A&D Series 57ZZ Manual de usuario descargar pdf (Pagina 27)

Acquisition Controls for Digitizing

Oscilloscopes

Digitizing oscilloscopes have settings that let you

control how the acquisition system processes a

signal. Look over the acquisition options on your

digitizing oscilloscope while you read this descrip-

tion. Figure 37 shows an example of an acquisition

menu.

Acquisition Modes

Acquisition modes control how waveform points are

produced from sample points. Recall from the first

section that sample points are the digital values that

come directly out of the Analog-to-Digital-Converter

(ADC). The time between sample points is called the

sample interval. Waveform points are the digital

values that are stored in memory and displayed to

form the waveform. The time value difference

between waveform points is called the waveform

interval. The sample interval and the waveform

interval may be, but need not be, the same. This fact

leads to the existence of several different acquisition

modes in which one waveform point is made up

from several sequentially acquired sample points.

Additionally, waveform points can be created from a

composite of sample points taken from multiple

acquisitions, which leads to another set of acquisi-

tion modes. A description of the most commonly

used acquisition modes follows.

• Sample Mode: This is the simplest acquisition

mode. The oscilloscope creates a waveform point

by saving one sample point during each wave-

form interval.

• Peak Detect Mode: The oscilloscope saves the

minimum and maximum value sample points

taken during two waveform intervals and uses

these samples as the two corresponding wave-

form points. Digitizing oscilloscopes with peak

detect mode run the ADC at a fast sample rate,

even at very slow time base settings (long wave-

form interval), and are able to capture fast signal

changes that would occur between the waveform

points if in sample mode. Peak detect mode is

particularly useful for seeing narrow pulses

spaced far apart in time.

• Hi Res Mode: Like peak detect, hi res mode is a

way of getting more information in cases when

the ADC can sample faster than the time base

setting requires. In this case, multiple samples

taken within one waveform interval are averaged

together to produce one waveform point. The

result is a decrease in noise and an improvement

in resolution for low-speed signals.

• Envelope Mode: Envelope mode is similar to peak

detect mode. However, in envelope mode, the

minimum and maximum waveform points from

multiple acquisitions are combined to form a

waveform that shows min/max changes over

time. Peak detect mode is usually used to acquire

the records that are combined to form the enve-

lope waveform.

• Average Mode: In average mode, the oscilloscope

saves one sample point during each waveform

interval as in sample mode. However, waveform

points from consecutive acquisitions are then

averaged together to produce the final displayed

waveform. Average mode reduces noise without

loss of bandwidth but requires a repeating signal.

A special note about DPO acquisition: The Digital

Phosphor Oscilloscope has a high display sample

density and an innate ability to capture intensity

(Z-axis) information. With its intensity axis, the DPO

is able to provide the same type of 3-dimensional,

real-time display that analog scopes are known for.

As you look at the waveform trace on a DPO, you can

see brightened areas. These are the areas where the

signal occurs most often. This makes it easy to

distinguish, for example, the basic signal shape from

a transient that occurs only once in a while. The

basic signal would appear much brighter.

DPOs also include all the acquisition modes

described above.

Figure 37. Example of an acquisition menu.

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