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Oscilloscope
Terms and Definitions
OSCILLOSCOPE
USE
B+K PRECISION
offers one of the industry's broadest lines of oscilloscopes with models
ranging from a 20 MHz analog dual-trace unit to a versatile 150MHz digital
storage oscilloscope, and a 100MHz lab scope. No matter what your
application-design, service, production or hobbyist, B+K PRECISION has an
oscilloscope to more than meet your requirements.
An oscilloscope
is a test instrument that visually displays an electronic signal on a
display screen. The display shows voltage (vertical) and time
(horizontal). You can view the screen and through interpretation of the
settings on the oscilloscope determine the instrument's voltage, and the
general characteristics of the signal.
WHERE ARE
OSCILLOSCOPES USED?
An oscilloscope
is a test instrument that can be used in a wide variety of applications:
- EDUCATION
- used in technical schools to demonstrate electrical theory
- DESIGN
- used in circuit design to verify design parameters
- SERVICE
- used for the repair of electronic equipment
- MAINTENANCE
- used to verify operation for set-up or repair equipment
- FIELD
SERVICE - used for in-the-field repair of equipment
- MANUFACTURING
- used as part of the manufacturing process to verify performance
parameters of designed equipment
- QUALITY
CONTROL - used for final testing of equipment.
WHAT IS
BANDWIDTH?
Bandwidth is the
frequency range of signals that can be viewed on the oscilloscope. When
selecting an oscilloscope, consider present and future bandwidth
requirements of the instrument.
ANALOG VS.
DIGITAL STORAGE
B+K Precision
provides analog, digital, and analog/digital operation oscilloscopes.
ANALOG Oscilloscope - range from 30 MHz to 100 MHz in bandwidth ANALOG /
DIGITAL Oscilloscopes - range from 20 MHz to 150 MHz in bandwidth with 200
MS/s sampling rate. The prime benefits of an analog/digital or digital
oscilloscope are:
- capability to
store waveforms for analysis
- ability to
view / store pre-trigger information
- ability to
detect / display / capture glitches
- ability to
get a hard copy printout of the capture signal
- ability to
view slow event
- ability to
view one time event
ARE
ANALOG/DIGITAL AND DIGITAL OSCILLOSCOPES HARD TO USE?
B+K Precision
analog / digital or digital oscilloscopes have a number of features that
provide ease of use. These features include:
- AUTOSET - provides automatic setup of time base, vertical
axis and trigger parameters of the signal being viewed. This allows
most signals to be displayed. You can then readjust the timebase and
vertical axis as you require.
- AUTOMATIC MEASUREMENTS - Up to 17 automatic measurements are
displayed by readouts on the screen.
- ANALOG OR DIGITAL OPERATION - B+K Precision analog / digital
oscilloscopes provide the benefits of both analog and digital
operation in one unit. A single button is used to go from analog to
digital storage operation.
OSCILLOSCOPE SELECTION
Refer to the following page for definitions of common digital
terminology. When selecting an oscilloscope, answer these questions:
Considering present and future needs, what maximum bandwidth will be
required? Will you need to store and view the signals you are viewing?
(consider present and future needs) Review the selection
chart for a preliminary choice. Then turn to the specific model number
page for complete specifications.
OSCILLOSCOPE TERMS
ACCELERATING VOLTAGE
The internal voltage that causes trace illumination on the oscilloscope
display. A higher voltage is needed at fast sweep speeds.
BANDWIDTH
The frequency range of signals that can be observed on the oscilloscope
with minimal degradation. Typically, bandwidth is specified in megahertz
(MHz) and is the maximum frequency at which signals are within 3 dB in
amplitude.
DELAYED TIME BASE
Allows a single signal to be viewed at two different sweep speeds, by
expanding a portion of the waveform and starting at some point after the
main time base begins. This is more useful than merely magnifying the
display because it allows all parts of the main sweep signal to be
observed with any desired amount of expansion or horizontal magnification.
DUAL TIME BASE
A dual time oscilloscope allows you to view one signal at two different
sweep speeds simultaneously, with delayed trigger. One sweep can be used
to observe a complete waveform (such as a full frame of a video signal)
while the second sweep is used to expand the signal and view only a
portion of it (such as a single line of the same video signal).
EXTERNAL TRIGGER
Externally supplied signal that starts the sweep.
