VTI Instruments EMX-4016B, Руководство пользователя

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APPENDIX B 39
Start
Once the measurement is initiated by the Initiate command, instrument completes all preparation
and becomes ready to start taking data immediately and 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 instrument complete all the preparation and hold in
that state, so that it can start taking data immediately without wasting time.
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 repeat 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 instruments FIFO priory to the trigger
event. For more information, see FIFO section.
Trigger Offset
(always zero if
TTI is used)
Trigger Delay > 0
Trigger
First data point
Sample
Interval
InitialX > 0
Waveform
Record
Trigger Holdoff
Trigger
Pre-Trigger
Samples
Re-arm Time
Figure 4-2: Positive Trigger Delay