Odor identifying apparatus and method

An odor identifying apparatus comprising a gas sensor unit including at least two sensors having different characteristics for simultaneously detecting odorous components arising from a sample and outputting detection signals, a display device for displaying detection results from the sensor unit as a single output signal, and an ozone gas generator for supplying ozone gas into a chamber in which the sample is placed. An odor identifying method is also disclosed which identifies odorous components by using this apparatus.

FIELD OF THE INVENTION 
The present invention relates to an odor identifying apparatus and method 
for detecting and identifying various odors. 
DESCRIPTION OF THE PRIOR ART 
The necessity often arises in the food industry and perishable food 
handling business to carry out quality control of various foods based on 
their flavors. Conventionally, such quality control takes the form of an 
organoleptic test by a panel of specialists or, where a stricter 
measurement is required, employs a gas analyzer such as a gas 
chromatograph or a gas chromatograph-mass spectrometer. 
The organoleptic test by a panel of specialists, however, inevitably 
produces measurement results influenced by differences among the 
individual panelists. It also has various problems such as of considerable 
cost and time necessary for training personnel to become specialists. The 
method of measuring odorous components with a gas analyzer lacks accuracy 
in direct identification of odorous components since the intensity of odor 
perceived by humans does not always agree with the amount of odorous 
components detected by the analyzer. Furthermore, the analyzer is a 
sophisticated machine troublesome to operate and requiring skill and time 
to use it in measurement. Besides, the analyzer itself is costly. 
SUMMARY OF THE INVENTION 
Having regard to the state of the art noted above, the object of the 
present invention is to provide an odor identifying apparatus which is 
free from the disadvantages of the prior art, capable of comparing and 
identifying various odors (volatile substances) easily, speedily and with 
high precision, and yet compact in construction and inexpensive. The 
present invention also intends to provide an odor identifying method 
utilizing this apparatus. 
In order to achieve the above object, an odor identifying apparatus 
according to the present invention comprises a gas sensor unit including 
at least two sensors having different characteristics for simultaneously 
detecting odorous components arising from a sample and outputting 
detection signals, and display means for displaying detection results from 
the sensor unit as a composite output signal, wherein an ozone gas 
generator is provided for supplying ozone gas into a chamber in which the 
sample is placed. 
An odor identifying method according to the present invention comprises the 
steps of placing a sample on a sample holder, simultaneously detecting 
odorous components arising from the sample with at least two gas sensors 
included in a gas sensor unit and having different characteristics, 
outputting detection results, and displaying the output signals at display 
means as a composite output signal, wherein, prior to detecting the 
odorous components, ozone gas generated by an ozone gas generator is 
supplied into a chamber in which the sample is placed. 
In the odor identifying apparatus according to the present invention, the 
characteristics of odorous components are picked up as an output ratio 
between a plurality of, for example, two, gas sensors, and detection 
results provided by the gas sensors are displayed as the trace of a single 
output signal. An ozone gas generator is disposed in a chamber in which a 
sample is placed, for generating ozone gas after the measurement. Ozone is 
used for the purpose of cleaning not only the sensor unit but also the 
odorimetric chamber. Consequently, the sensor outputs are easily and 
quickly adjusted to zero to allow a next measurement to be taken without 
influences of the residual gas. The odor identifying apparatus thus allows 
the number of measurements to be increased while maintaining high 
measuring precision, thereby enabling efficient measurement operations. 
Besides, this odor identifying apparatus is compact and inexpensive since 
it is constructed without incorporating any complicated mechanisms. 
In effecting quality control of products of the same kind by means of the 
odor identifying apparatus and method according to the present invention, 
for example, measurement is taken of the extent of deviation from quality 
characteristics of standard products determined in advance. This feature 
realizes great utility in that the qualities of the products subjected to 
the measurement may be judged promptly and reliably. 
