Abstract:
A thermal oxidation tester is shown for determining thermal stability of a fluid, particularly hydrocarbons when subjected to elevated temperatures. The tendency of the heated fluid to oxidize and (1) form deposits on a surface of a heater tube and (2) form solids therein, are both measured at a given flow rate, temperature and time. The measured results are used to determine whether a fluid sample passes or fails the test. Results of measurements are recorded in a memory device on one end of the heater tube on which the deposits were made.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    None 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    This invention relates to methods and devices for measuring the thermal characteristics of fluids. Specifically, this invention relates to the methods and devices for measuring the thermal oxidation tendencies of fuels used in liquid hydrocarbon-burning engines. 
         [0004]    2. Background Art 
         [0005]    When engines were developed for use in jet aircraft, problems began to develop for jet fuel due to poor fuel thermal stability. At higher temperatures, the jet fuels would oxidize and form deposits that would clog fuel nozzles and fuel filters. These deposits would also collect in the jet engine. 
         [0006]    While various tests were devised and used in the 1950s and 60s to rate the thermal oxidation characteristics of jet fuels prior to being used in jet aircraft, Alf Hundere developed the apparatus and method which became the standard in the industry. In 1970, Alf Hundere filed what became U.S. Pat. No. 3,670,561, titled “Apparatus for Determining the Thermal Stability of Fluids”. This patent was adopted in 1973 as ASTM D3241 Standard, entitled “Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels”, also known as the “JFTOT® Procedure”. This early Hundere patent was designed to test the deposition characteristics of jet fuels by determining (1) deposits on the surface of a heater tube at an elevated temperature and (2) differential pressure across a filter due to collection of particulate matter. To this day, according to ASTM D3241, the two critical measurements are still (1) the deposits collected on a heater tube and (2) differential pressure across the filter due to the collection of particulate matter on the filter. 
         [0007]    According to ASTM D3241, 450 mL of fuel flows across an aluminum heater tube at a specified rate, during a 2.5 hour test period at an elevated temperature. Currently six different models of JFTOT® 1  instruments are approved for use in the ASTM D3241-09 Standard. The “09” refers to the current revision of the ASTM D3241 Standard. 1 JFTOT is the registered trademark of Petroleum Analyzer Company, LP. 
         [0008]    While over the years various improvements have been made in the apparatus to run the tests, the basic test remains the same. Improvements in the apparatus can be seen in U.S. Pat. Nos. 5,337,599 and 5,101,658. The current model being sold is the JFTOT 230 Mark III, which is described in further detail in the “Jet Fuel Thermal Oxidation Tester—User&#39;s Manual”. The determination of the deposits that occur on the heater tube can be made visually by comparing to known color standards or can be made using a “Video Tube Deposit Rater” sold under the Alcor mark. 
         [0009]    The determination of the amount of deposits formed on the heater tube at an elevated temperature is an important part of the test. The current ASTM D3241 test method requires a visual comparison between the heater tube deposits and known color standard. However, this involves a subjective evaluation with the human eye. To take away the subjectivity of a person, an electronic video tube deposit rater was developed. 
         [0010]    Also, there has been considerable discussion as to the polish or finish of the heater tube. (See U.S. Pat. No. 7,093,481 and U.S. Patent Application Publication No. US 2002/083,760.) The finish of the heater tube is very important in determining the amount of fuel deposits that will form thereon. Therefore, it is important that the quality of the finish on heater tubes made today be consistent with the finish of heater tubes made since 1973. 
         [0011]    Once the thermal oxidation stability test has been performed on a batch of fuel, the recorded information and the heater tube are preserved to show the batch of fuel was properly tested. The information that was recorded when testing a batch of fuel is maintained separately from the heater tube itself. This can cause a problem if one or the other gets misplaced or lost. Inaccurate information and/or conclusions occur if the wrong set of data is associated with the wrong heater tube. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide an apparatus and method for testing thermal oxidation stability of fluids, particularly aviation fuels. 
         [0013]    It is another object of the present invention to provide an apparatus and method to measure the tendency of fuels to form deposits when in contact with heated surfaces. 
