Abstract:
A method and apparatus for monitoring a liquid undergoing anaerobic fermentation in a vessel is disclosed. The apparatus comprises an airlock containing a fluid for sealing the vessel and means to detect passage of bubbles through the airlock.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a Continuation-in-Part of U.S. application Ser. No. 10/289,033, filed Nov. 6, 2002, incorporated by reference herein. 
     
    
     
       REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX  
         [0002]    This patent includes a computer program listing appendix on compact disc. Two duplicate compact discs are provided herewith. Each compact disc contains a computer program listing as follows:  
           [0003]    Filename: Fermentometer_Interface3.vbp  
           [0004]    Size: 2 kilobytes  
           [0005]    Date Created: Aug. 20, 2003  
           [0006]    Filename: Main2.frm  
           [0007]    Size: 61 kilobytes  
           [0008]    Date Created: Aug. 20, 2003  
           [0009]    Filename: Module1.bas  
           [0010]    Size: 1 kilobyte  
           [0011]    Date Created: Aug. 20, 2003  
           [0012]    Filename: patent01.c  
           [0013]    Size: 20 kilobytes  
           [0014]    Date Created: Aug. 20, 2003  
           [0015]    Filename: hc11.h  
           [0016]    Size: 4 kilobytes  
           [0017]    Date Created: Aug. 20, 2003  
           [0018]    Filename: _const.h  
           [0019]    Size: 1 kilobyte  
           [0020]    Date Created: Aug. 20, 2003  
           [0021]    Filename: stdio.h  
           [0022]    Size: 1 kilobyte  
           [0023]    Date Created: Aug. 20, 2003  
           [0024]    The computer program listing appendix is hereby expressly incorporated by reference in the present application.  
         FIELD OF THE INVENTION  
         [0025]    The present invention relates generally to a method and apparatus useful during anaerobic fermentation, and more particularly to a method and apparatus for measuring the volume and rate of gas produced during anaerobic fermentation, this invention having particular utility during the making of alcoholic beverages.  
         BACKGROUND OF THE INVENTION  
         [0026]    It is common when making alcoholic beverages in the home to place the liquid subject to fermentation into a vessel for anaerobic fermentation, the vessel being closed by a fermentation airlock. The purpose of the fermentation airlock is to prevent undesirable dust and bacteria from contaminating the material being fermented. Therefore it is common to utilize an airtrap, the gas produced by fermentation bubbling though a liquid in the airtrap, the liquid typically containing water and a sterilizing agent such as sodium or potassium metabisulfite. Differing types of fermentation locks are employed, various examples being shown in U.S. Pat. Nos. 4,517,884, 4,842,869, and 5,950,524. A favorite form of airlock is the “S” type airlock, variations being shown in U.S. Pat. Nos. 2,023,153 and 4,717,031, and German patents 412,918 and 957,563. Another prior art form of “S” type airlock is shown in FIG. 1 of this application.  
           [0027]    The airlock may be molded from a clear plastic, all airlocks being quite uniform in size. It has been observed that when using some airlocks that each bubble has substantially the same volume, i.e., 1.7 ml. It is also known that during fermentation that equal mole volumes of CO 2  and alcohol are produced.  
         SUMMARY OF THE INVENTION  
         [0028]    The present invention broadly comprises a method and apparatus for measuring gas produced during anaerobic fermentation. The method comprises the steps of counting bubbles which pass through said airlock to determine a volume of gas produced and determining the amount of alcohol produced based on the volume of gas produced.  
       
    
    
       [0029]    The above objects, and other objects and advantages of this invention will become more apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of this invention is illustrated.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    It should be appreciated that, in the detailed description of the invention which follows, like reference numbers on different drawing views are intended to identify identical structural elements of the invention in the respective views.  
