Automated forced-choice dynamic-dilution olfactometer and method of operating the same

An automated forced-choice dynamic-dilution olfactometer has an odor evaluation module having two or more panelist stations, with a plurality of sniffing ports at each station. At least one signal element at each station is connected to a data control unit. Separate air lines are connected to one each of the sniffing ports at each station. One of the air lines has an odor introduction port. The method of detecting an odorous stream of air in an automated forced-choice dynamic-dilution olfactometer and method of operating the same olfactor system comprises the steps of providing an odor evaluation module having at least two panelist stations; providing a plurality of sniffing ports at each station; providing a data control unit and connecting the control unit to a signal element at each station, providing separate air lines to one each of the sniffing ports at each station so that individual panelists at each station can separately sniff the air in each line, introducing an odor into one of the air lines, having the panelists at each station sniff each sniffing port to determine which air line contains the odor, and having each panelist actuate the signal element to advise the data control system as to which air line contains the odor.

This application is based upon the applicants' provisional application Ser. 
No. 60/011,215 filed Feb. 6, 1996. 
BACKGROUND OF THE INVENTION 
The livestock industry in the United States is expanding rapidly. However, 
expansion is being restricted by environmental problems. Odor is one of 
the major environmental problems for the livestock industry. The odors 
produced by livestock units originate from manure, ventilation exhaust air 
from farm buildings, animals, and feed. 
Before progress can be made on the abatement of this odor nuisance, a 
reliable method is required for quantifying odor concentration. 
Olfactometric measurements are of prime importance in the study and 
evaluation of the odor problem. The concentration of odor in air is 
measured with an olfactometer. The olfactometer is being used in research 
aimed at reducing odor problems associated with the livestock industry. 
A variety of olfactometry techniques have been used to measure odor 
concentration. They include the syringe dilution method, the scentometer, 
the butanol olfactometer, and various dynamic olfactometers. Many of these 
devices do not produce reliable results and this has limited the 
effectiveness of past odor research and regulation. In most research and 
regulatory institutions in Europe and Australia, dynamic-dilution 
olfactometry is now accepted as the `de facto` standard. Research on 
current dynamic dilution olfactometers started in the United States in the 
1970's which led to the American Society of Testing Material (ASTM) 
standard E679. "Determination of odor and taste by a forced-choice 
ascending concentration series methods of limits" (ASTM, 1979). 
This invention is directed to an automatic forced-choice, dynamic-dilution 
olfactometer aimed at measuring odor concentration associated with air 
from and surrounding livestock buildings. 
Odor is the sensation caused by odorant acting on the sense of smell. Odor 
concentration measurement is basically a threshold measurement. It 
measures quantitatively how many times more concentrated the odor is than 
its threshold concentration. The measurement is made through an 
olfactometer and panelists. A variety of olfactometry techniques have been 
used to measure odor concentration. 
Dynamic Olfactometry 
Odor concentration is measured in terms of an odor unit (ou), or how many 
times more concentrated the sample is than the threshold concentration. 
Olfactometry is the use of the human nose as the sensor for odor. Dynamic 
olfactometry is the technique whereby a stream of odorous air is 
continuously diluted with a stream of odor-free air before being presented 
to a panel of people through a sniffing port. Odor concentration is 
determined by finding the odor detection threshold. This is defined as the 
dilution of the original odor sample at which half the panel can just 
detect the odor while the other half cannot detect the odor. Detection of 
the odor is the sole criterion and not recognition or assessment of the 
strength, character, or quality of the odor. The threshold is usually 1/2 
to 1/10 the recognition or quality threshold. 
The detection threshold is found by presenting the panel with a series of 
dilutions of the odor sample. These dilutions should cover the range from 
where none of the panelists can detect the odor to where all panelists can 
detect the odor. This procedure allows determination of the perception 
curve, or the relationship between dilution and the percentage of the 
panel which correctly detects the odor. 
