Method and apparatus for detecting odors

The invention involves the detection of odors using an odor detector including an n-type semiconductor sensor having an electric resistance responsive to odor molecules adsorbed thereonto. An ozonizer is provided within a test compartment to contact the detector with an ozone gas for the purpose of calibrating the detector to an initial zero setting. The test compartment also includes a ventilation fan operable to draw purging air into the compartment. In order to minimize the time required to bring the detector to the initial zero setting, a computer is used to selectively actuate the ozonizer and the ventilation fan in a controlled manner. Before starting a new detection cycle, an operator selects a specific table of optimal pattern for quick recovery to the zero setting from among a plurality of tables stored in the computer, based on certain factors such as the identity and concentration of previously detected odorant substances, etc.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to odor detectors and, more particularly, to a 
method and apparatus for shortening the time required to bring such an 
odor detector to a predetermined initial setting for the next detection 
cycle by purging a detection chamber containing the odor detector through 
a controlled operation of an ozonizer and a ventilation fan. In this 
invention, a plurality of tables may be provided for use with a computer 
to enable a rapid and efficient recovery of detector readings to the 
initial setting by reference to a specific table which is selected by an 
operator from among the tables depending upon certain factors including 
the identity and concentration of previously detected odorant substances. 
2. Description of the Prior Art 
Odorimetry plays an important role in the field of quality inspection. For 
example, objective odor determination can be made in the food processing 
industries, where the freshness and the quality of comestible products can 
be determined objectively through use of various odor detectors. An odor 
detector could also have many other applications such as control of 
fermentation, analysis of raw materials, testing of alcholic or other drug 
intoxication, etc. Likewise, there are many uses for such a device in the 
perfume and cosmetic industries. Gas chromatography has frequently been 
used for detecting the identity and concentration of odorant substances. 
This technique, however, has certain shortcomings: (1) Results of 
detection vary depending upon the particular sampling method used; (2) The 
detections have to be carried out by a person reasonably skilled in the 
test; (3) Apparatus useful in such gas chromatography is generally costly; 
and (4) It takes a considerable time before the results are given. 
Various types of odor or gas detectors have been proposed and developed 
which are capable of reliably detecting minute concentrations of odorant 
substances. U.S. Pat. No. 4,770,027 to Ehara et al discloses one such 
arrangement which provides the total concentration of odors emitting from 
an object such as comestible products as an indication of its specific 
quality including freshness and maturity. In the U.S. patent, an n-type 
metal oxide semiconductor is utilized as a sensing means which is heated 
to a predetermined high operating temperature by an electric heater 
disposed adjacent thereto. The n-type semiconductor, when heated, is 
responsive to odor molecules absorbed thereonto. Adsorption of odor 
molecules will cause electrons to be exchanged between the molecules and 
the semiconductor surface to cause a change in the electron concentration 
in the semiconductor. The changing electron concentration varies the 
electric resistance of the semiconductor thus permitting an accurate 
determination of the total concentration of the odors. 
In order to detect odorant substances using the detector of this type, it 
is necessary to bring the detector to an initial zero setting where the 
detector chamber is odorless, prior to starting a new detection cycle. 
Depending upon the identity and concentration of odorant substances, it 
usually takes ten to fifty minutes before such initial setting is 
attained. This will disadvantageously place a limitation on the number of 
detection cycles accommodated within a certain period of time. If odorant 
substances of high retentivity have been tested in the previous detection 
cycle or if a detection was made relatively close to a source of strong 
smell, the ambient air around the odor detector is "contaminated", or 
contains minute concentrations of such odors, which may require an 
unreasonably long time of recovery to the zero setting and sometimes make 
it impossible to restart detection cycles. 
It is a principal object of this invention to provide an improved method 
and apparatus which enable repeated detections of odorant substances in a 
quick and efficient manner with a view to overcoming the above-stated 
shortcomings of the prior art. 
It is another object of this invention to provide an improved method and 
apparatus which can shorten the time required to bring an odor detector to 
an initial zero setting for repeated and efficient detection of odorant 
substances. 
Yet another object of this invention is to provide an improved method and 
apparatus which uses an ozonizer along with a ventilation fan to purge a 
detection chamber prior to the commencement of a new detection cycle. 
