Tektronix DPO2304SX, Печатная инструкция

Страница: 736 / 920

You create math waveforms to support the analysis of your channel and reference waveforms. By combining and transforming
source waveforms and other data into math waveforms, you can derive the data view that your application requires. Create math
waveforms that result from:
■ Mathematical operations on one or several waveforms: add, subtract, multiply, and divide.
■ Functional transformations of waveforms, such as integration, differentiation, and so on.
■ Spectral analysis of waveforms, such as testing impulse response.
You can create up to four math waveforms.
Measurement scalars can be used in math expressions. For example, you can measure the average of a waveform (using the
measurement capabilities of the instrument) and subtract it from the original waveform to define a new math waveform.
Measurements 1 through 8 are allowed in a math definition, but not measurement functions, such as rise (Ch1).
This instrument supports the following operations for math waveforms:
■ Vertical display scaling and positioning
■ Taking automatic measurements
■ Taking cursor measurements
■ Using histograms
■ User defined vertical units
In addition to the operations listed above, you can save math waveforms as reference waveforms.
You cannot use the following math waveforms for some operations:
■ Circular Math-on-Math. You cannot use circular definitions of math waveforms. For example, if you define Math2 = Ch1 -
Math1, and then define a second math waveform as Math3 = Ch2 + Math2, you cannot define a third math waveform as
Math1 = Math2 + Ch3. If you do, the Math1 definition is rejected with an error because a circular definition is not allowed.
■ Fast Acquisitions. Math is not allowed in Fast Acquisitions mode.
■ Roll Mode. Math is not allowed in roll mode until you push STOP.
■ Different Length Sources. If you use two waveforms (channel and reference waveforms) of different lengths, the length of
the math waveform will be the shorter of the two lengths.
What do you want to do next?
Learn about creating math waveforms.
Go to a step-by step procedure for using math waveforms.
Math waveform differentiation
The math capabilities of the instrument include waveform differentiation. This allows you to display a derivative math waveform
that indicates the instantaneous rate of change of the waveform acquired.
Derivative waveforms are used in the measurement of slew rate of amplifiers and in educational applications. You can create a
derivative math waveform and then use it as a source for another derivative waveform. The result is the second derivative of the
waveform that was first differentiated.
The math waveform, derived from the sampled waveform, is computed based on the following equation:
Yn = (X( n + 1) - Xn) 1/T
Where: X is the source waveform, Y is the derivative math waveform, and T is the time between samples.
Since the resultant math waveform is a derivative waveform (see the next figure), its vertical scale is in volts/second (its
horizontal scale is in seconds). The source signal is differentiated over its entire record length; therefore, the math waveform
record length equals that of the source waveform.
Oscilloscope reference
704 DPO70000SX, MSO/DPO70000DX, MSO/DPO70000C, DPO7000C, and MSO/DPO5000B Series