         [0014]    It is another objective of the present invention to provide an apparatus and method for testing the thermal oxidation tendency of fuels utilizing a test sample to determine if solid particles will form in the fuel at an elevated temperature and pressure. 
         [0015]    It is another objective of the present invention to provide an apparatus and method for determining thermal oxidation stability of a batch of aviation fuel by testing a sample at an elevated temperature and pressure to determine (1) deposits that form on a metal surface and (2) solid particles that form in the fuel. 
         [0016]    It is another objective of the present invention to provide an apparatus and method for recording and storing the thermal oxidation tendency data of fuels in single location. 
         [0017]    It is yet another objective of the present invention to provide an intelligent heater tube on which a thermal oxidation stability test is performed with deposits collecting thereon and a memory device on one end of the intelligent heater tube to record all of the test information. 
         [0018]    It is another objective of the present invention to have an intelligent heater tube with a memory device on one end thereon on which all of the test information in association with that heater tube can be recorded. 
         [0019]    It is another object of the present invention to provide a memory device for an intelligent heater tube that has a ground and data connection with the memory device being connected to the heater tube. 
         [0020]    It is another object of the present invention to provide an apparatus and method for testing thermal oxidation tendencies of high performance fuels with the test results being written into a memory device on an intelligent heater tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a general block diagram of a thermal oxidation stability test apparatus illustrating flow and electrical controls. 
           [0022]      FIGS. 2 and 2A  are a more detailed block diagram showing a thermal oxidation test apparatus used to perform ASTM D3241 Standard. 
           [0023]      FIG. 3  is a pictorial diagram of the coolant flow for  FIGS. 2 and 2A . 
           [0024]      FIG. 4  is a pictorial diagram of the airflow in  FIGS. 2 and 2A   
           [0025]      FIG. 5  is a pictorial diagram showing flow of the test sample in  FIGS. 2 and 2A . 
           [0026]      FIG. 6  is a lengthwise view of an intelligent heater tube. 
           [0027]      FIG. 7  is an exploded perspective end view of the intelligent heater tube of  FIG. 6 , showing the EEPROM in broken lines inside of a memory device on the intelligent heater tube. 
           [0028]      FIG. 8  is an elevated view of the 1-Wire EEPROM used in the memory device of  FIG. 7 . 
           [0029]      FIG. 9  is a pictorial illustration of how to record data on the memory device of an intelligent heater tube. 
           [0030]      FIG. 10  is a schematic diagram of the writer module used to write on a 1-Wire EEPROM. 
           [0031]      FIG. 11  is a schematic diagram of a built-in Video Tube Deposit Rater for use with an intelligent heater tube. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]      FIG. 1  is a schematic block diagram of a thermal oxidation stability tester referred to generally by the reference numeral  20 . The thermal oxidation stability tester  20  has an embedded computer  21  with a touch screen  23  for user interface. While many different types of programs could be run, in the preferred embodiment, Applicant is running C++ in the embedded computer  21 . The touch screen  23  displays all of the information from the thermal oxidation stability tester  20  that needs to be conveyed to the user. The user communicates back and forth with the embedded computer  21  through the touch screen  23 . If a batch of fuel is to be tested, a test sample is put in the sample delivery system  25 . 
         [0033]    It is important to the test to make sure the test sample is oxygen saturated through aeration. Therefore, the embedded computer  21  operates a sample aeration control  31  for a period of time to make sure the sample is fully aerated. The aeration of the sample takes place at the beginning of the test. 
         [0034]    The embedded computer  21  turns on a sample flow control  27 , which is a pump used to deliver the sample throughout the thermal oxidation stability tester  20 . Simultaneous with the sample flow control  27  pumping the test sample throughout the system, sample pressure control  29  maintains a fixed pressure throughout the system. It is important to maintain pressure in the system to prevent boiling of the test sample when at elevated temperatures. In the present thermal oxidation stability tester  20 , the sample is maintained at approximately 500 psi when undergoing the thermal oxidation stability test. 
         [0035]    Also, the embedded computer  21  controls parameters affecting the intelligent heater tube  33 . The test data is recorded to the intelligent heater tube  33  via intelligent heater tube writer  35  from the embedded computer  21 . Critical test parameters are recorded on a memory device (as described subsequently) on an end of the intelligent heater tube  33  via the intelligent heater tube writer  35 . The rating of the deposit formed on the intelligent heater tube  33  will be recorded on the memory device at a later time. 
