Abstract:
A breath simulator for supplying a breath test analyzer with a sample effluent of ethyl alcohol that controls headspace and adjacent effluent passageway temperature.

Description:
This application is a Continuation-In-Part of our application for “Breath Test Simulator” filed Sep. 11, 2006, Ser. No. 11/530,489, now U.S. Pat. No. 7,404,311. 

   FIELD OF THE INVENTION 
   The invention relates to breath simulators that supply sample effluent containing a precisely controlled concentration of ethyl alcohol to a breath test analyzer for calibrating the analyzer. 
   DESCRIPTION OF THE PRIOR ART 
   The alcohol content in the breath of an individual is an indicator of the alcohol content in the blood of the individual. Breath test analyzers are commonly used to determine the alcohol content in the blood of an individual, typically the driver of a motor vehicle, by determining the alcohol content in the breath of the individual. 
   Breath test analyzers must be calibrated to maintain accuracy. A known means of calibrating an analyzer is to use a breath test simulator that flows air through a solution of water and ethyl alcohol of known concentration heated to an operating temperature to generate a breath test effluent sample having a known alcohol concentration. The effluent sample is flowed to an analyzer to calibrate the analyzer. Breath test simulators must provide breath test effluent samples having precisely controlled ethyl alcohol concentrations in order to calibrate breath test analyzers accurately. 
   Breath test simulators of the type disclosed in Fisher et al. U.S. Pat. No. 6,526,802 are manufactured by Guth Laboratories, Inc. of Harrisburg, Pa. These simulators include a jar sealed closed by a lid and containing a water-alcohol solution of known alcohol concentration and an effluent headspace over the solution. An immersion heater heats the solution to a desired operating temperature, typically 34° C., while a stirrer circulates the solution to assure even heating. An immersion sensor in the solution monitors the temperature of the solution. When the solution is at the desired operating temperature, outside air is bubbled through the solution. Air bubbled through the solution absorbs a known amount of ethyl alcohol from the solution and is collected in the headspace above the solution. The gas in the headspace includes air, water vapor and alcohol vapor. Headspace gas effluent is flowed from the headspace to a breath test analyzer to calibrate the analyzer. 
   Samples of headspace gas flowed to analyzers for calibrating the analyzers must have a known concentration of ethyl alcohol. This concentration may vary slightly within an acceptable range. More accurate control of the concentration of ethyl alcohol in the breath test sample is desirable and permits calibrating the analyzer more accurately so that the analyzer conducts breath tests with improved accuracy. 
   In known breath test simulators, headspace temperature is primarily dependent on the temperature of the water-alcohol solution below the headspace. As air is bubbled through the heated solution to form the headspace gas, headspace temperature decreases due to evaporation and the cooler temperature of air. The heater immersed in the solution does not directly heat the gas in the headspace to compensate for this temperature drop. The gas may be heated slightly by incidental heat given off by electric components mounted on the lid or on the body of the simulator. This heat does not compensate for the heat loss. 
   The temperature of the headspace gas produced by the simulator and the alcohol concentration in the gas would be more accurately controlled by heating the air and vapor in the headspace to the operating temperature and maintaining the air and vapor at the operating temperature. 
   Breath test effluent from the headspace passes through an outlet passage leading to the analyzer. Heat loss in the passage can effect the alcohol concentration in the effluent and can cause condensation. Calibration accuracy of simulators would be improved by heating the outlet passage to maintain the temperature of the effluent and prevent condensation. 
   Breath test simulator Model 2100 marketed by Guth Laboratories, Inc. of Harrisburg, Pa. uses a sealed jar containing a known concentration water-alcohol solution and has a headspace over the solution. A cap closes the jar at the top of the headspace and supports an immersion heater extending into the solution and an electric motor which rotates a stirrer extending into the solution. The lid also supports an immersion sensor for monitoring the temperature of the solution and an air inlet for flowing air into the solution. Effluent from the headspace is flowed to a breath test analyzer to calibrate the analyzer. Electrical components are mounted on the lid. During operation of the simulator incidental heat from these components does not compensate for heat loss. 