         [0031]    [0031]FIG. 1 illustrates a prior art “S” type airlock;  
         [0032]    [0032]FIG. 2 illustrates an airlock of a first embodiment of the present invention, an airlock being provided with electrodes;  
         [0033]    [0033]FIG. 3 shows a dust cap for the modified “S” type airlock, which dust cap is provided with suitable contacts for contacting the electrodes in the modified “S” type airlock;  
         [0034]    [0034]FIG. 4 shows a first embodiment of the present invention with the airlock being mounted on a vessel suitable for anaerobic fermentation;  
         [0035]    [0035]FIG. 5 shows a bubble interrupting the flow of current through between the electrodes, signaling a bubble event;  
         [0036]    [0036]FIG. 6 shows an embodiment of the electrical circuit of the control means;  
         [0037]    [0037]FIG. 7 shows an alternate embodiment of the electrical circuit of the control means;  
         [0038]    [0038]FIG. 8 illustrates a second embodiment of an airlock of the present invention;  
         [0039]    [0039]FIG. 9 illustrates a third embodiment of an airlock of the present invention;  
         [0040]    [0040]FIG. 10 illustrates a fourth embodiment of an airlock of the present invention;  
         [0041]    [0041]FIG. 11 illustrates a fifth embodiment of the present invention, comprising an optical sensor and communication means;  
         [0042]    [0042]FIG. 12 illustrates an embodiment of the present invention wherein multiple control means are connected to a single communication control means;  
         [0043]    [0043]FIG. 13 illustrates an alternate embodiment of the present invention wherein multiple control means are connected to a single communication control means;  
         [0044]    [0044]FIG. 14 illustrates a schematic of the electrical circuit for the fifth embodiment of the present invention, comprising an optical sensor;  
         [0045]    [0045]FIGS. 15 and 16 illustrate an embodiment of the present invention wherein the optical detector is arranged to mate with a portion of an airlock having two parallel sides and two arcuate sides;  
         [0046]    [0046]FIGS. 17 and 18 illustrate an embodiment of the present invention wherein the optical detector is arranged to mate with a portion of an airlock having a rectangular cross section; and,  
         [0047]    [0047]FIGS. 19 and 120 illustrate an embodiment of the present invention wherein the optical detector is arranged to mate with a portion of an airlock having a hexagonal cross section. 
     
    
     DETAILED DESCRIPTION  
       [0048]    With reference initially to FIG. 1, an airlock is illustrated, said airlock being indicated generally at  10 . This airlock consists of a molded clear plastic member indicated generally at  12 , the plastic member including an “S” shaped passageway which will be described later. Extending downwardly from the “S” shaped passageway is a mounting stem  14  which is inserted into the rubber bung or cork  16  of a fermenting vessel  18  so as to be an airtight fit. The airlock is provided with a dust cap  20  at its upper end.  
         [0049]    The “S” shaped passageway includes an upwardly extending portion  22  which is in direct communication with the stem  14 , the portion  22  being essentially cylindrical in cross section. A “U” shaped member  24  having a circular cross section connects the portion  22  with a downwardly extending portion  26  having upper, intermediate, and lower bulbs  26 . 1 ,  26 . 2 , and  26 . 3 , respectively. A further “U” shaped member  28  having a circular cross section connects the lower end of the downwardly extending portion  26  with an upwardly extending portion  30  provided with upper, intermediate and lower bulbs  30 . 1 ,  30 . 2 , and  30 . 3 , respectively. An upwardly extending member  32  is provided with a bulb  34  at its top end, which bulb receives the dust cap  20 . A clear plastic web or flashing  36  extends between the downwardly extending portion  26  and the upwardly extending portion  30 , and also between the downwardly extending portion  26  and the upwardly extending portion  22  to keep the various parts in fixed relationship to each other.  
         [0050]    After the liquid to be fermented is placed in the vessel, which liquid may be a wine must, the vessel is sealed with an airlock at the commencement of anaerobic fermentation. To this end, a sterilizing liquid is placed in the “S” shaped airlock, the sterilizing liquid filling the “U” shaped member  28  and ½ of each of the lower bulbs  26 . 3  and  30 . 3 , the sterilizing liquid being indicated generally at SL in FIG. 2. The sterilizing liquid typically contains either sodium or potassium metabisulfite, although other sterilizing agents may be used. During anaerobic fermentation the yeast is less active than during the initial aerobic fermentation, and the CO 2  produced with escape through the sterilizing liquid one bubble at a time.  
