User manual TEXAS INSTRUMENTS THE CBL 2 SYSTEM GETTING STARTED

[. . . ] Getting Started with the CBL 2TM System LabPro is a trademark of Vernier Software & Technology. Radio Shack is a trademark of Technology Properties, Inc. Safety Instructions Observe all warnings, cautions, and other safety instructions indicated on the product and in the documentation. These instructions are intended to reduce the risk of injury, possible electrical shock, or damage to the unit. Never attempt to measure AC voltages from a wall outlet. [. . . ] If this is correct, what would you expect the ratio to be between the light intensity measurements made at . 5 meter and 1 meter? What would you expect the ratio to be between the light intensity measurements made at 1 meter and 2 meters? What would you expect the ratio to be between the light intensity measurements made at 1. 5 meters and 3 meters? 4. Compare the ratios from the actual data to your predictions above. 2000, 2003 TEXAS INSTRUMENTS INCORPORATED GETTING STARTED WITH THE CBL 2TM SYSTEM 45 5. There is probably some difference between the predictions and the actual data. This frequently happens. There are two general reasons why this occurs. Either there are errors in the data or in the theory. In this activity we explore sources of experimental error. List several possible sources of experimental error. 6. One possible source of experimental error is in measuring the distance from the tip of the light probe to the light bulb. Make several different measurements trying to place the tip of the light probe exactly 1 meter from the light bulb. Describe the variation in the light intensity readings. 7. There are a number of things you can do to try to minimize this source of error. Describe some possibilities. 8. You can investigate the effects of errors in measuring the distance from the tip of the light probe to the light bulb by deliberately making errors. What is the effect of an error of 5 cm when the distance is supposed to be . 5 meter? 9. What is the effect of an error of 5 cm when the distance is supposed to be 1 meter? 10. Another source of error is other light in the room. You can investigate the effects of this source of error by deliberately introducing an extra light and comparing measurements made with this extra light on and with this extra light off. How can you correct for extra light in the room? Repeat the original experiment doing everything you can to minimize measurement error. 46 GETTING STARTED WITH THE CBL 2TM SYSTEM 2000, 2003 TEXAS INSTRUMENTS INCORPORATED Teacher Section Theory The relationship between light intensity and distance can be described by a function of the form I= A d2 but there are so many potential sources of error that students are likely to see discrepancies between theoretical predictions and the data. It is also very important for students to realize that not all such discrepancies can be dismissed as "experimental error. " This activity addresses this objective by attempting to identify and compensate for experimental error. The main sources of error your students should identify are: Errors in measuring distance. The light probe may not be zeroed that is, with no light the light probe may not read zero. One way to convey the idea that not all discrepancies can be dismissed as "experimental error" is by having students make light intensity readings using a fluorescent bulb. Because fluorescent bulbs flicker, these measurements jump around. Answers Sample data with sample answers: 1. The left half of a "U. " (Intensity falls off rapidly as distance increases. ) 2. Distance . 5 1 1. 5 2 2. 5 3 3. 5 Light Intensity . 228 . 070 . 034 . 026 . 020 . 014 . 013 2000, 2003 TEXAS INSTRUMENTS INCORPORATED GETTING STARTED WITH THE CBL 2TM SYSTEM 47 3. [. . . ] Results Returns data without converting Commands use of temperature input from user when making speed of sound calculations (must also send Command 4 for temperature compensation) When programming channel 21 (Digital In), use the syntax shown below: {1, 21, operation} operation 0 1 Off On When programming channel 31 (Digital Out), use the syntax shown below: {1, 31, operation, list of values} operation 0 1-32 Clears the channel until reprogrammed Count: number of data elements in list list of values Lists values output to digital output port Note: The list of values must have one element for each count. Command 2 Data Type This command is not used and should not be sent. However, it is included for compatibility with older CBLTM programs. Command 3 {3, . 1} Trigger Setup Repeats last Command 3 (used to quickly collect new data) {3, samptime, numpoints, trigtype, trigchan, trigthresh, prestore, (extclock), rectime, filter, fastmode} samptime >0 to 16000 0. 5 default Results Specifies number of seconds between samples numpoints -1 0 1 to 12, 000 Invalid Results Specifies REALTIME mode Returns error message Specifies NON-REALTIME mode and the number of points to collect GETTING STARTED WITH THE CBL 2TM SYSTEM B-3 2000, 2003 TEXAS INSTRUMENTS INCORPORATED trigtype 0 1 2 3 4 5 6 Immediate trigger Manual trigger Rising edge/rising edge Falling edge/falling edge Rising edge/falling edge Falling edge/rising edge Single sample Results Takes data immediately after GET command Takes data when START/STOP is pressed Takes data after input crosses threshold voltage Takes data after input crosses threshold voltage Takes data after input crosses threshold voltage Takes data after input crosses threshold voltage Takes one data point each time START/STOP is pressed trigchan 0 1 Results Disables the trigger Triggers on channel 1; channel must be active Hardware or software (hardware trigger only for Command 1 operation 5, 6, 7; software trigger for all others) Software only Software only Software only Triggers on channel 2; channel must be active Triggers on channel 3; channel must be active Triggers on channel 11; channel must be active 2 3 11 trigthresh - channel limit to + channel limit Results Begins taking data when signal crosses threshold in trigtype direction [channel limit is determined by the sensor that is attached to the channel] 1V default prestore 0% to 100% Results Retains this much data from before triggering (extclock) rectime 0 1 2 None Absolute Relative This parameter is ignored Results Does not record time during sampling Records absolute time Records relative time Note: This default is different from the original CBLTM. Default on original CBL was 0. filter 0 1 2 3 No filtering Results Disables the filtering process (RT* and NON-RT**) Uses Savitzsky-Golay 5 point filter (NON-RT) Uses Savitzsky-Golay 9 point filter (NON-RT) Uses Savitzsky-Golay 17 point filter (NON-RT) B-4 GETTING STARTED WITH THE CBL 2TM SYSTEM 2000, 2003 TEXAS INSTRUMENTS INCORPORATED 4 5 6 7 8 9 *RT = REALTIME **NON-RT = NON-REALTIME Uses Savitzsky-Golay 29 point filter (NON-RT) Uses Median Pruning 3 point filter (NON-RT) Uses Median Pruning 5 point filter (NON-RT) Uses Light Realtime tracking filter (RT) Uses Medium Realtime tracking filter (RT) Uses Heavy Realtime tracking filter (RT) fastmode 0 1 OFF ON Results Operates in normal mode Operates in FAST sampling mode Note: In FASTMODE, only one channel can be active, and it must be an analog channel. Sampling can be as fast as 20ms/sample in this mode. [. . . ]