TABLE 1 
______________________________________ 
Properties of dynamic olfactometry 
Item Setting 
______________________________________ 
Method used forced-choice 
Number of dilution steps 
5(minimum) 
Order of dilution steps 
increasing concentration 
Factor between dilutions 
2 &lt; factor &lt; 3 
Panel number provisionally 8 
Dilution range up to 25000 
Shape of sniffing ports 
conical with diameter 4-7 cm 
maximum angle 7.degree. 
______________________________________ 
As determined by olfactometry, concentration is a dimensionless quantity 
equal to the dilution factor that must be applied to the sample to reach 
the odor detection threshold. For example, if a sample is diluted by a 
factor of 100 before the threshold is reached, it will have an odor 
concentration of 100 DT. 
SUMMARY OF THE INVENTION 
The device of this invention will include the following: 
Four response buttons per panelist from which each panelist indicates the 
port believed to contain the odor; 
A signal light which tells each panelist to begin sniffing and to indicate 
the conclusion of each test; 
Data latches for each button that serve to store each panelist's response; 
A multiplexing system that allows the data latches for each panelist to be 
read in sequence through a computer link; 
A program used to analyze and process the data; 
An input/output analog signal board for the input analog signal from the 
pressure transducer and flow meter and for sending out analog signals to 
each instrument; 
A digital output signal board with relays for controlling the automatic 
valves; 
A personal computer linked to the DAAC system. 
The method of this invention comprises the following: 
Step 1. Operator secures an odorous sample and starts the olfactometer 
control system. The start-up control panel appears on the monitor. 
Step 2. The operator activates the START button and is instructed to enter 
the sample name. 
Step 3. After the sample name is entered, the operator is instructed to 
select the starting dilution level. 
Step 4. The operator selects a number from 1 to 12 corresponding to the 
desired dilution level from 1:2.sup.3 to 1:2.sup.14, respectively. The 
control system begins establishing the desired dilution level and responds 
with "System increasing pressure, please wait". The pressure signal 
display in the "Sample Pressure Box" changes dynamically until the 
pressure reaches 3.5 PSI; the program responds with "Dilution is level A 
please begin sniffing". 
Step 5. The four panelists begin sniffing their respective 3 ports and 
depress the button corresponding to the sniffing port which they perceive 
contains the odor. The response of the four panelists is displayed in the 
monitor by changing signal lights on the computer screen. There were 8 
signal lights (4 for the evaluation buttons and 4 for the accept buttons) 
located on the monitor. 
Step 6. If all four panelists select the correct port corresponding to the 
odorous sample, then the statement "Evaluation Successful" appears and the 
test concludes.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The principle of odor measurement is that all materials which come in 
contact with the odor must be of low absorption; suitable materials being 
glass, Teflon.RTM., and stainless steel pipes and fittings as were used in 
the olfactometer system. 
FIG. 1 is a schematic diagram of the dilution system. This system dilutes 
the odor sample to the required range, provides each panelist with three 
air streams (one odorous and two odor free) of the same airflow rate, and 
randomly switches the port containing the diluted odorous airflow. It also 
allows determination of the detection threshold for standard odorants. 
The odor free air is supplied by compressed air regulated to 32 PSI. The 
compressed air passes through an activated charcoal filter to remove 
particulates, oil and to remove water vapor before entering the dilution 
system. The total airflow descantant rate through the olfactometer is 
about 250 1/min, as described below. 
A combination of four on/off automatic valves (v5-v8) with four orifices o5 
(d=0.026 inch), o6 (d=0.024 inch), o7 (d=0236 inch) and o8 (d=0.0126 inch) 
allow odor-free air to enter the sample container forcing the sample air 
into the dilution system by positive displacement. 
The pneumatic dilution system also uses two on/off automatic valves v2 and 
v3 along with two orifice plates o2 (d=0.0635 inch) and o3 (d=0.070 inch) 
and an electronic proportioning control valve (Va) to dilute the sample 
with fresh-air to various rates depending on the dilution level desired. 