         [0036]    In performing the thermal oxidation stability test on a test sample, the intelligent heater tube  33  is heated by tube heater control  37 . The tube heater control  37  causes current to flow through the intelligent heater tube  33 , which causes it to heat up to the temperature setpoint. 
         [0037]    To prevent the hot intelligent heater tube  33  from heating other parts of the thermal oxidation stability tester  20 , bus-bar coolant control  39  provides coolant upper and lower bus-bars holding each end of the intelligent heater tube  33 . This results in the center section of the intelligent heater tube  33  reaching the prescribed temperature while the ends of the intelligent heater tube  33  are maintained at a lower temperature. This is accomplished by flowing coolant via the bus-bar coolant control  39  across the ends of the intelligent heater tube  33 . 
         [0038]    The test parameters, such as the dimension of the heater tube, pressure of the test sample or flow rate are fixed by ASTM D3241. However, the control of the equipment meeting these parameters are the focus of this invention. 
         [0039]    Referring now to  FIGS. 2 and 2A  in combination, a schematic flow diagram is shown connecting the mechanical and electrical functions. The embedded computer  21  and the touch screen  23  provide electrical signals as indicated by the arrows. A test sample is contained in the sample container  41 . To make sure the sample in the sample container  41  is fully aerated, an aeration pump  43  is turned ON. The aeration pump  43  pumps air through a dryer  45  where the air is dehumidified to remove moisture. From the dryer  45 , a percent relative humidify sensor  47  determines the humidity level of the pumped air and provides that information to the embedded computer  21 . Assuming the percent humidity of the pumped air is sufficiently low, the test procedure will continue pumping air through the flow meter  49  and aeration check valve  50  into the sample container  41 . During aeration, flow meter  49  should record approximately 1.5 liters of air per minute. Since the flow meter  49  runs for approximately six minutes, the aeration pump  43  will sparge approximately nine liters of air into the test sample. This is sufficient time to saturate the test sample with dry air. 
         [0040]    Within the sample container  41 , a sample temperature measurement  51  is taken and provided to the embedded computer  21 . The sample temperature measurement  51  is to ensure that the test sample is between 15°-32° C. If the test sample is outside of this temperature range, results can be impacted. Therefore, if the test sample is outside this temperature range, the embedded computer  21  would not let the test start. 
         [0041]    Once the test sample has been aerated and if all the other parameters are within tolerance, then the sample drive pump  53  will turn ON. The sample drive pump  53  is a single piston HPLC pump, also known as a metering pump. With every stroke of the piston, a fixed volume of the sample is delivered. The speed of the sample drive pump  53  is controlled so that it pumps 3 mL/min of the test sample. The sample drive pump  53  is configured for fast refill which minimizes the need for manual pump priming. Pulsations, associated with pumps of this design are minimized with the use of a pulse dampener and a coil tubing on the outlet side as will be subsequently described. 
         [0042]    To get air out of the tubing between the sample container  41  and the sample drive pump  53  at the start of the test, an auto pump priming valve  55  is opened, a sample vent valve  54  is closed and the aeration pump  43  is turned ON by the embedded computer  21 . The auto pump priming valve  55  opens and remains open while a combination of sample and air is discharged into waste container  57 . At the same time the aeration pump  43  provides positive pressure in the sample container  41  to force test sample from the sample container  41  to the sample drive pump  53 . The sample vent valve  54  closes to prevent venting of the air pressure to atmosphere to maintain a pressure of 2 to 3 psi. A sample vent check valve  56  across the sample vent valve  54  opens at 5 psi to prevent the pressure in the sample container  41  from exceeding 5 psi. Once the sample drive pump  53  starts pumping the test sample, auto pump priming valve  55  will close and the sample vent valve  54  will open. Thereafter, the sample drive pump  53  will pump the test sample through check valve  59  to the prefilter  61 . The check valve  59  prevents fluid from flowing backwards through the sample drive pump  53 . The check valve  59  operates at a pressure of approximately 5 psi. The check valve  59  prevents siphoning when the sample drive pump  53  is not pumping. Also, check valve  59  prevents fluid from being pushed backwards into the sample drive pump  53 . 
