User's Manual

Chapter 2 Hardware Overview
© National Instruments Corporation 2-9 NI 5911 User Manual
Figure 2-3.
Trigger Sources
Analog Trigger Circuit
The analog trigger on the NI 5911 operates by comparing the current
analog input to an onboard threshold voltage. This threshold voltage, the
trigger value, can be set within the current input range in 170 steps. This
means that for a ±10 V input range, the trigger can be set in increments of
20 V/170 = 118 mV. There may also be a hysteresis value associated with
the trigger that can be set in the same size increments. The hysteresis value
creates a trigger window the signal must pass through before the trigger is
accepted. You can generate triggers on a rising or falling edge condition as
illustrated in the following figures. The four different modes of operation
for the analog trigger are shown in Figures 2-4 to 2-7.
Gain
Analog
Input
High
Level
Low
Level
+
–
COMP
COMP
Analog
Trigger
Circuit
ATC_OUT
a. Analog Trigger Circuit
Trigger
Software
ATC_OUT
RTSI <0..6>
PFI1, PFI2
7
2
Arm
b. Trigger and Arm Sources