Details related to each dilution level are shown in Table 2. An on/off 
automatic valve v4 with orifice plate o4 (d=0.070 inch) is used to 
predilute the sample so that the maximum dilution level of 1:16384 can be 
attained. 
TABLE 2 
______________________________________ 
The calculation of dilution level 
dilution 
Level 
O.sub.3 
Q.sub.3 (l/min) 
Q.sub.pa,o.sbsb.4 
Q.sub.pa,f (l/min) 
O.sub.d 
Q.sub.d (l/min) 
ratio 
______________________________________ 
1 O.sub.6 
8 X 8 O.sub.2 
56 2.sup.3 
2 O.sub.7 
7.7 X 4.1 O.sub.3 
62 2.sup.4 
3 O.sub.8 
3.6 X 2 O.sub.3 
62 2.sup.5 
4 O.sub.6 
8 62 9.8 O.sub.3 
62 2.sup.6 
5 O.sub.8 
3.6 62 9.29 O.sub.2 
56 2.sup.7 
6 O.sub.8 
3.6 62 4.6 O.sub.3 
62 2.sup.8 
7 O.sub.8 
3.6 62 3.3 O.sub.3 
62 2.sup.9 
8 O.sub.8 
3.6 62 1.12 O.sub.3 
62 2.sup.10 
9 O.sub.8 
3.6 62 0.55 O.sub.3 
62 2.sup.11 
10 O.sub.8 
3.6 62 0.277 O.sub.3 
62 2.sup.12 
11 O.sub.8 
3.6 62 0.138 O.sub.3 
62 2.sup.13 
12 O.sub.8 
3.6 62 0.069 O.sub.3 
62 2.sup.14 
______________________________________ 
After the sample air and the odor free air pass through their respective 
paths they are mixed together to give the required dilution. A dilution of 
up to 1:16348 times can be obtained. Thus, concentrations of the odor can 
be delivered to the panelists in the range between 1:2.sup.3 and 
1:2.sup.14. The mixed air stream Vo was further divided into four streams; 
one for each panelist station 10 (see FIG. 1). 
FIG. 2 is a schematic diagram of the panel response system. In the forced 
choice olfactometer of this invention, each panelist tests the air from 
more than one, and preferably three, sniffing ports 10A, 10B and 10C. Each 
station 10 has four response buttons (A1, B1, C1, D1-A4, B4, C4, D4) 
operatively connected to computer 18 (FIG. 5). The A, B and C series 
buttons pertain to sniffing ports 10A, B and C, respectively. The D series 
buttons are the "accept" buttons. The panel response system of this 
invention uses six on/off automatic valves (v10-v15) (see FIG. 3) that 
allow the dilution system to switch the diluted odorous air stream 
randomly between the three lines, 12, 14 and 16 (FIG. 2A) (one odorous; 
two odor free) so that panelists have no knowledge of which port will 
contain the odor. The panelist has to decide which contains the odorous 
air. At concentrations near the threshold, the panelist will select the 
port that he or she believes is most likely to contain the odor. 
The main criterion of the sniffing ports (10A, 10B and 10C) is that the 
panelist should be supplied with the minimum flow required for breathing 
and that he or she should not inhale air from outside the sniffing port. 
Airflow rates of between 16 and 64 1/min (i.e. 0.96 to 3.84 m.sup.3 /h) 
should be used depending upon the design of the sniffing port. The airflow 
rate passing through each sniffing port should be 16 1/min and the shape 
of each sniffing port was conical with a diameter of 7 cm and an angle of 
approximately 7 degrees. 
