Acquiring and Displaying Waveforms
TDS 684A, TDS 744A, & TDS 784A User Manual 3–5
To ensure proper coupling of your input signals to the oscilloscope, consider the
following points when you use 50 W coupling with any channel:
The oscilloscope does not accurately display frequencies under 200 kHz if
AC coupling is selected.
The oscilloscope reduces the maximum volts/division setting for the channel
to 1 V from 10 V (to 10 V from 100 V with a X10 probe attached), since
input amplitudes appropriate for the higher settings would overload the
50 W input.
The oscilloscope switches to 50 W and disables AC coupling (and switches
coupling to DC if AC is selected) if you connect an active probe, such as the
P6245 probe. Such probes also reduce the maximum volts/div to 10 V as just
described. This behavior results in 50 W, nonAC coupling, which is
appropriate for such probes.
NOTE. If you remove an active probe, the oscilloscope does not switch coupling
back to 1 M (nor AC if it was previously selected). Nor does it restore a
volts/division setting limited due to 50  selection when you restore 1 M
coupling. In general, you must set channel scale, input coupling, and impedance
appropriate for your input coupling scheme. Be sure to switch to 1 M for any
input signal not from a 50 system.
To find a procedure for changing the coupling and input impedance settings, see
To Change Vertical Parameters on page 3–12.
To find a list of available probes, see Accessory Probes, on page A–4.
To find a guide for selecting probes for a variety of applications, see Appen-
dix E: Probe Selection, on page E-1.
Setting up Automatically: Autoset and Reset
The TDS Oscilloscope can automatically obtain and display a stable waveform
of usable size. It can also be reset to its factory default settings. This subsection
describes how to execute Autoset and reset, and lists the default settings in effect
after an Autoset.
Autoset automatically sets up the front panel controls based on the characteristics
of the input signal. It is much faster and easier than a manual control-by-control
setup. Autoset adjusts controls in these categories: Acquisition, Display,
Horizontal, Trigger, and Vertical.

Input Impedance

Considerations

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