction. This photocurrent is amplified by the light receiving amplifier 21 to detect smoke. However, even if there is no scattering of light due to smoke, a weak leak (leakage current) may flow under a reverse bias voltage if the photoelectric conversion element 2 deteriorates due to aging or the like. There was a problem that the current was of the order of nA, which was about the same as the weak current based on the scattered light, and it caused a false alarm.

The present invention has been made in view of the above circumstances, and an object thereof is to add a function of detecting an abnormal occurrence such as a leak of a photoelectric conversion element in a photoelectric smoke detector. , To prevent malfunction of the sensor.

[0005]

According to the present invention, in order to solve the above problems, as shown in FIG. 1, a photoelectric conversion element 2 detects scattered light of smoke to detect a fire. The photoelectric smoke detector is characterized in that means for detecting an abnormality in the photoelectric conversion element 2 is provided.

[0006]

In the present invention, the photoelectric smoke detector is provided with means for detecting an abnormality of the photoelectric conversion element 2 for detecting scattered light of smoke. Therefore, when an abnormality such as a leak occurs, the abnormality is immediately detected. It can be detected and the malfunction of the sensor can be prevented.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention. The circuit configuration will be described below. PM on the power line E
The source of the OS transistor Q1 is connected and PM
The drain of the OS transistor Q1 has resistors R1 and R2.
Is connected to the ground line G via a series circuit. Resistance R
The connection point between 1 and the resistor R2 is connected to the gate g of the NMOS transistor Q2. NMOS transistor Q2
The drain d is connected to the power supply line E via the resistor R3, and the source s is connected to the ground line G via the resistor R4. The cathode of the photodiode forming the photoelectric conversion element 2 is connected to the power supply line E, and the anode is connected to the NMOS transistor Q via the resistor R for current-voltage conversion.
2 sources s. The voltage across the resistor R is input to the amplification / operation circuit 20. The potential Vd of the drain d of the NMOS transistor Q2 is the amplification / operation circuit 2
0 and is input to the control circuit 10. Also, the control circuit 1
The control signal Vc from 0 is input to the gate of the PMOS transistor Q1.

The operation of this embodiment will be described below.
First, when the control signal Vc from the control circuit 10 is at the high level, the PMOS transistor Q1 is turned off, and no current flows through the resistors R1 and R2. Therefore, the potential Vg of the gate g of the NMOS transistor Q2 becomes Low level, and the NMOS transistor Q2
Turns off. Next, when the control signal Vc is at the Low level, the PMOS transistor Q1 is turned on, and the voltage between the power supply line E and the ground line G is applied to the series circuit of the resistors R1 and R2. The voltage divided by R1 and the resistor R2 is applied to the gate g of the NMOS transistor Q2. At this time, the voltage applied to the gate g is the threshold voltage Vt of the NMOS transistor Q2.
If the voltage division ratio of the resistors R1 and R2 is set to be slightly larger than h, the NMOS transistor Q2 is turned on when the control signal Vc is at the Low level.

With such a configuration, the photoelectric conversion element 2
In the state where there is no leakage (leakage current) in the NMOS transistor Q2 when the control signal Vc is at the high level.
When the control signal Vc is at the Low level, the potential Vd of the drain d of the NMOS transistor Q2 becomes the Low level, and the potential Vd of the amplification / operation circuit 2 becomes low.
0 is operated. The timing at which the amplifier / arithmetic circuit 20 operates coincides with the timing at which the light emitting element 1 is driven to emit light by the control circuit 10. At this time,
When there is scattered light due to smoke, the amplification / arithmetic circuit 20 can generate a smoke detection signal.

However, when a leak occurs in the photoelectric conversion element 2, the potential V of the source s of the NMOS transistor Q2 becomes V.
Since s rises, at the potential Vg obtained at the connection point of the resistors R1 and R2 when the control signal Vc is at the Low level, the gate-source voltage (Vg-Vs) of the NMOS transistor Q2 becomes lower than the threshold voltage Vth. It cannot be increased and the NMOS transistor Q2 cannot be turned on. At this time, the potential Vd of the drain d of the NMOS transistor Q2 is always at the high level regardless of the control signal Vc, and the amplification / operation circuit 2
Do not operate 0. Therefore, it is possible to prevent the occurrence of an erroneous alarm due to an abnormal current called a leak of the photoelectric conversion element 2.
Further, by feeding back the potential Vd of the drain d of the NMOS transistor Q2 to the control circuit 10, the abnormality of the photoelectric conversion element 2 can be detected in a short time.

[0011]

According to the present invention, a photoelectric smoke detector for detecting a fire by detecting scattered light of smoke with a photoelectric conversion element is provided with means for detecting abnormality of the photoelectric conversion element. Therefore, there is an effect that it is possible to prevent the occurrence of a false alarm due to an abnormality of the photoelectric conversion element.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional example.

[Explanation of symbols]

 2 Photoelectric conversion element 10 Control circuit 20 Amplification / arithmetic circuit Q1 PMOS transistor Q2 NMOS transistor R Current-voltage conversion resistance R1 resistance R2 resistance R3 resistance R4 resistance

Claims (1)

[Claims] 1. A photoelectric smoke detector for detecting a fire by detecting scattered light of smoke with a photoelectric conversion element, wherein photoelectric photoelectric smoke is provided with means for detecting abnormality of the photoelectric conversion element. sensor.