FIG. 3 is a schematic diagram of the distribution system. The airflow rate 
of the air stream passing through each sniffing port is 16 1/min. The 
distribution system allows 4 panelists to work simultaneously and each 
panelist has access to three sniffing ports. There are twelve sniffing 
ports with a total airflow rate required of 
(12 Port)(16 1/min/port)=192 1/min 
The total airflow was derived from two air streams; the odor free air 
stream and the odorous air stream. The odor free air stream passes through 
line A, and is distributed to a total of 8 sniffing ports with valves 
V.sub.13, V.sub.14 and V.sub.15. The maximum airflow rate for the 
odor-free air stream has a flow rate of: 
(8 ports)(16 1/min/port)=128 1/min 
The odor stream passes through line B as shown in FIG. 3 using one of the 
valves V.sub.10, V.sub.11 or V.sub.12. The odorous stream is then 
distributed to four sniffing ports; one for each panelist. The odorous air 
stream has a flow rate of: 
(4 ports)(16 1/min/port)=64 1/min 
The maximum dilution ratio (sample volume/total volume) required was 
selected as 1:16384 (1:2.sup.14) with a step factor of 2, resulting in 
dilution ratios of: 1:2.sup.3, 1:2.sup.4, 1:2.sup.5 . . . , 1:2.sup.14 
(V.sub.S :V.sub.T) where V.sub.S is the sample volume and V.sub.T is the 
total volume after dilution. The case of dilution ratio 1:2.sup.3 without 
pre-dilution is shown in FIG. 4. 
The diluted airflow rate passing through line B is 64 1/min and consists of 
two sources; one is the odor free airflow rate of 56 1/min passing through 
V.sub.2 (and orifice O.sub.2) ;the other one is the odorous air with a 
sample flow rate of 8 1/min which passes through valve V.sub.9 (and 
orifice O.sub.9) resulting in a dilution ratio of: 
8/64=1:2.sup.3 
The case of dilution ratio 1:2.sup.8 with pre-dilution will now be 
discussed. The electronic proportioning control valve (Va) can be 
continuously adjusted allowing the pre-diluted odorous air stream to pass 
through the flow meter at a flow rate QD of 4.7 1/min. The odor free air 
stream comes from valve V.sub.3 (and orifice O.sub.3) with an airflow 
Q.sub.D1 of 62 1/min resulting in a total airflow rate through line D of: 
4.7 1/min+62 1/min=66.7 1/min 
The airflow rate satisfies the required dilution ratio of 1:256 and the 
odorous airflow rate through line D becomes: 
##EQU1## 
The airflow rate of the stream passing through V.sub.3 was defined as 
Q.sub.K. The relationship between Q.sub.K, Q.sub.S, Q.sub.D and Q.sub.f is 
represented by Eqn. (1). 
##EQU2## 
where Q.sub.f is the pre-diluted odor free airflow rate of the stream 
which passes through valve V.sub.4 (and orifice O.sub.4) represented as; 
##EQU3## 
wherein: O.sub.3 : Orifice for sample. 
Q.sub.5 : Sample flow rate. 
Q.sub.pa, 04 : Predilution airflow rate measured by orifice O.sub.4. 
Q.sub.pa.f : Predilution flow rate measured by flow meter. 
O.sub.d : Orifice for diluted air. 
Q.sub.d : Diluted airflow rate measured by orifices O.sub.2 and O.sub.3. 
The DAAC (Data Acquisition, Data Analysis and Automatic Control System) of 
this invention provides panelists with a simple method for indicating 
which port they believe contains the odor. It also allows the olfactometer 
to signal to each panelist the start and finish of a test. The DAAC system 
developed for the olfactometer has the following components (see FIG. 5): 
Four response buttons per panelist from which each panelist indicates the 
port believed to contain the odor; 
A signal light which tells each panelist to begin sniffing and to indicate 
the conclusion of each test; 
Data latches for each button that serve to store each panelist's response; 
A multiplexing system that allows the data latches for each panelist to be 
read in sequence through a computer link; 
A program used to analyze and process the data; 
An input/output analog signal board for the input analog signal from the 
pressure transducer and flow meter and for sending out analog signals to 
each instrument; 
A digital output signal board with relays for controlling the automatic 
valves; 
A personal computer linked to the DAAC system. 
