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

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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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