Breath test simulator and method

A breath test simulator and method for accurately calibrating breath test instruments used to determine the concentration of ethyl alcohol in breath. The simulator includes concentric chambers filled with a known concentration of ethyl alcohol-water solution. Air flowed into the first chamber is bubbled up through the solution in that chamber, sputtered through openings formed in the wall separating the chambers, bubbled up through the solution of the second chamber and is flowed thence to the breath test instrument. The air pressure and temperature of the solutions are accurately controlled to assure the effluent precisely simulates human breath leaving a precisely known alcohol vapor concentration.

The invention relates to apparatus and methods for supplying a breath test 
instrument with an effluent having a precisely controlled concentration of 
ethyl alcohol. The effluent is used to calibrate breath test instruments 
prior to conducting a breath test to determine the concentration of 
alcohol in the breath of a subject and indirectly, the amount of alcohol 
in the subject's blood. Breath tests are commonly used to determine 
whether the subject has violated a drunk driving law. 
The accuracy of the breath test is directly dependent upon how accurately 
the machine is calibrated and the calibration test is only as accurate as 
the alcohol vapor concentration in the effluent supplied by the simulator. 
The simulator of the present invention flows air through an alcohol-water 
solution of given concentration and controlled temperature to provide a 
discharge effluent having a precisely controlled alcohol concentration. 
Repeated operation of the simulator will produce an effluent with the same 
alcohol concentration provided the alcohol in the solution is not 
depleted. By assuring that the effluent has a constant known alcohol 
concentration, the instrument is calibrated accurately and subsequent 
breath tests accurately measure the blood alcohol concentration of the 
subject. 
At present, breath test instruments are calibrated using breath test 
simulators having a single glass chamber for the alcohol-water solution 
and an attached top with dependent mercury column thermometer, heating 
element, bubbler tube and paddle wheel stirrer. In most cases, a manual 
squeeze bulb is used to flow ambient air to the bubbler tube. The air 
bubbles up through the 500 ml. alcohol water solution within the chamber 
and into the head space from which it is flowed to the breath test 
instrument. In some cases, an air pump may be used to flow a continuous 
discharge through the simulator and to the instrument. Conventional 
simulators of the type described are manufactured by Luckey Laboratories, 
Inc. of San Bernardino, Calif. 
Conventionally, breath test instruments used to determine blood alcohol 
concentrations are calibrated on the assumption that the simulator is a 
precision instrument and reliably and repeatedly provides an effluent 
having a known alcohol vapor concentration. In the field, there is no way 
of checking whether or not the simulator effluent alcohol concentration is 
correct. 
An analysis of the conventional breath test simulator and its mode of 
operation concludes that the alcohol concentration in the effluent 
unpredictably varies sufficiently so that there is no assurance that a 
breath test instrument can be calibrated accurately using the effluent. As 
a result, any subsequent breath test performed by the instrument is 
inaccurate. The inherent inaccuracy of the simulator renders the breath 
test inaccurate. See, Dubowski, Breath-Alcohol Simulators: Scientific 
Basis and Actual Performance, Vol. 3, Journal of Analytical Toxicology, 
September/October 1979, pp. 177-182. 
All breath test simulators generate an alcohol vapor effluent by bubbling 
air through an ethyl alcohol-water solution. The alcohol concentration in 
the solution is determined in accordance with Henry's Law to result in a 
desired alcohol vapor concentration at a given temperature. Most breath 
tests are conducted to closely simulate exhaled human breath having a 
temperature of 34.degree. C. with an alcohol concentration of 100 mg. per 
210 liters. This concentration theoretically yields a reading of 0.100 on 
a properly calibrated breath test instrument to reflect the standard 
assumed breath alcohol concentration/blood alcohol concentration ratio of 
2100:1. 
