Pulse Width A/B; Duty Factor A/B; Measurement Errors; Hysteresis - Fluke PM6690 Operator's Manual

ually adjust the relative trigger levels (in %)
when Auto Trigger is active. Both input
channel menus are used for entering the lev-
els, but only one channel is the active signal
input.
See the paragraph on Auto Trigger (page 4-16)
to find out how overshoot or ringing may af-
fect your measurement.

Pulse Width A/B

The function menu designation is Pulse. Ei-
ther input A or input B can be used for mea-
suring, and both positive and negative pulse
width can be selected.
–
Positive pulse width means the time be-
tween a rising edge and the next falling
edge.
–
Negative pulse width means the time be-
tween a falling edge and the next rising
edge.
The selected trigger slope is the start trigger
slope. The counter automatically selects the
inverse polarity as stop slope.

Duty Factor A/B

The function menu designation is Duty. Ei-
ther input A or input B can be used for mea-
suring, and both positive and negative duty
factor can be selected. See the preceding para-
graph for a definition of positive and negative
in this context.
Duty factor (or duty cycle) is the ratio be-
tween pulse width and period time. The coun-
ter determines this ratio by first making a
pulse width measurement, then a period mea-
surement, and calculates the duty factor as:
Pulse width
=
Duty factor
Period
+
The total measurement time will
be doubled compared to a single
measurement, because "Duty"
requires 2 measurement steps.
Measurement
Errors

Hysteresis

The trigger hysteresis, among other things,
causes measuring errors, see Figure 4-16. Ac-
tual triggering does not occur when the input
signal crosses the trigger level at 50 percent of
the amplitude, but when the input signal has
crossed the entire hysteresis band.
S t a r t
C h a n n e l A
S t o p
M e a s u r e d T i m e I n t e r v a l
C h a n n e l B
Fig. 4-16 Trigger hysteresis
The hysteresis band is about 20 mV with at-
tenuation 1x, and 200 mV with attenuation
10x.
To keep this hysteresis trigger error low, the
attenuator setting should be 1x when possible.
Use the 10x position only when input signals
have excessively large amplitudes, or when
you need to set trigger levels higher than 5 V.
Pulse Width A/B 4-15
Measuring Functions
T r i g g e r l e v e l