HP 54750A, User Manual, Page: 341 / 478

The General Function Menus
Display Menu
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Persistence
The P ersistence function determines how long a data point is kept on the
display before the instrument erases it from the display .
Y ou can have averaging and persistence on at the same time because when
averaging is on, the averaging is done before the data is sent to the display .
A veraging is controlled by the A cquisition menu.
K ey Path 4
Displa y
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Persistence
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variable By selecting variable persistence , you can vary the persistence time from
minimum to 40 s . When the persistence is set to minimum, all the displayed
data points are kept on the display for one acquisition sweep . With the
next acquisition sweep , all the previous data points are erased from the
display , and new data points are written to the display . As you increase the
persistence time , the previous data points are kept on the display depending
on the persistence time you have selected. Therefore , the longer the
persistence time , the longer each data point is left on the display before it is
erased from the display . Y ou can change the persistence time with the knob ,
arrow keys , or keypad.
The variable persistence mode has a feature called gray scaling. On older
digitizing oscilloscopes , pixels were either turned on to full brightness or
turned o. This gave you no feeling for how frequently events happened. In
contrast, the relative brightness of a trace on analog analyzers told you the
frequency of occurrence of events , but you usually used a viewing hood to see
the extremely dim trace .
With gray scaling, the brightness of the pixel fades through up to eight levels
of intensity , and the brightness of a pixel only depends on how often it is
illuminated by acquired data points .
Gray scaling lets you see how frequently an event is happening. The most
frequently occurring events tend to be brighter than less frequently occurring
events . Gray scaling is more visible with a low persistence time , about
100 ms to 800 ms , and with dynamic signals . Y ou can use gray scaling on
PRBS signals (pseudo random bit sequence) or frequency modulated signals .
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