Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-11-09
2003-06-24
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S554000, C356S337000, C356S338000
Reexamination Certificate
active
06583404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a photoelectric smoke detecting apparatus (also known as the smoke detector) for generating analog data concerning smoke density indicating occurrence of fire or the like event with the aid of a microcomputer or microprocessor. More particularly, the present invention is concerned with a photoelectric smoke detecting apparatus which is imparted with a self- or auto-compensation capability of automatically or spontaneously compensating for a time-dependent change or aged deterioration of a detection characteristic (light reception sensitivity) of a light receiving element incorporated in a smoke sensor of the smoke detecting apparatus due to contamination thereof.
2. Description of Related Art
Heretofore, a well known type of photoelectric smoke detecting apparatus is arranged such that a light emitting element is disposed within a well-ventilated chamber of a smoke sensor and is electrically driven periodically at a predetermined time interval for enabling a microcomputer or microprocessor to fetch the detection signal from the output of the smoke sensor thereby processing the same in order to decide whether a fire event is taking place in a place where the smoke sensor is installed or to detect the density of smoke prevailing in that place.
More specifically, the detection signal outputted from the light receiving element of the smoke sensor disposed for receiving light rays scattered by smoke particles is amplified by an amplifier circuit provided in association with the smoke sensor. The amplified signal is supplied to a microcomputer or microprocessor after analog-to-digital conversion (A/D conversion), whereon the digital data as fetched by the microcomputer is converted to corresponding smoke density data, which is then sent out in the form of an analog data signal to receiver equipment installed at a center station.
In the photoelectric smoke detecting apparatus of this type, contamination of an inner wall of a casing, a light emitting element and/or the light receiving element which constitute the smoke sensor will bring about a variation or change in the sensitivity characteristic of the smoke sensor and hence a change in the detection signal level which of course depends on the color of a contaminant.
Thus, when the contamination of the smoke sensor is detected, there arises the necessity of cleaning the sensor in order to restore the original state thereof to thereby prevent erroneous or false detection of the fire state. When such cleaning is difficult or practically impossible for some reason, it will then be required to take other appropriate measures such as exchange of the smoke sensor itself.
For having better understanding of the concept underlying the present invention, description will first be directed to the conventional photoelectric smoke detecting apparatus known heretofore by reference to
FIGS. 6 and 7
of the accompanying drawings.
FIG. 6
is a functional block diagram showing schematically a structure of a conventional photoelectric smoke detecting apparatus, whereas
FIG. 7
is a circuit diagram of the same.
Referring to
FIG. 6
, the conventional photoelectric smoke detecting apparatus includes a smoke sensor
10
which is composed of a light emitting element
11
and a light receiving element
12
. A shielding plate
13
is interposed between the light emitting element
11
and the light receiving element
12
. It is noted that the light emitting element
11
, the light receiving element
12
and the shielding plate
13
are disposed within a chamber enclosed by a labyrinth inner wall
14
which is employed for implementing the smoke sensor in an antireflection structure. By virtue of this structure, the light receiving element
12
can receive only the scattered light rays L
2
of the light rays L
1
emitted by the light emitting element
11
, whereby the detection value D indicating the smoke density within the chamber enclosed by the labyrinth inner wall
14
can be acquired in the form of a detection signal outputted from the smoke sensor
10
.
A control unit
20
which may be constituted by a microcomputer or microprocessor is designed or programmed to process the detection signal D outputted from the smoke sensor
10
to thereby output an analog data signal E indicative of the smoke density prevailing within the smoke sensor
10
. At this juncture, it should be mentioned that a plurality of photoelectric smoke detecting apparatuses each composed of the smoke sensor
10
and the control unit
20
may be disposed at various locations within a building or the like where the smoke detection is required.
The output data signals (analog data signals E) of the individual photoelectric smoke detecting apparatuses installed at various places are supplied to receiver equipment
30
installed at a center station through signal transmission via signal lines (not shown).
As can be seen in
FIG. 6
, the control unit
20
includes a driving circuit
21
for generating a driving pulse signal P for driving the light emitting element
11
, and A/D (analog to digital) converter
22
for converting the detection value D into digital data Dd and a smoke density arithmetic module
23
for determining arithmetically a smoke density value VKe on the basis of the digital data Dd by referencing a characteristic function table
23
T incorporated in the smoke density arithmetic module
23
. The control unit
20
is provided with a sender or transmission circuit
24
for sending or transmitting the smoke density value VKe in the form of an analog data signal E to the receiver equipment
30
of the center station.
In the characteristic function table
23
T, there are stored characteristic functions each approximated by a positive linear function (represented by a straight line), as described later on.
Next, description will be made by reference to
FIG. 7
in which reference characters
10
to
13
,
20
, L
1
and L
2
denote same items as those described above by reference to FIG.
6
.
Referring To
FIG. 7
, the microcomputer
40
constituting a major part of the control unit
20
includes a CPU (Central Processing Unit) which serves for the functions of the A/D converter
22
and the smoke density arithmetic module
23
shown in FIG.
6
and other peripheral components. A light emitting circuit
41
corresponds to the driving circuit
21
shown in FIG.
6
and serves for electric power supply to the light emitting element
11
as well as pulse-like light emission control thereof. A light receiving circuit
42
is electrically connected to the light receiving element
12
, and an amplifier circuit
43
is connected to the output of the light receiving circuit
42
for amplifying the detection signal, the amplified detection signal being then inputted to the microcomputer
40
.
An oscillator circuit
44
is provided for supplying a clock pulse signal CK to the microcomputer
40
. Further provided is an EEPROM (Electrically Erasable Programmable Read-Only Memory)
45
which is connected to the microcomputer
40
for storing preset data such as addresses and others.
An alarm lamp
46
is provided as an alarming means for generating an alarm upon occurrence of abnormality such as a fire. The alarm lamp
46
is driven or electrically energized by a lighting circuit
47
under the control of the microcomputer
40
.
A receiving circuit
48
serves for receiving signals such as external signals sent from the receiver equipment
30
(see FIG.
6
), which signal are then inputted to the microcomputer
40
. On the other hand, the output signals of the microcomputer
40
are sent to external apparatus via a transmitting circuit
49
. Incidentally, the receiving circuit
48
and the transmitting circuit
49
functionally correspond to the transmission circuit
24
shown in FIG.
6
.
A constant-voltage circuit
50
is provided for supplying electric power to the microcomputer
40
and others incorporated in the control unit
20
and other discrete circuits
41
to
49
.
A diode bridge
Nohmi Bosai Ltd.
Thomas Courtney
Wenderoth , Lind & Ponack, L.L.P.
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