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Appendix B: Algorithms
TDS 620A, 640A & 644A User Manual
AĆ9
End Ċ is the location of the end of the measurement zone (XĆvalue). It is
(RecordLength - 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 Ċ The hysteresis band is 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 digitizing oscilloscope to ignore minor fluctuations in the signal.
MCross Calculations
MCross1, MCross2, and MCross3 Ċ refer to the first, second, and third
MidRef cross times, respectively. See Figure AĆ1.
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 negaĆ
tive crossing, but if MCross1 is a positive crossing, MCross2 will be a negative
crossing.
The oscilloscope 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 Ċ is the polarity of first crossing (no default). It can be
rising or falling.
StartCycle Ċ is the starting time for cycle measurements. It is a floatingĆ
point number with values between 0.0 and (RecordLength - 1.0), inclusive.
StartCycle = MCross1
EndCycle Ċ is the ending time for cycle measurements. It is a floatingĆ
point number with values between 0.0 and (RecordLength - 1.0), inclusive.
EndCycle = MCross3