Component Snapshot At-a-Glance
- Model: 3500/33
- Alt. P/N: 149992-01 (standard); 149986-01 legacy discontinued
- Product Series: Bently Nevada 3500 Machinery Protection System
- Hardware Type: Full-height front rack relay main board + matching rear I/O daughter card
- Key Feature: 16 independent epoxy-sealed SPDT dry contacts, 4 groups of 4 channels switchable NE/ND fail-safe mode
- Primary Field Use: Executes user-programmed AND/OR alarm voting logic to drive site ESD trips, alarm horns, DCS fault interlocks, and machine shutdown circuits.
Hard-Numbers: Technical Specifications
- Protocol Support: Proprietary 3500 rack backplane bus; configured via 3500 Rack Configuration software
- Port Count: 16 SPDT relay channels via rear D-Sub I/O card; front panel TX/RX comm LEDs, per-channel ALARM LEDs
- Backplane Scan Rate: Synchronized rack-wide 10ms data polling
- Operating Temperature: -30°C to +65°C operational; -40°C to +85°C storage
- Isolation Rating: 1500V RMS galvanic isolation between backplane logic and field relay contacts
- Power Draw: 24VDC rack backplane, 12–15W typical load
- Relay Contact Rating: Max 6A resistive; 300VDC / 250VAC max switched voltage; min 100mA @12VDC minimum load
- Contact Life: 100,000 cycles at 5A 24VDC resistive load
- Channel Grouping: 4 banks of 4 channels with DIP switch for Normally Energized / Normally De-energized mode
- Hot-Swap Capable: Yes, backplane hold-up circuit maintains rack power during live replacement
- Dimensions Front Card: 241.3mm H × 24.4mm W × 242mm D
- Dimensions Rear I/O Card: 241.3mm H × 24.4mm W × 99.1mm D
- Weight (Full Assembly): ~1.1kg
The Real-World Problem It Solves
Low-channel 3500/32M 4-relay cards waste rack slots on large turbine setups requiring dozens of independent trip and alarm outputs. External PLC relay racks add extra wiring, single points of failure, and separate configuration databases.Where you’ll typically find it:
- Fossil / combined cycle steam & gas turbine 3500 protection racks for emergency trip logic
- Refinery high-speed centrifugal compressor ESD and fire/gas alarm interlock cabinets
- Hydro generator and large boiler feed pump vibration monitoring trip systems
This single-slot 16-channel relay card consolidates all machine alarm voting and hardwired trip outputs without external auxiliary relay racks.
Hardware Architecture & Under-the-Hood Logic
Onboard dedicated logic controller; no shared processing with monitor cards, paired mandatory rear I/O daughter card for field wiring breakout.
- Regulated 24VDC backplane power feeds isolated digital logic and relay drive circuits.
- Backplane bus continuously pulls Alert/Danger/Not OK status from all vibration, displacement, speed monitor cards.
- Onboard firmware executes user-defined AND/OR voting logic for each of the 16 relay channels.
- DIP switches set each 4-channel bank to NE (fail-safe energized) or ND (normal de-energized) operation.
- Isolated relay driver circuits actuate epoxy-sealed SPDT dry contacts routed to rear D-Sub I/O terminals.
- Front panel LEDs display module OK status, rack bus TX/RX activity, and individual channel alarm activation.
Field Service Pitfalls: What Rookies Get Wrong
Direct wiring high-inductive loads without external arc suppressionTechs wire solenoid trip coils or motor contactors straight to 3500/33 relays. Inductive flyback voltage burns relay contacts, creates contact welding and permanent channel failure.
- Quick Fix: Install external freewheeling diodes DC loads / RC snubbers AC loads; use intermediate interposing relays for loads above 2A.
Mismatched rear I/O daughter card or unlatched rear connectorsInstallers fit analog rear I/O hardware to relay front card or fail to lock rear card latches. Mismatched pinouts trigger constant I/O Mismatch event faults and zero relay operation.
- Field Rule: Only use matching 3500/33 rear relay I/O card; fully seat and lock both rear card latches, tug lightly to confirm no vibration play.
Incorrect DIP switch NE/ND setting for safety trip circuitsNew techs leave banks set to ND for critical ESD shutdown logic. Loss of rack power fails to drop trip contacts, creating unprotected machine run conditions.
- Field Rule: All safety shutdown channels set to Normally Energized (NE); horn/alarm non-critical outputs can use ND mode.
Commercial Availability & Pricing Note
Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.
