Physics307L F07:People/Rivera/Notebook/070827

Basic waveform measurement

Remember to record everything in your wiki lab notebook!

1. Hook up the output of the function generator to the oscilloscope
   • Set the function generator to output a sine wave. Say 200 Hz maybe, or pick your frequency.
   • Use BNC cables (why are they called BNC cables?)
   • Should you use a T connector and a terminator?

Everything hooked up fine

1. Fiddle with the oscilloscope settings so you can see the sine wave on the screen.

Got sine wave

Came up with no extra work.

1. Measure characteristics of a sine wave
   • Measure peak to peak voltage (thus amplitude) and measure the period (thus frequency)
     1. First, use the grid on the oscilloscope screen ("divisions" are the dotted lines)

Peak to peak voltage

150mV

1. • 1. Next, use the cursors

Peak to Peak

84mV-(-66mV)= 150mV

1. • 1. Finally, use the "measure" functions.

Peak to peak voltage

152mV

1. • Repeat this for a few different waves: Very large amplitude; very low amplitude; large DC offset

For lowest amplitude on wave generator: see comment

Steven J. Koch 14:29, 28 August 2007 (EDT):Good job with these measurements! In the future, one way to be able to estimate the error in your measurements would be to try to independently repeat the measurement at least three times.

Read 62.0mV peak to peak voltage using measure function
Using grid 60mV
Cursor reading 60mV

For highest amplitude on wave generator:

Read 2.2V Peak to peak voltage using measure function
Using grid ~2.2V
Cursor reading 2.16V

1. • • Are there waveforms that the oscilloscope cannot measure properly?

see comment

Steven J. Koch 14:29, 28 August 2007 (EDT):My guess is that it has a problem triggering...also, you may have found that the oscilloscope cannot measure very large voltages (the peaks of waves would start to get chopped off)

As the frequency approaches zero the scope seems to have a problem displaying the wave.

Triggering

1. Re-read Wikipedia section about triggering
2. Common way to trigger is on a rising edge (what does this mean?). What happens to the signal when you use different triggers? Be able to explain this orally.

The rising edge is the point on the wave where the slope is positive. Therefore it starts you
on the upswing of the curve. 
Edge gives a stable sine wave with 2 periods displayed an averaged view of the wave form.
Video shows the wave oscillating and moving across the screen as the wave is detected.
Pulse gives a view of the wave at a rate of 1 ms.

AC Coupling

This is a tricky concept at first!

1. This Wikipedia article on capacitive coupling isn't too helpful
2. Apply a large DC voltage to the oscilloscope input (we'll have to figure out how to do this). Compare DC coupling with AC coupling. You may need to adjust the triggering. Which mode is better for viewing any "ripple" on the DC voltage?

Edge triggering is better for viewing the "ripple" because it is a static image therefore easier
to take measurments on.

1. 

   Using rising part of square wave to measure fall time

   Measure the fall time of the AC coupling
   • Function generator: Square wave; zero DC offset; amplitude about 8.6 V
   • Use cursors to measure fall time (peak to 10% value)

276mV

10% value = 13.1mV
Fall time ~53ms

1. • Use "measure" function to measure fall time

57.48ms

1. What RC constant does this imply? (See Wikipedia article on rise time

This implies the RC time constant.

1. How does this compare with the expected value for the oscilloscope? (Can you find the answer on Google?)

see comment

Steven J. Koch 14:30, 28 August 2007 (EDT):Thank you for finding this article!

Found this article
Tektronix see question 13
Says "Counter Range: AC coupled, 10 Hz minimum to rated bandwidth" should be in the .1ms range.

FFT

1. Find the frequency of a sine wave using FFT "Math" function

My sine wave is at a frequency of 80.9Hz according to the FFT math tool.

1. Look at the harmonics in triangle and square wave

There is a lot of noise in the harmonics

1. Compare with what you see on this applet: Fourier series applet

The applet is much cleaner and seems to portray the same basic image I get on the oscilloscope.

1. Be able to explain what is going on with an FFT and when it may be useful

Would be useful for finding the frequency of noise that may be embedded in your signal.

Other

1. Play with XY mode to make some fun patterns
2. Build your own low or high pass filter using resistors, capacitors and breadboard.
3. Measure something else you find in the lab