         [0051]    With reference to FIG. 2, it can be seen that the “S” type airlock of the present invention is provided with two electrodes  40 ,  42 . Electrode  40  is embedded in the flashing  36  which extends between the downwardly extending portion  26  and the upwardly extending portion  30 . Additional flashing  44  is provided to one side of the upwardly extending portion  30  for the receipt of electrode  42 . As can be seen from FIG. 2, the electrodes have lower terminal ends that extend into the passageway  28 . Normally the ends of the electrodes are covered with the sterilizing liquid, which conducts electricity. Thus, when a voltage is applied between them, current flows between the electrodes. However, when a bubble passes through the tube  28 , the current flow between the electrodes is interrupted. Dust cap  20 , shown in FIG. 3, prevents dust from settling into the airlock when it is engaged with the top of airlock  12 . Conducting members  21  connect to electrodes  40  and  42 .  
         [0052]    As illustrated in FIG. 4, electrodes  40  and  42  are connected to control means  60  through conducting members  21 . Control means  60  comprises control buttons  65 A,  65 B,  65 C,  65 D, and  65 E, and a display  70 . Bottle  18  contains wine must W. Control means  60  counts the number of times the current between electrodes  40  and  42  is interrupted. Control means  60  determines the status of the fermenting liquid based on the history of bubbles detected. Control means  60  displays the status of the fermenting liquid on display  70 .  
         [0053]    The interruption of the current between the electrodes is illustrated in FIG. 5. Bubble  50 , created by the production of CO 2  during fermentation, envelops the exposed conductive material of both electrodes. Thus, with a low voltage drop across the electrodes, the gas does not conduct electricity between the electrodes. A preferred voltage drop across the electrodes is approximately 5 V, although other voltage drops might be suitable. The control means of the apparatus records each interruption in the current as a bubble event.  
         [0054]    [0054]FIG. 6 is a schematic of an embodiment of the electrical circuit of the control means. The circuit shown comprises electrodes  40  and  42 , a 5 V source, resistor  85 , operational amplifier (op amp)  87 , positive and negative power supplies V +  and V −  to power the op amp, and processor  90 . Processor  90  is a conventional microprocessor, well known to those in the electronics art. The 5 V source is connected across electrodes  40  and  42  through resistor  85 . When current exists between the electrodes, V in−  is 0 V. (The 5 V source is shorted to ground.) However, when a bubble interrupts the current through the electrodes, V in−  is no longer zero. (Ground is separated from V in−  by an open circuit.) V in+  is connected to ground. Thus processor  90  can determine the presence of a bubble between electrodes  40  and  42  from the output of operational amplifier  87 .  
         [0055]    [0055]FIG. 7 shows a second possible embodiment of control means  60 . This embodiment comprises a plurality of control buttons  65 A,  65 B,  65 C,  65 D,  65 E, and  65 F, electrodes  40  and  42 , a 5 V source, resistor  89 , pin  88  of processor  90 , audio alarm  92 , and visual alarm  94 . Pin  88  of processor  90  is connected to electrode  40  and to a 5 V source through resistor  89 . Electrode  42  is connected to ground. When current exists between the electrodes, pin  88  is shorted to ground. When the current is interrupted by a bubble, pin  88  will be lifted to a non-zero voltage. (The voltage level will depend on the resistance value of resistor  89 ). In this manner, processor  90  can determine the presence of bubbles between electrodes  40  and  42 .  
         [0056]    To use the above-described device, a measure volume of a liquid subject to fermentation, such as a wine-must, is placed in a container. (This is typically done after a period of aerobic fermentation and a hydrometer measurement to determine the proportion of sugar remaining.) The airlock of the present invention is inserted in the neck of the container. The user programs the volume of liquid present in the container using the control buttons.  
