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Appendix B: Algorithms
TDS 620A, 640A, & 644A User Manual
End — is the location of the end of the measurement zone (X-value). It is
( – 1.0) samples unless you are making a gated measurement.
When you use gated measurements, it is the location of the right vertical
cursor.
Hysteresis — The hysteresis band is 10% of the waveform amplitude. It is
used in , , and 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 point
before the measurement system is armed and ready for a positive crossing.
Similarly, after a positive 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 digitizing
oscilloscope to ignore minor fluctuations in the signal.
MCross Calculations
MCross1, MCross2, and MCross3 — refer to the first, second, and third
cross times, respectively. See Figure A-1.
The polarity of the crossings does not matter for these variables, but the
crossings alternate in polarity; that is, could be a positive or negative
crossing, but if is a positive crossing, will be a negative
crossing.
The oscilloscope calculates these values as follows:
1. Find the first in the waveform record or the gated region.
This is .
2. Continuing from , find the next in the waveform
record (or the gated region) of the opposite polarity of . This is
.
3. Continuing from , find the next in the waveform
record (or the gated region) of the same polarity as . This is
.
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 ( – 1.0), inclusive.
=
EndCycle — is the ending time for cycle measurements. It is a floating-point
number with values between 0.0 and ( – 1.0), inclusive.
=