Time Measurements
Introduction
Measuring the time between a start and a stop
condition on two separate channels is the basis
for all time interval measurements. In addition
to the fundamental function Time Interval A
to B, the counters also offer other channel
combinations and derived functions like
Pulse Width and Rise/Fall Time.
Triggering
The set trigger level and trigger slope define
the start and stop triggering.
If Auto is on, the counter sets the trigger level
to 50% of the signal amplitude, which is ideal
for most time measurements.
n
Summary of Conditions for
Reliable Time Measurements:
–
Auto Once, that is freezing the levels de-
termined by Auto Trig, is normally the
best choice when making time measure
-
ments. Choose Man Trig and press
AUTOSET once.
–
DC coupling.
–
1x Attenuation. Selected automatically if
AUTOSET was used before to set the
trigger levels.
–
High signal level.
–
Steep signal edges.
Even though the input amplifiers have high
sensitivity, the hysteresis band has a finite
value that would introduce a small timing er
-
ror for signals with different rise and fall
times, for instance asymmetrical pulse signals
like the one in Fig. 4-14. This timing error is
taken care of by using hysteresis compensa
-
Introduction 4-13
Measuring Functions
0 V
J
T r i g g e r p o i n t s
R e s e t p o i n t s
H y s t e r e s i s b a n d ( S E N S )
T r i g g e r l e v e l o f f s e t
Fig. 4-14 Time is measured be
-
tween the trigger point and the reset
point. Accurate measurements are
possible only if the hysteresis band is
narrow.
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