What is Telemetry? Remote Data Transmission • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors What is Telemetry? Remote Data Transmission • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

What is Telemetry? Remote Data Transmission

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Understanding Telemetry in Vibration Measurement

Definition: What is Telemetry?

Telemetry is the technology for transmitting measurement data from remote or inaccessible locations—particularly from rotating components—to stationary recording and analysis equipment. In rotating machinery context, telemetry enables measurements on shafts, rotors, and blades where direct wired connections are impossible due to rotation. Systems include sensors on rotating parts, rotating electronics for signal conditioning and transmission, rotating power supplies, and stationary receivers capturing transmitted data.

Telemetry is essential for specialized measurements like shaft strain (torsional stress), blade vibration with strain gauges, rotor temperature, and any parameter requiring sensing element mounted on rotating component. While complex and expensive, telemetry provides unique measurement capabilities unavailable through stationary sensors.

Types of Telemetry Systems

1. Slip Ring Telemetry

Oldest and most reliable:

  • Principle: Rotating rings connected to sensors, stationary brushes pick up signals
  • Channels: Multiple channels possible (4-64 typical)
  • Bandwidth: DC to MHz (excellent)
  • Reliability: Proven technology
  • Limitations: Brushes wear, noise from contact, speed limitations
  • Applications: Research, development testing, some production monitoring

2. FM/AM Radio Telemetry

  • Principle: Rotating transmitter broadcasts FM or AM modulated signals
  • Channels: 1-16 channels typical
  • Bandwidth: DC to 100 kHz per channel
  • Advantages: No contact, no wear
  • Limitations: Power hungry, limited channels, potential interference

3. Digital Wireless Telemetry (Modern)

  • Principle: Digital encoding, WiFi, Bluetooth, or proprietary protocols
  • Channels: Many channels multiplexed
  • Bandwidth: Depends on data rate
  • Advantages: Flexible, robust, error correction
  • Power: Lower than analog FM for equivalent performance
  • Trending: Becoming standard for new systems

4. Optical Telemetry

  • Data transmitted via modulated light (IR or visible)
  • High bandwidth potential
  • Immune to RF interference
  • Line-of-sight requirement
  • Specialized applications

Applications

Torsional Vibration Measurement

  • Strain gauges on shaft measuring shear stress
  • Direct measurement impossible without telemetry
  • Critical for engine-driven equipment
  • Validates torsional analysis models

Blade Stress Measurement

  • Strain gauges on turbine or compressor blades
  • Measures actual operating stress
  • Development testing and troubleshooting
  • Validates blade tip timing measurements

Rotor Temperature

  • Thermocouples on rotor windings or components
  • Monitors thermal conditions
  • Overheating detection
  • Cooling system effectiveness

Shaft Vibration

  • Accelerometers mounted directly on shaft
  • True rotor vibration vs. bearing housing
  • Research and special troubleshooting

Power Supply Methods

Batteries

  • Primary batteries (1-5 years typical)
  • Rechargeable batteries
  • Simplest but limited life
  • Replacement during maintenance outages

Slip Ring Power

  • Power transferred through slip rings
  • Unlimited operation time
  • Requires slip ring assembly
  • Common with slip ring data telemetry

Inductive Coupling

  • Wireless power transfer across air gap
  • Rotating coil picks up power from stationary coil
  • No contact, no wear
  • Limited power (typically < 10W)

Energy Harvesting

  • Harvest vibration energy (piezoelectric)
  • Thermal gradients (thermoelectric)
  • Supplements or replaces batteries
  • Enables autonomous operation

Challenges

Rotating Environment

  • Centrifugal forces on electronics
  • Temperature cycling
  • Vibration of components themselves
  • Oil mist, contamination

System Complexity

  • Rotating and stationary components
  • Synchronization and timing
  • Calibration challenges
  • Higher cost than stationary sensing

Maintenance

  • Battery replacement
  • Sensor/electronics failures
  • Requires machine shutdown for access
  • Spare modules needed

Modern Developments

MEMS and Miniaturization

  • Smaller, lighter electronics
  • Lower power consumption
  • More robust to shock/vibration
  • Enables new applications

Digital Signal Processing

  • Processing on rotating platform
  • Transmit results (FFT) not raw data
  • Reduces bandwidth and power needs

Standardization

  • Industrial wireless standards (WirelessHART, ISA100)
  • Interoperability improving
  • Lower costs from scale

Telemetry enables vibration and condition measurements on rotating components where stationary sensors cannot reach, providing access to critical parameters like shaft torsional stress, blade strain, and rotor temperatures. While complex and costly, telemetry systems deliver unique measurement capabilities essential for specialized applications in turbomachinery development, torsional analysis, and advanced rotor dynamics characterization.

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