Sync; Start; Arm; Trigger - VTI Instruments EX1401 User Manual

VTI Instruments Corp.

Sync

Sync is an event that synchronizes the entire system. The Sync interface is used to configure the
synchronization between cards. All cards are simultaneously started by the SYNC signal and then
they synchronize the state machine transition with each other through a coordination signal. The
Line and CoordinationLine properties define which PXI trigger lines and/or Alarms to use to send
these signals.

Start

Once the measurement is initiated by the Initiate command, the instrument completes all preparation
and becomes ready to start taking data immediately. Then the state machine moves to the Wait for
Start state. The Start interface provides methods and properties to advance to the next state. The
amount of time it takes to reach to Wait for Start after measurement Initiate command varies
depending on the measurement configuration. For example, it takes longer when the measurement
sample rate (or measurement span) is low because the filter settling time is longer. The Start
interface is useful when the user wants to have the instrument complete all the preparation and hold
in that state, so that it can start taking data immediately without any delay.

Arm

The instruments must be armed before triggering data acquisition. The Arm interface is used to
configure this arming condition. The Sources property in the Arm interface defines the arming event
sources. The default arming source is Immediate, which means automatic arming. The
SourceOperator property allows the user to define an arming condition by logically combining
multiple arming sources. The Delay property defines amount of time the instrument waits before
moving out from Wait for Arm state after the defined arming conditions are met. The ArmCount
property defines how many times the measurement repeats arming and triggering before it
completes. The default is once. Setting ArmCount to 0 forces the measurement to repeat arm and
trigger indefinitely until it is aborted by Abort command.

Trigger

Data acquisition begins when a triggering condition is met. The triggering condition is configured
using the Trigger interface. Similar to Arm interface, the Sources property in the Trigger interface
define the triggering event sources. Trigger sources can be logically combined using
SourceOperator in the Trigger interface. The Delay property defines the amount of time between
the trigger event and the beginning of the data acquisition. The Delay value can be negative
indicating pre-trigger data acquisition. In this case, the acquired data block starts earlier than the
trigger event. This is achieved by buffering the data in the instrument's FIFO prior to the trigger
event. For more information, see the Data Acquisition section.
74 EX1401 Instrument Drivers