As shown by Dubowski, the partition ratio for the ethyl alcohol-water 
solution is highly temperature dependent. Between 34.degree. C. and 
35.degree. C., the partition coefficient increases by 6.8 percent per 
degree of temperature increase. This large temperature dependence of the 
alcohol vapor concentration means that slight variations in the 
temperature of the solution can markedly change the concentration of 
alcohol in the effluent. Measurements of the solution temperature in the 
conventional simulator set at an operating temperature of 34.degree. C. 
indicate a true mean temperature of 34.16.degree. C. with a range of 
34.01.degree. C. to 34.33.degree. C. This temperature variation causes 
significant fluctuations in the effluent alcohol concentration and 
prevents accurate calibration of the breath test instrument. 
The alcohol concentration in the discharge effluent of conventional breath 
test simulators may vary due to changes in the temperature of the head 
space above the water-alcohol solution. The alcohol concentration in the 
head space vapor may be increased due to radiation heating from the 
simulator cover. Additionally, the rapid pulsed flow of ambient air into 
the simulator tends to cool the solution in the conventional single 
chamber simulator and increases temperature variations in the solution. 
Because of these and other problems inherent in conventional simulators, 
Dubowski concludes that they are not precision calibrating devices and 
should not be so used to calibrate breath test instruments. 
The disclosed simulator is a precision instrument capable of accurately and 
repeatedly calibrating breath test instruments for precision measurement 
of breath alcohol concentration. The instrument includes two 
interconnected chambers filled with ethyl alcohol-water solution with one 
chamber surrounding the other chamber. The chambers are interconnected 
through openings in the bottom of the common wall so that stirring of the 
inner chamber flows solution into and out of the outer chamber to 
continuously agitate and intermix the solution in both chambers. The 
temperature of the solution in the inner chamber is very accurately 
controlled by a precision temperature sensor and resistive heating 
elements in the inner and outer chambers energized by a proportional 
controller. The temperature of the inner solution, as measured by the 
sensor, is maintained to 34 plus or minus 0.02.degree. C., assuring that 
the effluent discharged from the head space above the inner chamber has a 
desired alcohol concentration of plus or minus 0.14 percent. The head 
space above the inner chamber is purged of collected vapor prior to a test 
to assure the vapor flowed to the instrument is not a uniform temperature. 
The improved simulator includes an air filter, pump and regulator adjusted 
to deliver filtered ambient air to the outer chamber at a pressure of 
about 8 to 10 inches of water, closely simulating the pressure of normally 
exhaled human breath. This air is flowed into an annular dispersion ring 
located within the outer chamber below the rest surface of the solution 
and above the mixing holes communicating the chambers. The ring includes a 
series of fine holes so that the air is formed into small bubbles which 
rise up the solution and collect in the closed outer chamber head space. 
Further flow of air into the outer chamber head space increases the volume 
of the head space to force solution in the outer chamber into the inner 
chamber through the mixing holes and through a series of closely spaced 
diffusion holes formed around the circumference of the common wall above 
the ring. When the level of the solution in the outer chamber is lowered 
to the level of the diffusion holes, air is bubbled up through the 
remaining solution in the outer chamber and then is sputtered into the 
solution in the inner chamber and rises up this solution. The flow of 
solution from the outer chamber increases the solution volume of the inner 
chamber to increase the bubble rise distance. Rotation of the stirring bar 
forms a vortex in the inner chamber with solution being thrown outwardly 
and up against the common wall to increase the rise distance. The air 
sputtered into the inner chamber through the diffusion holes rises up 
through the actively swirling vortex to the inner chamber head space and 
is flowed to the instrument. 
During the initial seconds of the breath test cycle, the vapor in the inner 
chamber head space is vented to the atmosphere to assure that the solution 
supplied to the breath test instrument is at the desired temperature. The 
flow of solution into the inner chamber during startup aids in ejecting 
the original head space vapor. 
The stir bar assures that the solution in the outer chamber is actively 
mixed with the solution in the inner chamber and maintained at 
approximately 34.degree. C. Heaters are provided in the outer chamber to 
compensate for heat loss through the exterior walls. The outer chamber 
effectively insulates the inner chamber from the heat loss through the 
common wall. 
