THRUST CURVE LOGGER V-4.200 There are several items that must be addressed prior to actual firing of the motor for data acquisition. These will be required in the Propellant Characterization process: Weigh a piece of pour tube. You will need this to subtract from the solid grain before drilling to determine the density of the propellant Weigh all propellant grains before drilling the core and use that information to determine the actual density of your propellant. Weigh and label all propellant grains after drilling the core. Record the nozzle diameter of each motor fired Record the nozzle s exit diameter of each motor fired The document titled PROPELLANT CHARACTERIZATION PROCEEDURE outlines the steps to obtain final propellant ballistics for use in motor simulation software programs. Before starting anything, use your computer s BIOS setup to configure the computer s parallel port to EPP mode. Using a good straight through male to female 25 pin parallel port cable (Do not use a cheap cable that does not have all 25 pins wired through), connect the Interface Box to the computer s parallel port. Power up the Interface Box.
Begin the Thrust Curve Logger program. You should get a screen that looks similar to this: When the screen opens you should see, in the System Check boxes (upper right corner) these values showing: Gnd =0 Half=2.5 Vcc=5 Voltage=>11 volts If necessary you can reinitiate this by clicking Test. Connect the load cell and pressure transducer to the Interface Box.
CALIBRATE THRUST Select the Thrust tab. With no weight on the load cell in appropriate orientation (horizontal or vertical) hit the top Calibrate button, next to Value=0. This will set 0 Offset to whatever value the load cell has without weight. Place a known weight on the load cell. (the higher the better). Place that known weight into the lower Value field. Hit the lower Calibrate button. The Offset field will now display whatever value the load cell has with that known weight. There are two vertical graphs to the left of this. (see top image) The first column is for thrust (weight), the second column is for pressure To confirm calibration place arbitrary weights on the load cell. Click on the Display check box in the System Check area. The left column should display those weights.
CALIBRATE PRESSURE Select the Pressure tab. Using a 1 to 5 volt Pressure Transducer use the following values. 0 Offset is 819 Using a 0 to 5 volt Pressure Transducer use the following values. 0 Offset is 0 Offset is 4095 Lower Value field is the peak pressure of the pressure transducer used. To confirm calibration apply arbitrary pressures on the pressure transducer. Click on Display check box in the System Check area The right column should display that pressure. Before test firing, the top Calibrate button should be clicked to calibrate the pressure transducer to the current atmospheric pressure.
TEST FIRING A MOTOR Unclick Display check box. Select which channel(s) you wish to log by turning on the appropriate check boxes (Thrust and/or pressure.) Select appropriate Start(s) value(s) when to initiate logging Set both Stop(s) to 99. Set Seconds (how long to log) desired. 60 Seconds should handle most motors as you may never fire a motor that burn for more than a minute. Set Average to 1. For a smoother curve increase as desired (ie: 2, 5, 10 etc.) Check the Fast box. This logs at maximum sample rate, and will turn off the display update, as well as the mouse and keyboard input during the data logging. This is not really necessary to display, as it will only slow down the data logger rate. Place the motor on the test stand and connect the igniter. Hit the large Arm button, lower right corner, this will start the logger looking for data. Fire the motor via your ignition system. If the need arises to abort the test, BEFORE actually firing the motor, hit the Disarm button next to it. This will cancel the timer and reset it for a restart. NOTE: With Seconds set at 60 the computer will become non responsive from the time of ignition to 60 seconds. Do not be alarmed and let the machine do its thing. The computer did not lock up so do not try to hit keys or stop the process by hitting the Disarm button. Once data is acquired you will have a thrust curve and summary data on screen. IMMEDIATELY save this data as a raw file with a unique name. Processing data can be preformed anytime after this save. To fire and collect data on additional motors simply reload the test stand with another motor. Place and connect the igniter and hit the big Arm button on the computer screen and fire the motor with your ignition system.
PROCESSING Load a desired file. On screen the thrust curve and data will appear. Zoom into the appropriate area to work with by click and dragging the mouse over the desired area. This will expand the workable area. You will now see two curves (if using a pressure transducer, Single curve without one). The motor thrust curve is in Black; the pressure curve will be in Blue. Zoom again until you now have what you want on the screen. (You can always display the entire graph, by right clicking on the graph and selecting Unzoom ). Now you want to crop the data by right clicking on the graph and select Crop Both. When asked do you want to delete all data to the left and right click Yes. This will remove all wasted space to the left and right of the good data. Save this data into the final data file. Do NOT use the same name as the original data file as you may wish to reuse or return to the original data..