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Data Zero - Manual (Zero Mn)

Controls: Zero Dialog >> Manual
Macro: ZeroData=Man

Data Zero Manual (shortened to Zero Mn on the toolbar button) allows a constant value to be subtracted from the raw data of each channel. This changes the vertical position of the waveform, or the horizontal position of a Histogram derived from it. For a PSTH, both peak position and shape can be affected.

Beneath the Manual button are Adjust controls to set specific zero levels for each channel, with Units in percent or volts (or User Units). Null buttons automatically set the level of any channel to the current average input. These values are applied to the data only when the Data Zero Manual button is active.

Unlike Data Zero Average and Peak, the values you set remain until specifically changed... there is no ongoing automatic adjustment when the waveform changes.

Like Data Zero Average and Peak, one possible use of Manual is to remove the constant (DC) value from a waveform to allow you to view only the varying (AC) portion.

A more typical use for Data Zero Manual is with DC-coupled measurement and/or output systems. A system that monitors a DC (or very slow) signal must be able to adjust the true zero position to compensate for sensor and circuit changes due to component tolerance, aging, or ambient temperature drift.

For cards with the Simple Unipolar DC Output modification, Data Zero Manual can be used to compensate for the card's internal reference voltage, usually in the +2 volt range. Follow the instructions under the Output Calibration section of that topic. (Note that to compensate for a positive voltage offset, you must enter the negative of that value.

Always set output volume or input sensitivity levels before setting Data Zero Manual.

Note that Data Zero Manual is independent of the polarity of either Full-Scale Range or External Gain settings.

Unlike Screen Zero, Data Zero modes do affect the cursor readouts, Trigger operation, and file output. For normal waveforms and for Linear or Exponential Waveform Averages you can change the settings after the data is captured, but Histogram and PSTH averages can't be modified after the fact.

Note that Data Zero is applied to the raw data before the Trigger Level threshold and Hysteresis operations, so you may need to readjust those after a change in the Data Zero Manual value for the trigger channel.

When a .DQA file is saved with Data Zero Manual active, the zero settings for each channel are saved with the file. For files other than Histogram and PSTH, they can be adjusted when the file is later opened. This can allow for after-the-fact correction of sensor or circuit drift.

With a drifting system, if the file covers a very long time span (perhaps via Decimation) you may want to adjust for different drift amounts at various points in the file analysis. You can make this easier by applying a known zero condition to the sensor at known time points while recording.

When Data Zero Manual is active, the main toolbar Zero button changes to 'Zero Mn'. Please note that the toolbar button state pertains to the Screen Zero option, but the button label indicates whether any Data Zero state is active, regardless of the toolbar button in/out state.

Macro Notes:

ZeroData=Man or ZeroData=3 sets Data Zero Manual mode. The numeric value can be supplied by a variable or expression.

ZeroData=0 cancels all Data Zero modes.

Note that attempts to use the ZeroData command when it is disabled in Spectrum, Spectrogram, or Pitch Track modes will result in "Control disabled. Aborting macro." You can check if this control is enabled via an E.IF.ZeroData= control enable IF test.

See also Zero (Screen and Data)


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