User:Thomas S. Mahony/Notebook/Physics 307L/2009/08/24
|Oscilloscope Lab|| Main project page|
SJK 00:34, 15 September 2009 (EDT)|
I couldn't figure out how to use the references, like so many wikipedia pages have. I tried using the same code for the little numbers as listed on the help page, but for some reason it isn't working yet.
There are lots of others people like, including some that cost money.
EquipmentSJK 00:25, 15 September 2009 (EDT)
We plugged a BNC cable from the Channel 1 port on the oscilloscope to the Lo Output on our function generator. After playing with the settings for a little bit to make sure both were working correctly, we started the lab.
Basic waveform measurement
We set the function generator to 20 Hz which was easily observed on the oscilloscope.Using the lines on the screen, we estimated the signal had an amplitude of 280 mV. We then used to the cursor to get the more precise measurement of 284 mV. We also used the measure function and got the same value of 284 mV. We then followed this same procedure for several other waves:
TriggeringSJK 00:27, 15 September 2009 (EDT)
AC coupling takes a signal and removes the DC component by using a capacitor. This method is useful for looking at the AC portion of a signal that may have a large bias voltage. It is, however problematic when used on a signal containing a wide range of harmonics, or very low frequencies. When such is the case, the signal gets distorted.<ref>http://www.allaboutcircuits.com/vol_3/chpt_4/11.html</ref> This distortion has a useful purpose, however. Like everything in the real world, the oscilloscope has some resistance and capacitance (especially as a capacitor is used in AC coupling). These quantities are multipled together to get the RC constant, which has many uses. To find the RC constant, we supplied a square wave with a large DC offset to the oscilloscope and turned on the AC coupling. We got a signal similar to one shown:
We then measured the fall time, or time it takes for the voltage to go from the peak to 10%, to be 56.0 ms. Since a capacitor charges and discharges at the same rate, the fall time is equivalent with the rise time. Using the formula:2
where tr is the rise time we calculated the RC constant to be 25.5 ms.This can be compared to the rise time listed in the oscilloscope's manual of <5.8 ns, which I found on Kyle Martin's lab page (Thanks Kyle!). SJK 00:30, 15 September 2009 (EDT)
<references/> 1 ref: http://www.allaboutcircuits.com/vol_3/chpt_4/11.html
2 ref: from wikipedia: http://en.wikipedia.org/wiki/Rise_time
Though I didn't have time to get to the FFT part of the part, I can still explain what it does. A FFT or Fast Fourier Transform is a method for taking the fourier transform of a signal. It basically maps a signal in the time domain to the frequency domain, breaking signals containing many frequencies into delta functions whose height corresponds to the amplitude of a particular frequency. Since the signals we put into the oscilloscope were coming from a function generator, I would expect to only see a single delta function when switching to FFT mode if we were putting in a sinusoidal signal. Sawtooth would be multiple frequencies, although there would be one dominant one, and square waves would have yet even more frequencies.