As the air is bubbled through the outer chamber, sputtered through the 
common wall into the inner chamber and bubbled up through the actively 
swirling vortex in the inner chamber, it is heated to the temperature of 
the solution and acquires an equilibrium concentration of alcohol vapor. 
The solution in the inner chamber is accurately maintained at 34.degree. 
plus or minus 0.02.degree. C. to assure that when the air enters the inner 
chamber head space it is essentially exactly at the desired temperature 
and, according to Henry's Law, contains the desired alcohol concentration 
dependent upon the concentration of alcohol in the solution. While in 
practice, the temperature of the solution in the outer chamber may vary 
slightly from the temperature of the solution in the inner chamber, the 
sputtering of the air into the inner chamber and the bubbling up through 
the actively swirling inner chamber vortex assure that the head space 
vapor is maintained at the desired temperature. 
During startup of the simulator, nonproportional boost heaters are powered 
until the temperature of the solution nears the desired temperature. These 
heaters are then deactived so that the temperature of the solution is more 
slowly raised by the proportionally controlled heaters to the desired 
operating temperature. In this way, the simulator may be heated to the 
operating temperature in as little as 5 minutes. 
The two-chamber simulator uses a one-liter charge of alcohol-water solution 
with about one-half liter of solution in each compartment. In contrast, 
the conventional simulator uses 500 ml. of solution. The use of a larger 
total volume of solution means that the concentration of alcohol in the 
solution is depleted more slowly per test than the concentration in the 
conventional simulator. In calibration tests requiring equal volumes of 
effluent, the solution in the present simulator will be depleted of 
alcohol twice as slowly as the solution in conventional simulators and 
will have to be replaced one-half as often. 
In the disclosed simulator, the common wall between the inner and outer 
chambers is sandwiched between the base and cover plate and the inlet 
pipe, outlet pipe, heaters and sensor are carried by the cover plate. This 
means that the chambers are easily cleaned by removing the cover plate and 
freely lifting the separating or inner wall from the base plate. The 
remaining outer wall and plates are then easily cleaned without having to 
reach into the narrow outer chamber. 
Other objects and features of the invention will become apparent as the 
description proceeds, especially when taken in conjunction with the 
accompanying drawings illustrating the invention, of which there are three 
sheets and one embodiment.

DESCRIPTION OF THE INVENTION 
Breath test simulator 10, shown in FIGS. 2 through 5, includes a 
rectangular base plate 12, removable rectangular cover plate 14 and inner 
and outer concentric cylinders 16 and 18. The lower end of the inner 
cylinder fits loosely a round recess 20 formed in the upper surface of 
plate 12. The bottom of the outer cylinder is sealed to the base plate at 
joint 22. The upper ends of cylinders 14 and 16 are at the same level, 
each including a central groove with O rings 24 fitted therein for forming 
fluid and gas-tight seals with the flat lower surface of cover plate. The 
cylinders 16 and 18 are held between plates 12 and 14 by four clamp bolts 
26. The clamp bolts extend through the corners of the base and cover 
plates and include heads engaging the lower corners and wing nuts 28 
engaging the cover plate. Tightening down of the wing nuts holds the two 
cylinders in position as shown in FIG. 2 to form an inner cylindrical 
chamber 30 defined by the inner wall of inner cylinder 16 and the adjacent 
portions of the inner walls of the base and cover plates and an outer 
hollow cylindrical chamber 32 defined by the outer surface of cylinder 16, 
the inner surface of cylinder 18 and the adjacent surfaces of the base and 
cover plates. Chambers 30 and 32 have approximately the same volume. 
The inner and outer cylinders 16 and 18 may be formed of transparent 
material, such as Lucite plastic although other materials may be used if 
desired. The base and cover plates may be formed of plastic or aluminum. 
