NI High-Speed Digitizers Help (NI-SCOPE)
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Reference levels are high, low, and mid range values that you set to take rise time,
duty cycle positive, and duty cycle negative measurements. Reference levels are
generally configured in terms of the percentage of the waveform you acquire. By default, the low value is
10% of the waveform, the mid level is 50%, and the high value is 90%.
Use the channel-based attributes to set the reference levels.
Refer to Attributes and Attribute Functions for an overview of attributes.
You can customize how NI-SCOPE configures the percentages used for the reference levels
with the Percentage Method attribute. This attribute uses any of the following
- Min Max—This method uses the measurement's voltage minimum and voltage maximum as 0% and 100%. These algorithms find the absolute minimum and maximum in the waveform, which is useful for sine waves and triangle waves where the histogram method does not work.
- Low High—This method uses the measurement's voltage low and voltage high as 0% and 100%. The voltage low is the voltage of the histogram bin with the most hits below 40% of the waveform's voltage peak-to-peak value. The voltage high is the voltage of the histogram bin with the most hits above 60% of the waveform's voltage peak-to-peak value. These measurements use the last-acquisition histogram method to find the most common high and low voltages, which is useful for ignoring the preshoot and overshoot on a square wave.
- Base Top—The voltage base and voltage top measurements correspond to 0% and 100% with this method. These measurements use the last-acquisition histogram method if the most common histogram bin contains a substantial number of the total points. Otherwise, it returns the absolute minimum and maximum values in the waveform. This is a useful default value for most waveform types.
You can also configure the reference levels in terms of voltage with
the Ref Level Units property or the