2 Telemetry Turbine

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23 May 2012 PMI Revision 00 1

TELEMETRY

FOR STEAM TURBINE

BLADE

VIBRATION MEASUREMENT


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WHAT IS TELEMETRY ?

Telemetering is defined as the complete measuring, transmitting, andreceiving for indicating at a distance, by electrical translating means, thevalue of a quantity.

The measurement is made by such transducers as the resistance strain

gage, thermocouple, pressure transducer, accelerometer, etc.

The transducer converts the measured quantity to an electrical signal,which is then transmitted without a conductor to a receiver.


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NEED FOR TELEMETRY IN BLADE

VIBRATION MEASUREMENT

Sensitive data such as blade surface stress, pressures andvibration from high speed rotating machine have been

traditionally obtained using slip ring arrangements thattypically involve the transfer of electrical signals fromrotating conductive rings to stationary brushes in contactwith these rings

Slip ring assemblies have limitations on rotational speed,restricting their use in high-speed rotational systems liketurbines.


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A viable alternative is the use of a telemetry system totransmit data from a high-speed rotating source to thelaboratory data acquisition system using radio signals in theFM bandwidth.

The advantage of this system is the in situamplification ofsource signals and non-contact type transmission of thesesignals, allowing high-speed testing and minimizing noise.The quality of data and the versatility of use make telemetryan excellent option for acquiring much-needed blade data.


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TYPICAL TELEMETRY SYSTEM BLOCK DIAGRAM


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CHALLENGES FOR APPLICATION OFTELEMETRY IN STEAM TURBINE

Telemetry systems for steam turbine applications facesevere challenges not associated with the common, long-range telemetry systems used in commercial and personalcommunications.

One of the most challenging requirements of rotor telemetryis that of providing power to the rotating transmitter modules

The steam-turbine environment is characterized by hightemperatures

high accelerations on rotating elements

surrounded by highly conductive metallic materials.


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TYPICAL POWER SUPPLY SCHEME FOR TELEMETRY


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SENSOR USED IN TELEMETRY SYSTEMS FORBLADE VIBRATION MEASUREMENT

STRAIN GAGE SENSORS

PIEZO FILM SENSOR

The sensitivity of piezo film as a receiver of mechanical workinput is awesome. In its simplest mode the film behaves like adynamic strain gage except that it requires no external power

source and generates signals greater than those fromconventional foil strain gages afteramplification.Frequency response is thus free from any limitations imposed bythe need for high gains and will extend up to the wavelength limitof the given transducer.The extreme sensitivity is largely due to the format of the piezofilm material. The low thickness of the film makes, in turn, a verysmall cross-sectional area and thus relatively small longitudinalforces create very large stresses within the material. It is easy to

exploit this aspect to enhance the sensitivity


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PIEZO FILM SENSOR & BASIC CIRCUITRY


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SIGNAL CONDITIONING The primary principles of signal conditioning include:

FilteringElectrical filters designed to give the desiredband pass

and band-rejection characteristics.

AveragingIf the desired signal exhibits periodicity, whilethe undesired signal is random, signal averaging canincrease the signal-to-noise ratio.

Common Mode RejectionBy wiring two equal areas of apiezo film electrode out-of-phase, unwanted common-modesignals can be made to cancel.


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FEATURES OF TELEMETRY

No Slip Rings

No Shaft Modifications Required Transmitters available for Strain, Torque, Pressure, Voltage,

Temperature.... almost any type of signal

Clamp-on Collar houses Transmitter(s) and Induction Power

Converter. Contains embedded transmitting antenna Transmits Sensor Signals via Radio Transmitter to a

Stationary Receiver Immune to electromagneticinterference, dust, oil, moisture, steam, etc.

Excellent precision and linearity (0.1%) Small and light enough to install to narrow space to take

data

High ability of frequency response

Multi-Channel Systems Available (36 channels)


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2 Telemetry Turbine

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