Advantech iDAQ-817, User Manual

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iDAQ-817_821 User Manual 12
3.1 Function Details
The iDAQ system relys on the chassis module as a platform to bring all the signals
together in order to achieve functions including synchronization, data streaming, and
timing control. This chapter describes all the functions that the iDAQ system provides
and how they work.
3.2 Analog Input
Insert an iDAQ module supporting analog input to perform analog input measure -
ment. The following sections describe the analog input acquisition mechanisms. For
detailed specifications of the analog input functions, please refer to the document for
the individual iDAQ module.
3.2.1 Instant Analog Input Acquisition
With instant analog input acquisition, the software controls the sample timing. The
analog-to-digital converter (ADC) is continuously converting analog input signals by
its maximum allowable conversion rate. Each time the software sends a “read instant
analog input sample” command, the most recent conversion result is sampled as
shown in Figure 3.1.
Figure 3.1 Instant analog input acquisition.
3.2.2 Buffered Analog Input Acquisition
With buffered analog input acquisition, the ADC conversion rate and the duration of
the acquisition is controlled by hardware timing signals. All conversion results are
sampled and stored in the buffer memory before sending back to the host computer
as shown in Figure 3.2.