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Oscilloscope - PowerPoint


									The University of Texas at Arlington
 Electrical Engineering Department

        Electric Circuit Lab

        The Oscilloscope
           Agilent 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
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
• Make sure probes are compensated.
• If you can't get the signal on screen:
- Check probe connection
- Touch: SETUP, Default Setup
- Check for offset (ground symbol). If offscale, adjust
vertical sensitivity and position
- Turn up signal brightness with intensity control
Digital Oscilloscope Block
 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 and set to proper scale
* If you can't get the signal on screen:
- Check Probe connection
- Touch: SETUP, Default Setup
- Check for offset (ground symbol). If offscale, adjust vertical
sensitivity. If still offscale, Touch:      Coupling

- Check Trigger Source                   1 DC AC
- Set Mode Auto
                     The Digitizing Oscilloscope
Status bar:
Vertical sensitivity                                      Autoscale     Measure: Vrms, tr, f  ,f
Sweep speed                                               Print         Trace /Setup Memory
Trigger time reference                                    Calibrate     Display: grid, vectors,
Channel(s) on                                                               averaging
                         1 1.00V      0s 2 us/ 1 RUN
                                                                          Storage: Auto-store,
                                                                          Erase, RUN/STOP
      Softkey            ----Setup memory----
                                         Undo   Default

      labels                                                      Triggering:
                                                                  Modes: Auto, Normal,TV
                                                                  Sources: Ch1, Ch2, Ext, Line
    Calibration source
    Power ON/OFF
    Screen brightness        Vertical position,                   Horizontal:
                                      sensitivity                Main Sweep Speed,
                             Math on/off                         Sweep Modes:
                                                                      Delayed, XY, Roll
                                                                 t = 0 Reference
Getting Started
 Getting Started:                                              4
     Line                               2
 1                      (Power ON)
     0 1

              Setup     (All settings                      5
 2   Setup                                  3
                        to default )
 3 Connect probe to calibrator

 4   scale

                                        1   1.00V       200    1 RU
                                                        us/      N
 5   Compensate probes:


Adjust screw to eliminate:                                     Default
1   1.00V   0.00s 200    1 RU
                                    Set probe attenuation factor:
                  us/      N               Press Channel key for
                                           selected probe.

                                      Probe    Toggle softkey for setting
                                    1 10 100
                                               that matches probe

                        1 10 100

                                            Trigger slope
 What the display says:
                                            is positive
                                                                       Blinks if
                                            (rising edge)
                                                                       no trigger
    Vertical sensitivity of CH1
    is 1Volt per major division         Time=0

                                  t<0            t>0
                                                                         Trigger source
                        1 1.00V                  0.00s
                                                 200us/      1 RU        is Channel 1
                                                               N           Scope is ready
                                                                           for trigger

                                                                 1       Ground (V=0)
                                                                       [If dc part of CH1 signal
                                                                       is too big, ground
                                                                       arrow points off-screen.
                        1                                   Probe      If this happens, adjust
                       Off On                             1 10 100     vertical sensitivity]

Channel 1 is ON
                   Horizontal sweep speed is                    Readings scaled
                   200 msec per major division                  for a 10:1 probe
What the main controls do:

                                     Horizontal    Trigger level     Line is only
                       Grid full     delay         visible when you turn the
    Display:                                       When signal is smaller than
                       Vectors off                 trigger level, scope stops

                                                        (sweep speed)

                Vertical                Vertical
                Volts/division          Position
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.


                              1                  Math Functions
                       - Enable channel             -Add waveforms
                       - Set up probe               -FFT (if equipped with
Horizontal Controls
Vertical Controls
Trigger Controls
Display (continue)
Other Functions
Other Functions (continue)
Other Functions (continue)
Other Functions (continued)
Other Functions (continued)
Other Functions (continued)
Making Measurements: Vp-p
      Measure Vp-p, using cursors:
 1    Hook Calibrator signal to CH1
                  Grid                                                            Cursor adjustment knob
  2   Display     None

  3    Cursors    Clear Clears any cursors already on
                  Cursor the screen
 4     1     Set for the correct channel

       |- Active Cursor -| Toggle to highlight
  5      V1 V2 T1 T2 the V1 cursor; Rotate
                           knob for waveform
                           minimum                                          D
                                                         V1= 31.25mV V2= 5.031V     V= 5.000V

       |- Active Cursor -|
  5                          Change to V2 cursor;
         V1 V2 T1 T2         Use knob to set to
                             waveform minimum                                      Answer

OR: Measure Vp-p, the easy way:
                                       |- Voltage Measurements -| Simply select Vp-p from the
                     1       Voltage       Vp-p Vavg Vrms         Voltage menu.
Making Measurements:

 1     Time      Menu

     |----------- Time Measurements -----------|   Rise(1) <4.000 us
 2       +Width -Width RiseTime FallTime

                          Risetime Answer
If answer needs more resolution:
     Time/Div                                                          90% line
                  Rotate for best display:                             10% line

                                                    Rise(1) 920 ns
Making Measurements:

                Rotate to show multiple
                cycles on screen
                                                         Rise(1) <4.000 us
 2    Main   |-------Horizontal Mode --------|                               Main/Delayed
     Delayed   Main Delayed XY Roll

 3              Rotate. See how
                upper bracketed part is
                exploded into lower              Rise(1)
                                                     Delayed      Cntr
                                                 920 ns

Making Measurements: FFT                   To do FFT, a
(Frequency Domain)                         Measurement/Storage
                                           Module must be installed
1   Setup: Default                         on back of scope.
2   scale
     +        |-- Function 2 --|
3              Off On Menu

    |-- Function 2 --|
4    Off On Menu         (Hit Menu key)

5      FFT

Hint: To look ONLY at FFT signal
without time domain signal, turn
channel off:          1
                1   Off On
                                                Use Time/Div to set
                                                FFT resolution
Hint: To return to FFT menu at any time,
use Math key                    +
    Storing Waveforms:                           store

      Auto-   Displays all waveforms
1     store    (Good for looking at jitter,
              noise, glitches)
     Example: Calibrator signal in CH 1.
3    Setup Default. AUTOSCALE. Touch
     Now move horizontal delay knob and
4    watch all waveforms stay on screen,
     making an overlapping pattern.
      Auto-   Touching Autostore again returns
5     store   display to normal mode.
    Storing Waveforms:
1   Example: Calibrator signal in CH 1.
    Setup Default. AUTOSCALE.
     Trace   Save to
2            Trace 1

     Trace 1
3    Off On

     Now move waveform with horizontal        Vertical position
4    delay and vertical position knobs.
     Note that Trace 1 still stays on screen,
     allowing comparison with stored              Horizontal delay

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