Teledyne LeCroy AORM - Advanced Optical Recording Measurements - Manual (Page 86)

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ISSUED: June 2013 923133 Rev A
T@PIT TIME AT PIT
Description
The Time-at-Pit parameter provides the time of each leading edge of every pit or space within the
nT range specified from the trigger point (time = 0). The value displayed is the time of the first pit
only.
The usefulness of this parameter is not in the displayed value, but in its trending. The intent is
that two parameters (t@pit and another ORM parameter) can be set up with identical
configurations: precisely the same number of pits or spaces is found in the waveform, and
precisely the same number of parameter measurements is made. When both of these parameters
are trended, the two trends will have the same number of events, and there will be a one-to-one
correspondence between each event in each trend. If both trends are displayed, and time cursors
are swept over each, values will be displayed for the ORM parameter value and the time within
the acquisition where the parameter measurement was made. These times are useful when
searching for abnormal events within a waveform.
Not only can the trend of t@pit provide the actual event time, it can be used as the x-axis in an
XY plot to examine modulation characteristics of particular parameter measurements.
Example
This example typifies the usage of the t@pit parameter. Step-by-step instructions are given.
A large optical recording waveform is to be acquired, and the ordinary pit/space widths that can
cause errors in the system need to be found. The waveform contains pits/spaces that have widths
that are ideal integer multiples of the clock period 231.5 ns in a range from 3 to 11 times this
clock period.
The scope is set up to acquire this waveform by assigning Channel 1 to the data signal at a
time/div of 0.2 ms. This signal will contain approximately 1800 pits/spaces. The ideal threshold
(determined by the pmidl parameter) is 1.9 mV.
The pwid custom parameter is assigned to P1 and the t@pit parameter to P2. Both parameters
are configured in the following manner:
hysteresis = 0.5 divisions
threshold = 1.9 mV
polarity = Both
range of n
low n = 0
high n = 25
period = 231.5 ns.
Using the Math Setup… dialog, define F1 as the trend of the pwid parameter, and F2 as the
trend of the t@pit parameter. For later use, define F3 as a zoom of Channel 1.