Data Acquisition System 
The test starts at any one of the 12 possible dilution ratios ranging 
between 1:2.sup.3 and 1:2.sup.14. The panelists depress the corresponding 
button when he or she determines the sniffing port believed to contain the 
odorous sample. Each of the four panelists can change their choice at any 
time before they push the "accept" button D. The new data will replace the 
data which was already latched by the register. After all four panelists 
have "accepted" their choice, the data is transferred to the computer 
through a digital signal input board. If all the panelists do not detect 
the odor, the DAAC system automatically decreases the dilution ratio by 
one step and the panelists are instructed to continue. FIG. 6 is a 
schematic diagram of the data acquisition system. 
Data Analysis System 
FIG. 6 identified the schematic of the data analysis system. The hardware 
interface stores each panelists response in buffers. The digital input 
signal produced by each button (0 or 1) is transferred to binary code by 
the hardware interface. Buttons A1, B1, C1, D1, A2, B2, C2, and D2 used by 
the first and second panelist correspond to 2.sup.0, 2.sup.1, 2.sup.2, 
2.sup.3, 2.sup.4, 2.sup.5, 2.sup.6, and 2.sup.7, respectively and in 
binary code range from; 
0 0 0 0 0 0 0 0 to 1 1 1 1 1 1 1 1 
and are stored in the 8-bit buffer 1. The same data format corresponding to 
buttons A3, B3, C3, D3, A4, B4, C4, and D4 for the third and fourth 
panelists were stored in the 8-bit buffer 2. The data analysis system 
processes the panelist's responses using the data sequence present in 
buffers 1 and 2. 
When panelists activate a button by physically depressing it, logic 
sequences are stored in buffers 1 and 2. For example, assume that for a 
particular sample tested, panelists 1, 2, 3, and 4 perceived the odor 
present in sniffing ports A, B, C, and C, respectively. The binary code 
storing this data in buffers 1 and 2 is shown in Table 3. As shown in 
Table 3, the binary code from each panelist's response, stored in buffers 
1 and 2, was identified as storage values AA.sub.1, AA.sub.2, AA.sub.3, 
and AA.sub.4, for panelists 1, 2, 3, and 4, respectively. 
TABLE 3 
______________________________________ 
Relation of the panelists and data 
panelist 
button buffer storage binary code 
______________________________________ 
first A.sub.1 1 AA.sub.1 
00000001 
second B.sub.2 1 AA.sub.2 
00100000 
third C.sub.3 2 AA.sub.3 
00000100 
fourth C.sub.4 2 AA.sub.4 
01000000 
______________________________________ 
A method was developed to detect when all panelists recorded the same 
response, resulting in two new storage values B and C. Values in B were 
the result of ANDing the values in buffers 1 and 2 with the 8-bit binary 
value 15, (00001111 or a hexadecimal H0F) where the ANDing operation was 
conducted bit-by-bit. The results are shown in Table 4 for the example 
response shown in Table 3. Values stored in C were the result of ANDing 
the values in buffers 1 and 2 with the 8-bit binary value 240 (11110000, 
or hexadecimal HF0), where again the ANDing operation was conducted 
bit-by-bit. The results are also shown in Table 4. 
TABLE 4 
______________________________________ 
The result of actual data AND reference data 
original 
binary 
A code B storage 
A AND H0F 
C storage 
A AND HF0 
______________________________________ 
AA.sub.1 
00000001 BB.sub.1 00000001 
CC.sub.1 
00000000 
AA.sub.2 
00100000 BB.sub.2 00000000 
CC.sub.2 
00100000 
AA.sub.3 
00000100 BB.sub.3 00000100 
CC.sub.3 
00000000 
AA.sub.4 
01000000 BB.sub.4 00000000 
CC.sub.4 
01000000 
______________________________________ 
The data values stored in C storage (Table 4) was shifted to the right 4 
places by dividing the C storage by 16 as shown in Table 5. This shifted 
data is again ANDed with binary 15, bit-by-bit, to form a new storage 
value D, designated DD.sub.1, DD.sub.2, DD.sub.3, and DD.sub.4, for 
panelists 1, 2, 3, and 4, respectively (Table 5). Any change from the 
panelists were saved as new data in storage E replacing the original data 
from Storage A (See Table 6). 
