Introduction
The model 84661-17 is a Magnetic Speed Sensor, also known as a Variable Reluctance (VR) Sensor or passive magnetic pickup. This is a robust, self-generating transducer designed to detect the speed and timing of rotating ferrous targets, such as gear teeth or keyed shafts. It operates on the principle of electromagnetic induction, generating an AC voltage signal whose frequency is directly proportional to the speed of the passing target. The -17 suffix typically indicates a specific configuration, often related to the electrical connector type, cable length, or temperature rating. Known for its durability and simplicity, it is a fundamental component for speed sensing and overspeed protection in demanding industrial environments.
Parameters / Specifications
The following table outlines the key technical parameters for the 84661-17 speed sensor.
| Parameter | Specification |
|---|---|
| Model Number | 84661-17 |
| 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, Self-Generating) |
| 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] |
| Electrical Connection | Integral, 2-conductor shielded cable or connector, as defined by the -17 suffix. |
| Housing Material | 400 Series Stainless Steel |
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. The exact connector type and cable length are defined by the -17 configuration code.
Application Scenarios
The 84661-17 magnetic speed sensor is a versatile and reliable component for speed measurement and protection across various industries.
Gas & Steam Turbine Overspeed Protection:
A primary application is on industrial turbines, 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, sequencing, and safety systems.
Tachometer Reference for Vibration Monitoring:
Used to provide a once-per-revolution "Keyphasor®" or "Zero Speed" signal for vibration monitoring systems on large pumps, fans, and gearboxes. This pulse is essential for determining vibration phase and for startup/shutdown analysis.
Heavy-Duty Mobile and Marine Equipment:
Employed on mining trucks, agricultural machinery, and marine propulsion systems for monitoring the speed of shafts, gears, and engines in extremely demanding environments where reliability is paramount.
General Industrial Speed Measurement:
Used anywhere a simple, robust, and maintenance-free speed detection solution is needed on ferrous rotating components, such as on conveyors, mixers, extruders, and other processing lines.
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