Optical Pyrometry System (Rotamap II)
Turbine Blade Mapping
A radiation pyrometer consists of an optical system, which collects radiation from a defined area of the surface being measured and relays it to a suitable detector. From the resulting radiation measurement and a suitable calibration the ‘Radiance Temperature’ of the measured surface can be deduced.
The ‘Radiance Temperature’ is the temperature of an ideal radiator (a black-body) that produces the same pyrometer output level. Measurement distance, temperature range and measured area size are controlled by the choice of detector and optical design.
Radiation pyrometers have been used for non-contact temperature measurements in many industries for over 50 years. They have been applied to Gas Turbines for engine development and control purposes for at least 40 years. Rotadata has supplied pyrometer systems to world leading gas turbine manufacturers to operate at extremes of engine operating and probe hardware environment conditions.
Wherever possible Rotadata Pyrometers use existing turbine access holes, for example, boroscope inspection holes. The design and subsequent manufacturing activities reflect Rotadata’s 25 years as a leading supplier of specialist gas turbine instrumentation.
Rotadata pyrometers use high speed digital data transfer to relay the 1 million measurements per second of blade radiation data and mirror or probe movement data to the Rotamap II ground station for recording, storage and analysis.
Rotadata measurement probes are designed in close collaboration with the customer to minimize the work required to meet a new application with minimum disturbance to any existing engine hardware whilst ensuring the maximum blade surface area can be thermally mapped. A range of standard radiation pyrometers is available for application with the appropriate blade viewing and scanning method. All scanning systems interface with a common ground station.
The optical system of the pyrometer is capable of working with a range of detector types to optimize the measurement temperature range. Standard working distances of between 80 and 200 mm are available with (usually) a 2 mm measurement spot at the specified distance.
It must be noted that each application is unique and therefore requires initial consultation with Rotadata staff. Consultation with our experienced workforce will ensure that the optimum system is supplied.
System Types
Three types of optical pyrometer system are available from Rotadata.
(1) Oscillating mirror with electro-mechanical actuation used mainly for military and civil aero-engine blade thermal mapping.
(2) Fixed mirror sight tube insertion with pneumatic actuation used for larger aero-engines and industrial gas turbines for blade thermal mapping.
(3) Fixed mirror sight tube with electro-mechanical actuation used mainly for power and industrial gas turbine blade thermal mapping.
In order to use our optical pyrometers successfully each requires a clean, dry air supply to cool the actuator and sight tube and a good quality once per revolution tachometer signal measuring on the engine rotor. The air supplies and tachometer signal are usually provided by the customer but if requested Rotadata can supply the appropriate equipment.
The oscillating mirror (1) and the pneumatically actuated
fixed mirror (2) pyrometers can be mounted on the outside of
the engine casing or, with suitable cooling and cable guards,
can be mounted inside the outer engine casing.
The electro-mechanical actuated fixed mirror pyrometer must
be mounted on the outside of the engine casing.
Method of Measurement.
The pyrometer optical and detector system views the blades via the mirror. As the rotor turns the viewed point is moved down the blade by moving the mirror. The total mirror movement time is measured in seconds and as the system is measuring continuously several hundred radial heights are scanned and recorded.
A complete Rotamap II pyrometer system would comprise:
- The applicable engine-mounted actuator and sight tube.
- A Ground Station giving System control, data management and data processing using Rotadata’s Rotamap II software.
- System Interconnecting Cables.
- A remote sight tube insertion air controller, where required.
- Sight tube and actuator cooling air and a suitable tachometer signal.
Typical Measurement Process.
The measurement cycle of ‘insert the sight tube (probe) - take the measurements - extract the sight tube’ is designed to minimise the time spent by the sight tube in the engine gas stream. In all cases the measurement process is the same.
One million measurements per second from a nominal 2.0 mm diameter spot on the blades. At an engine rotor speed of 12,000 revolutions per minute (rpm) this represents approximately 5,000 measurements per revolution. The data collection, storage and Rotamap II processing is identical for all scanning methods.
