Oscilloscope Tutorial

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Oscilloscope Tutorial

• The oscilloscope is basically a graph-displaying
  device
• It draws a graph of an electrical signal.
• In most applications the graph shows how signals
  change over time
• the vertical (Y) axis represents voltage
• the horizontal (X) axis represents time.

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Oscilloscopes
Horizontal sweeps at a constant rate. Vertical
plates are attached to an external voltage, the
signal you attach to the scope.
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Cathode Ray Tubes
Variation in potential difference (voltage)
placed on plates causes electron beam to bend
different amounts. Sweep refers to refreshing
repeatedly at a fixed rate.
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Scope (Cont)

• This simple graph can tell you many things about
  a signal
• You can determine the time and voltage values of
  a signal.
• You can calculate the frequency of an oscillating
  signal.
• You can see the "moving parts" of a circuit
  represented by the signal.
• You can tell if a malfunctioning component is
  distorting the signal.
• You can find out how much of a signal is direct
  current (DC) or alternating current (AC).
• You can tell how much of the signal is noise and
  whether the noise is changing with time.

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How does an Analog Scope work?
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How does a Digital Scope work?
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Triggering Stabilizes a Repeating Waveform
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Waveform shapes tell you a great deal about a
signal
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If a signal repeats, it has a frequency. The
frequency is measured in Hertz (Hz) and equals
the number of times the signal repeats itself in
one second
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Voltage, Current, Phase
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Performance Terms

• Bandwidth
• The bandwidth specification tells you the
  frequency range the oscilloscope accurately
  measures.
• Rise Time
• Rise time may be a more appropriate performance
  consideration when you expect to measure pulses
  and steps. An oscilloscope cannot accurately
  display pulses with rise times faster than the
  specified rise time of the oscilloscope.
• Vertical Sensitivity
• The vertical sensitivity indicates how much the
  vertical amplifier can amplify a weak signal.
  Vertical sensitivity is usually given in
  millivolts (mV) per division.
• Sweep Speed
• For analog oscilloscopes, this specification
  indicates how fast the trace can sweep across the
  screen, allowing you to see fine details. The
  fastest sweep speed of an oscilloscope is usually
  given in nanoseconds/div.
• Gain Accuracy
• The gain accuracy indicates how accurately the
  vertical system attenuates or amplifies a signal.
  
• Time Base or Horizontal Accuracy
• The time base or horizontal accuracy indicates
  how accurately the horizontal system displays the
  timing of a signal.
• Sample Rate
• On digital oscilloscopes, the sampling rate
  indicates how many samples per second the ADC can
  acquire. Maximum sample rates are usually given
  in megasamples per second (MS/s). The faster the
  oscilloscope can sample, the more accurately it
  can represent fine details in a fast signal..
• ADC Resolution (Or Vertical Resolution)
• The resolution, in bits, of the ADC indicates how
  precisely it can turn input voltages into digital
  values.
• Record Length
• The record length of a digital oscilloscope
  indicates how many waveform points the
  oscilloscope is able to acquire for one waveform
  record.

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Grounding

• Proper grounding is an important step when
  setting up to take measurements.
• Properly grounding the oscilloscope protects you
  from a hazardous shock and protects your circuits
  from damage.
• Grounding the oscilloscope is necessary for
  safety. If a high voltage contacts the case of an
  ungrounded oscilloscope, any part of the case,
  including knobs that appear insulated, it can
  give you a shock. However, with a properly
  grounded oscilloscope, the current travels
  through the grounding path to earth ground rather
  than through you to earth ground.
• To ground the oscilloscope means to connect it to
  an electrically neutral reference point (such as
  earth ground). Ground your oscilloscope by
  plugging its three-pronged power cord into an
  outlet grounded to earth ground.
• Grounding is also necessary for taking accurate
  measurements with your oscilloscope. The
  oscilloscope needs to share the same ground as
  any circuits you are testing.
• Some oscilloscopes do not require the separate
  connection to earth ground. These oscilloscopes
  have insulated cases and controls, which keeps
  any possible shock hazard away from the user.

