The University of Texas at Arlington

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• The University of Texas at Arlington
• Electrical Engineering Department
• Electric Circuit Lab
• The Oscilloscope
• Agilent 54621A

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• One of the most often used instruments in the
  electrical engineering lab is the oscilloscope
  which not only you can measure the waveform
  quantities, but also it allows you to display the
  waveform as a function of time.
• The oscilloscope (or simply, scope) consists of
  a display tube on which one can trace the
  waveform. An electron beam which is generated by
  electron gun accelerate toward the part of the
  display and is deflected by electric fields,
  writes figures on the fluorescent screen.
• Following figure shows the general principle and
  major subsystems of an oscilloscope

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General principle of an oscilloscope showing the
display tube and the deflection system.
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• There are two types of scopes, the analog and the
  digital ones. Digital scopes have more features
  than the analog scopes. Digital scopes can
  process the signal and measure its amplitude,
  frequency, period, rise and fall time. Some of
  them have built-in mathematical functions and can
  do fast Fourier transforms in addition to
  capturing the display and sending it out to a
  printer. The oscilloscopes in the EE
  Undergraduate Lab are Agilent 54621A type digital
  oscilloscopes which have most of the above
  functions built-in.

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• Following figure shows a typical probe used in
  measuring by oscilloscope. A probe is a high
  quality coaxial cable that has been carefully
  designed not to pick up stray signals originating
  from radio frequency (RF) or power lines. They
  are used when working with low voltage signals or
  high frequency signals which are susceptible to
  noise pick up. Also a probe has a large input
  resistance which reduces the circuit loading. The
  connections to the scope's will be made through a
  X 1 probe (where X 1 means that the probe does
  not attenuate, or reduce the signal if your
  probe has a X 1/ X 10 selector, set it to X 1).

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• If the voltage source to be measured has one
  terminal grounded, make sure that the ground of
  the probe is connected to the ground of the
  voltage source and not vice versa otherwise, the
  source will be shorted and may be damaged.

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• Review the front Panel of the scope

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Review the Rear Panel of the scope
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• Hints
• The Digitizing Oscilloscope
• The BNC shield is at earth ground. Use only the
  probe TIP
• for measuring high voltages. "Floating" the BNC
  shield or
• connecting it to a high voltage could cause a
  safety
• hazard.
• Make sure probes are compensated.
• If you can't get the signal on screen
• - Check probe connection
• - Touch SETUP, Default Setup
• - Touch AUTOSCALE
• - Check for offset (ground symbol). If offscale,
  adjust
• vertical sensitivity and position
• - Turn up signal brightness with intensity control

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Digital Oscilloscope Block Diagram
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Hints The BNC shield is at earth ground. Use
only the probe TIP for measuring high voltages.
"Floating" the BNC shield or connecting it to a
high voltage could cause a safety hazard. Make
sure probes are compensated and set to proper
scale (X1,X10,X100). If you can't get the
signal on screen- Check Probe connection-
Touch SETUP, Default Setup- Touch AUTOSCALE-
Check for offset (ground symbol). If offscale,
adjust vertical sensitivity. If still offscale,
Touch - Check Trigger Source- Set Mode Auto

• The Digitizing Oscilloscope

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The Digitizing Oscilloscope
Status bar Vertical sensitivity Sweep
speed Trigger time reference Channel(s)
on Run/stop
f
Autoscale Print Calibrate
Measure Vrms, tr, ,f Trace /Setup Memory
Display grid, vectors, averaging
Storage Auto-store, Erase, RUN/STOP
Softkey labels
Triggering Modes Auto, Normal,TV Sources
Ch1, Ch2, Ext, Line
Calibration source Power ON/OFF Screen brightness
Vertical position, sensitivity Math
on/off
Horizontal Main Sweep Speed, Sweep
Modes Delayed, XY, Roll t 0 Reference
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Getting Started
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1
Connect probe to calibrator

1.00V
200 us/
RUN
1

• 0.00s

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Adjust screw to eliminate
Default Setup
Overshoot Undershoot
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Press Channel key for selected probe.Toggle
softkey for setting that matches probe

• Set probe attenuation factor

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1
Trigger slope is positive (rising edge)
What the display says
Blinks if no trigger
Vertical sensitivity of CH1 is 1Volt per major
division
Time0
t gt 0
t lt 0
Trigger source is Channel 1

• 0.00s

200us/
1.00V
1
RUN
Scope is ready for trigger
Ground (V0) If dc part of CH1 signal is too
big, ground arrow points off-screen. If this
happens, adjust vertical sensitivity
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Channel 1 is ON
Readings scaled for a 101 probe
Horizontal sweep speed is 200 sec per major
division
m
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What the main controls do
Horizontal delay
Trigger level Line is only visible when you turn
the knob. When signal is smaller than trigger
level, scope stops sampling.
Grid full
Display
Vectors off
Time/division (sweep speed)

• Vertical
• Volts/division

Vertical Position
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Other main controls
Trigger holdoff Signals with multiple zero
crossings per cycle cause unstable
displays. Holdoff ignores the false triggers for
a given length of time.
Holdoff

• Math Functions
• -Add waveforms
• -FFT (if equipped with module)

- Enable channel - Set up probe
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Horizontal Controls
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Vertical Controls
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Trigger Controls
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Display
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Display (continue)
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Other Functions
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Other Functions (continue)
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Other Functions (continue)
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Other Functions (continued)
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Other Functions (continued)
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Other Functions (continued)
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Making Measurements Vp-p
Measure Vp-p, using cursors
Hook Calibrator signal to CH1
Grid
None
ClearCursors
Clears any cursors already on the screen
Source
Set for the correct channel
Toggle to highlight the V1 cursor Rotate knob
for waveform minimum
- Active Cursor -
V1 V2
T1 T2
- Active Cursor -
Change to V2 cursor Use knob to set to waveform
minimum
V1 V2
T1 T2
OR Measure Vp-p, the easy way
Simply select Vp-p from the Voltage menu.
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Making Measurements RISETIME
Next Menu
----------- Time Measurements -----------
Rise(1) lt4.000 us
2
Width -Width RiseTime FallTime

Risetime Answer
If answer needs more resolution
90 line
10 line
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Making Measurements RISETIME, Using DELAYED
SWEEP
Rotate to show multiple cycles on screen
Rise(1) lt4.000 us
Main/Delayed
Main Delayed

-------Horizontal Mode --------
Main Delayed XY Roll
Time/Div
Rotate. See how upper bracketed part is
exploded into lower window
Rise(1) 920 ns
Cntr
Delayed

Time/Div
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Making Measurements FFT (Frequency Domain)
To do FFT, a Measurement/Storage Module must be
installed on back of scope.
Setup Default
(Hit Menu key)
Hint To look ONLY at FFT signal without time
domain signal, turn channel off
1 Off
Use Time/Div to set FFT resolution
On
Hint To return to FFT menu at any time, use
Math key
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Storing Waveforms AUTOSTORE
Displays all waveforms (Good for looking at
jitter, noise, glitches)
Example Calibrator signal in CH 1. Setup
Default. AUTOSCALE. Touch AUTOSTORE. Now move
horizontal delay knob and watch all waveforms
stay on screen, making an overlapping pattern.
Touching Autostore again returns display to
normal mode.
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Storing WaveformsTRACE MEMORY
Example Calibrator signal in CH 1. Setup
Default. AUTOSCALE.
Save to Trace 1
Trace 1 Off On
Now move waveform with horizontal delay and
vertical position knobs. Note that Trace 1 still
stays on screen, allowing comparison with stored
waveform.