It is a further object of this invention to provide an improved method and 
apparatus which utilizes a computer to coordinate ozone generation with 
activation of a ventilation fan in such a manner as to minimize the time 
it takes for the odor detector to return to an initial zero setting. 
Yet a further object of this invention is to provide an improved method and 
apparatus in which an operator can select a specific table of optimal 
pattern for quick recovery to an initial zero setting for a subsequent 
detection cycle from among a plurality of tables stored in a computer. 
SUMMARY OF THE INVENTION 
The objects stated above and other related objects in this invention are 
accomplished by the provision of a method for detecting odors, comprising 
the steps of: providing an odor sensing means having an electrical 
property responsive to odor molecules adsorbed onto said sensing means; 
contacting said sensing means with an ozone gas by allowing the gas to 
pass through said sensing means; detecting the electrical property of said 
sensing means prior to exposing said sensing means to odorant substances, 
for the purpose of using the detected property value for an initial zero 
setting; exposing said sensing means to said odorant substances; and 
detecting the electrical property of said sensing means relative to said 
initial zero setting as an indication of the odors emitting from said 
odorant substances. 
Further in accordace with the present invention, there is provided a method 
for detecting odors, comprising the steps of: providing a test compartment 
for accommodating odorant substances therein; providing an odor sensing 
means in said test compartment, said odor sensing means having an 
electrical property responsive to odor molecules adsorbed onto said 
sensing means; detecting the electrical property of said sensing means 
prior to placing a first sample of odorant substances within said test 
compartment, for the purpose of using the detected property value for an 
initial zero setting; placing said first sample of odorant substances 
within said test compartment; detecting the electrical property of said 
sensing means relative to said initial zero setting as an indication of 
the odors emitting from said first sample of odorant substances; removing 
said first sample of odorant substances from said test compartment; 
contacting said sensing means with an ozone gas by allowing the gas to 
pass through said sensing means until the electrical property of said 
sensing means returns to said initial zero setting; placing a second 
sample of odorant substances within said test compartment; and detecting 
the electrical property of said sensing means relative to said initial 
zero setting as an indication of the odors emitting from said second 
sample of odorant substances. 
The present invention also contemplates an apparatus for the detection of 
odors, comprising: an odor sensing means having an electrical property 
responsive to odor molecules adsorbed onto said sensing means; means for 
contacting said sensing means with an ozone gas by allowing the gas to 
pass through said sensing means; means for calibrating said sensing means 
to an initial zero setting while being contacted with the ozone gas; means 
for exposing said sensing means to odorant substances; and means for 
detecting the electrical property of said sensing means relative to said 
initial zero setting as an indication of the odors emitting from said 
odorant substances. 
Still further in accordance with the present invention, there is provided 
an apparatus for the detection of odors, comprising: a test compartment 
for accommodating odorant substances therein; an odor sensing means 
disposed within said test compartment, said odor sensing means having an 
electrical property responsive to odor molecules adsorbed onto said 
sensing means; means for generating an ozone gas in said test compartment 
and for allowing the generated ozone gas to pass through said sensing 
means so as to contact it; means for calibrating said sensing means to an 
initial zero setting while being contacted with the ozone gas; means for 
detecting the electrical property of said sensing means relative to said 
initial zero setting as an indication of the odors emitting from said 
odorant substances. 
The odor sensing means comprises an n-type semiconductor having an 
electrical resistance responsive to odor molecules adsorbed thereonto. An 
ultraviolet lamp is utilized to generate the ozone gas. 
A fan means is provided on the test compartment to draw purging air into 
the compartment. The fan means is operable in response to the electrical 
property of the sensing means overshooting the initial zero setting, 
thereby causing the electrical property to converge into the initial zero 
setting. 
A computer is employed to cause the electrical property of the sensing 
means to converge into the initial zero setting by selectively contacting 
the sensing means with the ozone gas and the purging air in a controlled 
manner. The computer operates to cause the electrical property to converge 
into the initial zero setting by reference to a specific table which is 
selected by an operator from among a plurality of tables stored in the 
computer for quick return to the initial zero setting.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and particularly to FIGS. 1 , 2 and 3, there 
is illustrated an odor detector of the present invention generally 
designated by the numeral 10. As shown, the odor detector 10 comprises a 
suitable housing 12 to house the several parts, to be detailed 
hereinafter. The housing 12 is provided with a hinged door 14 for access 
to a test compartment 16 defined in the housing 12. The door 14, when in 
the illustrated position, sealingly closes the test compartment 16 to 
isolate it from the surrounding atmosphere. Preferably, the test 
compartment 16 may be lined with stainless steel or other suitable 
anti-corrosive materials. A sensor 18 is provided on the ceiling of the 
test compartment away from the door 14. 