The base plate is formed from a non-magnetic material because of the 
magnetic stirrer used to agitate the contents of chambers 30 and 32. If 
desired, the outer surfaces of the simulator may be insulated. 
A conventional magnetic stirrer motor 34 is secured to the lower surface of 
base plate 12 in the center of inner cylinder 16 and a magnetic stirrer 
bar 36 is positioned on the bottom of recess 120 over the motor 34 such 
that actuation of the motor 34 rotates the stirrer bar in the direction of 
arrow 38 shown in FIG. 3. 
Eight spaced solution mixing holes 40 are extend through the bottom of 
inner cylinder 16 slightly above the upper surface of base plate 12. The 
holes 40 are formed at an angle of approximately 45 degrees to a radius 
extending through the center of the inner end of each hole with the inner 
end of each hole located counterclockwise of the outer end of the hole 
when the cylinder is viewed from the top. In this way, solution in the 
inner chamber is rotated clockwise by the mixing bar 36 and is forced 
through the angled mixing holes and flows into the solution in chamber 32. 
The flow from the inner chamber to the outer chamber is in response to the 
passage of the ends of the stirrer bar 36. The solution flows back from 
the outer chamber to the inner chamber after passage of the ends. 
A series of closely spaced radial secondary diffusion holes 42 extend 
through the inner cylinder 16 in a ring with adjacent holes 42 spaced 
apart approximately three times the diameter of individual holes. The 
holes 42 are located in the middle of cylinder 16 between plates 12 and 
14. 
In a breath test simulator 10 having a total solution volume of 
approximately 1 liter, the inner chamber 30 may have a diameter of 
slightly less than four inches and the outer chamber may have a diameter 
of slightly less than 6 inches. Holes 40 may be about 1/4 inch in diameter 
and holes 42 may be approximately 1/16 inch in diameter and spaced apart, 
diameter to diameter, by approximately 3/16 inch. The row of holes 42 may 
be about 2 inches above the base plate 12. The height of the outer 
cylinder 18 is about 5 inches. 
Circular hollow air dispersion ring 44 is located in the center of outer 
chamber 32 approximately midway between the inner and outer cylinders and 
at a level about midway between the diffusion holes 42 and mixing holes 
40. Ring 44 is connected to and supported by an air inlet pipe 46 which 
extends through cover plate 14 and down the outer chamber to the ring. 
Circumferential rows of small bubble holes 48 are formed through the 
inside, outside and bottom of the dispersion ring so that air flowing 
through the inlet pipe 46 to the ring is flowed into the solution in the 
inner chamber in the form of a large number of fine bubbles. 
Effluent outlet pipe 50 extends through simulator top plate 14 into chamber 
30 with an inlet end 52 located on the axis of the concentric cylinders 16 
and 18 and facing upwardly toward the top plate. The end is connected to 
the remainder of the pipe by a reverse bend 54. An exhaust pipe 56 extends 
through cover plate 14 to the top of the outer chamber 32. 
Electric resistance heater 58 is immersed in the solution in inner chamber 
30 and is supported in the chamber on a rigid shaft 60 extending through 
the cover plate 14. Shaft 60 carries the power leads for heater 58. A pair 
of like resistance heaters 62 extend into the solution in the outer 
chamber 32 on diametrically opposite sides of the chamber. Another 
resistance heater 64 extends into the solution in chamber 32 between the 
heaters 62. Heaters 62 and 64 are supported on the cover plate 14 
similarly to heater 58. All the heaters have a 65-watt output when fully 
powered. An accurate resistive temperature sensor 66 is supported on the 
upper plate 14 and extends into the solution in the inner chamber 30 
across from the heater 58. The ends of the heater 58 and sensor 56 are 
above the path swept by magnetic stirrer bar 36. 
