DAQ VXI-SC-1102 Manuál s instrukcemi stáhnout pdf (Strana 42)

Chapter 4 516 Devices and DAQCard-500/700 Devices

DAQ Hardware Overview Guide 4-2 www.ni.com

516 Devices and DAQCard-500/700 Data Acquisition

The 516 devices and DAQCard-500/700 can perform single-channel

data acquisition and multiple-channel scanned data acquisition. For

single-channel data acquisition, you select a single analog input channel.

The device performs a single A/D conversion on that channel every sample

interval.

For multiple-channel scanned data acquisition, the device scans a sequence

of analog input channels. A sample interval indicates the time to elapse

between A/D conversions on each channel in the sequence. You need only

to select a single starting channel to select the sequence of channels to scan.

The device then scans the channels in consecutive order until channel 0 is

reached and the scan begins anew with the starting channel. If the starting

channel is channel 3, for example, the scan sequence is as follows:

channel 3, channel 2, channel 1, channel 0, channel 3, and so on

You can use both the single-channel and multiple-channel acquisitions with

the double-buffered mode. Double-buffered mode fills the user-specified

buffer continuously. You can call the NI-DAQ function

DAQ_DB_Transfer or the LabVIEW AI_Read.vi or

AI_Read_Buffer.vi to transfer old data into a second buffer before

overwriting the old data with new data. NI-DAQ transfers data out of one

half of the buffer while filling the other half with new data.

You cannot use SCXI with the 516 devices or the DAQCard-500.

Note

The DAQCard-700 uses half-FIFO mode by default when doing interrupt data

transfer operations for analog input with rates faster than 1.5 kS/s. You can select

between interrupt on every sample and interrupt on half-FIFO. When using external

conversions, you should select the mode appropriate for the acquisition rate. See

Set_DAQ_Device_Info function in the NI-DAQ Function Reference Online Help or the

Set_DAQ_Device_Info.vi in the LabVIEW DAQ Online Reference to set the interrupt

generation mode.

516 Devices and DAQCard-500/700 Data Acquisition

Timing

Timing for data acquisition can be performed by the onboard MSM82C54

Counter/Timer or externally. The MSM82C54 Counter/Timer has three

independent 16-bit counters/timers, which are assigned as follows:

• Counter 0 is a sample-interval counter for data acquisition that is

available if no data acquisition is in progress. Signals for Counter 0

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 150 151

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DAQ VXI-SC-1102 Manuál s instrukcemi Strana 42