CLAD Data Acquisition & Instrument Control 5

Question 1

What is 'aliasing' in the context of data acquisition, and how is it prevented?

Accepted Answer

It is distortion caused by undersampling; prevented by sampling at least twice the highest signal frequency (Nyquist)

Answer

Aliasing occurs when the sample rate is less than twice the signal bandwidth, causing high-frequency components to appear as false lower frequencies; an anti-aliasing filter and sufficient sample rate prevent it.

Question 2

In NI-DAQmx, what is the function of DAQmx Export Signal?

Accepted Answer

It routes internal timing and trigger signals to physical output terminals for synchronization

Answer

DAQmx Export Signal routes internal signals (sample clock, start trigger, etc.) to physical terminals (PFI lines, RTSI) to synchronize multiple DAQ devices or tasks.

Question 3

Which VISA attribute would you read to determine how many bytes are waiting in the instrument's output buffer before calling VISA Read?

Accepted Answer

VI_ATTR_ASRL_AVAIL_NUM (or VISA Bytes at Serial Port / InstrumentBytesAvailable)

Answer

The bytes-available attribute (often accessed via VISA Bytes at Serial Port or the InstrumentBytesAvailable property) tells you how many bytes the instrument has queued so you can size your Read call.

Question 4

What is the significance of 'simultaneous sampling' in a multifunction DAQ device?

Accepted Answer

All channels are sampled at exactly the same instant, eliminating inter-channel phase skew

Answer

Simultaneous sampling uses a dedicated ADC per channel so that all channels capture their value at the same moment, which is critical for phase-sensitive measurements.

Question 5

In LabVIEW, how do you programmatically change the sample rate of an existing NI-DAQmx task before starting it?

Accepted Answer

Use DAQmx Timing (Sample Clock) or set the Rate property via DAQmx Channel/Timing property node

Answer

You can call DAQmx Timing again before Start Task or write the Rate property through a DAQmx Task property node to change the sample rate programmatically.

CLAD Practice Test

CLAD Practice Test

CLAD Data Acquisition & Instrument Control 5