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TDS 620A, 640A & 644A User Manual
2Ć19
Acquisition
Acquisition is the process of sampling the analog input signal, converting it
into digital data, and assembling it into a waveform record. The oscilloscope
creates a digital representation of the input signal by sampling the voltage
level of the signal at regular time intervals (Figure 2Ć4).
Input Signal SampledPoints Digital Values
+5.0 V
-5.0 V
+5.0 V
-5.0 V
0V 0V 0V 0V
Figure 2Ć4:ăAcquisition: Input Analog Signal, Sample, and Digitize
The sampled points are stored in memory along with corresponding timing
information. You can use this digital representation of the signal for display,
measurements, or further processing.
You specify how the digitizing oscilloscope acquires data points and asĆ
sembles them into the waveform record.
The trigger point marks time zero in a waveform record. All record points
before the trigger event make up the pretrigger portion of the the waveform
record. Every record point after the trigger event is part of the posttrigger
portion. All timing measurements in the waveform record are made relative
to the trigger event.
Each time it takes a sample, the oscilloscope digitizer produces a numeric
representation of the signal.
The digitizer can use the extra samples to perform additional processing,
such as averaging or looking for minimum and maximum values.
The digitizing oscilloscope creates a waveform record containing a userĆspeĆ
cified number of data points. Each record point represents a certain voltage
level that occurs a determined amount of time from the trigger event.
Record Length
The number of points that make up the waveform record is defined by the
record length. You can set the record length in the Horizontal menu. The
digitizing oscilloscope provides record lengths of 500, 1000, and 2000
points.
Sampling and
Digitizing