DAQ VXI-SC-1102 Manual de Instruções descarregar pdf (Página 29)

Chapter 2 Lab and 1200 Devices

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

Lab and 1200 Devices Data Acquisition

The Lab and 1200 devices can perform single-channel data acquisition

and multiple-channel scanned data acquisition. For single-channel data

acquisition, you select a single analog input channel and gain setting. The

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

interval.

For multiple-channel scanned data acquisition, the devices scan a sequence

of analog input channels. A single gain setting is used for all channels

scanned. 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 then the scan begins anew with the starting channel. For

example, if the starting channel is channel 3, the scan sequence is as

follows:

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

The Lab and 1200 devices support interval scanning. A scan interval is the

time that elapses between two channel-scanning cycles.

You can combine both the single-channel and multiple-channel

acquisitions with any of the following additional modes:

• Posttrigger mode

• Pretrigger mode

• Double-buffered mode

• SCXI mode (except the DAQPad-1200)

Posttrigger mode collects a specified number of samples after the device

receives a trigger. You can initiate posttrigger acquisition through software

or when a pulse edge is applied to the EXTTRIG input. After the

user-specified buffer has been filled, the data acquisition stops.

Pretrigger mode collects data both before and after the device receives a

trigger. You can initiate data acquisition through software. The device

collects samples and fills the user-specified buffer without stopping or

counting samples until the device receives a pulse at the EXTTRIG input.

The device then collects a specified number of samples and stops the

acquisition. The buffer is treated as a circular buffer—when the entire

buffer has been written to, data is stored at the beginning again, overwriting

the old data. When data acquisition stops, the buffer has samples from

before and after the stop trigger occurred. The number of samples saved

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DAQ VXI-SC-1102 Manual de Instruções Página 29