In particular, the odor identifying apparatus according to the present 
invention directly detects odors of a sample by means of the sensors 
instead of employing the sampling method as practiced with the gas 
chromatograph and gas chromatograph-mass spectrometer in which odors of a 
sample are collected first and are then introduced to an injector. The 
direct odor detection in the apparatus of the present invention assures a 
high degree of reliability and reproducibility with regard to measuring 
precision and results of measurement. 
Furthermore, the identification of odorous components is effected without 
involving contact with the sample according to the present invention. This 
feature protects the sample from damage and minimizes contamination by the 
sample of the apparatus per se for facility of its maintenance. 
Other advantages of the odor identifying apparatus and method according to 
the present invention will be apparent from the detailed description of 
the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An odor identifying apparatus and method embodying the present invention 
will be described in detail hereinafter with reference to the drawings. 
FIG. 1 shows a constructional outline of the odor identifying apparatus, 
and FIG. 2 an outward appearance of a main body of the apparatus (i.e. 
excluding a display device). 
The odor identifying apparatus comprises a chamber 1 housing a sample 
holder including a vessel 5 and a table 4, and a gas sensor unit A 
including two gas sensors 2 and 3 having different characteristics. The 
apparatus further comprises an X-Y recorder 13 acting as display device 
for displaying detection results from the gas sensor unit A as a composite 
output signal, and driving power sources 10 and 11 connected, 
respectively, to a heater 7 mounted inside the table 4 and to an ozone gas 
generator 12 for adjusting the output of the gas sensor unit A to zero. 
As shown in FIG. 2, the chamber 1 is formed of removable transparent glass 
to allow visual observation from outside of a sample placed in the chamber 
1. The chamber 1, however, need not be transparent but will serve the 
purpose if formed of a material inadsorptive to odorous components. 
Materials having this property include tetrafluoroethylene resin such as 
Teflon, and glass. It is desirable for the sample holder and an outer 
frame of the gas sensor unit A, besides the chamber 1, to be formed of the 
materials inadsorptive to odorous components to enhance measuring 
precision. 
The ozone gas generator 12 need not be disposed inside the chamber 1 but 
ozone gas may be introduced into the chamber 1 from outside as shown in 
FIGS. 2 and 3. 
The heater 7 mounted inside the table 4 is for heating sample 6 placed on 
the vessel 5. The heater 7, although not an essential component of the 
apparatus, may be used to heat a sample having only slight odorous 
components and promote their evaporation in preparation for the 
measurement. Thus, the heater 7 has the effect of substantially enhancing 
sensitivity of this apparatus. When the sample is heated slowly, volatile 
substances evaporate at low temperatures whereas substances that are not 
volatile evaporate at high temperatures. Consequently, different odorous 
components, or component ratios, occur from the sample at low temperatures 
and at high temperatures, which facilitates identification of the sample. 
In other words, the entire shape of a curve displayed on the X-Y recorder 
13 may be seen as identification data. 
Furthermore, this apparatus may be used also as thermal gas analyzer for 
EGD or evolved gas detection as illustrated in FIG. 7 which will be 
described later. As seen from FIG. 1, instead of applying output of one of 
the sensors in describing a line on the X-Y recorder 13, a thermocouple 8 
for measuring sample temperatures may be connected through an electric 
converter 9 to the X-Y recorder 13 for describing a line. Then, voltage of 
the thermocouple 8 is input to the X-axis. This construction allows grasp 
of the odorous components resulting from heating. 
The chamber 1 defines an opening for putting sample 6 into and taking it 
out of the chamber 1. This opening preferably has a tight-sealing 
construction to seal the interior of the chamber 1 from ambient air. For 
example, an inner lid may be provided with a packing. 
The ozone gas generator 12 may comprise a lamp or the like for generating 
ultraviolet rays (having a wavelength of 2537.ANG., for example). Ion 
atmosphere may be used instead, which is generated from a needle electrode 
connected to a high voltage source, or other devices may be employed for 
the purpose of this invention. The ozone gas generator 12 allows the 
sensor output to be set to zero with ease and speed, which realizes a 
quick, stable and accurate measurement. The use of ozone gas generator 12 
provides the further advantage of cleaning the chamber interior. The ozone 
gas generation by the ozone gas generator 12 may be followed by injection 
into the chamber 1 of clean air having flowed through activated carbon or 
an inert gas such as argon gas or nitrogen gas, which step is taken for a 
fixed period with the ozone gas generator 12 turned off. 
