A strain gauge bridge on a rotating wind-turbine blade is conditioned by an amplifier…
PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Sensors, detectors and experimental instrumentation · Communication systems and RF engineering
Electronics for Measurement, Ch Modulation, receivers and the link that carries the measurement
Problem
A strain gauge bridge on a rotating wind-turbine blade is conditioned by an amplifier whose own noise limits its resolution to 2.0με rms (microstrain, 1με=10−6 strain), taken as a given front-end figure. The conditioned signal, spanning a full-scale range of 4000με peak-to-peak (that is, ±2000με), frequency-modulates a carrier and is sent by radio to a fixed base station. Above its threshold, the analogue link delivers an output signal-to-noise ratio of 45dB for a full-range sinusoidal test tone, measured in the strain baseband.
((a)) Find the rms value of a full-range sinusoidal tone on the 4000με peak-to-peak range.
((b)) Use the 45dB output ratio to find the rms strain noise the link itself adds at the base station.
((c)) Decide whether the analogue link or the front end limits the end-to-end strain resolution, giving the combined (quadrature) resolution.
((d)) The blade instead digitises the reading with an N-bit analogue-to-digital converter before transmission, sent as a reliable digital code (bit errors negligible at the link's operating margin). Find the smallest N that makes the quantisation step no coarser than the front end's 2.0με, and state which block then limits the end-to-end resolution.