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The Bently Nevada 76683-50 belongs to the 3300 XL 35 mm series of eddy-current proximity transducers. This sensor suits large shaft displacement measurement in steam turbines, compressors, and hydro generators. Its oversized 35 mm tip delivers a wide linear range for high-amplitude vibration monitoring.
Key Technical Specifications
| Parameter | Value |
|---|---|
| Model | 76683-50 |
| Category | 35 mm Proximitor Sensor |
| Probe Tip Diameter | 35 mm |
| Linear Range | 0 to 20 mm (typical) |
| Incremental Scale Factor | 1.5 V/mm ± 6.5% |
| Frequency Response | 0 to 2.7 kHz |
| Operating Temperature | -35°C to +200°C (probe) |
| Cable Length | 5 m or 9 m options |
| Weight | Approx. 1.2 kg (probe with cable) |
| Connector | Coaxial, 3-pin Mil-spec |
| Mounting Thread | M30 × 2 or 1.25-12 UNF |
| Power Supply | -17.5 Vdc to -26 Vdc |
| Output Impedance | 50 Ω nominal |
Measurement Principle and Interface
Eddy-current technology enables non-contact displacement measurement on ferrous targets. The driver supplies a high-frequency signal through the coaxial cable to the probe coil. Consequently, target movement modulates coil impedance and produces a proportional voltage output. The 76683-50 pairs with 3300 XL extension cables and Proximitor drivers for signal conditioning.
Installation and System Integration
Operators mount the probe through a threaded hole with a locknut. A minimum target size of 70 mm diameter ensures accurate linear response. Meanwhile, the 35 mm tip allows greater standoff distance than smaller probes. This design reduces risk of collision in large rotating machinery. The system also supports reverse-mount configurations for confined spaces.
Energy Storage and Power Considerations
The Proximitor driver draws power from a -24 Vdc rail, typically 12 mA maximum. No internal battery or capacitor stores energy in the probe itself. Instead, external modules handle signal demodulation and power regulation. Therefore, system designers must budget for a dedicated DC supply per channel.