The temperature of the solution in chambers 30 and 32 is accurately 
monitored and controlled by electric temperature control 68. When the 
simulator 10 is used in calibrating breath test instruments, the 
temperature of the water-alcohol solution should be maintained at exactly 
breath temperature, 34.degree. C. The control assures that the solution in 
simulator 10 is initially rapidly heated to a temperature slightly below 
the desired temperature, is then heated to the desired 34.degree. C., and 
is accurately maintained at the desired 34.00 temperature with a variation 
as small as 0.02.degree. C., as measured by sensor 66. Insulation 
surrounding the simulator may be used to help maintain the temperature 
accurately, particularly where the ambient temperature is low. 
The control 68 includes a digital temperature readout 70 which reads the 
temperature sensed by sensor 66. A control line for warm-up heater 64 
includes a temperature boost power source 72 and a non-proportional 
on/off, controller 74 for source 72. During warmup of the simulator, 
controller 74 actuates source 72 to energize heater 64 until the 
temperature sensed by sensor 66 is slightly less than desired operating 
temperature for the solution. In the case of a 34.degree. operating 
temperature, the cutoff temperature for controller 74 may be 32.5.degree. 
C. 
A control line for heaters 58 and 62 includes a proportional triactor power 
source 76 and a proportional controller 78 for actuating the triactor 
power source. When the simulator is used in calibrating breath tests at an 
operating temperature of 34.degree., the set points for the proportional 
controller 78 may be as small as 34 plus or minus 0.02.degree. C. 
The on time of controller 78 is determined on a time base by the deviation 
of the sensed temperature from the desired or set point temperature. As 
the set point temperature is approached during warm-up, the heaters 58 and 
62 are alternatively energized and de-energized. The length of each period 
when the heaters are de-energized or off is predetermined by a setting in 
control 68. The length of each on time interval is variable, depending 
upon the difference between the temperature sensed by sensor 66 and the 
desired operating temperature, the heating elements are energized for 
progressively shorter intervals of time until the sensed temperature 
reaches the operating temperature. Then, the heaters are deactivated until 
the sensed temperature falls below the operating temperature set point. 
When the simulator is at the operating temperature of 34.degree. C., the 
observed temperature is controlled to 34 plus or minus 0.02.degree. C. 
The energy supplied to the heaters when power source 76 is on is internally 
adjustable in control 68 as is the cycle rate for controller 78. For 
example, the cycle rate may vary from 2.4 seconds down to 0.150 second. 
Shorter cycle rates are preferred for accurate temperature control. The 
triactor of power source 76 is preferably zero-fired for full power line 
cycles. This effectively eliminates radio frequency interference noise and 
half-waving of the alternating current voltage. 
Control 68 includes an internal calibration source 80 which is preferably 
adjusted to a National Bureau of Standards reference for assured accuracy. 
The source has the properties of sensor 66 at the desired operating 
temperature, in the case of breath test analysis, 34.00.degree. C. The 
control 68 includes a switch for substituting source 80 for sensor 66. 
When this is done, readout 70 should read 34.00.degree. C. exactly. Any 
other readout is an indication of circuitry malfunction. The operator may 
check the circuitry of control 68 at any time by substituting source 80 
for sensor 66. 
FIG. 1 illustrates the breath test simulator 10, a breath test instrument 
82 and the various controls and lines used in conjunction with simulator 
10 for conducting a simulated breath test to calibrate the instrument. Air 
inlet line 84 includes a replaceable charcoal filter 86 on its free end, 
an air pump 88, pressure regulator 90 and normally open solenoid 
controlled valve 92 located in the line between the regulator and 
simulator air inlet pipe 46. Regulator 90 controls the simulator inlet air 
pressure and is usually set at 8 to 10 inches of water to simulate the 
pressure of human breath. 
Main control 94 includes an air pump timer 96 operable to actuate pump 88 
during a cycle of operation of the simulator 10. Manually operated switch 
98 shifts valve 92 so that filtered air from the pump bypasses simulator 
10 and flows directly to the breath test instrument through line 100 for 
an air blank test. During an air blank test, line 100 is connected to the 
inlet pipe of instrument 82. Air outlet line 102 extends from the 
simulator outlet pipe 50 through normally open solenoid control valve 104 
to the inlet pipe of breath test instrument 82. The main control 94 also 
includes an exhaust timer 106 which, when actuated, shifts valve 104 so 
that the flow through outlet pipe 50 is directed to atmosphere through 
vent 108. 
