A&D Series 57ZZ Uživatelský manuál Strana 10

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on the screen. The trigger is necessary to stabilize a
repeating signal. It ensures that the sweep begins at
the same point of a repeating signal, resulting in a
clear picture as shown in Figure 7.
In summary, when using an analog oscilloscope (or
any type of oscilloscope), you need to adjust three
basic settings to accommodate an incoming signal:
The attenuation or amplification of the signal.
Use the volts/div control to adjust the amplitude
of the signal to the desired measurement range
The time base. Use the sec/div control to set the
amount of time per division represented horizon-
tally across the screen
The triggering of the oscilloscope. Use the trigger
level to stabilize a repeating signal, or for trig-
gering on a single event
In addition, analog scopes have focus and intensity
controls that can be adjusted to create a sharp,
legible display.
Digital Storage Oscilloscopes
Some of the systems that make up DSOs are the same
as those in analog oscilloscopes; however, digitizing
oscilloscopes contain additional data processing
systems (see Figure 8). With the added systems, the
digitizing oscilloscope collects data for the entire
waveform and then displays it.
The first (input) stage of a DSO is a vertical amplifier,
just like the analog oscilloscope’s. Vertical attenua-
tion controls allow you to adjust the amplitude range
of this stage.
Next, the analog-to-digital converter (ADC) in the
acquisition system samples the signal at discrete
points in time and converts the signal’s voltage at
these points to digital values called sample points.
The horizontal system’s sample clock determines
how often the ADC takes a sample. The rate at which
the clock “ticks” is called the sample rate and is
expressed in samples per second.
The sample points from the ADC are stored in
memory as waveform points. More than one sample
point may make up one waveform point.
Together, the waveform points make up one wave-
form record. The number of waveform points used to
make a waveform record is called the record length.
The trigger system determines the start and stop
points of the record. The display receives these
record points after being stored in memory.
Depending on the capabilities of your oscilloscope,
additional processing of the sample points may take
place, enhancing the display. Pretrigger may be
available, allowing you to see events before the
trigger point.
Note that the DSO’s signal path includes a micro-
processor. The measured signal passes through this
device on its way to the display. In addition to
processing the signal, the microprocessor coordi-
nates display activities, manages the front-panel
controls, and more. This is known as a “serial
processing” architecture.
Digital Phosphor Oscilloscopes
The Digital Phosphor Oscilloscope (DPO) offers a
new approach to oscilloscope architecture. Like the
analog oscilloscope, its first stage is a vertical ampli-
fier; like the DSO, its second stage is an ADC. But
after the analog-to-digital conversion, the DPO looks
quite different from the DSO. It has special features
designed to recreate the intensity grading of an
analog CRT.
Rather than relying on a chemical phosphor as an
analog scope does, the DPO has a purely electronic
Digital Phosphor that’s actually a continuously
updated data base. This data base has a separate
4
Figure 7. Triggering stabilizes a repeating waveform.
Figure 8. Digital storage oscilloscope block diagram – “serial processing.”
Acquisition
Memory
Amp
Display
A/D
DeMux
µP
Display
Memory
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