Support/Technical Support http://www.vernier.com/tech/index.html -- Contact Tech Support http://www.vernier.com/tech/contact.html *see "Online Support Form" -- FAQ List http://www.vernier.com/til/list.html -- http://www.vernier.com/til/5.html Vernier Tech Info Library TIL #5 Question My Motion Detector gives noisy readings or will not work at more than 2 m. What can I do about this? Answer Some General Tips for the Motion Detector: 1. The maximum sample rate that you can use for the motion detector is 50 Hz, which equates to a sample interval of 0.02 seconds. Since the motion detector emits ultrasound and detects an echo, the speed of sound is a limiting factor in the use of the sensor. So when you use the sensor, the equipment has to give the ultrasound enough time to go out to the object and back. Therefore we don't recommend sampling faster than 50 Hz, i.e. more often than 0.02 seconds. If the room has hard ceilings, floors, or walls, the Motion Detector may detect an ultrasonic pulse that has bounced around the room instead of the direct reflection from the target. This problem is worse at high data rates. Try slowing down the rate of data collection, i.e. less than or equal to 30/s. 2. In using the Motion Detector, it is important to realize that the ultrasound is emitted in a spreading cone about 20 degrees wide. Anything within the cone of ultrasound can cause a reflection and possibly a spurious measurement. These unintentional reflections may come from a desk, chair, or computer in the room. This object can be very small. Remember that the Motion Detector stops checking for echoes when it gets its first recognizable echo. It does not do the following (which might be better if it were possible): Check all echoes that come back and then select the strongest one. 3. As you start doing experiments, everything works fine, except that as the target object moves more than two meters away from the Motion Detector, the Motion Detector still reports two meters. It is reporting the distance to the first object in the cone of ultrasound that sends back a strong echo, which in this case is a table two meters away from the Motion Detector and some distance to the side. You may be able to reduce this problem by moving the table, covering it with a soft cloth, or angling the Motion Detector away from the table. You also can get reflection from the surface of a table supporting the Motion Detector. This can be reduced by raising or tilting the Motion Detector above the table or covering the table with a soft cloth. 4. Look at Distance first. If you begin with a velocity or acceleration graph and obtain a confusing display, switch back to the distance graph to see that it makes sense. Sometimes a stray object will interfere, and it is much easier to detect the problem while looking at the distance information. 5. With a CBL, just monitor the object's position in the raw sensor reading mode until you're sure the Motion Detector is properly positioned. Don't get too close. The Motion Detector does not properly detect objects closer than 0.45 meters due to the time it takes to switch from ultrasound emission to ultrasound detection mode. The maximum range is about six meters, but stray objects in the wide ultrasound cone can be problematic at this distance. 6. Soft targets. Sometimes a target may not supply a strong reflection of the ultrasound. For example, if the target is a person wearing a bulky sweater, the resulting graph may be noisy. It helps for the person to carry a book or other hard, flat object to create a stronger reflection. 7. If the velocity and acceleration graphs are noisy, and the motion you're studying isn't too quick, try increasing the averaging rate by increasing the number of points used to find the velocity. You can also try to increase the strength of the ultrasonic reflection from the target by increasing the target's area. 8. Multiple Motion Detectors in the room can 'talk' to each other when they are within each other's active cone. 9. Sometimes isolating the detector from ambient vibrations can help. We find putting a paper towel under the detector when we are using it on something like a ramp helps. Also, make sure that the Motion Detector is at least one meter from the computer and the monitor. 10. When using a Motion Detector on a dynamics track or air track, where the maximum distance to be measured is just a meter or two, consider putting a sock or a wrist band over the Motion Detector. This may sound strange, but it reduces the strength of minor echoes coming from small objects around the area. In many cases, this will improve the results significantly. 