Description
Product Introduction
The Bently Nevada 3500/50 (main processing board part number 286566-02) is a 2-channel tachometer card designed for critical shaft speed measurement, acceleration tracking, and overspeed detection on rotating machinery. It mounts directly into any standard slot of a 3500 machinery protection rack, interfacing with proximity transducers or magnetic pickups to read multi-tooth gear wheels or keyway notches.
Unlike standard vibration monitors that focus on displacement or velocity, the 3500/50 evaluates rotational dynamics. It converts raw phase pulses into precise RPM values, rotor acceleration/deceleration trends, and zero-speed status indicators. The module conditions these signals to drive internal backplane trip relays for emergency machinery shutdown while supplying stable speed phase information across the backplane to vector-tracking monitor cards (like the 3500/42M and 3500/44M) and Bently Nevada System 1 software.
Key Technical Specifications
| Parameter | Specification Value |
| Full Model / Part Number | 3500/50 (Main Board: 286566-02 / 133388-01) |
| Channel Capacity | 2 independent, software-configurable speed channels |
| Supported Transducers | 3300 XL Proximitors, Magnetic Pickups, Optical Sensors |
| Speed Input Range | 0.9 Hz to 99 kHz (up to 99,999 RPM depending on event count per rev) |
| Transducer Power | Dedicated -24 VDC supply per channel (short-circuit protected) |
| Operating Modes | Speed Measurement, Rotor Acceleration, Zero Speed, Underspeed, Overspeed |
| Accuracy | Speed: Within ±1 RPM (or ±0.01% of actual speed) |
| Buffered Signal Outputs | 2 Front-Panel coaxial BNC outputs (100 Ω output impedance) |
| Power Consumption | 5.8 Watts typical |
| Operating Temperature | -30°C to +65°C (-22°F to +149°F) |
Application Scenarios & The “Trench” Experience
When a load rejection hits a 100 MW steam turbine, steam pressure instantly drives the unburdened shaft toward destructive speeds. If your speed detection card suffers signal lag, or misses a pulse edge because of noise on a passive magnetic pickup line, the rotor can reach terminal overspeed velocity before the trip throttle valve ever gets a signal—shattering turbine blading and compromising containment.
The 3500/50 provides hardware-level frequency tracking with sub-millisecond trip response, protecting your turbomachinery from overspeed catastrophe while providing reliable zero-speed interlocks for turning gear engagement.
- Power Generation – Main Steam & Gas Turbine Trains: Monitoring shaft RPM, acceleration rates during startup ramps, and driving fast-acting overspeed trip logic.
- Refining – Turbo-Compressor Packages: Interfacing 3300 XL proximity probes focused on a multi-tooth gear to drive underspeed/zero-speed safety interlocks.
- Chemical Plants – Extruders & Large Gearboxes: Providing clean speed signals to downstream PLC control loops and System 1 transient diagnostic tools.
Field Case Scenario: During an overhaul shutdown on an offshore platform, the operating team found that their 3500/50 module in slot 3 was reporting erratic speed spikes whenever the auxiliary oil pump kicked on, causing false overspeed alarm flags in the control room. Ground loop noise on an old magnetic pickup cable was corrupting the pulse threshold on the legacy board. We arrived with a pre-tested 286566-02 module surplus replacement, swapped out the aging card, adjusted the dynamic hysteresis thresholds in 3500 Rack Configurator, and restored clean, noise-free speed tracking before the main compressor restart window closed.
3500/50 286566-02
3500/50 286566-02
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; we test them on actual Bently Nevada 3500 racks.
- Inbound Visual & Component Check: We inspect board traces, verify backplane gold plating, check for heat-stressed power components, and validate OEM serial numbers.
- Backplane Handshake & POST: The 286566-02 board is seated into a live 3500 test chassis. We run Power-On Self-Tests (POST) to verify communication with the 3500/22M System Interface card without triggering rack fault codes.
- High-Frequency Pulse Signal Injection: Using precision signal generators, we feed high-frequency TTL and sine wave pulse trains (up to 50 kHz) into both channels to verify pulse counting accuracy, acceleration calculation, and Alert/Danger trip setpoints.
- Buffered BNC Signal Verification: Every front-panel BNC output is verified on an oscilloscope to ensure clean, unattenuated signal pass-through for diagnostic gear.
- Anti-Static Sealing: Verified modules are packaged directly into conductive ESD shielding bags with custom die-cut foam protection.
The Veteran’s Tech Trap Guide (Crucial Value-Add)
- ⚠️ Events Per Revolution (EPR) Setting Errors: Double-check your “Events Per Revolution” setting in the 3500 Rack Configuration Software. If your physical shaft gear has 60 teeth but your software configuration is set for 1 pulse per rev (Keyphasor style), the 3500/50 will read 60 times higher than actual shaft speed, instantly tripping your system on fake overspeed.
- ❗ Passive Magnetic Pickups vs. Proximity Probes: Passive magnetic pickups require minimum shaft surface speeds to generate sufficient AC voltage (>1.0 V peak-to-peak). If your turbine runs at low turning-gear speeds (e.g., 5 to 10 RPM), a magnetic pickup into a 3500/50 won’t register any speed signal. Use powered eddy-current Proximitor probes if low-speed or zero-speed tracking is required.
- ⚠️ Do Not Confuse 3500/50 with 3500/25 Keyphasor Modules: While both process speed pulses, the 3500/25 Keyphasor card is dedicated to providing phase timing reference signals across the rack backplane. The 3500/50 Tachometer Module is designed for continuous speed calculation, acceleration monitoring, and dedicated overspeed trip logic.
Frequently Asked Questions (FAQ for Conversion)
Q: Can the Bently Nevada 3500/50 286566-02 be used for API 670 overspeed protection?
A: Yes, the 3500/50 is fully API 670 compliant for speed, acceleration, and overspeed monitoring. However, for dedicated Electronic Overspeed Protection Systems (EOPS) requiring triple 2-out-of-3 voting redundancy, Bently Nevada often utilizes dedicated 3500/53 or specialized safety modules.
Q: Is the 3500/50 286566-02 tachometer card hot-swappable?
A: Yes, the front main module can be hot-swapped while the 3500 rack is powered. To be honest, pulling a speed card tied to active plant trip logic carries risk—always bypass downstream overspeed trip relays before pulling the module.
Q: What is the difference between part number 286566-02 and older 133388-01?
A: Part number 286566-02 is an updated/revised main processing board assembly for the 3500/50 module, featuring upgraded onboard component logic and improved noise immunity while remaining 100% backwards compatible with the 133388-01 hardware design.
Q: Does this module include the Rear I/O board?
A: The 286566-02 number designates the front main tachometer processing module. If you also require the matching Rear I/O module (e.g., 133396-01 Standard I/O with Euro-style screw terminals), let us know and we can supply the complete assembly.
Q: What warranty is provided with this module?
A: All our Bently Nevada 3500/50 286566-02 modules—whether factory-sealed new surplus or fully rig-tested stock—come backed by our full 12-month replacement warranty.
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