TABLE 5 
______________________________________ 
Data shifting 
Data C 
Binary code 
Data C/16 
Data C/16 AND H0F 
Storage D 
______________________________________ 
CC.sub.1 
00000000 xxxx0000 00000000 DD.sub.1 
CC.sub.2 
00100000 xxxx0010 00000010 DD.sub.2 
CC.sub.3 
00000000 xxxx0000 00000000 DD.sub.3 
CC.sub.4 
01000000 xxxx0100 00000100 DD.sub.4 
______________________________________ 
Table 6: The relationship of data B, data D and data E 
TABLE 6 
______________________________________ 
The relationship of data B, data D and data E 
Data B 
Binary code 
Data D Binary code 
E storage 
Binary code 
______________________________________ 
BB.sub.1 
0000 0001 DD.sub.1 
0000 0000 
EE.sub.1 
0000 0001 
BB.sub.2 
0000 0000 DD.sub.2 
0000 0010 
EE.sub.2 
0000 0010 
BB.sub.3 
0000 0100 DD.sub.3 
0000 0000 
EE.sub.3 
0000 0100 
BB.sub.4 
0000 0000 DD.sub.4 
0000 0100 
EE.sub.4 
0000 0100 
______________________________________ 
The analysis system compares the data in storages B and D with the 
reference data H08, i.e. 0 0 0 0 1 0 0 0. If the data in storages B and D 
are smaller than H08, then the data in storages B and D which were not 
equal to zero were transferred to storage E. Table 6 shows the results of 
the example after performing this operation. Note that storage E contains 
the binary equivalent of the panelists original response. Recall that the 
sample presented, shown in Table 3, had panelists 1, 2, 3, and 4 selecting 
buttons A, B, C, and D, respectively which corresponds to binary code 
00000001, 00000010, 00000100, and 00000100, respectively. 
After the panelists push the "accept" button (D1, D2, D3 or D4), the 
storage G is created storing this information as shown in Table 7. After 
all four panelists have pushed the accept button D, the data in storage E 
is transferred to storage F. Storage F, as shown in Table 7, is the final 
accepted data from the four panelists, for the current dilution level. 
TABLE 7 
______________________________________ 
Final data 
Data G Binary code Data F Binary code 
______________________________________ 
GG.sub.1 0000 1000 FF.sub.1 
0000 0001 
GG.sub.2 1000 0000 FF.sub.2 
0000 0010 
GG.sub.3 0000 1000 FF.sub.3 
0000 0100 
GG.sub.4 1000 0000 FF.sub.4 
0000 0100 
______________________________________ 
The above process in independent. If the first and second panelists push 
the "accept" button, only data FF.sub.1 and FF.sub.2 can transfer from 
Storage E to Storage F. The program will keep running until the responses 
from all four panelists are received. 
After all the data is transferred to storage F, the data analysis system 
will check whether data FF.sub.1, FF.sub.2, FF.sub.3, and FF.sub.4 are all 
the same. If they are not the same, implying that all four panelists have 
not detected the odor, then the program will repeat the entire process 
with a new dilution level and will continue until all the data in storage 
F is equal. The analysis system will compare storage F with a randomly 
generated integer K which determines the sniffing port containing the 
odor. If data F is equal to integer K, the test is completed; otherwise, 
the dilution level will be decreased to a higher level and the program 
will repeat the entire process. 
