CET Data Quality & Completeness 2 — Questions and Answers
Question 1: In digital signal processing, which condition is required by the Nyquist-Shannon sampling theorem to prevent aliasing?
- Sample rate must equal the signal frequency
- Sample rate must be at least twice the highest signal frequency (Correct answer)
- Sample rate must be half the signal frequency
- Sample rate must be ten times the signal frequency
Correct answer: Sample rate must be at least twice the highest signal frequency
The Nyquist-Shannon theorem requires a sample rate of at least twice the highest frequency component to accurately reconstruct the signal.
Question 2: A technician notices that an ADC output consistently reads 5 LSBs higher than the true analog input. This is an example of:
- Quantization noise
- Offset error (Correct answer)
- Gain error
- Differential nonlinearity
Correct answer: Offset error
Offset error is a fixed, constant deviation between the actual ADC output and the ideal output across all input levels.
Question 3: Which data integrity check method appends a value to a data block so that the sum of all bytes equals a predetermined value?
- CRC
- Checksum (Correct answer)
- Parity bit
- Hamming code
Correct answer: Checksum
A checksum sums all bytes in a data block and appends the result (or its complement) so receivers can verify data integrity.
Question 4: When calibrating a measurement instrument, 'traceability' means:
- The instrument has a unique serial number
- Measurements can be related to national or international standards through an unbroken chain (Correct answer)
- The instrument logs all measurements automatically
- The instrument is certified for use in hazardous locations
Correct answer: Measurements can be related to national or international standards through an unbroken chain
Traceability means calibration results are linked through an unbroken chain of comparisons to recognized national or international measurement standards.
Question 5: A data acquisition system exhibits integral nonlinearity (INL). What does this indicate?
- The system introduces random noise into measurements
- The actual transfer function deviates from the ideal straight line across the full input range (Correct answer)
- The least significant bit changes inconsistently between adjacent codes
- The system has incorrect offset at zero input
Correct answer: The actual transfer function deviates from the ideal straight line across the full input range
INL measures the maximum deviation of the actual ADC transfer function from the ideal straight line spanning the full input range.
Question 6: In a PCM (Pulse Code Modulation) system, increasing the number of quantization bits from 8 to 12 primarily improves:
- Bandwidth efficiency
- Dynamic range and signal-to-noise ratio (Correct answer)
- Transmission speed
- Clock synchronization
Correct answer: Dynamic range and signal-to-noise ratio
Each additional bit in PCM adds approximately 6 dB of dynamic range, so increasing from 8 to 12 bits improves SNR by about 24 dB.
Question 7: Which error type in a data measurement system causes readings to be consistently higher or lower than true values but with random scatter around that offset?
- Random error only
- Systematic error only
- A combination of systematic and random errors (Correct answer)
- Gross error
Correct answer: A combination of systematic and random errors
A consistent offset from true value indicates systematic error, while random scatter around that offset indicates random error — both can coexist.
CET Data Quality & Completeness 2
In digital signal processing, which condition is required by the Nyquist-Shannon sampling theorem to prevent aliasing?