Data Acquisition and Validation Flashcards

What is the significance of the Nyquist-Shannon sampling theorem for choosing sample rates in test instrumentation?

Answer: Sample rate must be at least twice the highest frequency of interest to reconstruct the signal accurately

The Nyquist-Shannon theorem states that the sample rate must exceed twice the maximum signal frequency to allow perfect reconstruction without aliasing.

Which onboard recorder characteristic is most critical for high-vibration flight test environments?

Answer: Solid-state memory with no moving parts

Solid-state recorders use flash memory with no mechanical components, making them inherently resistant to shock and vibration that can cause hard-drive failures.

A 'cold junction compensation' circuit is required when using thermocouples because:

Answer: The reference junction temperature affects the output voltage and must be measured and corrected

Thermocouple output depends on the temperature difference between the measurement and reference junctions, so the reference junction temperature must be known and compensated.

When validating synchronized data from two independent systems, a time correlation check is performed to:

Answer: Confirm that events recorded by each system align within acceptable time tolerances

Time correlation verification confirms that time-stamped events visible in both data sources coincide within acceptable limits, proving the systems share a common time reference.

In PCM telemetry, 'minor frame' and 'major frame' are related by the fact that:

Answer: A major frame consists of a fixed number of minor frames, allowing lower-priority channels to be sampled at submultiples of the basic rate

The major frame superstructure groups multiple minor frames together so that channels needing lower sample rates appear once per major frame rather than in every minor frame.

Which condition would cause a pressure transducer to output a value that reads correctly at calibration but drifts over a flight test?

Answer: Thermal sensitivity causing the zero offset or sensitivity to shift with temperature changes

Temperature-induced drift in the transducer's zero and span causes readings to deviate from calibration values as the sensor's operating temperature changes during flight.

What is the purpose of a Built-In Test (BIT) function in a flight test data acquisition unit?

Answer: Generate synthetic test signals to verify system health and detect faults without external stimuli

BIT injects known internal reference signals to verify that each acquisition channel is operating correctly and to detect instrumentation faults before or during a test.