   Conventional simulators are not capable of rapid warm up heating of the solution and headspace gas from ambient temperature to an operating temperature of 34° C. and rapid stabilization of the solution and headspace gas at the desired operating temperature within 10 minutes of activation. Operators are required to wait for a considerably longer period of time before stabilization occurs and the simulator is ready to be used to calibrate breath test analyzers. In some cases, a warm up period of 35 to 40 minutes is required. 
   Long warm up periods are undesirable. Operator time is wasted. The simulators may be powered by a battery. In such a case, a long warm up time unduly discharges the battery and wastes energy. 
   Therefore, there is a need for a breath test simulator that quickly warms up to an operating temperature and then precisely controls headspace temperature to allow stabilized generation of breath test effluent having a known concentration of ethyl alcohol. 
   SUMMARY OF THE INVENTION 
   The invention is a breath test simulator with an improved headspace heater for rapid warm up and controlled maintenance of the temperature of the headspace gas. 
   The simulator has a sealed jar containing an ethyl alcohol-water solution of known concentration and a headspace over the solution. An immersion heater heats the solution to a desired operating temperature and maintains the solution at the temperature. The headspace heater quickly heats and maintains the temperature of gas located in the headspace at the operating temperature. The headspace heater also heats an effluent outlet passage leading to the analyzer. 
   The simulator includes a black anodized aluminum jar lid heated by a resistor on the lid. A temperature sensor on the lid actuates a switch to flow current through the resistor when the temperature of the lid falls below a low temperature and to stop current flow through the resistor when a high temperature is reached. The resistor heats the lid by conduction so that heat radiates evenly down from the lid into the headspace and heats the gas in the headspace. Heat also radiates up from the lid and heats the effluent outlet passage. 
   The heaters rapidly warm the solution and the headspace gas to an operating temperature and maintain very precise temperature control of the headspace gas and resultant effluent samples flowed to breath test analyzers to improve the accuracy of analyzer calibration. 
   Other objects and features of the invention will be apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of the breath test simulator; 
       FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 ; and 
       FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The breath test simulator  10  disclosed herein relates to the breath test simulator of Fisher et al. U.S. Pat. No. 6,526,802, the disclosure of which is incorporated herein by reference in its entirety. 
   Portable breath test simulator  10  includes a case or body  12  and a sealed container or jar  14 . Jar  14  is mounted on the underside of support arm  16  extending outwardly from one side of body  12 . Container  14  may be a plastic jar that is screwed into lid  18  mounted on the underside of support arm  16 . 
   A circumferential gasket  20  is mounted on the lower surface of the lid to engage the top of the jar and prevent leakage into or out from the interior of the chamber  14 . Lid  18  is mounted under opening  22  in the lower wall of arm  16 . A circumferential thermal gasket  24  is provided between lower wall of the arm and the lid to prevent the lid from heating the arm. Jar  14  is partially filled with an ethyl alcohol-water solution  26  of known concentration. An effluent headspace or chamber  28  in the jar is located above the top of solution  26  and below lid  18 . 
   Arm  16  and lid  18  support a number of components that extend downwardly into jar  14 . Inunersion heater tube  30  extends through lid  18  and down into the solution in jar  14 . Heater tube  30  includes an immersion solution heater  32  at the lower end thereof for heating the solution in the jar. The solution heater may be a resistance heater or other type of heater, including a small halogen light bulb. 
   Air inlet or blow tube  38  extends from inlet port  40  located to one side of arm  16 , though the arm sidewall, through inner arm space  42  and to and down through lid  18  into jar  14 . Closed lower end  44  of the blow tube is located in the solution adjacent to the bottom of jar  14 . A number of small diameter air dispersion holes or air outlets  46  extend through the immersed end of tube  38  adjacent lower end  44  to disperse air blown through tube  38  and out holes  46  into the alcohol-water solution in the jar. Port  40  is mounted on arm  16  by insulating gasket  48 . 
