“Instrumentation on rapidly rotating aero-engine parts” Transducer Tempcon 1-3 July 1980 at Wembly Conference Centre, London. Paul Howard Riley

RB211 aero engine Although the RB211-22b is a large engine, the space for telemetry is very small

Fast rotating modules High pressure (HP) shaft Typical Measurements ~11,00 rpm Typical Measurements Temperature Dynamic strain High shaft rotation speed Large “G” forces Most IC’s fail before this

Effect of High G force Compressor blades The lead wires in ICs Mass of 10’s grams Weigh 5 tonnes The lead wires in ICs Gold will buckle at about 10,000 g Aluminium works Point contact diodes Fail Must use bonded junctions

Thick film Hybrid module Left is a cutaway You can see gold bond wires Connected to an IC Before spin test the wires are in tact

Gold bonded IC. After spin test, this gold bond wire in a thick film hybrid failed at about 10,000g. You can see it buckle and touch the circuit board below

Typical Mark 16 Telemetry module Circuit boards Carefully selected components Source controlled (only aluminium bond wires) (Expanded) dual PC board Fully encapsulated into a module About 31 x 28 x 12 mm Modules Epoxy encapsulated Hand wired together in a Titanium toroid Strong enough to resist g force Power and signal Non contacting

Typical module interior Top PCB: Surface mount ICs and passives Tight tolerance resistors for bridge completion circuit Bottom PCB, through hole and surface mount. 2 PCB per module Tuning inductors and capacitors on power module

Power and Signal Electrical power for all the modules Sent via 485 KHz inductive loop Via stator to rotating member at ~ 11,000 rpm Rotating pickup tuned to maximise power transfer Signal send from rotor to stator Between 40 and 80MHz by segmented aerial In frequency separated bands frequency modulated Dynamic strain takes one band Temperature used time division multiplex

Environment The toroid housing in the modules is cooled with air Even so, max ambient temp is 125C Measured temperature Up to 1000C using type K surface mounted thermocouples

Temperature measurement Measured temperature Up to 1000C using type K surface mounted thermocouples Many temperatures time division multiplexed Zero between each measurement to compensate for amplifier offset drift. Extensive calibration at selected ambient temperatures Volts = k* temperature T1, T2, T3, T4 Time

High bandwidth measurements Dynamic strain Uses half bridge surface mounted gauges for temperature compensation Full bridge completed on rotor by resistive completion module Because of bandwidth requirement, only one gauge per transmitter channel used Metalwork must be demagnetised To reduce once per rev interference Much care with transmitter design needed Rotation can pull transmitter frequency inducing further once per rev interference Transmitters in faraday cage Low coupling between power output and FM oscillator is needed