Automatic Control System (Feedback Control) 
The feedback loop is the dominant technique used in process control. A 
representation of a feedback loop is given in FIGS. 7A and 7B in 
conjunction with the olfactometer and shows its applications to airflow 
rate control of a dilution system. The value of the controlled variable is 
measured with a flowmeter, and is compared with the desired value (also 
know as set point). The difference between the set point and the control 
variable is known as the controller error. The output of the controller is 
determined as a function of this error, and is used to adjust the 
manipulated variable. 
In this dilution system, the flowmeter (OMEGA Engineering, Inc. Model 
FMMA-219) has its output change to a dc voltage varying between 0 v and 5 
v corresponding to airflow rates between 0 1/min and 10 1/min. The 
received signal is then converted to a mathematical number, with 5 v 
corresponding to binary 4095 (12-bit A/D converter) while 0v corresponds 
to binary 0. There were 12 set points used for this dilution system 
corresponding to the 12 different dilution ratios. The program compares 
the input signals with the set points and measures the difference, or 
error. 
In the dilution system example as shown in FIGS. 7A and 7B, the set point 
was chosen as 2.3 1/min to satisfy a dilution ratio of 1:2.sup.9. The set 
point 2.3 1/min was converted to binary 942 (2.3*4096/10) and stored in 
the computer. If the actual value measured by the flowmeter was 2.5 1/min, 
the analog output signal should be 1.25 v because 10 1/min corresponds to 
5 v and the output of the flowmeter is linear. This signal was converted 
to binary 1024, and was compared with the set point 924 for an error of 
82. The output signal was determined by a function of the error and the 
gain of the control. The relationship between the input and output signal 
at this point is the control action. If the gain was chosen as 40 then the 
output signal 3280 was converted to a 4 vdc voltage and was transmitted to 
the electronic proportioning control valve Va (FIG. 4), to adjust the flow 
rate of the stream which passes through the flowmeter. The feedback 
control loop was finally closed when the adjustment to the control valve 
Va affects the process, giving a new value of the measured variable 
received by the flowmeter. 
The olfactometer of this invention is operated with the following steps: 
Step 1. Operator secures an odorous sample and starts the olfactometer 
control system. The start-up control panel appears on the monitor. 
Step 2. The operator activates the START button and is instructed to enter 
the sample name. 
Step 3. After the sample name is entered, the operator is instructed to 
select the starting dilution level. 
Step 4. The operator selects a number from 1 to 12 corresponding to the 
desired dilution level from 1.2.sup.3 to 1:2.sup.14, respectively. The 
control system begins establishing the desired dilution level and responds 
with "System increasing pressure, please wait". The pressure signal 
display in the "Sample Pressure Box" changes dynamically until the 
pressure reaches 2 PSI; the program responds with "Dilution is level A 
please begin sniffing". 
Step 5. The four panelists begin sniffing their respective 3 ports and 
depress the button corresponding to the sniffing port which they perceive 
contains the odor. The response of the four panelists is displayed in the 
monitor by changing signal lights on the computer screen. There were 8 
signal lights (4 for the evaluation buttons and 4 for the accept buttons) 
located on the monitor. 
Step 6. If all four panelists select the correct port corresponding to the 
odorous sample twice, then the statement "Evaluation Successful" appears 
and the test concludes. 
If the four panelists do not select the odorous sample, then the statement 
"Evaluation Failed, Increasing Dilution Level. Please Wait" appears and 
the control system adjusts the dilution to a new level and steps 5 and 6 
are repeated. 
If at the conclusion of the final dilution level (1:2.sup.3) the four 
panelists still have not selected the odorous sample correctly, then the 
statement "Sorry, Sample is Odor Free" appears on the monitor and the test 
is concluded. 
The olfactometer of this invention was developed for the measurement of 
odor concentration which will reduce test time, increase the range and 
accuracy of the dilution level, as well as provide for data acquisition 
and data analysis. Thus, the objects of this invention have been met.