Test apparatus for measuring heat release of certain materials
TECHNICAL FIELD 
     This invention relates to calorimeter devices which measure heat. More particularly, it relates to automated control systems for such devices. 
     This specification includes a microfiche appendix totalling three sheets of microfiche having approximately 133 frames. Such appendix is available to the public for inspection pursuant to 37 C.F.R. §1.96(b)(1). 
     BACKGROUND ART 
     The commercial aircraft industry is continually looking for ways to improve aircraft fire safety. Aircraft fires can, of course, arise from a number of situations including crashes, in-flight fires caused by either passengers and/or aircraft system malfunctions, cargo compartment fires, or situations where a fire is initiated and propagated in an untended aircraft. 
     Improving aircraft fire safety involves the development of better and more fire-resistant construction materials. With regard to those materials which are currently used to construct interior cabin surfaces, e.g. primarily flammable materials in the passenger cabin, it has been determined fire safety is directly related to the amount of heat they release when they burn, and when they release it. For this reason, the Federal Aviation Administration (FAA) has imposed specific heat-release requirements for such materials, although it should also be appreciated the industry has for many years conducted its own tests independently of FAA regulations in order to improve fire safety. 
     Dr. Edwin Smith, a Professor of Chemical Engineering at Ohio State University, invented a calorimeter which measures heat release and smoke generation rates from burning materials. This calorimeter has come to be known in the field as the &#34;OSU calorimeter&#34; and has been specifically designated for use by the FAA in heat release testing of cabin surface material. Unfortunately, using it to run large numbers of tests using numerous material samples has long been known to be a tedious and time-consuming process, primarily because it involves manual control of calorimeter operation and manual coordination of data acquisition with calorimeter operation. The present invention eliminates these drawbacks by providing a calorimeter of the OSU type whose functions are automatically controlled by a computer in accordance with specific user-selected inputs, and which automatically reduces data immediately upon test completion. 
     DISCLOSURE OF THE INVENTION 
     An apparatus constructed in accordance with this invention includes a calorimeter whose functions is to measure the heat release rate and smoke generation rate of burning materials. The calorimeter includes an inner chamber where burning takes place. This chamber has a doorway which is automatically opened or closed for the purpose of permittinng chamber access for placing a test specimen or sample inside. The sample is so placed by an actuator ram which is also automatically controlled. 
     Air continually flows through the chamber at a certain calibrated rate. In actual practice, the flow rate for any given test will be dictated by the FAA. Electrical radiant heating elements inside the chamber provide sufficient heat to promote burning of the sample. Ignition of the sample is induced by flamelets which also help ignite gases produced by the sample as it burns. 
     The temperature of the air and any combustion products exiting the chamber is continuously monitored by suitable sensors such as thermocouples. The increase in exit gas temperature is known to be directly proportional to the heat released by the test sample, and therefore, exit gas temperature data can be directly converted into heat release data. Integrating such data over a given period of time gives the total amount of heat released by the sample. 
     The calorimeter also includes a light source and photocell positioned across from each other in a manner so that the exit gas passes between them. Any smoke in the gas decreases the amount of light transmitted to the photocell. The decrease in percent of light transmission is known to be logarithmically related to the increase in smoke generation thus making it possible to obtain total smoke generation data. 
     The apparatus includes a programmable computer operatively connected to the various above-described hardware elements of the calorimeter. The computer has conventionally-known input/output devices which, respectively, permit the user to input and receive computer information. The computer&#39;s programming causes it to display certain user-selectable options which are to be employed during any given test for controlling calorimeter hardware. Such options include, for example, selection of the times at which the chamber&#39;s doorway is to be automatically opened and closed, and operation of the ram to move the sample into the chamber. Also the user selects the total time the sample remains in the chamber during burning, the rate of airflow through the chamber, and the radiant heat supplied to the sample during burning. 
     The computer maintains both this information and certain additional calibration information which it uses in the calculation of heat release and smoke generation rates. Then, the computer operates the calorimeter in accordance with the user-selected options and continually measures the resultant exit gas temperature and decrease in photocell light reception, which is used to calculate heat release and smoke generation data. The computer also makes this data immediately available to the user. 
     An advantage of the present invention is that it provides a menu-driven integrated data acquisition/control/reduction system which automatically controls the chamber doorway and sample ram, senses temperature changes and photocell readings, and calculates heat and smoke release results. It is also an advantage that test results are reported immediately to the user after each test is completed. 
     The apparatus can be used with a minimum amount of user effort and training. Also, any changes in desired testing conditions or procedures which formerly required time-consuming revisions can be implemented immediately. These advantages, and others, will become apparent to the reader upon considering the following description in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference numerals refer to like parts throughout the various views, and: 
     FIG. 1 is a schematic view of a calorimeter constructed in accordance with the invention, and shows the various hardware elements of the calorimeter; and 
     FIG. 2 is a schematic view of the invention and shows how a computer is operably connected to the hardware elements of the calorimeter shown in FIG. 1. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     (1) General Description of the System 
     Referring to the drawings, and first to FIG. 1, therein is shown at 10 a schematic of a calorimeter constructed in accordance with the invention. It includes a burn chamber 12 in which is received a plurality of radiant heating elements in the form of silicon carbide glow bars 14. Preferably, there are four of these positioned in a vertical plane and parallel with respect to each other. 
