Introduction
The model 81546-01 is a Magnetic Speed Sensor, commonly referred to as a Variable Reluctance (VR) Sensor or magnetic pickup. This passive device is designed to detect the speed and timing of rotating equipment without requiring an external power supply. It generates an AC voltage signal whose frequency is directly proportional to the speed of a passing ferrous target, such as a gear tooth or keyed shaft. The 81546-01 is known for its ruggedness and reliability, making it a staple for speed sensing and tachometer applications in harsh industrial environments, particularly in the oil and gas, and heavy machinery sectors.
Parameters / Specifications
The following table outlines the key technical parameters for the 81546-01 speed sensor.
| Parameter | Specification |
|---|---|
| Model Number | 81546-01 |
| Description | Magnetic Speed (Variable Reluctance) Sensor |
| Physical Dimensions | Approx. 96 mm (3.78 in) overall length. Body Diameter: 19 mm (0.75 in) hex. Thread Size: 5/8-18 UNF. |
| Weight | Approx. 0.25 kg (0.55 lb) |
| Operating Principle | Variable Reluctance (Passive) |
| Output Signal | AC Sine Wave (Amplitude and frequency increase with speed) |
| Supply Voltage | Not Required (Self-generating) |
| Air Gap (Recommended) | 0.25 to 1.5 mm (0.010 to 0.060 in) from gear tooth |
| Output Voltage | Dependent on speed, air gap, and target size. Typically several Volts AC to over 50 VAC at higher speeds. |
| Temperature Range | -40°C to +120°C (-40°F to +250°F) [Standard]; Up to +150°C (+302°F) available. |
| Electrical Connection | Integral, 2-conductor shielded cable (length varies by order code). |
| Housing Material | 400 Series Stainless Steel |
| Compatibility | Commonly used with Woodward and other speed controllers/overspeed protection systems. |
Note: The output voltage is highly dependent on operational conditions. At very low speeds, the signal may be too weak for some monitoring systems to detect reliably. Always confirm the exact cable length and temperature rating for the specific order code.
Application Scenarios
The 81546-01 magnetic speed sensor is a fundamental component for speed measurement and overspeed protection across various industries.
Gas Turbine Speed Monitoring & Overspeed Protection:
A primary application is on industrial gas turbines and turbo-machinery, where it serves as a key input for the governing control system and provides critical speed data for overspeed trip protection to prevent catastrophic failure.
Engine and Compressor Speed Sensing:
Widely used on reciprocating engines and compressors in the oil and gas industry to monitor engine RPM and compressor speed for control and safety systems.
Tachometer Reference for Rotating Machinery:
Used to provide a once-per-revolution "Keyphasor®" or "Zero Speed" signal for vibration monitoring systems on large pumps, fans, and gearboxes, enabling phase analysis and startup/shutdown monitoring.
Heavy-Duty Mobile Equipment:
Employed on mining, agricultural, and marine equipment for monitoring the speed of shafts, gears, and engines in demanding environments where reliability is paramount.
General Industrial Speed Measurement:
Used anywhere a simple, robust, and passive speed detection solution is needed on ferrous rotating components, such as on conveyors, mixers, and processing lines.
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