Acquiring and Displaying Waveforms
3–24 TDS 684A, TDS 744A, & TDS 784A User Manual
NOTE. TDS 700A models only: Selecting Hi Res mode in the Acquire menu will
automatically reduce the record length to a value that prevents overflow of
acquisition memory. Because Hi Res mode uses twice the acquisition memory
that the other acquisition modes use, allowing selection of the longer horizontal
record lengths with Hi Res mode would cause the oscilloscope to run out of
memory.
TDS 700A models only: To limit the oscilloscope to real-time sampling or let it
choose between real-time or equivalent-time sampling:
Press SHIFT ACQUIRE MENU ➞ Repetitive Signal (main) ➞
ON or OFF (side).
ON (Enable ET) uses both the real-time and the equivalent-time sampling
as appropriate.
OFF (Real Time Only) limits the oscilloscope to real-time sampling. If the
oscilloscope cannot accurately get enough samples for a complete waveform,
it will interpolate.
The sampling speeds and the number of channels you choose affect the mode the
oscilloscope uses to sample waveforms. If the time base is set slow enough, the
oscilloscope always uses real-time sampling; if set fast enough, it always uses
equivalent-time sampling or interpolation. For speeds in between, the oscillo-
scope creates waveform records differently depending on the number of input
channels turned on. See Table 3–4 for the TDS 744A or Table 3–5 for the
TDS 784A.
Table 3–4: TDS 744A Sampling Mode Selection (When Fit to Screen is Off)
Time Base1One Channel Two Channels Three or Four Channels
u50 ns Real-time Real-time Real-time
50 ns Real-time Real-time Equiv.-time or interpolate
25 ns Real-time Equiv.-time or interpolate Equiv.-time or interpolate
t25 ns Equiv.-time or Interpolate Equiv.-time or Interpolate Equiv.-time or Interpolate
1“u” means “slower than”; “t” means “faster than.”
Selecting RepetitiveSampling