Using LoggerPro “Nothing is more terrible than to see ignorance in action.” J. W. Goethe (1749-1832) LoggerPro is a general-purpose program for acquiring, graphing and analyzing data. It can accept input from a video camera, read a video file or, through the LabPro interface device, acquire data from a variety of other sensors. Pictorial data can be reduced to x-y coordinates of selected objects, while sensor data is presented in tabular form as a function of time. The program will prepare plots of the data, compute statistics like the mean, fit specified curves to a data series, and calculate derived quantities. Basic operations will be described here, with more detail provided for each exercise. To start LoggerPro you can click on the caliper icon in the main toolbar, or double-click on one of the startup files with a .cmbl extension on the desktop. The startup file can configure graphs, sensors and other features for a particular experiment, so this is the preferred method. If the program is already running, you can get a clean copy with File > New on the taskbar, or load a new startup file with File > Open... When doing so, or when quitting the program, you will be prompted to save your previous work. This is usually not necessary but if you do wish to save, use File > Save As... and follow the dialog to create a new file so that the original is available for other students. DATA COLLECTION - SENSORS Be sure that the power supply for the LabPro is plugged in, and that it is connected to the computer by a USB cable. The sensors needed for a particular exercise will usually already be connected to the LabPro interface, but the program needs to know what sensors are connected to each port, and how they should be calibrated or actuated. Loading the startup file specified for each exercise will provide the proper configuration, a data table with useful columns, and graphs as needed. In the unlikely event that the startup file settings are not adequate, the sensor configuration can be modified by following Experiment > Set Up Sensors > LabPro I. Changes to the data collection rate and other parameters can be made with the window under Experiment > Data Collection.... If you do make changes, do not save them under the original file name. Once the program and sensors are configured, you start data collection by clicking the Collect button. After a brief pause, the sensors will be read at regular intervals until the Stop button is clicked or the time limit is reached. Data will appear in the table and on the graph, ifPHYS 111 Using LoggerPro 2 present, as it is obtained. When data collection is complete, you can use the graphing and data analysis functions as described below. Motion detector The motion detector, or "sonic ranger", works by sending out short pulses of high frequency (ultrasonic) sound and measuring the time between when the pulse is emitted and when the first echo is detected. Using the known speed of sound, the time interval is converted to a distance interval and then plotted on a computer screen. The software that accompanies the sonic ranger will also estimate the velocity of the object as a function of time by computing differences of successive distances. For example, the simplest estimate of velocity would be v !d(t2) " d(t1)t2" t1 (1) The time interval is necessarily short, so the distances are likely to be nearly equal and their difference will be very sensitive to small uncertainties in either value. In order to minimize this sort of error the program actually averages over several points: 3, 5, 7, 9, or 15. The algorithm is very effective at smoothing the noise but it will also smooth out real changes if they are rapid. You will need to take this effect into account, and perhaps change the averaging, as you analyze your data. Operationally, there are several factors to be aware of when using the ranger. If an object is too close, the echo overlaps the transmitted pulse and cannot be detected. The minimum distance our units can measure is about 0.5 m. The ‘beam’ of sound is not sharply defined, but diverges in about a 15 cone from the transmitter. If the slider is outside the beam it will not be measured, but undesired objects which intrude into the beam may be seen instead of the slider. Fortunately aiming is not too critical, and you can locate the center of the cone by looking for your own reflection in the metal surface of the diaphragm on the ranger. Force probe The force probe is a plastic box containing a metal beam with a hook. When a force is applied to the hook, the beam bends like a spring. Internal sensors measure the bending, and report it as a force. Two ranges are available, ±10 N or ±50 N, selectable with a switch on the box. The probe only measures forces parallel to the longer axis of the box, not perpendicular. Do not exceed a force of 50N, on either scale, to avoid permanent deformation of the beam. Try to avoid sudden changes in the applied force, because doing so excites vibrations in the force probe which may cause the readings to oscillate for several tenths of a second. Before taking serious data you must calibrate the force probe by applying two known forces to it, usually with weights. Set up the probe in the same orientation, horizontal or vertical,PHYS 111 Using LoggerPro 3 as it will be in operation. Then go to Experiment > Calibrate..., and pick the desired sensor from the pull-down menu. The Sensor Settings window should open on the Calibrate tab. Verify that the probe name is Force-Dual Range with the correct range setting, and then click the Calibrate Now button. With nothing connected to the force probe, enter 0 in the box and click Keep. Apply a known force to the probe, enter the force in Newtons, and click Keep. The software will perform a linear interpolation so that subsequent readings are converted to Newtons for this probe. Exit from the calibration routine by clicking the Done button. Repeat the process for the second probe if it is in use. DATA COLLECTION - VIDEO Video is used to measure and analyze the motion of objects, often in two dimensions. Two steps are required: A movie of the desired motion is captured in a LoggerPro