CTC Data Acquisition and Validation 2 — Questions and Answers
Question 1: Which type of transducer converts mechanical strain into an electrical signal for data acquisition?
- Thermocouple
- Strain gauge (Correct answer)
- Pitot tube
- Hall effect sensor
Correct answer: Strain gauge
A strain gauge changes electrical resistance proportional to the mechanical deformation applied to it.
Question 2: What is the primary purpose of anti-aliasing filters in a data acquisition system?
- Amplify weak signals before digitization
- Remove frequencies above the Nyquist limit before sampling (Correct answer)
- Synchronize multiple data channels
- Convert analog signals to digital format
Correct answer: Remove frequencies above the Nyquist limit before sampling
Anti-aliasing filters attenuate signal components above half the sample rate to prevent aliasing artifacts in the digitized data.
Question 3: A PCM (Pulse Code Modulation) stream is used in flight test telemetry primarily to:
- Encrypt sensitive performance data
- Multiplex multiple analog channels into a single digital bit stream (Correct answer)
- Increase signal voltage for long-range transmission
- Reduce ground station antenna size
Correct answer: Multiplex multiple analog channels into a single digital bit stream
PCM time-division multiplexing encodes multiple channels sequentially into one digital stream for efficient telemetry transmission.
Question 4: Which validation technique compares measured data against a known reference standard to confirm sensor accuracy?
- Cross-correlation analysis
- Calibration check (Correct answer)
- Signal conditioning
- Zero-offset correction
Correct answer: Calibration check
Calibration checks verify that sensor output matches a known reference standard within specified accuracy tolerances.
Question 5: In flight test data acquisition, 'frame synchronization' refers to:
- Aligning video footage with instrument data
- Identifying the correct starting point of a PCM frame in the bit stream (Correct answer)
- Synchronizing clocks between aircraft and ground station
- Matching GPS coordinates with radar tracks
Correct answer: Identifying the correct starting point of a PCM frame in the bit stream
Frame synchronization detects the unique sync word pattern that marks the beginning of each PCM data frame.
Question 6: What does 'measurement uncertainty' quantify in a test data context?
- The probability that instrumentation will fail during a test
- The range within which the true value of a measurement is expected to lie (Correct answer)
- The maximum data dropout rate allowed on a telemetry link
- The time delay between sensor input and recorded output
Correct answer: The range within which the true value of a measurement is expected to lie
Measurement uncertainty expresses the statistical range encompassing the true value of a measured quantity at a stated confidence level.
Question 7: A data acquisition system records a parameter at 200 samples per second. What is the highest frequency that can be accurately captured without aliasing?
- 200 Hz
- 100 Hz (Correct answer)
- 400 Hz
- 50 Hz
Correct answer: 100 Hz
By the Nyquist theorem, the maximum unambiguous frequency is half the sample rate, so 200 sps captures up to 100 Hz accurately.
CTC Data Acquisition and Validation 2
Which type of transducer converts mechanical strain into an electrical signal for data acquisition?