   Stirrer mechanism  50  is mounted on lid  18  and includes post  54  which extends down into jar  14 . The stirrer mechanism includes magnetically actuated stirrer vanes  52  on the immersed end of the post. A magnet is mounted in the outer end of each vane for rotation by a magnetic stirrer drive mounted on body  12  adjacent the jar. Solution temperature sensor  36  is mounted on the lower end of post  54 . Alternatively, post  54  may be eliminated and the stirrer mechanism and sensor  36  may be mounted on another component that extends downward into jar  14 . 
   A horizontal baffle plate  56  is located in the jar above the top surface of solution  26  in the bottom of the jar to prevent air bubbled up through the solution from drawing liquid droplets of solution into headspace  28 . Heater tube  30 , air inlet tube  38  and post  54  extend through openings formed in the baffle plate. The baffle plate is spaced inwardly from the container sidewalls  58  to define a narrow gap  60  between the baffle plate and the sides of the chamber. The baffle plate is supported by post  62  mounted on lid  18 . 
   Air outlet tube  64  extends from effluent inlet end  66  located in the top of effluent headspace  28 , through lid  18 , through arm space  42 , through a sidewall of arm  16  to effluent outlet port  68 , mounted in outlet insulating gasket  70  in the sidewall adjacent inlet port  40 . The portion of tube  64  extending from lid  18  to port  68  is directly above lid  18 . 
   Electric resistance heater  72  is mounted to the top of lid  18 . The heater is in direct contact with the lid to efficiently transmit heat to the lid. Lid lower surface  74  faces headspace  28  and forms a headspace wall. Upper lid surface  76  faces space  42 . Lid  18  is formed from heat conductive material, which may be aluminum. Surfaces  74  and  76  are dark and preferably anodized black. Black surface  76  enhances flow of heat from heater  72  into lid  18 . Black surfaces  74  and  76  enhance even radiation of heat from lid  18  into headspace  28  and into the arm space  42 . 
   A set point switch control unit  80  includes a temperature sensor on surface  76  and control circuitry for flowing electricity through the resistor  72  when the temperature of the lid falls below an “on” set point temperature and stopping the flow when the temperature of the lid rises to an “off” set point temperature. The “on” set point temperature may be 35.8° C. and the “off” set point temperature may be 36.2° C. The temperature of the lid is maintained between 35.8° C. and 36.2° C. The heated lid maintains the temperature of the breath test gas in the headspace at 34°±0.5° C. Control unit  80  may be part No. DS1620 manufactured by Dallas Semiconductors of Dallas, Tex. The unit  80  is mounted on the upper surface  76  of the lid in direct heat flow contact with the lid. 
   The aluminum lid may have a thickness of about 0.1 inches and has an appreciable heat sink mass for receiving heat from heater  72  and evenly radiating heat through black surface  74  into the headspace  28  and through black surface  76  into arm space  42 . The relatively large mass of thick lid  18  assures that heat is radiated evenly down into the headspace  28  to heat effluent in the headspace. Heat is also radiated upwardly into arm space  42  to heat the portion of air outlet tube  64  in the arm space and heat effluent flowing through tube  64  to heat the effluent and prevent condensation in the tube. 
   Operation of breath test simulator  10  will now be described. 
   The breath test simulator and the alcohol solution to be placed in the breath test simulator are typically stored prior to use at an ambient temperature of between 18° C. and 28° C. In order to prepare a simulator for use, it is necessary to remove jar  14  from simulator  12 , pour in an appropriate volume of alcohol-water solution into the jar and remount the jar on the simulator. The simulator is then turned on to actuate heaters  32  and  72  and the drive for stirrer  50 . The heaters and stirrer are maintained on during a warm up period of about 10 minutes necessary to increase the temperature of solution  26  in the jar and the temperature of the gas in the headspace  28  to a maintained, stable temperature of 34° C. 
