Description
Product Description
The Bently Nevada 3500/50 Tachometer Module is a dual-channel rotational speed monitoring module engineered for use within the Bently Nevada 3500 Series Machinery Protection System. The module continuously measures shaft rotational speed, rotor acceleration, and shaft rotation direction using proximity probes or compatible magnetic pickup sensors.
Designed for critical turbomachinery and rotating equipment applications, the module processes real-time speed signals and compares them against configurable alarm thresholds defined through the 3500 Rack Configuration Software. The module also supports conditioned Keyphasor® signal distribution through the rack backplane, reducing the requirement for additional signal interface hardware.
The Bently Nevada 3500/50 supports independent channel operation and provides flexible monitoring modes for speed alarming, acceleration analysis, reverse rotation indication, and zero-speed detection.
Key Features
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Dual independent tachometer input channels
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Compatible with proximity probes and magnetic pickup sensors
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Real-time shaft speed and rotor acceleration monitoring
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Reverse rotation indication capability
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Configurable alarm thresholds and speed bands
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Integrated peak speed and reverse rotation event storage
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Buffered transducer outputs available on front panel
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Keyphasor® signal conditioning and backplane distribution
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LED diagnostics for module condition and communication status
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Rack-based configuration through 3500 software platform
Technical Specifications
| Parameter |
Specification |
| Product Type |
Tachometer Monitoring Module |
| Series |
3500 Machinery Protection System |
| Channels |
2 Independent Channels |
| Supported Sensors |
Proximity Probes, Magnetic Pickups |
| Input Voltage Range |
+10 VDC to –24 VDC |
| Standard Input Impedance |
20 kΩ |
| TMR Input Impedance |
40 kΩ |
| Internal Barrier Impedance |
7.15 kΩ |
| Buffered Outputs |
1 Coaxial Output per Channel |
| Typical Power Consumption |
5.8 Watts |
| Alarm Functions |
Speed, Speed Band, Acceleration, Reverse Rotation |
| Configuration Method |
3500 Rack Configuration Software |
| Front Panel Indicators |
OK, TX/RX, Bypass |
| Data Retention |
Peak-Hold Speed and Rotation Events |
Operating Modes
The module can be configured in several monitoring combinations depending on machine protection requirements:
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Speed Monitoring with Alarm Setpoints and Speed Band Detection
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Speed Monitoring with Zero-Speed Notification
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Speed Monitoring with Rotor Acceleration Alarming
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Speed Monitoring with Reverse Rotation Detection
Input and Signal Compatibility
The module accepts dynamic pulse signals from:
Magnetic pickup sensors are supported for standard speed measurements; however, they are not recommended for applications requiring highly accurate low-speed detection, reverse rotation analysis, or zero-speed monitoring due to reduced signal edge quality at low rotational velocities.
Application Areas
Typical applications include:
Engineering Notes
The Bently Nevada 3500/50 is intended for machinery condition monitoring and alarm annunciation. It is not designed to function as an independent overspeed trip device or closed-loop speed control system.
Protective shutdown applications requiring SIL-rated or redundant overspeed protection should use dedicated overspeed systems compliant with applicable machinery safety standards.
FAQ
Can the 3500/50 module detect reverse shaft rotation?
Yes. The module supports reverse rotation indication when configured with compatible proximity probe inputs.
Does the module support magnetic pickup transducers?
Yes. Magnetic pickups are supported for standard speed monitoring applications, although proximity probes are preferred for low-speed and directional measurements.
Can the module replace a dedicated Keyphasor module?
In many applications, yes. The module can distribute conditioned Keyphasor® signals through the 3500 rack backplane.
Is the module suitable for overspeed trip protection?
No. The module is intended for monitoring and alarm indication only and should not be used as the primary overspeed shutdown system.