         [0057]    In a preferred embodiment, control means  60  are configured as follows. First, the batch size must be set. Button  65 A increases the batch size by 10 liters each time it is pushed. Button  65 B increases the batch size one liter each time it is pushed. Button  65 C accepts the batch size when it is pushed, if the batch size is non-zero. (Buttons  65 D and  65 E have no function in setup mode). After the batch size is set, the user can enter a user specified time alarm, to be activated when the enter amount of time passes without a bubble being detected. Button  65 A increases this alarm time by one hour each time it is pushed. Button  65 B increases this alarm time by one minute each time it is pushed. Button  65 C accepts the current alarm time. (Zero may be entered if no user specified time alarm is desired.) When the user specified alarm is set, the user can then enter an alcohol alarm level. Button  65 A increases the alcohol level alarm by one percent each time it is pushed. Button  65 B increases the alcohol level alarm by one tenth of one percent each time it is pushed. Button  65 C accepts the current alcohol level. After the alcohol level alarm is set, the user can activate the 24 hour alarm. Button  65 A enables the 24 hour alarm. Button B disables the 24 hour alarm. Button  65 C accepts the current 24 hour alarm status. The control means then detects the bubbles of gas escaping from the airlock and displays the status of the liquid on display  70 .  
         [0058]    The status is determined based on the history of bubbles detected by control means  60 . In one embodiment, airlock  12  is configured such that the escaping bubbles have a volume at room temperature and 1 atmosphere of pressure of 1.7 ml. (It is assumed that the fermentation is done at a constant temperature, thus an equal amount of gas is contained in each bubble). Thus, by counting the number of bubbles, control means  60  can determine the amount of gas to escape from the airlock. According to calculations known in the art, the amount of alcohol generated during anaerobic fermentation can be determined based on the volume of CO 2  generated (assuming substantially all of the escaping gas is CO 2  generated by fermentation) and the amount of liquid present in the container (input using the control buttons, as discussed above). Accordingly, control means  60  can calculate the volume of alcohol generated and display this amount on display  70 .  
         [0059]    In a preferred embodiment the buttons of the control means function as follows. Button  65 A scrolls the display of the bubble events towards the most current event. Button  65 B scrolls the display of the bubble events towards the least recent event. Button  65 C deletes the display of the displayed event if pressed alone. Button  65 D caused the control means to reenter setup mode. Button  65 E silences current alarms and calls up a screen to review past alarms. Display  70  is set to the most recent event when button  65 E is released. When buttons  65 C and  65 E are pressed simultaneously, past alarms are cleared.  
         [0060]    As discussed above, a user can preprogram a percentage of alcohol desired with the control buttons. In this case, control means  60  displays a countdown of the amount of alcohol still to be generated. Control means  60  can include an audible alarm  94  and/or visual alarm  96  to signal a user when the desired amount of alcohol has been produced. This can be especially useful in making beverages wherein some fermentation is desired after the liquid is bottled. The alarm can be set to alert the user when a portion of the desired alcohol has been produced. The user can then transfer the beverage to individual bottles for the remaining fermentation. This is also useful for the production of a sweet beverage. The user can stop fermentation before all the sugar has been consumed by the yeast. This alarm also allows a user to add further ingredients at different stages of the fermentation, such as the addition of malolactic cultures, nutrients, and other ingredients known in the art. The present invention allows for greater quality control in production by determining to a greater accuracy the proper time to add additional ingredients.  
         [0061]    Control means  60  also includes timing means to determine the amount of time between each bubble. Counting means displays the amount of time since the last bubble on display  70 . Audible and/or visible alarms can be activated to alert the user after a specified time without a bubble has been reached. In one embodiment, this time period is 24 hours. In another embodiment, this time period is set by the user using the control buttons (the user specified alarm discussed above).  