INPUT IMPEDANCE
The AC and DC resistance that a signal "sees" at the
oscilloscope input.
RISE TIME
The minimum time that it takes the CRT beam to rise from the 10% mark
on the CRT graticule to the 90% mark on the graticule. Oscilloscope rise
time specifications are directly related to bandwidth.
SWEEP
The motion of the CRT beam from left to right that causes the trace to
appear. A sweep time of 0.1 ms/div means that the beam moves across one
division of the CRT in 0.1 ms. Faster sweep speeds are required to view
higher frequency signals.
SWEEP MAGNIFIER
Allows a portion of a displayed waveform to be magnified (typically
X10) without actually shortening the sweep time setting. This is an
advantage over simply increasing the sweep speed because increasing the
sweep speed can result in the desired portion of the waveform disappearing
off the screen. Additionally, this feature increases the maximum sweep
speed by the magnification factor.
TRIGGER
Signal that starts the sweep of the oscilloscope CRT beam across the
display. The trigger level controls the amplitude at which the sweep will
begin.
VERTICAL SENSITIVITY
The signal level required to cause a single division of vertical
deflection. For example, for a vertical attenuator setting of 5 mV/div, a
5 mV peak signal will produce one division of vertical deflection.
V MODE TRIGGERING
V mode triggering permits each waveform viewed to become its own
trigger signal. In dual trace operation, the trigger source alternates
between channels. Sometimes referred to as alternate triggering.
VERTICAL ATTENUATOR
The precision input circuit controls the level of the input signal.
Usually this circuit consists of calibrated steps in a 1-2-5 sequence (i.
e., 10 mV/div, 20 mV/div, 50 mV/div. etc) which allow the oscilloscope to
display signals with levels from many volts to only a few millivolts.
VIDEO SYNC
Allows vertical (TV V) or horizontal (TV H) video sync pulses to be
selected for triggering. Vertical sync pulses are selected to view
vertical fields or frames of video and horizontal sync pulses are selected
for viewing horizontal lines of video. Sometimes referred to as TV sync.
X-Y DISPLAY
Mode of operation which displays a graph of two voltages. The Y axis is
the vertical axis (usually channel 1) and the X axis is the horizontal
axis (usually Channel 2).
Z-AXIS
Allows an external signal to control the intensity of the CRT beam.
Also referred to as intensity modulation.
DIGITAL OSCILLOSCOPE TERMS
BYTE
Usually contains eight bits of digital information (sometimes contains
10 to 12 bits). Also referred to as a word.
EQUIVALENT TIME SAMPLING
A method of sampling used by some Digital Storage Oscilloscopes to
allow them to capture repetitive waveforms with frequencies that are
higher than the sampling rate.
HARD COPY
A paper copy of the displayed waveform made by an external plotter.
HORIZONTAL RESOLUTION
The number of points possible across the oscilloscope display. Usually,
if the horizontal resolution is 1 K (1024), there will be 1000 points
(samples) plotted across the display from the far left vertical graduation
to the far right graduation. (100 points or samples per division).
INTERFACE
Ability to talk to and/or receive commands from an external computer or
other electronic device.
MEMORY
The electronic circuitry that stores the digitized signal. For DSO's,
memory is usually specified in kilobytes. One kilobyte contains 1024 bytes
of information.
PRE-TRIGGER
The ability of a DSO to view signals before the trigger. This allows
the user to determine the cause of many undesired effects in electrical
and electronic equipment.
REFRESH MODE
The trace moves across the CRT from left to right (just like a
conventional oscilloscope) and the display is refreshed (updated) each
time a trigger occurs.
ROLL MODE
The trace moves across the CRT from right to left (like a chart
recorder) and is continually updated.
SAMPLE
The digital representative of an instantaneous value of the digital
storage oscilloscope's input signal. The DSO works by taking sample of the
waveform at various points.
SAMPLING RATE
The rate at which the input signal is converted to a digital signal.
Maximum sampling rate is usually expressed in MS/s (megasamples per
second).
SINGLE SHOT MODE
Used for capturing one-time events or pre-trigger information.
VERTICAL RESOLUTION
The number of vertical points that are possible on the oscilloscope
display. An eight bit DSO allows a vertical resolution of 256, a ten bit
DSO allows 1024 points, and a twelve bit DSO allows 4096 points. |
