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Acquiring Waveforms

3-18

CSA7000B Series & TDS7000B Series Instruments User Manual

H Signals with multiple or unstable signal periods

H Signals with too low amplitude

H No recognizable trigger signal

H Signals with a frequency >50 Hz

H Signals with a frequency above the bandwidth of the instrument

H Signals with high offset and low peak-to-peak variations

Vertical Acquisition Window Considerations. You can set the vertical size,

position, and offset of each channel independently of other channels. Vertical

scale and offset specify the vertical acquisition window for each channel. Parts of

the signal amplitude that fall within the vertical window are acquired; parts

outside (if any) are not.

The offset control subtracts a constant DC level from the input signal before the

vertical scale factor is applied, and the vertical position control adds a constant

number of divisions of signal after the scale factor is applied to the resulting

difference.

The vertical scale and position controls have the following effects on the vertical

acquisition window and the displayed waveform:

H The vertical volts per division that you set determines the vertical size of the

acquisition window, allowing you to scale it to contain all of a waveform

amplitude or only part. Figure 3--2 on page 3--19 shows two vertical

acquisition windows that contain the entire waveform, but only one window

contains the entire waveform in the graticule on screen.

NOTE. Amplitude-related automatic measurements (for example, peak-to-peak

and RMS) will be accurate for vertical windows like those shown in Figure 3--2a

and b because neither waveform is clipped (that is, both waveforms are

acquired). But if signal amplitude were to extend outside the vertical acquisition

window, the data acquired is clipped. Clipped data causes inaccurate results if

used in amplitude-related automatic measurements. Clipping also causes

inaccurate amplitude values in waveforms that are stored or exported for use in

other programs.

If the scale of a math waveform is changed so that the math waveform is clipped,

it will not affect amplitude measurements on that math waveform.

H The vertical position adjusts the acquisition, and therefore the display, of the

acquired waveform relative to the vertical acquisition window. Figure 3--2b

shows how vertical position moves the acquired waveform vertically in the

acquisition window to place the acquired waveform in the graticule display.

Tektronix CSA7404B User Manual

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