         [0062]    A potential problem with fermentations that can take a long period of time is the evaporation of the sterilizing liquid. If the sterilizing liquid evaporated to the point wherein outside air may pass into vessel  18 , then the fermentation may be spoiled. The present invention warns a user when the level of the sterilizing liquid is low. Electrodes  40  and  42  are placed in member  28  such that they are exposed to air before the liquid level drops to an extent that air could reenter vessel  18 , as shown in FIG. 2. Control means  60  times the length of the bubbles. If the sterilizing liquid has partially evaporated, then the electrodes will be exposed to air continuously. Thus, when control means  60  detects an interruption of the current that lasts an extended period of time (in one embodiment 1 hour), it displays a low liquid level warning on display  60 . Audible and/or visible alarms may also be activated. In addition, bubble detection indicator  92  is lit when a bubble is being detected (when current is not flowing between electrodes  40  and  42 .) This can also allow a user to determine there is a problem if the bubble detection indicator remains lit for an extended period of time. The low liquid level warning and bubble detection indicator allow a user to replace the lost sterilizing liquid before the fermenting liquid is spoiled.  
         [0063]    [0063]FIGS. 2, 4, and  5  show the present invention being practiced with an “S” type airlock. However, it should be readily apparent to one skilled in the art that other airlocks or valves may be modified to practice the present invention. FIGS.  8 - 10  illustrate several valves known in the art. FIG. 8 shows a flapper check valve  110 . Electrodes  140  and  142  contact conducting strip  145  on flapper  115  when the valve is closed. Thus, when the valve is closed, current flows from electrode  140  to electrode  142  through strip  145 . When flapper  115  is forced open by gas pressure, the current flowing between electrode  140  and electrode  142  is interrupted. Thus, the number of times gas escapes from the valve can be counted. The amount of gas that escapes each time is measured and programmed into control means  60 . In this manner, a fermentation process can be monitored as described above. In a similar manner, FIG. 9 shows a piston check valve  210  comprising electrodes  240  and  242 , and valve member  215  having conducting strip  245  on a surface thereon. When the valve is closed, current flows from electrode  240  to electrode  242  through strip  245 . When member  215  is forced open by gas pressure, the current flowing between electrode  240  and electrode  242  is interrupted. FIG. 10 shows ball check valve  310  comprising electrodes  340  and  342  and conducting ball  345 . When the valve is closed, current flows from electrode  340  to electrode  342  through conducting ball  345 . When ball  345  is forced up by gas pressure, the current flowing between electrode  340  and electrode  342  is interrupted. The amount of gas released each time the valve opens is used to determine how much gas is produced during fermentation, in the manner described above. These modifications, including the use of the practicing of the present invention with other valves not shown, is intended to be within the spirit and scope of the invention as claimed. In the present specification and claims, the word “airlock” is intended to mean any airlock or valve known in the art or hereafter developed that can be modified as described herein to practice the present invention.  
         [0064]    An embodiment of the present invention may be arranged to have the elevation of the apparatus entered using the control buttons or through the communication means described below. The processing means adjusts the calculated alcohol percentage by volume based on the altitude of the apparatus. This corrected alcohol percentage by volume is used in computing the amount of alcohol present in the solution being fermented. An embodiment of the present invention can also include a flow rate alarm, where the flow rate, for example computed in cubic centimeters of alcohol produced per hour per liter of liquid, can be corrected based on the elevation of the apparatus. When the flow rate of alcohol exceeds a threshold in put by a user, the alarm is sounded. This may be a visual or optical alarm, as discussed above. Software that implements the above-described functions is included in the appendix.  
         [0065]    An embodiment of the present invention including communication means  480  is shown in FIG. 11. Apparatus  410  comprises control means  460 , display  470 , and communication control means  475 . Control means  460  comprises control buttons  465 A,  465 B,  465 C,  465 D, and  465 E. Apparatus  410  also includes optical sensor  450  arranged to mate with portion  428  of airlock  412 . Wire  448  connects sensor  450  to control means  460 . Airlock  412  contains sterilizing liquid SL. The display and control buttons function as described above for the first embodiment. Communication control means  475  communicates with information system  490  with communication means  480 . Communication means  480  may comprise a hard wire or a wireless connection, both of which are known in the art. Information system  490  may comprise a single personal computer, a local area network, a wide area network such as the Internet, a wireless phone system, a pager system, a personal digital assistant system, or any other information system known in the art. Thus, apparatus  410  is arranged to transmit and receive messages over communication means  480  to and from information system  490 . (For example, the appendix contains a software listing that, when loaded on a general purpose microprocessor, transmits messages to a digital cellular phone.)  
