Chapter 11
Triggering
X Series User Manual
11-6
ni.com
1.
Analog Edge Triggering with Hysteresis
—Hysteresis adds a
programmable voltage region above or below the trigger level that an
inp
u
t signal m
u
st pass thro
u
gh before the DAQ device recognizes a
trigger condition, and is often
u
sed to red
u
ce false triggering d
u
e to
noise or jitter in the signal.
–
Analog Edge Trigger with Hysteresis (Rising Slope)—When
u
sing hysteresis with a rising slope, yo
u
specify a trigger level and
amo
u
nt of hysteresis. The high threshold is the trigger level; the
low threshold is the trigger level min
u
s the hysteresis.
For the trigger to assert, the signal m
u
st first be below the low
threshold, then go above the high threshold. The trigger stays
asserted
u
ntil the signal ret
u
rns below the low threshold. The
o
u
tp
u
t of the trigger detection circ
u
itry is the internal Analog
Comparison Event signal, as shown in Fig
u
re 11-6.
Figure 11-6.
Analog Edge Triggering with Hysteresis Rising Slope Example
–
Analog Edge Trigger with Hysteresis (Falling Slope)—When
u
sing hysteresis with a falling slope, yo
u
specify a trigger level
and amo
u
nt of hysteresis. The low threshold is the trigger level;
the high threshold is the trigger level pl
u
s the hysteresis.
For the trigger to assert, the signal m
u
st first be above the high
threshold, then go below the low threshold. The trigger stays
asserted
u
ntil the signal ret
u
rns above the high threshold. The
o
u
tp
u
t of the trigger detection circ
u
itry is the internal Analog
Comparison Event signal, as shown in Fig
u
re 11-7.
An
a
log Comp
a
ri
s
on Event
Hy
s
tere
s
i
s
High thre
s
hold
(Level)
Low thre
s
hold
(Level – Hy
s
tere
s
i
s
)
Fir
s
t
s
ign
a
l m
us
t go
b
elow low thre
s
hold.
Then
s
ign
a
l m
us
t
go
ab
ove high thre
s
hold
b
efore
An
a
log Comp
a
ri
s
on Event
ass
ert
s
.
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