CTC Data Acquisition and Validation 3 â Questions and Answers
Question 1: Which error source causes all channels in a multiplexed DAS to have a slight timing difference between their samples?
- Quantization noise
- Aperture jitter
- Skew error (Correct answer)
- Common-mode noise
Correct answer: Skew error
Skew error arises because time-division multiplexing samples channels sequentially rather than simultaneously, introducing a time offset between channels.
Question 2: In telemetry data validation, a 'gap' in the data record most commonly indicates:
- A sensor calibration failure
- A loss of RF link or recorder dropout during acquisition (Correct answer)
- Incorrect engineering unit conversion
- A frame sync failure caused by incorrect bit rate
Correct answer: A loss of RF link or recorder dropout during acquisition
Data gaps typically result from a temporary RF link outage or recording medium dropout causing missing frames in the time history.
Question 3: The term 'bit error rate' (BER) in a telemetry system measures:
- The number of analog channels sampled per second
- The ratio of incorrectly received bits to total transmitted bits (Correct answer)
- The frame synchronization acquisition time
- The signal-to-noise ratio at the receiver antenna
Correct answer: The ratio of incorrectly received bits to total transmitted bits
BER is the fraction of bits received in error compared to the total number of bits sent, indicating link quality.
Question 4: What is the function of a signal conditioner in a data acquisition chain?
- Convert digital data back to analog for display
- Amplify, filter, and convert raw sensor output to a range suitable for the ADC (Correct answer)
- Store raw data on an onboard recorder
- Encode data into a PCM format
Correct answer: Amplify, filter, and convert raw sensor output to a range suitable for the ADC
Signal conditioning adapts raw transducer outputsâthrough amplification, filtering, and excitationâto match the ADC's input requirements.
Question 5: A zero-order hold (ZOH) artifact in sampled data appears as:
- Random spikes at the Nyquist frequency
- A staircase-like distortion of the reconstructed waveform (Correct answer)
- Phase reversal above the cutoff frequency
- Loss of DC offset in AC-coupled channels
Correct answer: A staircase-like distortion of the reconstructed waveform
ZOH reconstruction holds each sample value constant until the next sample, producing a staircase approximation of the original continuous signal.
Question 6: During post-flight data review, a parameter shows a constant value for an extended period that is physically implausible. This most likely indicates:
- Sensor saturation or a 'stuck' reading from sensor or recorder failure (Correct answer)
- Normal steady-state flight condition
- Correct data with high anti-aliasing filter attenuation
- A calibration coefficient applied correctly
Correct answer: Sensor saturation or a 'stuck' reading from sensor or recorder failure
A physically implausible constant value typically signals sensor saturation, a failed sensor outputting a rail value, or a frozen data channel.
Question 7: Which IRIG standard is most commonly referenced for time code formats used in flight test data acquisition?
- IRIG-106
- IRIG-200
- IRIG-B (Correct answer)
- IRIG-A
Correct answer: IRIG-B
IRIG-B is the most widely used time code format in flight test, providing a modulated or DC-level shifted signal with 1-second frame resolution.
CTC Data Acquisition and Validation 3
Which error source causes all channels in a multiplexed DAS to have a slight timing difference between their samples?