         [0066]    The apparatus may receive parameters for programming the apparatus from the information system. Thus, a local personal computer, a computer connected to the Internet, a personal digital assistant, or any of the other information system known in the art may be used to program the present invention. The apparatus may transmit the status of any of the above-described alarms to any of the information systems known in the art. Thus, for example, a user can be warned by cell phone, pager, or personal digital assistant that the alcohol alarm is active. The status of the fermentation may be emailed to a user, or it may be posted on a website. The communication means can receive all of the parameters used to program the control means, as discussed above, such as altitude, batch size, user specified time alarm setting (alarm activated when no bubbles are detected for specified time), alcohol level alarm (alarm activated when alcohol level reaches specified level), and enabling/disabling the 24 hour alarm. The data received by the communication means can comprise commands to clear any specific alarm, or all alarms. The data transmitted by the communication means can comprise: alcohol level, alarm status, time since the last bubble detection, bubble count, or any other parameter stored in the control means. It should be readily apparent to one skilled in the art that other parameters may be used by the control means, and these parameters may be sent over the communication means. These modifications are within the spirit and scope of the invention as claimed. The communication means may transmit messages using RS-232 protocol, Transfer Control Protocol/Internet Protocol (TCP/IP), Universal Serial Bus (USB) protocol, or any other protocol known in the art. (For example, the software listing in the appendix, when loaded on a conventional general purpose microprocessor, sends messages using the RS-232 protocol.) It should be readily apparent to one skilled in the art that other communication means and information systems are possible, and these modifications are within the spirit and scope of the invention as claimed.  
         [0067]    An embodiment of the present invention may also be configured to log the data sent to and received form the control means. This allows a user to evaluate the batch either by comparison to an ideal fermentation, or comparison to other fermentation batches, for example graphically. It should be readily apparent to one skilled in the art that data from the present invention can be logged into a database program and displayed graphically, with commercially available software packages, as described above.  
         [0068]    [0068]FIG. 12 illustrates an embodiment of the present invention wherein communication control means  475  sends and receives data from multiple control means  460 A,  460 B, and  460 C. Communication control means  475  communicates with information system  490  over communication means  480 . Communication control means  475  comprises at least one port  477 . As shown in FIG. 12, control means  460 A,  460 B, and  460 C are each connected to communication control means  475 . The connection is made by connecting wire  478  between port  477  of communication control means  475  and port  462  of control means  460 A,  460 B, and  460 C, respectively. FIG. 13 shows another embodiment of the present invention wherein control means  460 A,  460 B, and  460 C are daisy chained together. Control means  460 A is connected to control means  460 B with a wire  478  connected between port  462  of control means  460 A and port  462  of control means  460 B. Control means  460 B is connected to control means  460 C with a wire  478  connected between port  462  of control means  460 B and port  462  of control means  460 C. Control means  460 C is connected to communication control means  475  with a wire  478  connected between port  462  of control means  460 C and port  477  of communication control means  475 . As should be readily apparent to one skilled in the art, any combination of direct connections to a communication control means and daisy chaining multiple control means are possible, and these modifications are within the spirit and scope of the invention as claimed. The present invention may also be practiced as shown in FIG. 11, wherein communication control means  475  is integral with control means  460 . In this case, each control means  460  communicates with the information system  490  through its respective communication control means  475 . It should be readily apparent to one skilled in the art that the control means  460  shown in FIGS. 12 and 13 may comprise optical sensors as shown in FIG. 11, or may comprise two electrodes, as shown in FIG. 4. Any bubble counting apparatus comprising communication means for transmitting and receiving data to and from an information system is within the spirit and scope of the invention as claimed.  
