A subsea temperature sensor is mounted a distance from a shore station and reads its…
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 subsea temperature sensor is mounted a distance d=3km from a shore station and reads its measurand over 0 to 100 degrees Celsius. Its analogue front end (sensor plus signal-conditioning amplifier) is known, from its own noise budget, to resolve the temperature to 0.05 degrees Celsius rms; the reading is then digitised there by a 12-bit analogue-to-digital converter spanning the full 100 degree Celsius range and sent up as a digital code. Two candidate media are compared for the 3km run: single-mode optical fibre, attenuation 0.20dBkm−1 at 1550nm, launched at Pt=+3dBm, with 4.0dB of connector and splice loss along the route; twisted-pair copper cable, attenuation 20dBkm−1 at the signalling frequency used, launched at Pt=0dBm. Both receivers need at least −32dBm at their input for a negligible bit-error rate, and the design rule of thumb is that a link needs at least 10dB of margin above that figure to be dependable.
((a)) Find the received power and the margin over the −32dBm sensitivity, for each medium.
((b)) State which medium meets the 10dB margin rule and which does not.
((c)) Given the working link carries the digitised code reliably (negligible bit errors at its operating margin), decide whether the link or the front end limits the end-to-end temperature resolution, using the ADC's quantisation step on the 100 degree Celsius range.