1. The University of Texas at Arlington Electrical Engineering Department
Electric Circuit Lab
The Oscilloscope
Agilent A

2. 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

3. General principle of an oscilloscope showing the display tube and the deflection system.

4. There are two types of scopes, the analog and the digital ones
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.

5. 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).

7. 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.

8. Review the front Panel of the scope

9. Review the Rear Panel of the scope

10. 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

11. Digital Oscilloscope Block Diagram

12. The Digitizing Oscilloscope
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 1
Coupling
DC AC

13. 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 1 0s
2 us/
RUN
1.00V
----Setup memory----
Undo Default
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

14. Getting Started

15. Getting Started: 4 Line 2 1 0 1 (Power ON) (All settings to default )
Compensate probes:
(Power ON)
Setup
Default
(All settings to default )
Auto-
scale 1 2 4 3 5
Line
0 1 2 3 4 5 1
Connect probe to calibrator 1
1.00V
200 us/ 1
RUN
0.00s 1
Adjust screw to eliminate:
Default
Setup
Overshoot
Undershoot

16. Set probe attenuation factor:
10:1 1
0.00s
200 us/
RUN
1.00V
Probe 10
Match
Set probe attenuation factor:
Press Channel key for selected probe. Toggle softkey for setting that matches probe

17. m Trigger slope What the display says: is positive (rising edge)
Blinks if
no trigger
Vertical sensitivity of CH1
is 1Volt per major division
Time=0
t < 0
t > 0
Trigger source
is Channel 1 1
1.00V
200us/
0.00s 1
RUN
Scope is ready
for trigger 1
Ground (V=0)
[If dc part of CH1 signal
is too big, ground
arrow points off-screen.
If this happens, adjust
vertical sensitivity] 1
Off On
Probe 10
Channel 1 is ON
Horizontal sweep speed is
200 sec per major division
Readings scaled
for a 10:1 probe m

18. 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

19. -FFT (if equipped with module)
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.
Trigger
Holdoff
Holdoff=11.5 us +
Math Functions
-Add waveforms
-FFT (if equipped with module) 1
- Enable channel
- Set up probe

20. Horizontal Controls

21. Vertical Controls

22. Trigger Controls

23. Display

24. Display (continue)

25. Other Functions

26. Other Functions (continue)

27. Other Functions (continue)

28. Other Functions (continued)

29. Other Functions (continued)

30. Other Functions (continued)

31. Making Measurements: Vp-p
Measure Vp-p, using cursors: 1
Hook Calibrator signal to CH1
Grid
Answer
V1= 31.25mV V2= 5.031V V= 5.000V D
Cursor adjustment knob 2
Display
None 3
Cursors
Clear Cursors
Clears any cursors already on
the screen
Source 4 1
Set for the correct channel
|- Active Cursor -|
Toggle to highlight
the V1 cursor; Rotate
knob for waveform
minimum 5
V1 V2
T1 T2 5
|- Active Cursor -|
Change to V2 cursor;
Use knob to set to
waveform minimum
V1 V2
T1 T2
OR: Measure Vp-p, the easy way:
Voltage
|- Voltage Measurements -|
Vp-p Vavg Vrms
Simply select Vp-p from the
Voltage menu. 1

32. Making Measurements: RISETIME
Next
Menu 1
Time
| Time Measurements | 2
Rise(1) <4.000 us
+Width -Width RiseTime FallTime
Risetime Answer
If answer needs more resolution:
Rise(1) 920 ns
Rotate for best display: 3
Time/Div
90% line
10% line

33. RISETIME, Using DELAYED SWEEP:
Making Measurements:
RISETIME, Using DELAYED SWEEP:
Time/Div 1
Rotate to show multiple cycles on screen
Rise(1) <4.000 us 2
Main
Delayed
Main/Delayed
| Horizontal Mode |
Main Delayed XY Roll
Time/Div 3
Rotate. See how
upper bracketed part is exploded into lower window
Rise(1) 920 ns
Delayed
Cntr
Time/Div

34. Making Measurements: FFT (Frequency Domain)
To do FFT, a Measurement/Storage Module must be installed
on back of scope. 1
Setup: Default 2
Auto-
scale 3 +
|-- Function 2 --|
Off On Menu 4
|-- Function 2 --|
Off On Menu
(Hit Menu key)
Operation
FFT 5
Hint: To look ONLY at FFT signal without time domain signal, turn channel off: 1
Off 1
Use Time/Div to set FFT resolution On
Hint: To return to FFT menu at any time, use Math key +

35. Storing Waveforms: AUTOSTORE 1 2 3 4 5 Displays all waveforms
(Good for looking at jitter, noise, glitches) 1 2
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. 3 4
Auto-
store 5
Touching Autostore again returns display to normal mode.

36. Storing Waveforms: TRACE MEMORY
Vertical position
Horizontal delay 1
Example: Calibrator signal in CH 1. Setup Default. AUTOSCALE.
Save to
Trace 1 2
Trace
Trace 1
Off On 3
Now move waveform with horizontal delay and vertical position knobs. Note that Trace 1 still stays on screen, allowing comparison with stored waveform. 4