         [0069]    [0069]FIG. 14 is a schematic of an exemplary embodiment of an electrical circuit for an embodiment of the present invention comprising optical sensor  450 . Sensor  450  comprises optical beam emitter  452  and optical beam detector  454 . In the embodiment shown, emitter  452  is an LED and detector  454  is a phototransistor. Beam emitter  452  emits a light beam towards detector  454 . The beam passes through the wall  428 A of airlock portion  428 . Wall  428 A is normal to the line connecting emitter  452  and detector  454 . Thus, the beam enters the interior of airlock portion  428  normal to the surface of wall  428 A. If no bubble is present in the sterilizing liquid, the beam passes through the sterilizing liquid, through wall  428 B of the airlock portion  428 , and is incident on detector  454 . When light is incident on phototransistor  454 , current may flow through the phototransistor. This shorts connection  456  to ground. When bubble  50  passes through airlock portion  428 , the edges  52  will refract the incident light that is propagating in a direction normal to walls  428 A and  428 B in a direction that is not normal to walls  428 A and  428 B. Thus, when bubble edge  52  is located between emitter  452  and detector  454 , light will not be incident on detector  454 . This disables current from flowing through phototransistor  454 , which isolates pin  456  from ground. The 5 V source pulls pin  456  up to 5 V. When the bubble is between the emitter and detector, the beam passes through the gas mixture to the detector. This allows current to flow through the phototransistor, pulling pin  456  down to 0 V. Thus, for each bubble that passes through airlock portion  428 , the light beam will be interrupted briefly twice by each bubble edge  52 , leading to two voltage pulses of 5V, compared to the normal value of 0V. Pin  456  is connected to a general purpose microprocessor programmed to monitor the voltage transitions at pin  456  between 0 V and 5 V. Thus, the processor increments the bubble count by 1 for each pair of interruptions of the light beam (each pair of 5 V pulses at pin  456 ). Optical sensor  450  may comprise a sensor such as the Omron® EE-SX198, EE-SX199, EE-SX1018, EE-SX1025, EE-SX1041, EE-SX1042, E-SX1070, or EE-SX1071, available from Omron Corporation, Shiokoji Horikawa, Shimogyo-ku, Kyoto, 600-8530 Japan. The processor is programmed to use the bubble count as described above for the first embodiment. The appendix contains a software listing for a processor using the optical sensor of the present embodiment.  
         [0070]    It should be readily apparent to one skilled in the art that any airlock may be used with the embodiment comprising an optical sensor, providing it comprises a portion with two parallel sides. For example, FIGS. 15 and 16 show optical sensor  450  arranged to detect bubbles passing through airlock portion  428  having two parallel sides  428 A and  428 B, and two arcuate sides  428 C. FIGS. 17 and 18 show optical sensor  450  arranged to detect bubbles passing through airlock portion  428  having a rectangular cross section, with two parallel sides  428 A and  428 B and two parallel sides  428 D that are perpendicular to sides  428 A and  428 B. FIGS. 19 and 20 show optical sensor  450  arranged to detect bubbles passing through airlock portion  428  having two parallel sides  428 A and  428 B, and sides  428 E that form a hexagonal cross section. It should be readily apparent to one skilled in the art that airlocks having portions with cross sections of other shapes, with two parallel sides are possible, and these modifications are within the spirit and scope of the invention as claimed.  
         [0071]    While a preferred form of this invention has been described above and shown in the accompanying drawings, it should be understood that applicant does not intend to be limited to the particular details described above and illustrated in the accompanying drawings, but intends to be limited only to the scope of the invention as defined by the following claims. In this regard, the term “means for” as used in the claims is intended to include not only the designs illustrated in the drawings of this application and the equivalent designs discussed in the text, but it is also intended to cover other equivalents now known to those skilled in the art, or those equivalents which may become known to those skilled in the art in the future.