11. If using Motion Detectors with air tracks, try playing with the air pressure you deliver to the track. Sometimes the air currents created by an air track will cause spurious reflections of the ultrasound. Some air tracks can be used with motion detectors, others just never seem to work. Created by: jmcbride on August 30 1993 Last updated by: jhopkins on August 12 2004 -- http://www.vernier.com/til/webview.html?KB_ID=410 Vernier Tech Info Library TIL #410 Question Can you create new match files for Logger Pro? Answer Using any version of Logger Pro Method 1. One way to create a match is to physically move an object to create a new graph to be matched. Open the Motion Detector file found in the Logger Pro experiment folder. Set up your Motion Detector and have a person or object ready to move in front of the Motion Detector. Click on Collect and collect the data. When you get a good run, choose Store Latest Run. Click on the vertical axis of the graph and make sure that the Run 1 data that you want to have matched is visible on the graph. There should be no data in Latest. Save the experiment file with a distinctive name. You are now ready to use this file as a new match file. Have students open the file and click on Start. New data will then be collected on top of the Run 1 data. Some teachers have one student group make up a challenge for the next group. Using Logger Pro 2.1 or newer: Method 2. Logger Pro 2.1 and newer contains distance match and velocity match experiment files. You can use manually entered data to create new match files. If the new file you want to create will have the same experiment length as one of the Logger Pro files, follow these instructions. If not, use method 3. a) Open one of the match files that can be found in the set of Logger Pro experiment files. The two files are called Distance Match and Velocity Match. b) Pull down the Window menu and choose Table Window at the bottom of the list. c) You'll notice that the data table has two runs, Latest and Run 1. The graph that the students try to match comes from the Match column in Run 1. Notice that only a few numbers appear in this column. The program simply connects the points to create straight-line segments. d) To create a new match, edit the numbers in the Match column. You can edit the cells by simply clicking a cell, entering a new value and pressing the Enter or Return key. e) After entering these points, pull down the Window menu and choose the Graph Window. f) Now save the file with a unique name. Method 3. If you want to create a file that has a different experiment length than the existing file, you'll have to take a few extra steps. a) Open one of the match files that can be found in the set of Logger Pro experiment files. The two files are called Distance Match and Velocity Match. b) After opening the file, click the x-axis maximum and enter a new time. This will change the length of the data collection. c) Click the collect button and let the computer collect a new set of data. d) Pull down the Data menu, choose Delete, and then select Run 1 from the list of runs. The match line segments will disappear. e) Pull down the Data menu and choose Store Latest run. f) Click the y-axis label. The Y-Axis Selection dialog box will appear. Make sure that only the following items are checked in this dialog box: Match for Run 2 and Distance (or Velocity) for Latest. g) Pull down the Window menu and choose Table Window at the bottom of the list. h) You'll notice that the data table has two runs, Latest and Run 1. The graph that the students try to match comes from the Match column in Run 1. When you deleted Run 1, the Match column was cleared out. You can now manually enter numbers in this column. You can edit the cells by simply clicking a cell, entering a new value and pressing the Enter or Return key. The program will draw straight-line segments between these points. i) After entering these points, pull down the Window menu and choose the Graph Window. j) Now save the file with a unique name. Method 4. You might want to challenge the students to match a mathematical function, e.g. 0.02*Time^2. This can be done by creating a calculated new column. The Distance Match 2 file is an example of such a file. Here are step-by-step instructions for this method: a) Open one of the match files that can be found in the set of Logger Pro experiment files. The two files are called Distance Match and Velocity Match. b) Pull down the Window menu and choose Table Window at the bottom of the list. You'll notice that the data table has two runs, Latest and Run 1. The graph that the students try to match comes from the Match column in Run 1. Notice that only a few numbers appear in this column. The program simply connects the points to create straight-line segments. c) To replace these numbers with a function, start by pulling down the Data menu and choose Delete Column. Select the Match column. d) Pull down the Data column, choose New Column, and then select Formula. e) A dialog box will appear. Enter Match for the column name. f) Click the Definition tab and enter the mathematical formula in the Equation field, e.g. 0.02*Time^2. Click OK. g) Click the y-axis label. The