Measurements and Math Functions 5
InfiniiVision 7000B Series Oscilloscopes User’s Guide 191
Differentiate
d/dt (differentiate) calculates the discrete time derivative of the selected
source. You can use differentiate to measure the instantaneous slope of a
waveform. For example, the slew rate of an operational amplifier may be
measured using the differentiate function.
Because differentiation is very sensitive to noise, it is helpful to set
acquisition mode to Averaging in the Acquire Menu.
d/dt plots the derivative of the selected source using the “average slope
estimate at 4 points” formula. The equation is:
Where
d = differential waveform
y = channel 1, 2, 3, or 4, or g(t) (internal arithmetic operation) data
points
i = data point index
t = point- to- point time difference
1 Press the [Math] key, press the Function softkey and select f(t), press the
Operator softkey and select d/dt. Press the Source, Scale, or Offset sofkeys
if you want to change the source, scaling, or offset for the differentiate
function.
• Source — selects the source for d/dt. (See page 184 for information
about using g(t) as the source.)
• Scale — lets you set your own vertical scale factors for d/dt expressed
in units/second/division, where units can be V (Volts), A (Amps), or
W (Watts). Units are set in the channel Probe Menu. Press the Scale
softkey, then turn the Entry knob to rescale d/dt.
• Offset —lets you set your own offset for the dV/dt math function. The
offset value is in units/second where units can be V (Volts), A
(Amps), or W (Watts) and is represented by the center horizontal
grid line of the display. Press the Offset softkey, then turn the Entry
knob to change the offset for d/dt.
d
i
= y
i+4
+ 2y
i+2
– 2y
i- 2
– y
i- 4
8t
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