Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-07-24
2001-12-11
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C347S057000, C347S062000, C347S063000, C250S573000, C250S574000, C356S432000, C356S434000
Reexamination Certificate
active
06329922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fire detector in which a light emission section is driven to glow at regular intervals, light emitted from the light emission section and varied depending on smoke stemming from a fire is received by a light reception section and sampled as a smoke detection signal, and a noise de-influence method for the fire detector.
2. Description of the Related Art
In photoelectric fire detectors for detecting smoke that stems from a fire, a light emission section is driven to glow at regular intervals. Light emitted from the light emission section and then scattered or attenuated due to smoke stemming from a fire is received by a light reception section, converted into an electric signal, and sampled as a smoke detection signal proportional to the concentration of the smoke.
The fire detectors fall into analog fire detectors and so-called on-off fire detectors. The analog fire detectors sample the smoke detection signal in response to a command sent from an upper-level device such as a receiver or a relay, and transmit the smoke detection signal to the upper-level device. The upper-level device finally judges whether a fire has broken out. The on-off fire detectors transmit a fire detection signal to the upper-level device when detecting that the smoke detection signal has exceeded a fire level.
The conventional photoelectric fire detectors must take measures against noises occurring on a power supply line or noises occurring in the air for fear they may malfunction. Recently, there is an increasing demand for fire detectors unsusceptible to high-frequency noises along with prevalence of portable telephones. Moreover, international standardization organizations including the International Electrotechnical Commission (IEC) tend to stipulate stricter standards concerning noises.
Conventional countermeasures against noises include addition of noise absorption elements to a circuit and devised patterning of a printed-circuit board. In the analog fire detector, a microprocessor (hereinafter MPU) is included for suppressing a variation of a sampled smoke detection signal caused by a noise according to the method of moving averages or the like.
However, the noise-related standards have come to cover high-frequency noises. Moreover, the intensities of the noises have increased. The addition of noise absorption elements or the devised patterning has therefore reached its limitations. Besides, when the MPU is used to reduce a variation of a sampled smoke detection signal according to the method of moving averages, a caused by an instantaneous noise can be reduced. However, when a noise persists for a long period of time, the MPU cannot reduce the noise, at the worst case, a malfunction occurs.
Another countermeasure against noises is such that the printed-circuit etc, board are encapsulated in a shield case in order to block radio waves (refer to U.S. Pat. No. 4,897,634).
In this case, as shown in
FIG. 11
, the circuitry for a fire detector circuit base
100
is realized in the form of a double-sided printed-circuit board
115
whose lower surface is coated with a copper foil in order to block radio waves. A metallic shield case
120
is placed on the printed-circuit board
115
, thus de-influencing the adverse effects of radio waves on circuit elements
116
. Moreover, a light-emitting element
108
, a light-receiving element
109
, and a capacitor
117
mounted on the lower surface of the double-sided printed-circuit board
115
are covered with a light-emitting element holder, a light-receiving element holder
107
, and a capacitor holder
114
and thus unsusceptible to radio waves.
However, particularly, the light-receiving element
109
should be protected by the noise. So the light-receiving element
109
was only protected by metal-sealed-cap (not shown), which is in the element holder
107
.
In
FIG. 11
, there are shown a body cover
101
, a contact pin
102
, an outer cover
103
, a smoke inlet
103
a
, and a smoke-sensing section
104
. A wire net
102
prevents invasion of insects into the smoke-sensing section
104
.
When a seal member shields for a fire detector heavily, the number of components increases and the number of assembling steps increases. This may lead to an increase in costs.
An object of the present invention is to provide a fire detector that is prevented from malfunctioning because of noises, and a noise de-influence method for the fire detector.
SUMMARY OF THE INVENTION
For accomplishing the above object, according to the present invention, there is provided a photoelectric fire detector having a light emission section, a light reception section, and a smoke detection section. The light emission section is driven to glow at regular intervals. The light reception section receives light emitted from the light emission section and varied depending on smoke. The smoke detection section samples as a smoke detection signal a signal output from the light reception section when the light emission section glows, and updates a previous smoke detection signal.
According to the present invention, the photoelectric fire detector includes a noise detection section and a noise de-influence unit. The noise detection section samples as a noise detection signal a signal output from the light reception section when the light emission section does not glow. When the noise detection signal exceeds a predetermined noise judgment level, the noise de-influence unit processes to eliminate influence of a noise or de-influences a noise.
When the noise detection signal exceeds the predetermined noise judgment level, the noise de-influence unit disables updating of a previous smoke detection signal with a smoke detection signal newly sampled by the smoke detection section, and thus processes to de-influences a noise.
In the fire detector in accordance with the present invention, an analog signal output when an LED included in a light emission section does not glow is sampled as a noise detection signal by the noise detection section. When the noise detection signal whose level is initially zero rises due to a noise and exceeds the predetermined noise judgment level, it is judged that smoke detection is affected by the noise. When it is judged that smoke detection is affected by a noise, a smoke detection signal output at that time is canceled for fear the fire detector may judge that a fire has broken out. Thus, the noise is de-influenced.
It can therefore be reliably prevented that the fire detector malfunctions because of a smoke detection signal to which a noise is continuously appended during an action period during which a received light amplification circuit is in action.
A lot of noise absorption elements that cost high need not be included. Noises can be coped with using a minimum necessary number of noise absorption elements. Moreover, it is unnecessary to heavily shield a fire detector. Besides, devised patterning to be achieved through cutting and trial is not needed. Once patterning is devised to some extent, noises can be coped with. It takes little time to retrofit a fire detector so that the fire detector will become unsusceptible to noises.
The light reception section includes the received light amplification circuit that acts for a certain period starting before and ending after a glowing period during which the light emission section glows. The noise detection section samples a noise detection signal for a time other than the glowing period within the action period of the received light amplification circuit. Thus, noise detection is carried out during the action period of the received light amplification circuit except the glowing period. This obviates the necessity of adding another received light amplification circuit.
According to the present invention, the noise detection section included in the fire detector samples a noise signal when a time, during which noise detection is unaffected by the light emission section, has elapsed after the glowing period of the light emission section.
Ito Masayuki
Kosugi Naoki
Hochiki Kabushiki Kaisha
Lackenbach Siegel Marzullo Aronson & Greenspan
Pham Toan
Wu Daniel J.
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