In accordance with a preferred embodiment of the invention, the sensor 18 
comprises a simple substance of an n-type metal oxide semiconductor such 
as sintered body of 99.999% pure tin oxide (SnO.sub.2) containing Al.sub.2 
O.sub.3 as a binder. As an alternative, a 0.6 mm thick ceramic plate 
having a thin film of such a metal oxide deposited thereon by vacuum vapor 
deposition may be employed. A simple substance of n-type zinc oxide (ZnO) 
may also be used to form the sensor 18. Although not specifically shown, 
the sensor 18 has associated therewith a suitable electric heater for 
maintaining the sensor at a predetermined high, constant, operating 
temperature so that sensor readings may be independent of the temperature 
and humidity of the ambient air. The sensor 18 may not be required to have 
the capability of discriminating various kinds of odors but is sufficient 
to be able to give an indication of the total concentration of such odors. 
A plurality of like sensors having their characteristic curves staggered 
by maintaining the respective sensors at different temperatures may be 
used in place of a single sensor. 
As best seen in FIG. 2, the odor detector 10 includes an ozonizer in the 
form of an ultraviolet lamp 20 which is provided on the back surface of 
the door 14. For this purpose, for example, an ultraviolet lamp 
manufactured under the designation of QGUL-11-65Z by Prince Electric Co., 
Japan, may be employed. In an alternate embodiment of the invention, it is 
possible to provide such an ultraviolet lamp outside the test compartment 
16 such that after completion of one detection cycle, the sensor 18 may be 
removed from the compartment for exposure to the ultraviolet lamp outside 
thereof. The test compartment 16 is suitably formed to allow easy access 
for insertion and removal of an odor carrying object and is lined with 
stainless steel, as described above. The ceiling of the test compartment 
16 is formed near its center with a purging gas or air inlet port 22. The 
air inlet port 22 is in communication with a ventilation fan compartment 
16 through a vertically disposed cylindrical conduit 26 and a horizontally 
disposed cylindrical conduit 28 which are coupled to each other in an 
air-tight manner. Although not shown in FIG. 3 for clarity of 
illustration, a ventilation fan 30 is provided in the compartment 16 to 
draw the ambient air into the test compartment so as to purge it in the 
manner to be described later in more detail. Also, it is preferred that 
the vertically disposed conduit 26 includes a filter containing various 
absorbent materials such as activated charcoal, which are capable of 
irreversibly removing from the incoming air certain undesirable or 
interfering molecules. 
The purging air inlet port 22 has associated therewith a first isolating 
valve 32 which, when closed, acts to prevent entry of the ambient air 
through the inlet port 22 into the test compartment 16. In the illustrated 
embodiment, the first isolating valve 32 comprises a generally square 
plate 34 which normally is horizontally disposed so as to seal off the 
lower circumferential end of the vertically disposed conduit 26 that 
extends slightly downward from the ceiling of the test compartment 16. The 
square plate 34 has provided near its corners four studs 36 which extend 
through holes formed in the compartment ceiling in a manner to surround 
the air inlet port 22. A coiled spring 38 is provided on each stud 36 
between its head portion and the upper surface of the ceiling to normally 
bias the square plate 34 upwardly to close off the air inlet port 22. As 
best seen in FIG. 3, an operating link 40 is provided in a manner to 
connect the head portions of the two studs 36 and is operatively 
associated with a horizontally disposed operating rod 42 which forms a 
part of a solenoid device 44. The solenoid device 44, when actuated, acts 
to move the horizontally disposed operating rod 42 downwardly, causing the 
operating link 40 to move downwardly so as to move the square plate 34 
away from sealing engagement with the air inlet port 22. 
Referring back to FIG. 2, the test compartment 16 includes a purging gas or 
air outlet port 50 formed in the opposite inside surface to the door 14. 