         [0043]    The prefilter  61  removes solid particles in the test sample that could affect the test. The prefilter  61  is a very fine filter, normally in the order of 0.45 micron in size. The purpose of the prefilter  61  is to make sure particles do not get into the test filter as will be described. The prefilter  61  is replaced before every test. 
         [0044]    From the prefilter  61 , the test sample flows through an inlet  63  into the cylindrical heater tube test section  65 . Outlet  67 , while illustrated as two separate outlets, is actually a single outlet at the upper end of the cylindrical heater tube test section  65 . Extending through the cylindrical heater tube test section  65  is the intelligent heater tube  69 , sealed at each end with ceramic bushings and an o-ring (not shown). While the test sample flows through the cylindrical heater tube test section  65  via inlet  63  and outlet  67  and around the intelligent heater tube  69 , the housing of the cylindrical heater tube test section  65  is electrically isolated from the intelligent heater tube  69 . Only the test sample comes in contact with the center section of the intelligent heater tuber  69 . Inside of the intelligent heater tube  69  is a thermocouple  71  that sends a signal back to the embedded computer  21  as to the temperature of the center section of the intelligent heater tube  69 . 
         [0045]    Test sample flowing from the cylindrical heater tube test section  65  flows through a differential pressure filter  73 , commonly called the “test filter”. In a manner as will be explained in more detail, the intelligent heater tube  69  heats up the test sample inside of the cylindrical heater tube test section  65  to the test parameter set point. Heating of the test sample may result in degradation of the test sample, or cause solid particles to form. The solid particles may deposit on the center section of the intelligent heater tube  69 , and/or may collect on the differential pressure filter  73 . The pressure drop across the differential pressure filter  73  is measured by differential pressure sensor  75 . Pressure across the differential pressure filter  73  is continuously monitored by the embedded computer  21  through the differential pressure sensor  75 . When the pressure across the differential pressure filter  73  exceeds a predefined differential of approximately 250 mm to 280 mm of mercury, the differential pressure bypass valve  77  opens to relieve the pressure. By test definition, exceeding a differential pressure of 25 mm Hg results in failure of the test. 
         [0046]    For this test to be performed, the test sample must remain as a liquid. At typical testing temperatures of 250° C. to 350° C., many hydrocarbon fuels will transition to the vapor phase at ambient pressures. To keep the test sample in the liquid phase, the back pressure regulator  79  maintains approximately 500 psi pressure in the system. This system pressure is monitored by the system pressure sensor  81 , which reports information to the embedded computer  21 . During a test, normal flow of a test sample is through differential pressure filter  73  and through the back pressure regulator  79 . From the back pressure regulator  79 , the test sample flows through sample flow meter  83  to waste container  57 . The sample flow meter  83  accurately measures the flow rate of the test sample during the test. The sample flow meter  83  provides sample flow rate information to the embedded computer  21 . 
         [0047]    A system/safety vent valve  85  is connected into the system and controlled via the embedded computer  21 . The system/safety vent valve  85  acts to relieve excess system pressure in the case of power loss, improperly functioning system components or other system failures. In the event of this occurrence, the system pressure sensor  81  sends a signal to the embedded computer  21 , triggering the system/safety vent valve  85  to open and relieve excess pressure. Also, at the completion of a test, the system/safety vent valve  85  opens to vent pressure from the system. The system/safety vent valve  85  is normally set to the open position requiring a program command from the embedded computer  21  to close the system/safety vent valve  85 . Therefore, if power is lost, the system/safety vent valve  85  automatically opens. 
         [0048]    At the end of the test, after the system/safety vent valve  85  is opened and system pressure is relieved, the flush air pump  87  turns ON and flushes air through flush check valve  89  to remove the test sample from the system. The flush air pump  87  pushes most of the test sample out of the system via the system/safety vent valve  85  into the waste container  57 . 
         [0049]    The system may not operate properly if there are air pockets or air bubbles in the system. During a test, it is important to maintain an air-free system. Therefore, at the beginning of each test, the solenoid operated differential pressure plus vent valve  91  and the differential pressure minus vent valve  93  are opened, flushed with test sample, and vented to remove any air pockets that may be present. During the beginning of each test, the position of the differential pressure vent valves  91  and  93  ensure there is no air in the differential pressure lines. 
