Adc; Analog Input Data Acquisition Methods; Software-Timed Acquisitions; Hardware-Timed Acquisitions - National Instruments SC Express NI PXIe-4300 User Manual

ADC

The analog-to-digital converter (ADC) digitizes the AI signal by converting the analog
voltage into a digital number. The NI PXIe-4300 module has 8 ADCs. Multiplexers (mux) are
used to select filter settings and to select external or internal sources for calibration.
Settling time refers to the time it takes the PGIA to amplify the input signal to the desired
accuracy before it is sampled by the ADC.
The PGIA can amplify or attenuate an AI signal to ensure that you use the maximum
resolution of the ADC.

Analog Input Data Acquisition Methods

When performing analog input measurements, you can either perform software-timed or

hardware-timed acquisitions.

Software-Timed Acquisitions

With a software-timed acquisition, software controls the rate of the acquisition. Software
sends a separate command to the hardware to initiate each ADC conversion. In NI-DAQmx,
software-timed acquisitions are referred to as having on-demand timing. Software-timed
acquisitions are also referred to as immediate or static acquisitions and are typically used for
reading a single sample of data.
Hardware-Timed Acquisitions
With hardware-timed acquisitions, a digital hardware signal (AI Sample Clock) controls the
rate of the acquisition. This signal can be generated internally on your device or provided
externally.
Hardware-timed acquisitions have several advantages over software-timed acquisitions:
• The time between samples can be much shorter.
• The timing between samples is deterministic.
• Hardware-timed acquisitions can use hardware triggering.
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Chapter 2 Using the NI PXIe-4300
NI PXIe-4300 User Manual