The simulator exhaust pipe 56 is connected to a level-return line 110 
carrying the solenoid control valve 112 and having a discharge end open to 
atmosphere. The valve 112 is controlled by an end test timer 114 in main 
control 94 such that when the valve 112 is opened, gases in the outer 
chamber 32 are vented to atmosphere. The main control 94 also includes a 
digital counter 116 which provides a numerical indication of the number of 
tests run using a single charge of alcohol-water solution in simulator 10. 
Simulated breath tests are run for calibrating breath test instruments 
automatically upon actuation of a single initiaion switch 118. Tests 
should not be run until the electric temperature control 68 has heated the 
solution in simulator 10 to the desired operating temperature. To this 
end, a cutout switch 120 may be provided between switch 118 and main 
control 94 isolating the two until the solution within the simulator is 
heated to the desired temperature level and appropriate circuitry closes 
switch 120. 
OPERATION OF THE BREATH TEST SIMULATOR 
Prior to conducting a simulated breath test to calibrate a breath test 
instrument, the operator checks to determine whether the alcohol-water 
soluition in the simulator is sufficiently depleted of alcohol to 
jeopardize the accuracy of the calibration. If so, the solution must be 
replaced with a fresh solution having the required alcohol concentration. 
The solution is changed by releasing wing nuts 28 and removing the cover 
plate 14 and the various heaters, sensors and pipes supported by the cover 
plate from within the chambers. The cover plate and its supported elements 
are then carefully cleaned and rinsed. Upon removal of the cover plate, 
the inner cylinder 16 and stir bar 36 are freely lifted from recess 20 and 
washed and cleaned. The water-alcohol solution within the sumulator is 
discarded and the chamber is thoroughly cleaned and rinsed. Removal of the 
inner cylinder 16 from the base plate 12 makes it an easy matter to clean 
the interior of the simulator. Following cleaning of the various simulator 
parts, the simulator is reassembled and filled with a volume of a 
specially prepared ethyl alcohol-water solution having a precisely known 
concentration of alcohol per unit volume of water. The alcohol-water 
solution may have 1.21 grams of alcohol per liter of water to produce an 
effluent having a concentration of 0.100 grams of alcohol vapor per 210 
liters of air at 34.degree. C. This concentration of alcohol solution is 
conventionally used in breath test simulators to calibrate breath test 
instruments to a reading of "0.100", corresponding to an assumed 
blood-alcohol concentration breath-alcohol concentration ratio of 2100:1. 
The inner chambers of simulator 10 are filled with one liter of the 
alcohol-water solution. Once equalized between the inner and outer 
chambers 30 and 32, the solution has a level 122 slightly above the 
circumferential row of secondary air diffusion holes 42 in the inner 
cylinder 15. 
The simulator 10 is connected to the heating and control circuitry shown in 
FIGS. 1 and 6, counter 116 is zeroed and motor 34 is turned on. The 
electric temperature control is turned on to heat the solution within the 
simulator to the desired 34.degree. C. operating temperature. Normally 
when the control is turned on, the temperature of the solution within the 
simulator is considerably lower than the 32.5.degree. C. set point for the 
nonproportional 74 controller for heater 64 so that all four heaters 58, 
62 and 64 are energized to rapidly heat the solution. When the solution 
reaches the set point for controller 74, heater 64 is de-energized and the 
remaining heating of the solution is accomplished by heaters 58 and 62 
controlled by the proportional controller 78 in a manner previously 
described. The use of heater 64 enables the solution to be rapidly brought 
up to temperature. After the heater 64 is deactivated the proportionally 
controlled heaters 58 and 62 are used through the more accurate controller 
78 to bring the solution to the very accurately controlled operating 
temperature of 34 plus-or-minus 0.02.degree. C. 