As shown in FIG. 4 in particular, clean air having flowed through activated 
carbon is injected into the chamber 1 by means of a clean gas injector 
after the ozone gas generation, whereby the sensor output is set to zero 
with increased speed. In FIG. 4, reference a represents a case where the 
gas is not introduced after measurement, reference b represents a case 
where clean air having flowed through activated carbon is introduced after 
a measurement, reference c represents a case where ozone gas is generated 
and introduced after a measurement, and reference d represents a case 
where ozone gas is introduced and then clean air having flowed through 
activated carbon is introduced after a measurement. 
As shown in FIG. 3, the clean gas injector may comprise a pump 15 which 
injects clean air into the chamber 1 through a filter 14 provided below 
the table 4 and including activated carbon and a dehydrating agent. In 
this case, the ozone gas generator 12 is stopped and the pump 15 is 
actuated whereby fresh air is allowed to flow from an intake opening 14' 
through the filter 14, and discharged through an exhaust opening 15'. An 
ozone gas decomposing filter 16 is provided for preventing an adverse 
effect resulting from the passage of ozone gas through the pump 15. 
Reference number 17 in FIG. 2 indicates a timer switch for setting an 
ozone gas generating time, number 18 indicates a power switch, number 19 
indicates a measurement start switch, number 20 indicates zero adjustment 
knobs connected to the respective sensors, number 21 indicates a range 
switching knob, number 22 indicates a sensor unit connector, number 23 
indicates digital display panels for displaying outputs of the respective 
sensors, number 24 is an X-Y recorder connector, and number 25 indicates a 
power switch for the heater. 
The odor identifying method using the foregoing apparatus will be described 
next. 
First, the ozone gas generator 12 is actuated to generate ozone gas, which 
is introduced into the chamber 1. Next, the pump 15 is actuated to 
introduce clean air into the chamber 1, completely remove the ozone gas 
from the chamber 1 and clean the chamber interior. Thereafter the sensor 
outputs are adjusted to zero by means of the zero-point adjusting knob 20. 
Then a suitable amount of sample 6 is placed in the vessel 5 and the 
chamber 1 is sealed. The heater 7 is used to heat the sample 6 as 
appropriate if the sample 6 is a substance that does not readily give off 
odorous components. 
The odorous components produced from the sample 6 are detected by the two 
gas sensors 2 and 3 having different characteristics. The results of 
detection are displayed and recorded by the X-Y recorder 13. The two gas 
sensors 2 and 3 detect the odorous components independently of each other, 
which result in biased graphs reflecting the nature of the odorous 
components. 
Thus, a quality dispersion in products of the same kind may be determined 
with ease and products falling outside a quality control range found 
easily and positively by measuring the odorous components of a standard 
sample and recording these odorous components in the X-Y recorder 13 
together with the control range in advance, which range is fixed with 
reference to standard sample data. A device may readily be provided for 
automatically giving an alarm when a product checked is outside the 
control range. 
The device for displaying the detection results from the gas sensor unit as 
a single output signal may comprise, instead of the X-Y recorder, a CPU 
for comparing the detection results from the two sensors and processing 
the biases provided by the respective sensors. The results provided by the 
CPU may, for example, be displayed on a CRT display. 
Experiments have been conducted on the identifying apparatus and method of 
the present invention in which the odorous components of various samples 
are detected. The particulars of these experiments will be described now. 
Experiment 1 
Tea, instant coffee powder and coffee bean powder were used as samples, and 
their odorous components were detected by the two sensors. The X-axis 
sensor comprised a semiconductor gas sensor of the sintered type 
manufactured by adding an alkaline earth metal oxide (CaO) to tin dioxide 
(SnO.sub.2). The Y-axis sensor comprised a film type semiconductor gas 
sensor manufactured by depositing tin dioxide (SnO.sub.2) on a 
heat-resistant insulating substrate. 