         [0050]    If the waste container  57  is properly installed in position, a signal will be fed back to the embedded computer  21  indicating the waste container  57  is correctly connected. This also applies for the sample container  41  which sends a signal to the embedded computer  21  when it is properly connected. The system will not operate unless both the waste container  57  and the sample container  41  are properly positioned. 
         [0051]    The center portion of the intelligent heater tube  69  is heated to the test parameter set point by flowing current through the intelligent heater tube  69 . Instrument power supplied for current generation and all other instrument controls is provided through local available power  95 . Depending on local power availability, local available power  95  may vary drastically. In some areas it is 50 cycles/sec. and in other areas it is 60 cycles/sec. The voltage range may vary from a high of 240 Volts down to 80 Volts or less. A universal AC/DC converter  97  takes the local available power  95  and converts it to 48 Volts DC. With the universal AC/DC converter  97 , a good, reliable, constant 48 Volts DC is generated. The 48 Volts DC from the universal AC/DC converter  97  is distributed throughout the system to components that need power through the DC power distribution  99 . If some of the components need a voltage level other than 48 Volts DC, the DC power distribution  99  will change the 48 Volts DC to the required voltage level. 
         [0052]    To heat the intelligent heater tube  69 , the 48 Volts from the universal AC/DC converter  97  is converted to 115 Volts AC through 48 Volt DC/115 Volts AC inverter  101 . While taking any local available power  95 , running it through a universal AC/DC converter  97  and then changing the power back to 115 Volts AC through a 48 Volts DC/115 Volts AC inverter  101 , a stable power supply is created. From the 48 Volts DC/115 Volts AC inverter  101 , power is supplied to the heater tube module  103 . The heater tube module  103  then supplies current that flows through the intelligent heater tube  69  via upper clamp  105  and lower clamp  107 . The heater tube module  103  is controlled by the embedded computer  21  so that during a normal test, the thermocouple  71  inside of the intelligent heater tube  69  will indicate when the intelligent heater tube  69  has reached the desired temperature. 
         [0053]    While the center section of the intelligent heater tube  69  heats to desired test set point, the ends of the intelligent heater tube  69  should be maintained near room temperature. To maintain the ends of the intelligent heater tube  69  near room temperature, a coolant flows through an upper bus-bar  109  and lower bus-bar  111 . The coolant inside the upper bus-bar  109  and lower bus-bar  111  cools the upper clamp  105  and lower clamp  107  which are attached to the ends of the intelligent heater tube  69 . The preferred cooling solution is a mixture of approximately 50% water and 50% antifreeze (ethylene glycol). As the coolant flows to the coolant container  115 , the flow is measured by flow meter  113 . To circulate the coolant, a cooling pump  117  pumps the coolant solution into a radiator assembly  119 . Inside of the radiator assembly  119 , the coolant is maintained at room temperature. The radiator fan  121  helps remove heat from the coolant by drawing air through the radiator assembly  119 . From the radiator assembly  119 , the coolant flows into the lower bus-bar  111  then through upper bus-bar  109  prior to returning via the flow meter  113 . 
         [0054]    The flow meter  113  is adjustable so that it can ensure a flow of approximately 10 gal./hr. The check valve  123  helps ensure the cooling system will not be over pressurized. Check valve  123  will open at around 7 psi, but normally 3-4 psi will be developed when running the coolant through the entire system. 
         [0055]    To determine if the intelligent heater tube  69  is shorted out to the housing (not shown in  FIGS. 2 and 2A ), a heater tube short detector  110  monitors a short condition. If a short is detected, the embedded computer  21  is notified and the test is stopped. 
         [0056]    On one end of the intelligent heater tube  69  there is a memory device  125  to which information concerning the test can be recorded by IHT writer  127  as will be discussed in more detail. While a test is being run on a test sample, the IHT writer  127  will record information into the memory device  125 . At the end of the test, all electronic information will be recorded onto the memory device  125  of the intelligent heater tube  69 , except for the manual tube deposit rating. To record this information, the intelligent heater tube  69  will have to be moved to another location to record the deposit rating either (a) visually or (b) through a Video Tube Deposit Rater. At that time, a second IHT writer will write onto the memory device  125 . The Video Tube Deposit Rater may be built into the system or may be a standalone unit. 
