National Instruments M Series User Manual page 155

Chapter 11 Triggering
In above-level analog triggering mode, shown in Figure 11-4, the trigger is generated when
the signal value is greater than Level.
Figure 11-4. Above-Level Analog Triggering Mode
Analog Comparison Event
Analog Edge Triggering with Hysteresis—Hysteresis adds a programmable voltage
•
region above or below the trigger level that an input signal must pass through before the
DAQ device recognizes a trigger condition, and is often used to reduce false triggering due
to noise or jitter in the signal.
– Analog Edge Trigger with Hysteresis (Rising Slope)—When using hysteresis with a
rising slope, you specify a trigger level and amount of hysteresis. The high threshold
is the trigger level; the low threshold is the trigger level minus the hysteresis.
For the trigger to assert, the signal must first be below the low threshold, then go above
the high threshold. The trigger stays asserted until the signal returns below the low
threshold. The output of the trigger detection circuitry is the internal Analog
Comparison Event signal, as shown in Figure 11-5.
Figure 11-5. Analog Edge Triggering with Hysteresis Rising Slope Example
Hysteresis
First signal must go
below low threshold.
Analog Comparison Event
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Level
Then signal must
go above high threshold before
Analog Comparison Event asserts.
High threshold
(Level)
Low threshold
(Level – Hysteresis)