The University of Texas at Arlington Electrical Engineering Department Electric Circuit Lab The...
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Transcript of The University of Texas at Arlington Electrical Engineering Department Electric Circuit Lab The...
The University of Texas at ArlingtonElectrical Engineering Department
Electric Circuit Lab
The OscilloscopeAgilent 54621A
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
General principle of an oscilloscope showing the display tube and the deflection system.
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.
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).
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.
Review the front Panel of the scope
Review the Rear Panel of the scope
HintsThe Digitizing Oscilloscope• The BNC shield is at earth ground. Use only the probe TIPfor measuring high voltages. "Floating" the BNC shield orconnecting it to a high voltage could cause a safetyhazard.• 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, adjustvertical sensitivity and position- Turn up signal brightness with intensity control
Digital Oscilloscope Block Diagram
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
1CouplingDC AC
The Digitizing Oscilloscope
1 0s 2 us/1RUN1.00V
1
----Setup memory----
Undo Default
Status bar:Vertical sensitivitySweep speedTrigger time referenceChannel(s) onRun/stop
Softkeylabels
Calibration sourcePower ON/OFFScreen brightness
Measure: Vrms, tr, ,fTrace /Setup Memory Display: grid, vectors, averaging
Triggering: Modes: Auto, Normal,TVSources: Ch1, Ch2, Ext, Line
Vertical position, sensitivityMath on/off
Storage: Auto-store, Erase, RUN/STOP
Horizontal:Main Sweep Speed, Sweep Modes:
Delayed, XY, Rollt = 0 Reference
AutoscalePrintCalibrate
Getting Started
1 0.00s200 us/
1 RUN
1.00V
1
DefaultSetup
Connect probe to calibrator
Adjust screw to eliminate:
2
3
4
5
1
Getting Started:
Compensate probes:
(Power ON)
Setup
DefaultSetup (All settings
to default )
Auto-scale
1
2
4
3
5
Line0 1
OvershootUndershoot
Press Channel key for selected probe.
Toggle softkey for setting that matches probe
Set probe attenuation factor:
10:1
1 0.00s
200 us/
1 RUN
1.00V
1
Probe1 100 10
Match
1
Probe1 100 10
1 0.00s200us/
1 RUN
1.00V
1
Probe1 100 10
What the display says:
Vertical sensitivity of CH1is 1Volt per major division
Horizontal sweep speed is200 sec per major division
Channel 1 is ON
Ground (V=0)[If dc part of CH1 signalis too big, groundarrow points off-screen.If this happens, adjustvertical sensitivity]
Trigger slope is positive(rising edge)
Trigger source is Channel 1
Scope is ready for trigger
Time=0
Blinks ifno trigger
t > 0t < 0
Readings scaledfor a 10:1 probe
1Off On
What the main controls do:
VerticalVolts/division
VerticalPosition
Horizontaldelay
Time/division(sweep speed)
Trigger level Line is onlyvisible when you turn the knob.When signal is smaller than trigger level, scope stops sampling.
Display:
Grid full
Vectors off
Other main controls:
+Math Functions
-Add waveforms-FFT (if equipped with module)
Trigger holdoffSignals with multiple zero crossings per cycle cause unstable displays.Holdoff ignores the false triggers for a given length of time.
- Enable channel- Set up probe
Trigger
Holdoff
Holdoff=11.5 us
1
Ho
rizo
nta
l Co
ntr
ols
Vertical Controls
Trigger Controls
Display
Display (continue)
Other Functions
Other Functions (continue)
Other Functions (continue)
Other Functions (continued)
Other Functions (continued)
Other Functions (continued)
ClearCursors
Making Measurements: Vp-p
Source 1
1
4
3
GridNone
Hook Calibrator signal to CH1
2
Cursors Clears any cursors already onthe screen
Set for the correct channel
|- Active Cursor -|V1 V2 T1 T2
Toggle to highlight the V1 cursor; Rotateknob for waveformminimum
5
|- Active Cursor -|V1 V2 T1 T2
Change to V2 cursor;Use knob to set to waveform minimum
Measure Vp-p, using cursors:
Answer
V1= 31.25mV V2= 5.031V V= 5.000V
Cursor adjustment knob
OR: Measure Vp-p, the easy way:
1 Voltage|- Voltage Measurements -|
Vp-p Vavg VrmsSimply select Vp-p from the Voltage menu.
Display
5
Risetime Answer
Making Measurements: RISETIME
1 NextMenu
If answer needs more resolution:
2
Time
|----------- Time Measurements -----------|+Width -Width RiseTime FallTime
Rotate for best display:3
Time/Div
Rise(1) 920 ns
90% line
10% line
Time
Rise(1) <4.000 us
Rotate to show multiple cycles on screen
Time/Div
Rise(1) <4.000 us
2
1
Main/Delayed
Time/Div
MainDelayed
3
Main Delayed XY Roll|-------Horizontal Mode --------|
Rise(1) 920 nsDelaye
dCntr
Rotate. See how upper bracketed part is exploded into lower window
Time/Div
Making Measurements: RISETIME, Using DELAYED SWEEP:
(Hit Menu key)
To do FFT, a Measurement/Storage Module must be installedon back of scope.
Making Measurements: FFT (Frequency Domain)
Setup: Default
+
Auto-scale
1
2
4
3
5
|-- Function 2 --|Off On Menu
|-- Function 2 --|Off On Menu
OperationFFT
Use Time/Div to set FFT resolution
1
Hint: To look ONLY at FFT signal without time domain signal, turn channel off: 1
Off On
Hint: To return to FFT menu at any time, use Math key +
Auto-store
Storing Waveforms:AUTOSTORE
Displays all waveforms (Good for looking at jitter, noise, glitches)
Auto-store
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.
Auto-store
Touching Autostore again returns display to normal mode.
1
2
4
3
5
Storing Waveforms:TRACE MEMORYExample: Calibrator signal in CH 1. Setup Default. AUTOSCALE.
Trace
Now move waveform with horizontal delay and vertical position knobs. Note that Trace 1 still stays on screen, allowing comparison with stored waveform.
Save to Trace 1
Trace 1 Off On
Vertical position
Horizontal delay
1
2
4
3