     An airflow is delivered into the bottom of the chamber as shown at 16. The rate of such airflow is user-selectible although it should be understood that in order to encourage uniformity in industry testing, the FAA may require a certain predetermined flow rate. For example, the preferred bottom airflow rate may be 10 liters per second. The bottom air is delivered into a chamber space 18 which is below a perforated pan 20. The pan 20 creates a uniform airflow upwardly through the chamber as indicated by arrows 22. 
     The top of the burn chamber has inner and outer walls 24, 26. An airflow is delivered into the space 28 between them, as is shown at 30. In preferred form, the flow rate of this top airflow should be 30 liters per second, meaning the total airflow delivered to the calorimeter 10 and exiting from the burn chamber&#39;s stack 31 should be approximately 40 liters per second. The sole purpose of the top airflow 30 is to cool the burn chamber&#39;s outer walls thus preventing them from getting too hot. 
     Access into the chamber 12 is provided by doors 32, 34. These doors are shown in a closed position, but may be opened by swinging them outwardly. Conventionally-known actuators, controlled by relays, are used to swing the doors. An actuator ram 36 has a rod 38 that is extendible and retractable into the burn chamber 12 for insertion/removal of a test sample 42. At the end of the rod 38 is a holder 40 shaped to fixedly hold the sample 42. Since the amount of heat any particular sample releases is also a function of the sample&#39;s mass, uniform sample sizing has been established by the FAA. Typically, for example, sample size will be 6 inches by 6 inches and up to one and one-half inches thick, although it should be appreciated the invention has the capability of handling many sizes different from this. 
     The sample 42 is placed in holder 40 when rod 38 is retracted into a holding chamber 44 that is positioned outside and over doors 32, 34. The doors 32, 34 are then opened and the rod 38 is extended, thrusting the sample 42 into the chamber airflow. There, it is subject to heat by glow bars 14 and is ignited by pilot flame 43. The doors 32, 34 close immediately after the sample 42 is placed in the chamber 12. The doors have slots which permit them to close over the extended rod 38. 
     The temperature of the airflow 46 or gas exiting the burn chamber through stack 31 is continuously monitored by a plurality of thermocouples 48, preferably five in number that are connected in series. Their hot junctions are placed across the stack&#39;s opening as shown at 50 and their cold junctions are placed in bottom chamber 18, below pan 20 as shown at 52. The circuit created by thermocouples 48 provides an uncompensated output which roughly measures exit gas temperature. A compensator tab thermocouple 54 is also used to compensate their output. This latter thermocouple has a hot junction connected at 56 directly to the wall of the chamber&#39;s stack 31, and its cold junction is suitably connected somewhere in the conduit 16 which delivers incoming air to bottom chamber 18. As would be familiar to a person skilled in the art, both the uncompensated and compensated thermocouples 48, 54 provide output signals in milli-volts. 
     The purpose of the circuit created by the compensator tab thermocouple 54 is that the uncompensated thermocouples 48 have a relatively slow response time, meaning they respond slowly to any rapid changes in exit gas temperature during a particular test. Their response time can be improved by using the &#34;compensated&#34; signal from thermocouple 54, by subtracting its output from the output of thermocouples 48. Hence, the compensated output is determined as follows: 
     
         T.sub.comp =T.sub.uncomp -T.sub.tab 
    
     In practice, use of the compensated signal results in a slightly higher peak release rate calculation than use of the uncompensated signal, at least for those materials which rise quickly to a peak heat release rate and then immediately drop off. However, the total heat release results integrated over a certain period of time are virtually identical using either method. 
     Mounted to the top of the chamber&#39;s stack 31 is a light source 58 and photocell receptor 60. Smoke produced by the burning sample 42 passes between them and reduces the percentage of light received by the photocell 60. The photocell&#39;s output is also in milli-volts. 
     The outputs of thermocouples 54, 48 and photocell 60 are shown, respectively, at 62, 64 and 66 in FIG. 1. These outputs are transmitted to a computer as indicated at 68. Referring to FIG. 2, therein is shown a preferred computer 70 operatively connected to the calorimeter 12. By way of illustrative example, a computer suitable for use with this invention is the Compaq (trademark) Deskpro 286 which would be familiar to a person skilled in the art. A conventional color monitor 72 and laser printer 74 are used in connection with the computer 72 as a means for displaying output information. As a person skilled in the art would realize, the Compaq (trademark) computer 70 has a conventional keyboard which provides the user with a means for inputting data. 
     A conventional analog-to-digital converter 76 interfaces the computer 70 with the calorimeter&#39;s previously-described hardware elements. As described above, thermocouple and photocell signals are in the form of milli-volts which are received directly by the interface 76 and converted into digital form. If desired, the output of the uncompensated thermocouples 48 may be compensated by a summing junction in accordance with the above equation, and output in milli-volts as shown at 78 to the interface 76. The computer also operates the relays governing door and ram control digitally as shown at 82, 84, respectively, in accordance with instructions specified by the user. 