         [0057]    The intelligent heater tube  69  is approximately 6¾″ long. The ends are approximately 3/16″ in diameter, but the center portion that is heated is approximately ⅛″ in diameter. Due to very low electrical resistance of aluminum, approximately 200 to 250 amps of current flows through the intelligent heater tube  69 . Both the voltage and the current through the intelligent heater tube  69  is monitored by the embedded computer  21 , but also the temperature of the center section of the intelligent heater tube  69  is monitored by the thermocouple  71  which is also connected to the embedded computer  21 . The objective is to have the center section of the intelligent heater tube  69  at the required temperature. To generate that type of stable temperature, a stable source of power is provided through the universal AC/DC converter  97  and then the 48 VDC/115 VAC inverter  101 . By using such a stable source of power, the temperature on the center section of the heater tube  69  can be controlled within a couple of degrees of the required temperature. 
         [0058]    Referring now to  FIG. 3  of the drawings, a pictorial representation of the coolant flow during a test is illustrated. Like numbers will be used to designate similar components as previously described. A pictorial illustration of the heater tube test section  129  is illustrated on the lower left portion of  FIG. 3 . Coolant from the radiator assembly  119  is provided to the lower bus-bar  111  and upper bus-bar  109  via conduit  131 . From the upper bus-bar  109 , the coolant flows via conduit  133  to flow meter  113 . From flow meter  113 , the coolant flows through conduit  135  to the coolant container  115 . The cooling pump  117  receives the coolant through conduit  137  from the coolant container  115  and pumps the coolant into radiator assembly  119 . If the pressure from the cooling pump  117  is too high, check valve  123  will allow some of the coolant to recirculate around the cooling pump  117 .  FIG. 3  is intended to be a pictorial representation illustrating how the coolant flows during a test. 
         [0059]    Likewise,  FIG. 4  is a pictorial representation of the aeration system for the test sample. Similar numbers will be used to designate like components as previously described. An aeration pump  43  pumps air through conduit  139  to a dryer  45 . The dryer  45  removes moisture from the air to prevent the moisture from contaminating the test sample during aeration. From the dryer  45 , the dried air will flow through conduit  141  to humidity sensor  47 . If the percent relative humidity of the dried air blowing through conduit  141  exceeds a predetermined amount of 20% relative humidity, the system will shut down. While different types of dryers  45  can be used, it was found that Dry-Rite silica gel desiccant is an effective material for producing the desired relative humidity. 
         [0060]    From the percent humidity sensor  47 , the dried air flows through conduit  143  to flow meter  49 , which measures the air flow through conduit  143  and air supply conduit  145 . From air supply conduit  145 , the dried air flows through aeration check valve  50  and conduit  146  sample container arm mounting clamp  147  and sample container arm  149  to aeration conduit  151  located inside of sample container  41 . In the bottom of sample container  141 , a glass frit  153  connects to aeration conduit  151  to cause the dried air to sparge through the test sample in sample container  41 . When the sample container  41  is in place and the sample container arm  149  is connected to the sample container arm mounted clamp  47 , contact  155  sends a signal to the embedded computer  21  (see  FIG. 2 ) indicating the sample container  41  is properly installed. 