The X-axis sensor was particularly sensitive to gases of alcohol, aldehyde 
and other oxygen-containing organic compounds. The Y-axis sensor was 
non-selective and was sensitive to all types of gas. 
FIG. 5 shows results of the measurement obtained from the combination of 
the above sensors. 
In FIG. 5, reference A represents measurement data of tea powder, reference 
B measurement data of instant coffee powder, and reference C measurement 
data of coffee bean powder. 
It will be seen that each sample is identifiable from the unique curve it 
describes. In particular, there is a clear distinction between instant 
coffee powder and coffee bean powder though they are both coffee products. 
Experiment 2 
This experiment employed Geraniol, 1-Citronellol and a 1:1 mixture of the 
two substances as samples. The results of the measurement are shown in 
FIG. 6 as referenced D, E and F, respectively. 
It will be seen that these samples may also be clearly identified. 
Experiment 3 
This experiment employed two types of tea powder, i.e. Lipton's Orange and 
Twining's Bergamot, and coffee powder. The results of the measurement are 
shown in FIG. 7 as referenced J, K and L, respectively. The measurements 
were taken by incorporating a time factor in this case. Reference J 
corresponds to 15 minutes from start till finish of the measurement, 
reference K to 10 minutes, and reference L to 3 minutes. It is clear from 
the measurement results that there are considerable differences in time 
dependence among the two different types of tea powder and coffee powder 
with respect to generation of odorous components. 
Thus, the odor identifying apparatus according to the present invention is 
adaptable as an identifying apparatus of increased sensitivity which 
allows grasp of overall shapes by adding the time factor. 
Experiment 4 
This experiment employed cigarette filters before and after use as samples 
and measured odorous components produced through heating. The results are 
shown in FIG. 8. 
In FIG. 8, reference H represents detection data relating to the unused 
cigarette filter, and reference I detection data relating to the used 
filter. The graph clearly shows that tar and the like produced through 
smoking had been absorbed in the used filter and began to evaporate as 
odorous components at a relatively low temperature below 100.degree. C. 
Apart from the sensors employed in the above embodiment, the following 
various sensors may be used in combination for measuring odorous 
substances: 
(1) a sintered type sensor manufactured by adding lanthanum trioxide 
(La.sub.2 O.sub.3) or other rare earth oxide as well as an alkaline earth 
metal oxide to tin dioxide for detecting alcohol, aldehyde, ketone, acid, 
ester and other oxygen-containing organic compounds, 
(2) a film type sensor having tin dioxide and zinc oxide as main components 
for detecting hydrogen sulfide, mercaptan, sulfide and other 
sulfur-containing organic compounds, 
(3) a sintered type sensor manufactured by adding palladium or the like to 
tin dioxide for detecting ammonia, amine and other nitrogen-containing 
organic compounds, and 
(4) a sintered type sensor manufactured by controlling surface activity of 
tin dioxide or adding a noble metal catalyst to tin dioxide for detecting 
benzene, xylene, methylcyclohexane, hexane and other unsaturated or 
saturated hydrocarbons. 
While two sensors having different characteristics are used in the 
foregoing embodiment, the number of sensors may be increased according to 
purpose. Measuring precision may be enhanced for a higher identifying 
performance by using an operating device such as a CPU for processing the 
sensor outputs and allowing composite display and recording of these 
outputs. 
Further, in the foregoing embodiment only solid samples are used as objects 
to be identified but the samples may also be in fluid form such as liquid. 
The odor identifying apparatus and method according to the present 
invention may be used for various purposes, such as freshness rating of 
perishable foods, standard setting for shipment of various food, quality 
control of cosmetics, and flavoring. In other words, the present invention 
has a very wide range of application, and may be used in any fields of 
industry that handle volatile substances.