     To summarize the invention&#39;s hardware elements or parameters as described above, the computer must have a separate input channel for the uncompensated thermocouple and tab thermocouple circuits 64, 62, the actual compensated thermocouple circuit 78 and the photocell circuit 66. The computer must also have separate digital output channels 82 and 84 for controlling opening and closing movement of the door, and ram extension and retraction. 
     (2) System Programming Requirements 
     As stated above, an important feature of the invention is that it is menu-driven and minimizes the amount of training and time required to operate it. All necesssary test variations are incorporated into a menu of options displayed to the user who is prompted by the computer 70 to provide the test parameters he or she desires. This makes it possible for a user totally unfamiliar with the invention to conduct a test after only a few minutes familiarization with the system. The programming requirements for the system can be separated into separate sections including menu-driven options; calibration; automated door operation and test sample insertion; data retention; and data acquisition and reduction. Although all programming requirements would be readily understood by a person skilled in the art upon consideration of the appended computer program, some of the key programming requirements are summarized below. 
     MENU-DRIVEN OPTIONS 
     The software causes the computer to prompt the user to select a number of options displayed on the color monitor 72. These options are instantly selected and implemented during a particular test run. The options include: 
     b. Heat flux selection; 
     c. Calibration constant selection; 
     d. Compensated or uncompensated thermocouples; 
     e. Blank run or no blank run; 
     f. Number of specimens per set; 
     g. Number of thermocouples in uncompensated thermopile; 
     h. Airflow rate; 
     i. Specimen surface area; 
     j. Change of channels read by computer; and 
     k. Monitoring channels of the analog-to-digital converter. 
     Most of the above options are self-explanatory to a person skilled in the art. Briefly, time sequencing includes specifying the entire time during which a test sample is to remain in holding chamber 44, sequencing the times of door opening and closing movement along with ram extension and retraction, specifying the total time the sample is to remain in the burn chamber, and specifying the times at which data is to be reported to the user. Heat flux selection provides the amount of heat generated by the adjustable glow bars 14. The calibration constant selection relates to known heat transfer calibration constants which are develoed by burning known flow rates of methane in the calorimeter burn chamber 12, and then recording the resultant compensated and uncompensated thermocouple or thermopile outputs. Compensated or uncompensated thermocouple selection permits the user to select solely the output of uncompensated thermocouples 48 if he or she desires. 
     Specifying a blank run means that a test run is to be made exactly the same way as an actual test run with the exception that a sample material is not placed in holder 40. The purpose of a blank run is that it is known that when a test specimen is initially injected into burn chamber 12, there is an immediate rush of cold air from holding chamber 44 into the chamber. This consequently reduces the temperature of the exit gas, albeit briefly. Furthermore, a good deal of heat is lost in heating up the specimen holder itself. If these heat losses are not taken into account, the test will show a &#34;negative heat release&#34; at the start of every test. Data generated from a blank run is subtracted from actual test run data to cancel out these losses. 
     The user is permitted to conduct a series of tests using a number of specimens. Therefore, the user has the option of specifying any number of specimens or samples up to twenty, although this number can be easily varied if desired. Since, as described above, five thermocouples are preferably connected in series across calorimeter stack 31, the user is provided with the option of determining the number of thermocouples in this thermopile which are to be used. 
     Airflow rate requires the user to insert air pressure and temperature data so that the computer can automatically provide a calculated airflow rate. The options specified in paragraphs i-j are self-explanatory. 
     SOFTWARE CALIBRATION 
     The software facilites calibration of heat flux, smoke and airflow. All input/output channels can be monitored simultaneously permitting easy computer computation of any necessary calibration constants. With regard to smoke, the software prompts the user to insert glass filters for photocell calibration tests prior to burning any test samples. The software automatically takes milli-volt data from the use of such filters and makes a best curve fit to provide a calibration curve for converting photocell milli-volt data, taken during an actual test, into smoke release rate data. 
     AUTOMATED DOOR OPERATION AND SAMPLE INSERTION 
     In accordance with the above-described menu-driven options, the software triggers door and ram relays at selected times to open doors 32, 34 and insert the test sample. The software also triggers the relays to withdraw the test sample at the end of the test. 
     DATA RETENTION 
     All original milli-volt data provided to the computer is retained, so that any prior test run can be reprinted at the user&#39;s option. Any reprint can be made into a different format than the original test report by changing those options listed under menu-driven options above. 
     Included as an appendix hereto is a copy of a suitable computer program which embodies all of the above-discussed features. This program is written in IBM PC Pascal, Version 2.0, which would be familiar to a person skilled in the art. It is readily compatible for use in the above-identified Compaq computer. Having this program along with the above-described calorimeter and computer hardware, would enable a person skilled in the art to easily practice the invention. 
     Thus, a preferred embodiment of the invention has been presented above. It is to be understood that certain changes could be made to the invention without departing from the spirit and scope thereof. Any patent protection which is due as a result of this disclosure is not to be limited by the preceding description, but rather is to be limited only by the patent claim or claims which follow, wherein such claims are to be interpreted in accordance with the doctrines of patent law. ##SPC1##