User:Boleszek/Notebook/Physics 307l, Junior Lab, Boleszek/2008/10/06
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Speed of LightSJK 01:42, 20 October 2008 (EDT) Good primary lab notebook. I realize you lost a bunch of hard-earned data, and I'm sorry about that. Initial setupWe find the apparatus already set up according to the procedure, nonetheless we check to make sure that everything is correctly connected. We turn on the oscilloscope and make sure it is set to DC coupling to correctly recieve the signals from the TAC and the annode. We turn on the LED power supply and set it to 150V. We turn on the High Voltage, starting at 0V and stepping it up until we get a nice sized signal on the scope. Now we fool around with voltage levels and different triggers to get the best signal. We were able to adjust the frequency of the LED light by watching the CH1 signal fq indicator on the scope while adjusting the LED power supply voltage. We set it to about 11kHz. Trigger sourse was set to CH1 falling edge with DC coupling. The annode stopping signal has the shape of a sharp cliff that ends in a point and curves back up. The TAC signal seems to try to approximate a square wave. We decide to set the stopping signal to -500mv. We check the voltage rise on the TAC signal for all delays. In order to stabilize our measurements we go to the acquire menu and set the average function to its highest value (128). Instrumentation
CalibrationSince our time delay signal will be displayed to us as a voltage signal we must calibrate our system so that we can relate voltage amplidude to seconds. We do this by measuring the displayed voltage (using the measure function on the scope) for each successive delay value. SJK 01:00, 20 October 2008 (EDT)I put more comments about your calibration method on the matlab code talk page. I have more questions: did you account for changes in the PMT signal due to the added delays? I'm guessing not. And I'll repeat: how would you know to trust your own calibration more than what the manual says? We take two sets of calibration data:
Day 2We realized that our setup from Day 1, though providing stable results, was flawed because we calibrated our instrument with the LED far into the tube so that when we pulled it out for further measurements we were unable to maintain the -500mV peak of the anode output signal. This time will we initially calibrate our instrument with the LED pulled far out.
We let the instrumentation run for a while so as to stabilize any initial running errors (voltage from power supply and solid state circuitry may react slightly to heating). We notice that the measure function of the scope has a .04V resolution. The reading initially oscillates between 5.72V and 5.76V. We have determined to acquire data across 1.5m in 10cm increments. We will repeat this as many times as is practical starting from slightly different positions. We will then add several extra measurements that are only at the extremes, i.e. 1.5m apart. We're taking both types because we want to be able to look at the fine data, and we also expect that there may be some instrument drift and the second set of measurements will be less susceptible to this. Also First Calibration Data taken prior to acquisition at what we expect to be one end of range Time vs Voltage Data delay(ns) : Voltage 0 : 5.64 0.5 : 5.76 1 : 5.88 2 : 6.16 4 : 6.60 6 : 6.84 8 : 7.12 10 : 7.32 Distance vs Voltage data We did not try to ascertain the actual distance between lights, simply picked our initial position and used that as 0 Pushing in to change distance, being careful to approach measurement from same direction distance(cm) : Voltage 0 : 5.80 10 : 5.72 20 : 5.64 30 : 5.52 40 : 5.44 50 : 5.40 60 : 5.36 70 : 5.28 80 : 5.28 90 : 5.12 100 : 4.96 110 : 4.96 120 : 4.96 130 : 4.88 140 : 4.64 150 : 4.64 Seccond run. Started out 5-cm further back and obtained a new zero point. distance(cm) :Voltage 0 : 5.76 11 : 5.68 (Improper step size is due to tape obscuring the meter stick) 20 : 5.56 30 : 5.56 40 : 5.52 50 : 5.36 60 : 5.32 69 : 5.28 80 : 5.16 90 : 5.08 99 : 5.00 110 : 4.92 120 : 4.92 131 : 4.80 140 : 4.88 150 : 4.76 !!Suffered the loss of all the rest of our data due to Wiki logging us out prior to saving, we didn't know, tried to save and here we are!!#$%*! Retook the last calibration Second Calibration taken at end of data acquisition and at other end of range delay(ns) : Voltage 0 : 5.00 0.5 : 5.12 1 : 5.24 2 : 5.44 4 : 5.88 6 : 6.28 8 : 6.64 10 : 6.88
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