JPS6133594A - Smoke sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a smoke sensor that detects smoke by scattering light.

[Background technology 1] Normally, the sensitivity of this type of smoke detector is checked periodically,
If the sensitivity has fallen below a specified value, the sensitivity is adjusted by changing the setting level or cleaning the lens. However, if the optical system becomes extremely dirty by the time of the next inspection due to sudden changes in environmental conditions, there is a risk of a false alarm in the event of a fire.

[Objective of the Invention 1] The present invention has been made in view of the above-mentioned problems, and is designed to issue an alarm immediately when the sensitivity of a smoke detector drops to a specified value, thereby eliminating the risk of false alarms and improving the sensitivity. The purpose is to save the labor of inspection.

[Disclosure 1 of the Invention] The present invention provides a smoke detection section configured such that when smoke enters the optical system, light from a light projecting element is scattered by smoke particles and enters a light receiving element, In a smoke detector equipped with a comparison circuit that outputs an alarm signal when the upper limit value for detection is exceeded, a second comparator circuit that outputs an alarm signal when the incident light level becomes smaller than the lower limit value for detecting deterioration of the optical system is provided. It is characterized by being equipped with a comparison circuit,
In scattered light type smoke detectors, the lower limit of the normal incident light level is set by taking advantage of the fact that even in normal conditions with zero smoke concentration, the incident light level does not reach zero due to reflection from the wall of the optical system. By doing so, it is possible to detect dirt on the optical system.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, the optical axes of the light emitting element 1 and the light receiving element 2 are almost orthogonal to each other, and only when smoke flows into the optical system 3, the light from the light emitting element 1 is scattered by smoke particles. Light is made incident on the light receiving element 2. Reference numeral 4 denotes an oscillation circuit for supplying a pulse current to the light projecting element 1, and this configuration prevents noise caused by external light and the like.

The received light signal is amplified by the amplifier circuit 5 and then input to the first comparison circuit 7 and the second comparison circuit 8 via the signal processing circuit 6. The first comparison circuit 7 compares the incident light level X with the upper limit value a for fire detection, and outputs an alarm signal when the incident light level Sends a line short circuit signal to the side. In the second comparison circuit 8, the incident light level X is compared with the lower limit value C for detecting contamination of the optical system, and when the incident light level It is sent to the receiver side via. 10 is a power supply circuit.

FIG. 2 shows the operating principle of the present invention, and A shows the characteristic curve of the smoke detector in a state where the optical system is not contaminated when the smoke detector is first installed. The left end of curve A represents the normal incident light level b due to reflection from the wall of the optical system when the smoke density is zero, and as the smoke density increases, the incident light level X also increases, and at point D the incident light level When reaches the upper limit value a, the first comparator circuit 7 outputs an alarm signal. The range of points where this curve A intersects with X = a is determined by the standard to be from smoke density d1 to d2, and the characteristics of the smoke detector may change from curve B due to dirt on the optical system lens or deterioration of the light emitting/receiving element. If the incident light level X reaches the upper limit value a, the point E at which an alarm is issued will be outside the right end of the standard range, and there is a possibility that an alarm will not be issued in the event of a fire. Therefore, by setting the value C at the left end of the curve B as the lower limit value of the incident light level under normal conditions, it is possible to detect the limit sensitivity due to deterioration of the optical system.

[Effect of the Invention 1 As described above, in the present invention, in a scattered light type smoke detector equipped with a first comparison circuit that outputs an alarm signal when the incident light level exceeds the upper limit value for fire detection, Since it is equipped with a second comparison circuit that outputs an alarm signal when the level becomes smaller than the lower limit value for detecting optical system deterioration, the sensitivity will rise or fall above the specified value due to dirt on the lens or deterioration of the light emitting/receiving element. In such a case, an alarm signal can be issued to notify the alarm immediately, and there is therefore no risk of missing alarms as in the conventional case, and there is an advantage that the trouble of patrol inspection can be saved.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing one embodiment of the smoke detector of the present invention, and FIG. 2 is a characteristic diagram showing the principle of operation of the same. 1 is a light emitting element, 2 is a light receiving element, 3 is an optical system, 4 is an oscillation circuit, 5 is an amplifier circuit, 6 is a signal processing circuit, 7 is a first comparison circuit, 8 is a second comparison circuit, 9 is a switching circuit, 1
0 is the power supply circuit, a is the upper limit, C is the lower limit, and × is the incident light level.

Claims (1)

[Claims] (1) A smoke detection section configured so that when smoke enters the optical system, light from the light emitting element is scattered by smoke particles and enters the light receiving element, and when the incident light level exceeds the upper limit for fire detection. A smoke detector equipped with a comparison circuit that outputs an alarm signal, characterized by comprising a second comparison circuit that outputs an alarm signal when the incident light level becomes smaller than a lower limit value for detecting deterioration of the optical system. Smoke detector.