VTI Instruments EX1401, Руководство пользователя

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VTI Instruments Corp.
90 EX1401 Instrument Drivers
Analog Front End
While some parameters can be changed during data acquisition, most configuration options should
be performed prior to data acquisition to avoid data glitches. Most front end parameters can be
configured independently for each input channel. The front end configuration includes input range,
voltage/temperature input function, and cold junction settings. Note that not all of these properties
are supported by the EX1401.
M
EASUREMENT
I
NITIATION
After the user has completed configuring the instrument, the user can initiate the data acquisition
process by calling the
Initiate method in the Measurement interface. During measurement initiation,
the instrument starts to prepare for the actual data acquisition. If the ADC has not been synchronized,
the SYNC signal is sent and ADC then begins digitization. When the ADC’s reference oscillator
has been changed, the ADC sampling clock must be re-locked with the PLL. Filter settling also
occurs at this time. Once the filters have settled and the instrument is ready to acquire valid data,
the measurement moves to the
Wait for Start state. The source of the Start event is Immediate by
default. In this case, the measurement starts automatically. Otherwise, it must be started by an event
specified by the
Source property of the Start interface.
During this period, the digitized signal from the A/D converter is continuously filtered and discarded
until the filters have settled. Once settled, the filtered data samples are stored in the internal data
buffer.
M
EASUREMENT
L
OOP
Once the measurement begins, the state machine cycles through arming and triggering for the
number of times specified by
ArmCount and TriggerCount. The measurement stops when the
specified number of arm and trigger loops are completed, when it is aborted by an Abort command,
or when the FIFO buffer becomes full and the FIFO mode is set to Stop .
A
RMING
Arm is the gating condition to acquire data. In order to trigger data acquisition, the measurement
must be armed first. There are several ways to arm a measurement. The default condition is to arm
automatically (or
Immediate arming).
Self-arming
When the Immediate arm source is enabled, the EX1401 arms by itself.
Arming by User’s Command
The EX1401 arms by the SendSoftwareArm method when a Software arm source is enabled.
Arming at a Certain Time Interval
The EX1401 can be armed at a specific time interval using the ALARM0-1 arm sources. In addition
to enabling the alarm as an arm source, it must be configured and enabled using the
Alarm interface.
Arming by External Pulse
The EX1401 can receive an arm from the back panel trigger SMB connector by enabling the EXT
arm source.
Arming from DIO Lines
The EX1401 can receive an arm event from the digital I/O port by enabling the DIO arm sources.