   Heater  32  heats the solution  26  by conduction. Heater  72  heats the lid by conduction. Heat radiates from the lid into the headspace to heat the headspace gas. 
   Unit  80  flows electricity to heater  72  until the temperature of the lid reaches 36.2° C. and then deactivates the heater. When the temperature of the lid falls to 35.8° C. the heater is reactuated. Maintenance of the lid temperature between 36.2° C. and 35.8° C. radiates heat into headspace  28  and into arm space  42  to heat both spaces. The heat radiated into headspace  28  heats the headspace gas from initial ambient temperature to the desired operating temperature of 34±0.5° C. in about 10 minutes. The heater  72  heats air space  42  to heat tubes  38  and  64  sufficiently to prevent formation of condensation in the tubes as air and vapor are flowed through the tubes during testing of a breath test analyzer. 
   Solution in the jar is rapidly warmed up from ambient temperature to a stable operating temperature of 34°±0.05 C in about 10 minutes. Heating and stabilization of the simulator are accelerated by controlled heating of lid  18  and radiant heating of the headspace  28  under the lid. 
   Rapid heating and stabilization of the simulator within a 10 minute period of time reduces the amount of time required to prepare a simulator for calibration of breath test analyzers. Conventional breath test simulators, including the previously discussed simulators disclosed in U.S. Pat. No. 6,526,802 and Guth Laboratories simulator Model 2100, discussed above, require appreciably longer periods of time to be heated from ambient temperature to an operating temperature of 34° C. The time required to heat a conventional simulator without a controlled, dedicated headspace heater from ambient temperature to a stable operating temperature of 34° C. may be as long as 30-45 minutes. Reduction of the time required to bring the simulator to a stable operating temperature reduces the amount of electricity required during the warm up period, which is significant when the simulator is used to calibrate an analyzer in the field and is powered by a battery. 
   Simulator  10  may be used to calibrate a breath test analyzer when the solution in jar  14  and the headspace gas reach a stabilized temperatures, as described. Breath test analyzers are calibrated by attaching a blow tube to inlet port  40  on arm  16 . The blow tube preferably includes a breath test mouthpiece or trap that captures solids contained in the breath flowed through the tube to prevent solids from entering air inlet tube  38  and 10 clogging dispersion holes  46 . The mouthpiece may be of the type disclosed in Guth, U.S. Pat. No. 4,292,978. 
   A discharge tube is attached to outlet port  68 . The other end of the discharge tube is connected to the breath test inlet of the analyzer being tested. The control circuits will cycle the solution heater and the headspace heater on and off through operation of the simulator to maintain effluent samples at the operating temperature as described. 
   Blowing of outside air into jar  14  increases the pressure in the jar and flows the heated, stabilized headspace gas through outlet tube  64  and to an analyzer being tested. The alcohol in the effluent is measured by the analyzer to generate an analyzer breath alcohol readout. If the readout is high, the analyzer must be adjusted to lower the reading to the known alcohol concentration. If the readout is low, the analyzer must be adjusted to increase the readout. No adjustment is required if the readout is accurate. The simulator may be programmed to produce samples of alcohol effluent having a desired concentration at an operating temperature other than 34° C. The simulator can be programmed to activate the solution heater and headspace heater at variable temperature set points. 
   In an alternative embodiment, the headspace  28  may be heated by a heater or heaters mounted on the lid and extending down into the headspace. A temperature sensor may be mounted on the bottom of the lid in order to directly sense headspace gas temperature and activate and deactivate the heater or heaters as required to maintain desired headspace temperature. In both embodiments heat is radiated into the headspace by a heated wall defining the headspace. Resistance heater  72  is disclosed. Other types of electrical heaters may be used including halogen lamps. 
   While we have illustrated and described preferred embodiments of our invention, it is understood that this is capable of modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.