         [0061]    Referring now to  FIG. 5 , a pictorial illustration of the flow of the test sample in connection with  FIGS. 2 and 2A  is shown in a schematic flow diagram. The test sample is contained in sample container  41 , which is connected via sample container arm  149  to the sample container arm mounting clamp  147 . Vapors given off by the test sample are discharged through a vent  157 , normally through a vent hood to atmosphere. Simultaneously, the sample drive pump  53  draws some of the test sample out of the sample container  41 . The sample drive pump  53  is a single stroke HPLC pump connected to a pulse dampener  159 . While the pulse dampener  159  may be configured a number of ways, the pulse dampener  159  in the preferred configuration has a diaphragm with a semi-compressible fluid on one side of the diaphragm. This fluid is more compressible than the test sample thereby reducing pressure changes on the test sample flow discharged from the sample drive pump  53 . The sample drive pump  53  is connected to auto pump priming valve  55 . During start-up, the closed auto pump priming valve  55  opens until all of the air contained in the pump and the lines are discharged into the waste container  57 . In case it is needed, a manual priming valve  161  is also provided. Additionally, the aeration pump  43  (see  FIG. 2 ) is turned ON to provide a slight pressure in the sample container  41  of about 2 to 3 psi. The sample vent valve  54  closes to prevent this pressure from escaping to atmosphere. This pressure will help push the fluid sample from the sample container  41  to the inlet of the sample drive pump  53 . The 5 psi check valve  56  prevents the pressure in the sample container exceeding 5 psi. During the test, coil  163  also provides further dampening in addition to the pulse dampener  159 . Check valve  59  ensures there is no back flow of the sample fuel to the sample drive pump  53 . However, at the end of a test, flush check valve  89  receives air from flush air pump  87  to flush the test sample out of the system. 
         [0062]    During normal operation of a test, the sample fuel will flow through check valve  59  and through a prefilter  61  removing most solid particles. Following the prefilter  61 , the test sample flows into the heater tube test section  129  and then through the differential pressure filter  73 . Each side of the differential pressure filter  73  connects to the differential pressure sensor  75 . Also connected to the differential pressure filter  73  is the back pressure regulator  79 . The pressure on the system is continuously monitored through the system pressure transducer  81 . If for any reason pressure on the system needs to be released, system/safety vent valve  85  is energized and the pressurized test sample is vented through the four-way cross connection  165  to the waste container  57 . 
         [0063]    At the beginning of the test, to ensure there is no air contained in the system, the differential pressure plus vent valve  91  and the differential pressure minus vent valve  93  are opened to vent any pressurized fluid through the four-way cross connection  165  to the waste container  57 . 
         [0064]    In case the differential pressure filter  73  clogs so that the differential pressure exceeds a predetermined value, differential pressure bypass valve  77  will open to relieve the pressure. 
         [0065]    To determine the exact flow rate of the test sample through the system, the sample flow meter  83  measures the flow rate of test sample from the back pressure regulator  79  before being discharged through the waste container arm  167  and the waste container clamp  169  into the waste container  57 . The waste container  57  is vented all the time through vent  171 . 
       Intelligent Heater Tube (IHT) 
       [0066]    The intelligent heater tube (IHT)  69  is shown in  FIG. 6 . The intelligent heater tube  69  is cylindrical in shape as described previously. The top  173  and bottom  175  are 3/16″ in diameter. The test section  177  is ⅛″ in diameter. Extending longitudinally along the center axis of the intelligent heater tube  69  is a center bore  179 . The thermocouple  71  (previously described in conjunction with  FIG. 2A ) is located inside the center bore  179 . At the end of the enlarged bottom  175  is a memory device  125 . The memory device  125  is slightly smaller in diameter than the heater tube bottom  175 . 
         [0067]    As shown in  FIGS. 7 and 8  in combination with  FIG. 6 , an EEPROM  181  is located inside of the memory device  125 . The EEPROM  181  only has a data signal and a ground signal. The ground signal connects to ground stick  183  and the data signal connects to data plate  185 . The ground stick  183  fits inside of the center bore  179  of the intelligent heater tube  69 . The EEPROM  181  is contained inside of insulated housing  187  of the memory device  125 . The data plate  185  is on the end of the insulated housing  187  and is slightly smaller in diameter than the insulated housing  187 . The only two connections to the memory device  125  are through the ground stick  183  and the data plate  185 . 
         [0068]    While the EEPROM  181  has a total of six solder connections  189 , only two of them are connected to either the ground stick  183  or data plate  185 . The data plate  185  is made from a material that will not tarnish easily such as phosphorous bronze or beryllium copper. The entire memory device  125  is resistant to degradation from jet fuel or related materials. To ensure there is no accidental electrical connection, the data plate  185  is slightly smaller in diameter than the insulated housing  187  of memory device  125 , which in turn is slightly smaller in diameter than the enlarged bottom  175  of the intelligent heater tube  69 . 
