Product Core Brief
- Model: 3500/50, Front Card PWA 133388-02
- Brand: Bently Nevada (Baker Hughes)
- Series: 3500 Turbine Supervisory Instrumentation (TSI) Machinery Protection Platform
- Core Function: Dual-channel tachometer module processing pulse signals from Keyphasor proximity probes or magnetic pickups to calculate shaft RPM, overspeed, acceleration, and reverse rotation; distributes rack-wide Keyphasor timing for orbit and spectral vibration diagnostics
- Product Type: Full-height hot-swappable split front/rear base M-series speed monitor; lacks onboard isolated 4–20 mA analog outputs
- Key Specs: 2 isolated pulse input channels | 1–99,999 RPM range | 5.8 W typical power draw | TMR redundant overspeed voting support
- Condition: New Original (New Surplus), legacy active OEM spare with scheduled long-term production run, no immediate obsolescence date
Key Technical Specifications
| Parameter | Defined Value |
|---|---|
| Channel Layout | Two fully independent galvanically isolated pulse input channels for primary/backup redundant speed sensing |
| Supported Transducers | 3300 XL Keyphasor proximity probes; variable reluctance magnetic speed pickups |
| Input Signal Window | +10 VDC to -24 VDC differential pulse, internal transient clamping for overvoltage protection |
| Max Input Pulse Frequency | 20 kHz, compatible with high-tooth-count gear speed pickups for high-speed gas turbines |
| RPM Measurement Range | Configurable 1 RPM to 99,999 RPM |
| Measurement Accuracy | ±0.1 RPM below 100 RPM; ±0.01% full scale above 10,000 RPM |
| Supported Monitoring Modes | Overspeed/underspeed trip bands, zero-speed detection, rotor acceleration alarms, reverse rotation lockout logic |
| Backplane Keyphasor Output | Standardized synchronous timing pulse broadcast to all rack vibration monitor modules |
| Power Consumption | 5.8 W steady-state draw from rack 24 VDC backplane bus |
| Matching Rear Termination Bases | Standard safe-area base PN 133389-01; hazardous zone internal IS barrier base PN 136712-01 |
| Channel Isolation Rating | 1500 VAC isolation separating field pulse wiring and internal backplane logic circuits |
| Standard Operating Temp | -30°C to +65°C; conformal coated variants rated -40°C to +85°C offshore cabinet environments |
| Physical Dimensions | 241.3 mm H × 24.4 mm W × 241.8 mm D; front card weight 0.82 kg |
| Compliance Standards | API 670, CE EMC, UL Class I Div 2, ATEX Zone 2 Ex nA IIC T4, SIL 2 functional safety |
| Front Panel Indicators | OK (module health), TX/RX (backplane bus traffic), CH FAULT (open/shorted speed sensor wiring) |
Product Introduction
This tachometer module delivers redundant shaft speed safety monitoring and rack-wide phase reference signals in one rack slot, eliminating separate half-height Keyphasor hardware in many standard TSI layouts. It executes configurable overspeed trip logic that integrates with 3500/33 relay output cards to trigger hard shutdown interlocks on gas and steam turbines.
The split rear terminal base lets technicians rework speed sensor cabling without removing the front measurement hardware during planned outages. The unit cannot process RTD thermal, 4–20 mA process, or raw seismic vibration signals; dedicated 3500/60, 3500/62, and 3500/42M monitors handle those measurement tasks. It differs from the newer 3500/50M (286566-02) variant by omitting native isolated 4–20 mA speed transmit outputs for DCS interface.
Firmware/Software Versions & Upgrade Notes
Minimum compatible rack gateway firmware: 3500/20 TDI Revision G (1.07); minimum rack configuration software: 3500 Rack Configuration Software v3.50 for full reverse rotation feature support. All M-series modules installed in the chassis must run matching firmware builds; mismatched revisions disable TMR overspeed voting and rack-wide Keyphasor timing synchronization.Downgrades below Revision G remove reverse rotation fault detection and reduce pulse capture response speed to 25 ms, increasing overspeed trip latency risk on high-speed machinery. Firmware flashes over the rack backplane bus via official Bently rack configuration software. Always export full channel setup (tooth count, overspeed trip thresholds, acceleration alarm limits) before initiating firmware updates to avoid complete rework of speed safety logic. No firmware resides on rear terminal bases; all pulse signal processing logic resides on the front board assembly.
Frequently Asked Questions (FAQ)
- Is hot-swapping the front measurement card safe while the 3500 rack remains energized?Yes, the front card supports hot-swap with rack power active. Active overspeed alarm states retain their last valid reading during replacement, so machine safety trip interlocks do not drop out mid-service. The paired rear terminal base cannot be detached while powered, as this breaks field sensor isolation and locks persistent channel fault flags.
- Is this part scheduled for obsolescence, and are direct drop-in hardware upgrades available?This monitor remains an active OEM catalog spare with no formal end-of-life date. The direct hardware upgrade variant is 3500/50M with PWA 286566-02, which adds per-channel isolated 4–20 mA analog outputs for DCS speed trending; it requires minor software reconfiguration and is not a zero-modification plug-and-play swap. No revised second-generation uncoated front card exists with identical feature set.
- Will gear tooth count scaling, overspeed trip thresholds, or Keyphasor timing logic erase if the full rack loses power?No, all RPM scaling values, Alert/Danger speed trip limits, acceleration ramp thresholds, and phase reference parameters store in non-volatile flash memory on the unit itself. Full rack power loss does not permanently erase any channel configuration data; the rear terminal base contains zero user-programmable settings.
- What warranty terms separate New Surplus inventory from refurbished alternatives?New Surplus stock carries a 12-month functional warranty covering pulse signal conditioning circuits, backplane transceivers, channel isolation barriers, and LED diagnostic hardware. Refurbished units typically offer only 3–6 month limited coverage and carry hidden risks of aged electrolytic capacitors, untested channel isolation, and undocumented prior field fault exposure that cause erratic RPM readings during unit load transients.
- Why does New Surplus pricing sit higher than generic used/refurbished marketplace listings?All New Surplus inventory completes mandatory QC validation: serial traceability cross-check against OEM production logs, 24-hour continuous thermal load bench testing with simulated Keyphasor pulse signals across both channels, 500 V megger insulation testing verifying >10 MΩ channel-to-ground isolation, full firmware backup, and anti-static sealed foam packaging. Refurbished lots skip this multi-step validation workflow, introducing avoidable operational risk for safety-critical turbine overspeed protection racks.
- Can raw RTD temperature probes or 4–20 mA process transmitters wire directly to the input channels?No, the unit only processes pulse signals from proximity Keyphasors and magnetic speed pickups. Thermal monitoring requires 3500/60; analog process variable trending uses 3500/62. Verify with the OEM datasheet before modifying field wiring to prevent permanent channel circuit damage.
- Does the unit locally store overspeed fault snapshots or long-term machine RPM trending logs?No, all speed trending records, timestamped overspeed fault events, and sensor diagnostic counters are captured and retained exclusively by the Slot1 3500/20 TDI master communication gateway. The unit performs real-time RPM conversion, overspeed alarm comparison, and backplane Keyphasor distribution only, with no on-board data storage memory.