During heating of the solution and operation of the simulator that the 
stirrer bar 36 rotates on the surface of recess 20 in the direction of 
arrow 58. Rotation of the stirrer motor actively rotates the solution 
within the inner chamber 30 to assure the solution is maintained at a 
uniform temperature. The rotation of the stirrer bar 36 forces solution at 
the bottom of the inner chamber into the outer chamber through the angled 
solution mixing holes 40. After the ends of the bar pass adjacent holes to 
force solution in the outer chamber, solution flows back into the inner 
chamber through the same holes. In this way, there is active intermixing 
of the heated solution between the inner and outer chambers. The actively 
rotating solution within the inner chamber 30 is thrown out and up against 
the inner cylinder 16 to form vortex 104. 
Since sensor 66 measures the temperature of the solution in the inner 
chamber, the outer chamber solution is less actively stirred than the 
inner chamber solution and the outer chamber includes a large surface area 
outer wall, the temperature of the solution in the outer chamber may be 
slightly cooler than the temperature of the solution in the inner chamber. 
When the operator observes the temperature of the solution as indicated on 
readout 70 has stabilized at desired operating range and cutout switch 120 
has been closed, a breath simulation test may be initiated by actuating 
the test switch 118. Prior to actuating the switch, the manually 
controlled valve 92 is in its normal position communicating the regulator 
90 with air inlet pipe 46. Solenoid controlled valve 104 is in its normal 
position communicating outlet pipe 50 with breath test instrument 82 and 
solenoid controlled valve 112 is in its normal closed position. When 
switch 118 is actuated, air pump 88 is powered to draw air through filter 
86 into the line 84 and flow the air through regulator 90, valve 92 and 
into the air inlet pipe 46 and, ultimately, to the dispersion ring 44 
immersed within the alcohol-water solution within the outer chamber 32. 
The filter 86 removes solids and undesirable gases from the air pumped to 
the simulator. Regulator 90 is adjusted to control the pressure of the 
output to simulate the pressure of exhaled human breath. 
The air flowing down inlet pipe 36 and into ring 44 bubbles out holes 48 
into the solution in the outer chamber and rises up through the solution, 
past the secondary diffusion holes 42 to the outer chamber head space 106 
located above the solution. The air flow forms a dense bubble cloud 
distributed throughout the solution in the outer chamber above the ring 
44. Some bubbles are initially forced below the ring but rapidly rise to 
the outer chamber head space 128 with the rest of the flow. The ring 44 is 
positioned approximately 1 inch above the top of bores 40 to assure that 
the bubbles are not drawn into the inner chamber 30 through the bores 40. 
The air flowing from ring 44 is initially collected in head space 128 so 
that the volume of air in the head space 128 is increased, increasing the 
pressure in the head space and correspondingly lowering the level of the 
solution in the outer chamber from level 122 shown in FIG. 2 until the 
solution reaches level 126 shown in FIG. 5 at the circumferential row of 
secondary diffusion holes 42 in the inner cylinder 16. When the solution 
in the outer chamber is lowered to level 126, additional air flowing into 
head space 128 is sputtered through the diffusion holes 42 and into the 
swirling solution in inner chamber 36. These bubbles flow upwardly through 
the inner chamber, break through the surface of vortex 104 and collect in 
the inner chamber head space 130. Air from head space 130 flows through 
the inlet 52 and through outlet pipe 50 to valve 104. 
During the first five seconds of each cycle of operation in simulator 10, 
timer 106 shifts valve 104 to vent vapor discharged from head space 30 to 
atmosphere through line 108. The reverse bend 54 in outlet pipe 50 reduces 
the probability that solution droplets are drawn into the outlet pipe 
together with the effluent. 
