Macro: ZeroMode=Peak

Zero Peak (shortened to Zero Pk on the toggle buttons) determines the DC value of the waveform by scanning for the maximum positive and negative peaks in the 1024 samples of the trace, then subtracting their midpoint from each waveform sample. As with Zero Average, this process is repeated on every trace as long as Zero Pk is active.

The purpose of Zero Peak, like the preceding Zero Average, is to remove the constant (DC) value from a waveform to allow you to view only the varying (AC) portion. Unlike Zero Cursor, these do affect the cursor readouts and .TXT file output, though they don't change the data for other file formats. (You can always apply any Zero function later when you open the file.)

If a signal is a known symmetrical waveform (like a sine wave, triangle, ramp, square, etc.) and especially if its frequency is low relative to the sample rate (so that you only see a few cycles per trace), this Zero Peak is probably better than Zero Average. The reason is that Zero Average is only correct if there are an integer number of full cycles being averaged.

To appreciate this, consider that all the integer cycles together average to zero, so the overall average value will be simply the average of the odd half-cycle... which will typically not average to zero and will thus give a misleading report of where the zero position is.

Any waveform that has a different number of positive and negative half-cycles in the 1024 trace samples will exhibit such an error. The error becomes smaller as the frequency increases, since the odd half-cycle is a smaller percentage of the total.

The Zero Peak mode avoids that problem as long as the sample set includes at least one positive and one negative peak.

What if the waveform is not symmetrical? Consider a waveform consisting of large, narrow pulses at a slow rate: The Average value will decrease as the frequency decreases, but the Peak will remain the same.

Macro Notes:

ZeroMode=Peak sets Zero Peak mode. Note that attempts to use this command in Spectrum or Histogram modes will result in "Control disabled. Aborting macro."

See also Zero (Cursor, Average, or Peak)

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