Y-Axis Selection dialog box will appear. Make sure that only the following items are checked in this dialog box: Match for Run 2 and Distance (or Velocity) for Latest run. h) Pull down the Window menu and choose the Graph Window. i) Now save the file with a unique name. Method 5. You might want to mix straight-line segments and mathematical functions into the same match. For example you might want to have a horizontal segment followed by a short quadratic section. The Distance Match 3 file is an example of such a file. This is somewhat more difficult. To summarize, you will load one of the existing match files, copy part of the time data, apply a mathematical function to the time data in a spreadsheet program, and paste the edited values back into the Logger Pro. Here are step-by-step instructions for this method: a) Open one of the match files that can be found in the set of Logger Pro experiment files. The two files are called Distance Match and Velocity Match. b) Pull down the Window menu and choose Table Window at the bottom of the list. c) You'll notice that the data table has two runs, Latest and Run 1. The graph that the students try to match comes from the Match column in Run 1. d) Click and drag through the section of the Time column where you want the function to apply to. Pull down the Edit menu and choose Copy. e) Open a spreadsheet program such as Excel and paste the contents of the clipboard into the first column of the spreadsheet. f) In the second column of the spreadsheet enter a function into first cell of the second column using the first cell, e.g. =.05 * A1^2. g) Copy this formula down the column. h) Copy the contents of the second column and paste them into the appropriate section of the Match column in the Logger Pro data table. i) Pull down the Window menu and choose the Graph Window. j) Now save the file with a unique name. Created by: dvernier on August 10 1998 Last updated by: dvernier on September 10 2001 -- http://www.vernier.com/til/webview.html?KB_ID=655 ***Vernier Tech Info Library TIL #655 Question How can I combine two or more data files when using your Graphical Analysis for Windows software? Answer Using version 3.0 and newer: You can copy a data set from an experiment by going to the Data Browser, highlighting the name of the Data Set and choosing Copy from the Edit menu. The copied data set can then be pasted into any other file. Using versions before 3.0: Data sets can be combined by doing the following: 1) Highlight the entire data set (by clicking the data set header) then choose Copy Data from the Edit menu. 2) Open the file that contains the other data set. 3) Create the number of columns you have on the clipboard in the current data set. 4) Highlight the columns and then choose the Paste Data from the Edit menu. The column headers from the old file will not be brought into the new columns so you will need to re-enter these values. An alternative way to combine data sets is to use a spreadsheet program. Again, copy the data set from each file to the target spreadsheet, one at a time, then save the spreadsheet as a tab-delimited text file. This file can then be imported back into Graphical Analysis. Created by: dgardner on February 11 2000 Last updated by: dvernier on April 07 2002 -- http://www.vernier.com/til/webview.html?KB_ID=1143 Vernier Tech Info Library TIL #1143 Question The Light Sensor reading fluctuates, but the light appears steady Answer The problem is usually 60 or 120 Hz flicker of the light level from fluorescent or other lamps. Your eye does not pick this up, but the sensor will. You may be thinking that you should not see this flicker, since you are sampling only slowly, but due to the way most of our interface collect data, the flicker may show up even at slow rates. To see if this is the problem try one of the following: 1. Eliminate all artificial light sources (except battery powered flashlights) and try the experiment. 2. Do the following quick test with the light sensor hooked up and positioned as you plan to use it. Set the sampling to be 1000 points/second for 0.1 seconds. If the flicker is the problem, you will see a drastic variation in the light intensity with a period of 60 or 120 Hz (50 or 100 Hz outside North America). To minimize this problem in Logger Pro, turn up the Oversampling in dialog box where you control the data collection rate. In Logger Pro 2x, set the oversampling to as large a number as you can. On Logger Pro 3.1, just turn on Oversampling. You can also set the sample rate to a number not a factor of 60 to improve things. (So, using 30, 20, 15, 10, 5, 2 samples per second would be worse then using 17, 23, 27 samples per second.) Created by: dvernier on February 04 2003 Last updated by: jhopkins on March 24 2003 -- http://www.vernier.com/tech/manuals.html User's Manuals - Logger Pro 3 http://www2.vernier.com/manuals/LP3QuickRefManual.pdf ***see p. 7, "Storing Data"