         [0069]    Referring to  FIG. 9 , a pictorial example of how to connect to the memory device  125  of the intelligent heater tube  69  when running a test of a sample fuel is shown. The intelligent heater tube  69  is held in position by lower clamp  107 . The ground stick  183  of the EEPROM  181  is contained inside of center bore  179  of the enlarged bottom  175 . 
         [0070]    To write to and from the EEPROM  181 , an IHT writer  127  as shown in connection with  FIG. 2A  is used. The IHT writer  127  has a data line that connects to a spring-loaded contact  191  that pushes against, and makes electrical contact with, the data plate  185 . The other side of the IHT writer  127  connects to ground via lower clamp  107 , intelligent heater tube  69  and ground stick  183 . The output from the IHT writer  127  can either go directly to the JFTOT, to a video tube deposit rater, or to a personal computer. Normally, there will be two IHT writers  127 . One IHT writer  127  will be located inside of a jet fuel thermal oxidation stability tester (JFTOT®). Another IHT writer  127  will be used to record the deposit information as collected on the test section  177  of the intelligent heater tube  69  as is recorded either (a) manually from a visual inspection or (b) with the Video Tube Deposit Rater. The IHT writer  127  when installed on the test apparatus only communicates with the embedded computer  21  shown in  FIG. 2 . After the test has been run, the only information lacking on the memory device  125  is recording the heater tube deposit rating. This will be recorded either from a manual inspection of the intelligent heater tube  69  or from a video tube deposit rater, either of which will require a separate IHT writer module  127 . 
         [0071]    Referring now to  FIG. 10 , the IHT writer module  127  is shown in more detail. The IHT writer module  127  uses 5 Volts DC as its normal power. A USB port  193  is used to connect the IHT writer  127 . USB port  193  has four wires for a positive supply voltage VCC, a negative voltage D−, a positive voltage D+ and a ground GND. Also, the IHT writer  127  has a RS 232 port  195  with four wires being used to transmit data TXD, received data RXD, ground GND, and positive supply voltage VCC. From the IHT writer  127 , one wire is for data and one wire is for ground which are used when connecting to the memory device  125  containing the EEPROM  181 . The USB port  193  and the RS 232 port  195  supplies data through the IHT writer  127  to the memory device  125 . Inside of the IHT writer  127  is a UART TTL level  197  that converts the data to the appropriate form to communicate to EEPROM  181 . The abbreviation UART stands for “Universal Acrosynchrinous Receiver/Transmitter”. TTL is an abbreviation for “Transistor-Transistor Logic”. 
         [0072]    The JFTOT 230 Mark III can be configured with or without a Video Tube Deposit Rater, to work with the intelligent heater tube  69  having the memory device  125  as shown in the combination of  FIGS. 10 and 11 . The embedded computer  21  connects through RS 232 port  195  to the second intelligent heater tube writer  201 , which is similar to IHT writer  127 . If the test system does not have a video tube deposit rater module, then IHT writer  203  may be used to write to the memory device  125  of the intelligent heater tube  69 . In this manner, the IHT writer  203  can be used to manually input the data into the memory device  125 . 
         [0073]    On the other hand, if the testing apparatus does have a Video Tube Deposit Rater, RS 232 port  196  connects the embedded computer  21  to the Video Tube Deposit Rater (VTDR) module  205 . By pressing the eject/close device  207 , the door of the VTDR module  205  will open and the intelligent heater tube  69  may be inserted. By pushing the start button  209 , deposits collected on the intelligent heater tube  69  during the test are rated. The rating is automatically recorded onto the EEPROM chip  181  (not shown in  FIG. 11 ) contained in the memory device  125 . 
         [0074]    Also, the image data from the VTDR module  205  may be retrieved by VTDR LAN connection  211 . 
         [0075]    It is important to remember that two different IHT writer modules are used in the full system. One writer module is used while the heater tube is in the run position. The other writer module is used when the deposit rating is being recorded. 
         [0076]    After the information has been recorded on the memory device  125 , eject/close device  207  is pressed to open the door to allow removal of the intelligent heater tube  69 . Now, all of the information recorded from that test is contained with the intelligent heater tube  69 . Since most users keep the recorded data and the heater tube, this allows both to be archived together