Smoke density monitor system

A smoke density monitor system comprises an imaginarily dividing a space to be monitored two-dimensionally into a plurality of imaginary subspaces so that plural paths passing through a plurality of arbitrary subspaces are arranged to intersect each other; measuring the transmittance of light along each path; calculating a transmittance of light at each imaginary subspace using a mathematical method in which the measured result of the transmittance of the each path are placed into matrices and the solution to an equation involving the matrices is carried out with matrices; and determining a smoke density at each of the imaginary subspace on the basis of the transmittance at each subspaces.

RELATED INVENTIONS 
This invention is related to applicant's prior U.S. Pat. No. 4,972,178 
issued Nov. 20, 1990 titled "FIRE MONITORING SYSTEM". 
BACKGROUND OF THE INVENTION 
This invention relates to systems for monitoring smoke density in a 
monitored space. 
Systems for monitoring smoke density covering an extensive monitored space 
have been heretofore proposed and applied to detect fires and the like. A 
system for detecting the smoke density based on the transmittance of light 
radiated from a light source, allowing a comparatively large monitored 
space to be covered, is popular and widely used. One specific application 
of this system is an attenuation type smoke detector employed in, e.g., 
fire detecting equipment. The smoke detector is such that a light source 
is arranged so as to confront a light detector with a monitored space 
interposed therebetween so that the transmittance of light reaching the 
light detector from the light source is monitored and that the monitored 
transmittance is compared with a predetermined value to obtain a smoke 
detection signal. 
In the case where the smoke density of the monitored space is monitored by 
the transmittance of light, it is advantageously that one set of devices 
permit monitoring an extensive space in one direction. 
However, when the space to be monitored is too long, it becomes difficult 
to accurately detect a local rise of smoke density, and hence to locate a 
fire or the like. Assuming that a monitored space extending linearly from 
the light source to the photo detector is a collection of imaginary 
subspaces, only the accumulated value of the transmittances of each 
subspaces is obtained as a result of detection. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to overcome the above 
disadvantage. 
The smoke density monitor system according to the present invention 
comprises the steps of: imaginarily dividing a space to be monitored 
two-dimensionally into a plurality of imaginary subspaces so that plural 
paths passing through a plurality of arbitrary subspaces are arranged to 
intersect each other; measuring the transmittance of light along each 
path; calculating a transmittance of light at each imaginary subspace 
using a mathematical method in which the measured result of the 
transmittance along each path is placed into matrices and the solution to 
an equation involving the matrices is carried out with matrices; and 
determining a smoke density at each of the imaginary subspace on the basis 
of the transmittance at each subspace. Therefore, the smoke density 
monitor system detects any rise in local smoke density in a longitudinally 
and latitudinally large monitored space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The smoke density monitoring system of the invention will now be described 
with reference to the accompanying drawings. 
FIG. 1 is a diagram showing the main portion of an exemplary embodiment of 
smoke density monitoring device to which the smoke density monitoring 
system of the invention is applied. A plurality of pairs, each consisting 
of first and second groups of light sources 2 respectively along the left 
and upper sides of space 1 and first and second groups of light detectors 
3, respectively along the right and lower sides of space 1 and having a 
smoke monitored space 1 therebetween, and a plurality of light paths 4 are 
arranged in a lattice form. The paths 4 consist of paths parallelly 
arranged and paths perpendicular arranged to form the lattice. Each light 
source 2 is turned on and off sequentially in response to an output from 
an activating means such as a counter 6 for counting the output of an 
oscillating circuit 5. Each light detector 3 converts light radiated from 
the confronting light source 2 into an electric signal. A signal generated 
at each light detector 3 is converted into a digital signal according to 
the radiated light through an amplifier 7, a sample hold circuit 8, and an 
analog/digital converter 9. The converted signal is thereafter sent to a 
central processing unit (CPU) 10. The CPU 10, based on the signal sent 
from each light detector 3, calculates a transmittance of the current 
light compared with the transmittance at the time each path 4 is clear and 
temporarily stores the calculated transmittance in a storage unit which 
belongs to the device. Once the transmittances of all of the paths have 
been calculated in this way, the CPU 10, deeming each intersecting point 
Of the paths 4 as an imaginary subspace, calculates the transmittance of 
light at such imaginary subspace on the basis of the measured result of 
the transmittance of the each path in the same manner as the solution for 
each element of a matrix is determined. A smoke density of each imaginary 
subspace can then be calculated from the calculated transmittance of light 
at each imaginary subspace. The smoke density of each imaginary subspace 
is compared with an alarm value and if there is any imaginary subspace 
whose smoke density is greater than this alarm value, such occurrence and 
location are displayed on a CRT display 11 or the like. In addition to 
such data, the CRT display 11 displays a smoke density distribution by 
showing the smoke density at each virtual small space on a plan view 
covering the entire monitored space so that location of a fire, flow 
direction of smoke, determination of escape passageways and the like can 
be facilitated. 