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Scope Probes Most passive probes have some
degree of attenuation factor, such as 10X, 100X,
and so on. By convention, attenuation factors,
such as for the 10X attenuator probe, have the X
after the factor. In contrast, magnification
factors like X10 have the X first
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Vertical Controls

• Position and Volts per Division
• The vertical position control lets you move the
  waveform up or down to exactly where you want it
  on the screen.
• The volts per division (usually written
  volts/div) setting varies the size of the
  waveform on the screen. A good general purpose
  oscilloscope can accurately display signal levels
  from about 4 millivolts to 40 volts.
• Often the volts/div scale has either a variable
  gain or a fine gain control for scaling a
  displayed signal to a certain number of
  divisions.

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Input Coupling

• Coupling means the method used to connect an
  electrical signal from one circuit to another.

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Horizontal Controls

• Position and Seconds per Division
• The horizontal position control moves the
  waveform from left and right to exactly where you
  want it on the screen.
• The seconds per division (usually written as
  sec/div) setting lets you select the rate at
  which the waveform is drawn across the screen
  (also known as the time base setting or sweep
  speed). This setting is a scale factor. For
  example, if the setting is 1 ms, each horizontal
  division represents 1 ms and the total screen
  width represents 10 ms (ten divisions). Changing
  the sec/div setting lets you look at longer or
  shorter time intervals of the input signal.

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Trigger Position

• The trigger position control may be located in
  the horizontal control section of your
  oscilloscope. It actually represents "the
  horizontal position of the trigger in the
  waveform record." Horizontal trigger position
  control is only available on digital
  oscilloscopes.
• Varying the horizontal trigger position allows
  you to capture what a signal did before a trigger
  event (called pretrigger viewing).
• Digital oscilloscopes can provide pretrigger
  viewing because they constantly process the input
  signal whether a trigger has been received or
  not. A steady stream of data flows through the
  oscilloscope the trigger merely tells the
  oscilloscope to save the present data in memory.
  I
• n contrast, analog oscilloscopes only display the
  signal after receiving the trigger.

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Trigger Controls (cont)
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Pulse and Rise Time Measurements
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Multimeter tutorial

• A meter is a measuring instrument. An ammeter
  measures current, a voltmeter measures the
  potential difference (voltage) between two
  points, and an ohmmeter measures resistance.
• A multimeter combines these functions, and
  possibly some additional ones as well, into a
  single instrument.

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To measure current, the circuit must be broken to
allow theammeter to be connected in
series Ammeters must have a LOW resistance
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To measure potential difference (voltage), the
circuit is not changed the voltmeter is
connected in parallelVoltmeters must have a
HIGH resistance
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To measure resistance, the component must be
removed from the circuit altogether Ohmmeters
work by passing a current through the component
being tested
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Digital MultimetersDigital meters give an
output in numbers, usually on a liquid crystal
display.Most modern multimeters are digital and
traditional analogue types are destined to become
obsolete.Digital multimeters come in a wide
range of sizes and capability. Everything from
simple 3 ½ digit auto ranging pocket meters to
larger 8 ½ digit bench model with operator or
computer (IEEE488 compatible) settable range
selection
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Function Generator

• An electronic instrument that generates various
  waveforms such as
• Sine wave
• Square wave
• Pulse trains
• Sawtooth
• The amplitude, DC offset, frequency are
  adjustable.

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Function Generators (cont)

• Like multimeters there is a wide variety of
  device offering various
• Amplitude characteristics
• Bandwidth
• Adjustments of rise and fall times
• Modulation capability (AM, FM, Pulse, etc.)

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Power Supply

• This is the device that transfers electric power
  from a source to a load using electronic
  circuits.
• Typical application of power supplies is to
  convert utility's AC input power to a regulated
  voltage(s) required for electronic equipment.
• Depending on the mode of operation of power
  semiconductors PS can be linear or switching.
• In a switched-mode power supply, or SMPS power
  handling electronic components are continuously
  switching on and off with high frequency in order
  to provide the transfer of electric energy. By
  varying duty cycle, frequency or a phase of these
  transitions an output parameter (such as output
  voltage) is controlled. Typical frequency range
  of SMPS is from 20 kHz to several MHz.

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Power Supply (cont)

• Power supplies like many of the other electronic
  instruments, come in many varieties with a wide
  range of capabilities
• Parameters that are Power Supply specific
  include
• Voltage levels
• Current
• Regulation
• Protection
• Output impedance
• Noise (ripple)
• Its the designer (or researcher) responsibility
  to identify the characteristics required.

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Oscilloscope
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Oscilloscope(continue)

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