Waveform Processing - Tektronix 7D20 Operator's Manual

triggering is used, the 7D20 will simply retain the last triggered information . At that
point, HOLD should be pressed to eliminate the chance of a stray signal or noise
from destroying the data . Alternately, HOLD NEXT may also be used for a triggered
hold.
This application is intended to aid in the SOA process and by no means represents a
complete or rigorous method for making such measurements . A more complete
discussion of this subject is available from Tektronix, Instrument Division, Lab
Scopes Marketing .
APPLICATION 6
USING THE 7D20 WITH THE 7854
FOR WAVEFORM PROCESSING
Applications-7D20
The 7854 is a waveform processing oscilloscope which allows you to manipulate
waveforms similar to using a scientific programmable calculator . The 7854 digitizer
has a single event capture speed slightly above the audio spectrum. The 7D20
extends this ability to capture single events into the video spectrum .
Also, the settings of the 7D20 may be remotely programmed for use in an
automated measurement environment . In this application, it is important to point
out that this combination is not the most efficient system component when speed is
considered . However, it may be desirable since it greatly reduces the software
impact on the system engineer . The 7854's waveform functions eliminate the need
to create and verify many commonly used algorithms . In this sense, the 7854 and
7D20 provide the shortest path to designing a waveform measurement system .
Before proceeding, a few technical points must be considered to explain the use of
these two instruments .
The 7D20 is a waveform digitizer . Its measurement accuracy is derived from its
waveform memory . The 7D20 produces a refreshed display (when installed in any
7000 Series mainframe) which is in no way time related to the events which it
captures . Also, the height, width, and position of the display can be adjusted from
the front panel which can seriously affect measurements made with the graticule .
However, the contents in memory are not disturbed and the cursor readout will
remain accurate because it is independent of the display adjustments .
The 7854 acquires waveform information from the plug-ins based on the height,
width, and position of the display . Accuracy of the 7854 is limited primarily by the
plug-ins installed in it . Hence, the display output of the 7D20 does not present the
most accurate representation of its memory contents . Errors are also compounded
when the 7854 digitizes the 7D20's output . Quantization, noise, and linearity all
contribute to this error .
There is a simple solution to this dilema, the IEEE-488 interface . The only logical
way to accurately represent a 7D20 waveform in the 7854 is to transfer the actual
digital data .
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