REU Internship

Week 1

During the first week, we spent the time visiting the various labs which we could possibly participate in during his summer internship. We also learn some valueable skills using the machine shop and various heavy equipment. I am now a novice machinist, along with being a knowledgable elctrician and drywaller.

Week 2

Continued visiting more labs and now must decide which lab i will be working in. The decision is easy for me because engineers are useable anywhere. Basically, any of the labs will make me happy. I have gotten the pleasure to work with Joel in the Elementary experimental Particle Physics lab.

Week 3

So far i have learned mainly about coax. They are designing equipment to be installed in the fermi lab and use coax to transmit the data. The data transfers at a rate of 1GHz. In order for the cable to handle these rates, the integrity of the terminal connections must be maintained. When attaching a connector you run the risk of scoring the inner wire and that would interfere with the capacity of data being able to be transfered. I was assigned the detail of designing a working pulse generator to run an oscillation at 100kHz so we can test the cable connections. Below is a schematic of the design given to me to work on and find values for.

The inverter we used was a Schmitt Trigger which counters the hysteresis created in the circuit. Hysteresis is the effects on a circuit from the history of the circuit. Basically it turns a sparatic signal into a nice crisp on or off.
This graph shows how a Schitt Trigger turns a sparatic signal into a crisp oscillator. The Schmitt switches to on when the input pulse reaches the voltage level of V_t+ and turns off when the voltage reaches V_t- ignoring whatever the input pulse does besides that. Since we have an RC circuit to control the voltage of the input to control the oscillation. V_f = V_ie^{-t / (RC)}. The Schmitt Trigger, at 5V, has a V_t+ = 2.6V and V_t- = 2.0V. This is what we want V_f to equal. Now we can solve for RC.
RC = -t ⁄ (Ln[V_t+ ⁄ V_i]) when the signal emitted from the Schmitt is 0 and RC = -t ⁄ (Ln[1 - V_t- ⁄ V_i]) when the pulse emitted form the Schmitt is 1, or on. We wanted a frequency of 100kHz oscillation. This would yield a time to be on and off of
ν = 1 ⁄ Τ → τ = 1 ⁄ ν → t = ½Τ → t = 1 ⁄ (2ν)
Plugging in values for these formulas yields.
RC = 7.646E-06 for the switch from high to low.
RC = 9.788E-06 for the switch from low to high.
The average was taken to determine a rough 100kHz oscillation since that number was made up anyways. I chose a 0.1μF capacitor and that yielded an 80Ω resistor.
To rough this example I built a breadboard model to test it on an oscilloscope. It oscillated too fast. We added a bigger capacitor, 6.8μF capacitor, across the V_CC to ground. This gave us about a 300kHz frequency, which was good enough. I then got to build a "Dead Bug Board" which was really fun and a little complicated since the resistor i chose to use was as big as a period in this sentence and i had to "weld" it to a leg of a chip. In the end, the dead bug board worked and we were able to view it on the O-scope. We looked up the velocity of the cable online and can now determine the length of any cable by merely putting the pulse generator output on channel 1 and the end of a cable on channel 2 then measure the time it takes for the signal to leave the generator and reach the end of the cable.
The velocity of this particular cable was 83% the speed of light and thus gave a ;ength of approximately 100m which is exactly what the length of the cable was.
Also we can determine the frequency of the oscillation rate by measuring the period of the cycle.
Not to mention compare the signal created form a good cable to that of a random cable and determine the integrity of the line based on the differences in the two end-line signals.