Another horizontally disposed conduit 52 extends through the test 
compartment 16 and the back surface of the housing 12 to serve as the air 
outlet port 50. The air outlet port 50 has associated therewith a second 
isolating valve 54 which is similar in structure to the first isolating 
valve 32. A vertically disposed plate 56 is normally biased against the 
circumferential end of the conduit 52 by coiled springs 58 on four studs 
60 extending from the plate 56, in a manner to seal off the outlet port 
50. Another operating link 62 is provided which connects the head portions 
of two adjacent studs 60 and includes a wire 64 having one end secured to 
the operating link 62 at its midpoint. Two pulleys 66 and 68 are provided 
to operatively connect the operating link 62 to the solenoid device 44 by 
way of the wire 64. In this arrangement, the solenoid device 44, when 
actuated, acts to pull the wire 64 upwardly, causing the operating link 62 
to move toward the back surface of the test compartment 16 so that the 
vertically disposed plate 56 is moved away from sealing engagement with 
the circumferential end of the conduit 52 to open the outlet port 50. It 
should be noted that, in the illustrated embodiment, the operations of the 
ventilation fan 30, the first and second isolating valves 32 and 54 are 
coordinated such that in response to an operator command, both of the 
isolating valves are moved to the open positions simultaneously with the 
activation of the ventilation fan to purge the test compartment 16 in an 
effective and efficient manner. 
Referring back to FIG. 1, the housing 12 is provided with a control panel 
70 which includes a display 72 for providing a digital reading of the 
electric current through the sensor 18 as an indication of the 
concentration of odors. A power switch 74 is provided for a suitable power 
supply (not shown) which may be self-contained or supplied from an 
external power line (not shown). Also shown on the housing 12 is a fan 
switch 76 which permits a selective activation of the ventilation fan 30. 
A control knob 78 is provided to vary the magnitude of the voltage to be 
applied to the sensor 18. Another control knob 80 is provided just below 
the knob 78 to enable a zero adjustment of the digital reading on display 
72. Disposed above these control knobs is a voltmeter 82 for providing a 
reading of the voltage applied to the sensor. A knob 84 for holding a peak 
value of the concentration of odors as detected is also provided on the 
control panel 70. 
FIG. 4 is a block diagram showing the exemplary hardware for controlling 
the atmosphere in the test compartment 16 so as to make the odor detector 
10 ready to start a new detection cycle. As shown, the hardware includes a 
computer 86 which may take the form of a personal computer or a 
mini-computer. The computer 86 is coupled via an RS 232C cable to the 
sensor 18 to receive therefrom electric signals indicative of the 
operational status of the ozonizer and the ventilation fan. The computer 
is also connected to an interface 88 including relays R1 and R2 which are 
in turn connected to the ozonizer 20 and the ventilation fan 30, 
respectively. Command signals from the computer 86 will control the 
operations of the relays R1 and R2 which determine the operational status 
of the ozonizer and the ventilation fan. 
In operation, the power switch 74 is turned "ON" and then the control knob 
78 is manually adjusted to provide a predetermined voltage to the sensor 
18, with the door 14 closed. This will start heating the sensor to a 
predetermined, constant operating temperature. The next step is to 
determine that the sensor current on the digital display 72 has become 
stable, which means that the semiconductor sensor 18 is now ready for 
operation so that the new detection cycle can start. The fan switch 76 is 
then actuated, which simultaneously causes the first and second isolating 
valves 32 and 54 to open, as described above. This will introduce the 
purging gas or air into the test compartment 16 to make the compartment 
odorless, enabling the odor detector 10 to be calibrated to a 
predetermined initial zero setting. Specifically, this calibration is 
accomplished by turning the control knob 80 for zero adjustment. It should 
be understood that it may not be necessary to purge the test compartment 
16 with the purging air prior to commencing a first detection cycle. In 
this case, the detection cycle can be started immediately after the zero 
adjustment of the odor concentration reading on the digital display 72 is 
made. 
Next, the door 14 is opened to place a sample of odorant substances in the 
test compartment 16, and the door 14 is closed to seal off the 
compartment. Gases carrying the odors start to fill the test compartment, 
coming into contact with the semiconductor sensor 18. Adsorption of the 
odorant substances will occur on the semiconductor sensor, causing the 
sensor to undergo an electric resistance change. The changing resistance 
alters the electric current through the sensor, causing a corresponding 
variation in the digital reading on the display 72. The peak value of the 
digital reading is proportional to the amount of adsorption taking place 
on the sensor, accordingly the total concentration of odors emitted from 
the sample. 