The enlargement of head space 128 by the upward flow of bubbles from ring 
44 forces the solution in the outer chamber into the inner chamber through 
the holes 40 and 42. Thus, as illustrated in FIG. 5, the volume of 
solution in the inner chamber is increased to increase the height of the 
solution or column for the bubbles flowing into the inner chamber through 
the secondary diffusion holes 42. The height of solution of the column 
above the holes 42 is increased by the swirling of the solution which 
throws the solution up on the cylinder 16 with formation of vortex 104 and 
an increase of the height or column of solution above holes 42. The gas 
flowing through holes 42 prevents the solution in the inner chamber from 
flowing into the lower level outer chamber. 
After the initial five second venting of the head space 130, simulator 10 
flows effluent to the breath test instrument 82. The operator may then 
calibrate the instrument according to its particular procedures. Control 
94 is adjusted so that end test timer 114 ends the test run only after a 
sufficient volume of effluent has been flowed to instrument 82 to meet the 
requirements of the instrument. 
The effluent includes an air-alcohol vapor-water vapor mixture in 
equilibration with the alcohol-water solution within the simulator. The 
vapor-solution equilibration is achieved by first passing the ambient 
temperature air through the agitated solution in the outer chamber 32, 
sputtering the gas through the secondary diffusion holes 42 and into the 
inner chamber and bubbling the gas through the solution column in the 
inner chamber. The resultant effluent closely simulates human breath and 
contains a precisely known correlation of alcohol vapor. 
After the breath test instrument 82 has been supplied with sufficient 
effluent to complete the calibration breath test, timer 96 deactivates 
pump 88 and end test timer 114 is actuated to open valve 12 thereby 
venting the outer chamber head space 128 to atmosphere so that the 
solution in the outer chamber raises from level 126 to original level 122 
and the level of the solution in the inner chamber lowers back to level 
122. Counter 116 is actuated to indicate that the alcohol-water solution 
within the simulator has been used to conduct a breath test. Since each 
breath test removes alcohol from the solution, the concentration of the 
alcohol vapor in the effluent is progressively decreased with each 
successive test run using the same solution. Counter 116 counts each test 
run and is used to determine when it is necessary to replace the solution 
within the simulator in order to assure that the concentration of alcohol 
within the effluent is maintained within desired limits to assure that 
instrument 82 is accurately calibrated. 
Following calibration of instrument 82, line 102 is disconnected from the 
instrument allowing air to flow through the line and back into the inner 
chamber head space 130. This retrograde flow through line 102 reduces 
condensation in the line. Condensation trapped in the line could adversely 
affect the accuracy of a subsequent calibration test. 
Frequently in the calibration of breath tests instruments, it is desirable 
to run a "blank run", that is a test when the gas supplied to the 
instruments is known to be free of alcohol vapor. This type of test is 
used to assure that the instrument gives a proper reading in the absence 
of alcohol vapor and is free of alcohol. A "blank run" may be conducted 
using the FIG. 1 system by disconnecting the instrument end of line 102 
from the instrument 82 and connecting the free end of line 100 to the 
instrument in its place. Switch 98 is tripped to connect line 84 to line 
100 thereby flowing filtered, pressure regulated alcohol-free air directly 
from the regulator to the instrument. The pump 88 is then actuated for the 
desired time interval required by the particular instrument. At the end of 
the "blank run", valve 98 is deactuated and line 102 is reconnected to the 
instrument. 
Simulator 10 has been described in connection with the generation of a 
precision effluent having a precisely controlled temperature and alcohol 
concentration for use in calibrating breath test instruments. The 
invention is not limited to such applications and, for instance, may be 
used to generate other types of precisely controlled alcohol vapor 
effluents for calibration or other uses or may be used to generate other 
precision effluents formed by bubbling a gas through a liquid. The liquid 
need not be aqueous. 
While I have illustrated and described a preferred embodiment of my 
invention, it is understood that this is capable of modification, and I 
therefore do not wish to be limited to the precise details set forth, but 
desire to avail myself of such changes and alterations as fall within the 
purview of the following claims.