5-21
Making Measurements
Differentiate
Differentiated/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. Since differentiation i s very sensitive to noise, it is
helpful to set acquisition mode to Ave raging in the Acquire menu.
d/dt plo ts the de ri vat iv e o f th e s el ec ted so ur ce u si ng th e "a ve ra ge slo pe es tim at e
at 4 points" formula. Equation is as follows:
Where
d = differential waveform
y = channel 1, 2, or function 1 + 2, 1 – 2, and 1 * 2 data points
i = data point index
∆t = point-to-point time difference
In Delayed sweep horizontal mode, the d/dt function does not display in the
delayed portion of the display.
•Press the Math key, pre ss t he d/dt softkey, then press the Settings softkey
if you want to change the source, scaling, or offset for the differentiate
function.
Source selects the source for d/dt. The source can be any analog channel, or
math functions 1 + 2, 1 – 2, and 1 * 2.
Scale allows you to 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. P ress the Sca le softkey, then turn the
Entry knob to rescale d/dt.
Offset allows you to 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 i s r ep r e s en t e d by t h e ce n t e r g r a t ic u l e of t h e d is p l a y. Pr e s s th e Offset s o f tk e y,
then turn the Entry knob to change the offset for d/dt.
A scale unit of U (undefined) will be displayed fo r scale and off set when 1-2 or
1+2 is the selected source if channel 1 and channel 2 are set to dissimilar units
in the channel Probe Units softkey.
di = yi+2 + 2yi+1 – 2yi-1 – yi-2
8∆t