User's Manual Part 2

Plot–Assisted Setups
RVP8 User’s Manual
April 2003
4–2
4.1 Oscilloscope Connections
All that is required to view the graphical displays is an oscilloscope with a single vertical input
channel. Setup the scope as follows:
Vertical Input BNC cable to “Q” output of RVP8, terminated in 50W or 75W
according to cable type.
Vertical Channel Variable gain, approximately 1V full–scale deflection.
High frequency rejection enabled (to “soften” the appearance)
Horizontal Time Base 100 msec/division (1ms full sweep), no holdoff.
Trigger Source From vertical channel, rising edge, DC coupled.
Trigger Level Either –0.3V or +0.3V (approximately)
Trigger Mode Use “Norm” rather than “Auto”, so that the display will be blank when
nothing is being plotted.
The RVP8 synthesizes a waveform on its “Q” channel consisting of a repeating sequence of
graphical “strokes”, each of which is 1ms in duration. A typical plot will have between five and
fifteen strokes that blend together to form the complete image. In between each stroke is a
0.5ms idle period in which the output voltage remains at its lowest level (bottom of the screen).
The idle period ends with a 2.0msec “trigger” pulse to the top of the screen, followed by the next
1.0ms drawing stroke.
Because the oscilloscope is set to trigger on the rising edge of its input, these brief trigger pulses
will initiate the horizontal sweeps that draw each stroke of the image. Thus, the waveform is
self triggering, and no external trigger signal is required. This model assumes that the 0.5ms
idle period (50% of the full sweep time) is long enough for the scope’s horizontal time base to
retrace and begin waiting for the next trigger event. Most scopes can easily do this; but if not,
try increasing the holdoff ratio (See setup question on page 3–12) until a clean and stable display
is observed.
Z-axis (intensity) modulation is not required since the oscilloscope automatically blanks its beam
between sweeps. When a plot requires certain strokes to be appear brighter than others, the
RVP8 accomplishes this merely by drawing that particular stroke more than once in the overall
sequence.
The plotting technique relies on the luminance persistence of the oscilloscope phosphor to blend
the multiple strokes into a single, flicker free, complex display. This happens automatically on
an analog scope, but can be awkward if a digital sampling scope is used. This is because a
digital scope is usually intended to capture and hold a single trace of data, rather than to sweep
out multiple traces and allow them to blend into a single image. Digital scopes are not
recommended here, but if one must be used, try experimenting with its controls that affect
persistence and overwriting.