Once the detection cycle has been completed, an operator gives a specific 
command to the computer 86 to start the necessary procedure for bringing 
the odor detector 10 to the initial zero setting for subseqent detection. 
A flow chart of the steps performed by the computer 86 of FIG. 4 is 
illustrated in FIG. 5. As shown, the first step is to provide the start 
command to the computer 86, as described above. The next step is to select 
a specific table from among a plurality of tables stored in the computer 
memory (not shown), based on the identity and the peak concentration 
recorded from the previous detection cycle, the estimated rate of decrease 
of odor concentration toward the zero setting, the expected time interval 
between check points, the "ON" duration for the ultraviolet lamp 20, the 
ON duration for the ventilation fan 30, etc. The computer 86 is programmed 
to execute a series of steps in accordance with the specific software 
stored in the memory so as to bring the odor concentration in the test 
compartment 16 to the zero setting by periodically comparing the 
concentration reading with that specified by the selected table at every 
check point to selectively operate the ozonizer 20 and the ventilation fan 
30. A typical example of a table by reference to which the atmosphere in 
the test compartment 16 is controlled into the zero setting is shown 
below: 
______________________________________ 
Odor Rate of Check UV Lamp Ventil. Fan 
Concentration 
Decrease Interval Duration 
Duration 
______________________________________ 
&gt;1800 4 (/sec.) 
30 (sec.) 30 (sec.) 
&gt;1600 4 30 30 
&gt;1400 4 30 30 
&gt;1200 4 30 30 
&gt;1000 4 30 30 
&gt;800 4 30 30 
&gt;600 4 30 30 
&gt;400 4 30 30 
&gt;200 4 30 30 
&gt;100 4 30 30 
&gt;50 4 30 30 
&gt;20 4 20 20 
0 4 20 20 
&lt;-20 2 20 3 (sec.) 
&lt;-100 1 20 3 
&lt;-200 1 20 5 
&lt;-800 1 20 5 
______________________________________ 
As will be seen, the ultraviolet lamp 20 is generally maintained in an "ON" 
condition until the odor concentration decreases to the zero setting. This 
is accomplished by causing the relay R1 to be kept energized in response 
to a computer command. The ultraviolet lamp acts as an ozonizer to 
neutralize the odors remaining in the test compartment 16. If the 
ultraviolet lamp 20 is kept "ON" too long, it has been found that the odor 
concentration decreases below the zero setting. When this occurs, the 
computer 86 automatically gives a command to the interface 88 that causes 
the relay R2 to be energized to actuate the ventilation fan 30. It has 
been found through experimentation that introducing the purging air will 
cause the odor concentration in the compartment to increase toward the 
zero setting. Once the odor concentration has been returned to the zero 
setting, it will be appreciated that the odor detector 10 is ready to 
perform the next detection cycle. 
It should be understood that in accordance with the preferred embodiment of 
the present invention, the odor detector can be brought to the initial 
zero setting in a minimum of time. The use of the ozonizer and the 
ventillation fan which are selectively activated depending upon the 
current concentration of odors from the previously tested odorant 
substances will result in a remarkable reduction in the time required to 
bring the detector to the zero setting. Furthermore, computer control of 
the atmosphere in the test compartment using a plurality of stored tables 
will contribute greatly to a quick return to the zero setting, which will 
accommodate more detection cycles within a certain period of time. The 
following table shows comparative data between the odor detector of the 
invention and a typical detector of conventional type, regarding the time 
required to bring the detector to the zero setting after a detection cycle 
of four minutes during which a particular sample was placed in the test 
compartment. 
______________________________________ 
Time Required To Return 
To Zero Setting 
Sample This Invention 
Conventional Type 
______________________________________ 
Soy Sauce 4 mins. 10 mins. 
Ground Coffee 
6 mins. 8 mins. 
Adhesive 10 mins. 25 mins. 
Ethanol 10 mins. 50 mins. 
Aceton 10 mins. 60 mins. 
______________________________________ 
As will be seen, the present invention can shorten the time required to 
bring the odor detector to the zero setting, by the factor of 3/4 to 1/6 
as compared to the conventional detector. 
Although the present invention has been described in terms of what are at 
present believed to be its preferred embodiments, it will be apparent to 
those skilled in the art that various changes may be made without 
departing from the scope of the invention. It is therefore intended that 
the appended claims cover such changes.