Tektronix, Inc. P6240, User Manual

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Appendix B: Algorithms
TLS 216 User Manual
B–3
Hysteresis is a band comprising 10% of the waveform amplitude. It is used in
MCross1
,
MCross2
, and
MCross3
calculations.
For example, once a crossing has been measured in a negative direction, the
waveform data must fall below 10% of the amplitude from the
MidRef
point
before the measurement system is armed and ready for a positive crossing.
Similarly, after a positive
MidRef
crossing, waveform data must go above 10%
of the amplitude before a negative crossing can be measured. Hysteresis is useful
when you are measuring noisy signals, because it allows the logic scope to
ignore minor fluctuations in the signal.
MCross1, MCross2, and MCross3
refer to the first, second, and third
MidRef
cross
times, respectively. See Figure B–1.
The polarity of the crossings does not matter for these variables, but the
crossings alternate in polarity; that is,
MCross1
could be a positive or negative
crossing, but if
MCross1
is a positive crossing,
MCross2
will be a negative
crossing.
The logic scope calculates these values as follows:
1. Find the first
MidRefCrossing
in the waveform record or the gated region.
This is
MCross1
.
2. Continuing from
MCross1
, find the next
MidRefCrossing
in the waveform
record (or the gated region) of the opposite polarity of
MCross1
. This is
MCross2
.
3. Continuing from
MCross2
, find the next
MidRefCrossing
in the waveform
record (or the gated region of the same polarity as
MCross1
. This is
MCross3
.
MCross1Polarity is the polarity of first crossing (no default). It can be rising or
falling.
StartCycle is the starting time for cycle measurements. It is a floating-point
number with values between 0.0 and (
RecordLength
– 1.0), inclusive.
StartCycle
=
MCross1
EndCycle is the ending time for cycle measurements. It is a floating-point
number with values between 0.0 and (
RecordLength
– 1.0), inclusive.
EndCycle
=
MCross3
MCross Calculations