Acquiring and Displaying Waveforms
3–8
TDS 500D, TDS 600B, & TDS 700D User Manual
NOTE. The TDS 794D Oscilloscope requires a P6339A probe for AC, 10 M,
and bandwidth selections to appear in the menus.
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 active probes (probes with a level 2 or 3 interface do not
display W in the readout).
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 the oscilloscope,
when you restore 1 M coupling, return to a volts/division setting that was
reduced due to the 50 selection. 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 3–18.
To find a list of available probes, see Accessory Probes on page A–6.
To find a guide for selecting probes for a variety of applications, see Appen-
dix D: Probe Selection on page D–1.
Input Impedance
Considerations
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