5-41
Making Measurements
Making time measurements automatically
Fall Time
The f all tim e of a si gn al i s th e ti me d iff er enc e be twe en t he c ro ssi ng o f th e up per
threshold and the crossing of the lower threshold for a negative-going edge. The
X cursor shows the edge being measured. For maximum measurement
accuracy, set the sweep speed as fast as possible while leaving the complete
falling edge of the waveform on the display. The Y cursors show the 10% and
90% points.
Rise Time
The rise time of a signal is the time difference between the crossing of the lower
threshold and the crossing of the upper threshold for a positive-going edge. The
X cursor shows the edge being measured. For maximum measurement
accuracy, set the sweep speed as fast as possible while leaving the complete
rising edge of the waveform on the display. The Y cursors show the 10% and
90% points.
+ Width
+ Width is the time from the 50% threshold of the rising edge to the 50%
thr e s h ol d o f th e n ex t f a ll i n g ed g e . Th e X c ur s o r s s h o w t h e p ul s e b ei n g m ea s u r ed .
The Y cursor shows the 50% point.
– Width
– Width is the time from the 50% threshold of the falling edge to the 50%
thr e sh ol d of t he n e xt ri s in g ed g e. T he X cu r so r s s h ow t he p ul s e b e in g me a su r ed .
The Y cursor shows the 50% point.
X at Max
X at Max is the X axis value (usually time) at the first displayed occurr ence of
the wavefo rm Maxim um, star ting fro m the left -side of the displ ay. For per iodic
signals, the position of the maximum may vary throughout the waveform. The
X cursor shows where the current X at Max val ue is being measured.
To measure the peak of an FFT:
aSelect FFT as the math function in the Math menu.
b Choose Math as the source in the Quick Meas menu.
c Choose Maximum and X at Max measurements.
Maximum units are in dB and X at Max units are in Hertz for FFT.