CLAD Data Acquisition & Instrument Control 2 — Questions and Answers
Question 1: Which NI-DAQmx function is used to read analog input samples into a LabVIEW waveform data type?
- DAQmx Read (Analog Wfm 1Chan NSamp) (Correct answer)
- DAQmx Read (Analog 1D DBL NChan NSamp)
- DAQmx Read (Digital U32 1Chan NSamp)
- DAQmx Read (Counter U32 1Chan NSamp)
Correct answer: DAQmx Read (Analog Wfm 1Chan NSamp)
DAQmx Read (Analog Wfm 1Chan NSamp) returns a waveform that bundles the data array with timing (t0 and dt) for a single analog input channel.
Question 2: What is the purpose of the DAQmx Timing (Sample Clock) VI?
- It configures how and when samples are acquired or generated (Correct answer)
- It synchronizes two independent DAQ devices
- It sets the analog input voltage range
- It defines the FIFO buffer size for USB devices
Correct answer: It configures how and when samples are acquired or generated
DAQmx Timing (Sample Clock) sets the source, rate, active edge, and sample mode (finite vs. continuous) for a DAQmx task.
Question 3: In NI-DAQmx, what does setting the sample mode to 'Continuous Samples' require compared to 'Finite Samples'?
- A loop that calls DAQmx Read repeatedly to drain the buffer (Correct answer)
- A higher sample rate than 1 kHz
- External clocking from a function generator
- An additional DAQmx Stop Task call before reading
Correct answer: A loop that calls DAQmx Read repeatedly to drain the buffer
Continuous acquisition fills a circular buffer indefinitely, so the application must call DAQmx Read in a loop to consume samples and prevent buffer overflow.
Question 4: Which VISA function opens a communication session with an instrument and returns a session reference?
- VISA Open (Correct answer)
- VISA Write
- VISA Find Resource
- VISA Assert Trigger
Correct answer: VISA Open
VISA Open establishes a session with a specified resource name and returns a VISA session refnum used by all subsequent VISA calls.
Question 5: A strain gauge sensor outputs 0–10 mV. Which DAQ hardware feature should you enable to measure it accurately without amplifying the signal externally?
- Instrumentation amplifier / programmable gain (Correct answer)
- Simultaneous sampling
- Digital filtering
- Hardware-timed single-point mode
Correct answer: Instrumentation amplifier / programmable gain
An instrumentation amplifier with programmable gain amplifies the low-level millivolt signal to match the ADC's full input range, improving resolution and SNR.
Question 6: What is the maximum safe common-mode voltage concern when using a differential analog input measurement?
- The common-mode voltage must remain within the device's common-mode input range (Correct answer)
- The common-mode voltage must equal the signal amplitude
- The differential voltage must not exceed 5 V
- The common-mode voltage must be tied to AIGND
Correct answer: The common-mode voltage must remain within the device's common-mode input range
Even in differential mode the average of the two input voltages must stay within the device's specified common-mode input range to avoid measurement errors or damage.
Question 7: Which terminal mode is most appropriate when measuring a floating signal source (e.g., a battery) with an NI DAQ device?
- Differential (DIFF) (Correct answer)
- Referenced Single-Ended (RSE)
- Non-Referenced Single-Ended (NRSE)
- Ground-referenced single-ended
Correct answer: Differential (DIFF)
Differential mode with bias resistors to ground is the recommended configuration for floating sources because it rejects noise and provides a defined path for bias currents.
CLAD Data Acquisition & Instrument Control 2
Which NI-DAQmx function is used to read analog input samples into a LabVIEW waveform data type?