While the above embodiment requires that the pair of light source 2 and 
light detector 3 be disposed at every path, an embodiment shown in FIG. 2 
uses pairs whose number is smaller than the sum of the paths. 
FIG. 2 is a diagram showing the main portion of another exemplary 
embodiment of smoke density monitoring device using the smoke density 
monitor system of the invention. Similar to the embodiment shown in FIG. 
1, the device has a plurality of pairs, each consisting of a group of 
light sources 2 and a group of light detectors 3 and a smoke monitored 
space interposed therebetween, and is so constructed that each light 
source 2 is turned on and off sequentially using an oscillating circuit 5 
and a counter 6 and that a signal from the light detector 3 is converted 
into a digital signal through an amplifier 7, a sample hold circuit 8 and 
an analog/digital converter 9 and thereafter sent to a CPU 10. In the 
embodiment shown in FIG. 2, an optical element 12 is disposed in front of 
each light source 2 and acts as a means to direct a light beam toward a 
plurality of light detectors so that the light can be radiated to all the 
light detectors 3 and an optical element 13 is disposed in front of each 
light detector 3 so that the light radiated from all the light sources 2 
can be focused on each light detector. 
An optical element having such functions and cylindrical lenses as shown in 
FIG. 3A and 3B are well known. 
When each light source 2 is turned on and off in sequence, each light 
source 2 forms a light path 4 toward each light detector 3. As a result, 
25 intersecting paths are formed in this embodiment. The CPU 10, as in the 
previous embodiment, calculates the transmittance of the current light 
compared with that at each path 4 when it is clean from a signal sent from 
each light detector 3 and temporarily stores the calculated transmittance 
of the current light in a storage unit that belongs to the device. When 
the transmittances of all the paths have been calculated, the CPU 10 
calculates the transmittance of light at each imaginary subspace on the 
basis of the transmittance of the each path in the same manner as the 
solution for each element of a matrix is determined. A smoke density at 
each imaginary subspace is obtained from such calculated transmittance of 
light. 
While this embodiment usually requires that the optical elements be 
disposed in front of both the light source and light detector, only the 
optical element in front of the light source may be necessary if a light 
detector, which is less directional so that light can be detected from a 
wide range of angles, is employed. 
While this embodiment arranges the optical element 12 in front of each 
light source 2 so that the light can be radiated to all the light 
detectors 3, each light source and light detector may be arranged on a 
rotatable stand not only to allow the light to be radiated to all the 
light detectors but also to allow the light to be detected from all the 
light sources. However, such an arrangement may become complicated. 
As a result of the above construction, any rise in local smoke density at a 
point in an elongated monitored space can be detected accurately, thereby 
not only contributing to locating a fire or the like but also allowing a 
rise in local smoke density in a longitudinally and latitudinally large 
space. In addition, the display of the smoke density distribution over the 
imaginary subspaces on the plane view covering the entire monitor space 
facilitates location of fires, flow direction of smoke, determination of 
escape passageways and the like.