Product Brief: Bently Nevada 3500/91 ETS Logic Module (161204-01)
The 3500/91 ETS Logic Module (part number 161204-01) is a dedicated safety-critical module within the Bently Nevada 3500 series machinery protection system. It provides programmable logic for generating electronic trip outputs based on alarms from other 3500 monitoring modules (e.g., vibration, temperature, speed, position). The module is designed for overspeed protection systems and emergency shutdown (ESD) applications in rotating machinery.
Key Features
Standalone logic solver for ETS (Electronic Trip System) applications.
Accepts digital/analog trip signals from other 3500 series monitors.
Provides configurable voting logic (e.g., 1oo1, 1oo2, 2oo2, 2oo3) for safety integrity.
Includes first-out indication for troubleshooting.
Supports redundant configuration for high availability.
Can override vibration or temperature trips during start-up (start-up inhibit logic).
Meets API 670 (5th edition) ETS requirements.
Parameters (Table)
| Parameter | Specification |
|---|---|
| Model | 3500/91 |
| Part Number | 161204-01 |
| Product Type | ETS (Electronic Trip System) Logic Module |
| Dimensions (Height x Width x Depth) | 241 mm x 25 mm x 242 mm (9.5 in x 1.0 in x 9.5 in) – occupies one slot in 3500 rack |
| Weight (approx.) | 0.85 kg (1.87 lb) |
| Number of Inputs | Configurable (receives alarm status from up to 14 monitoring modules via backplane) |
| Number of Trip Outputs | Up to 4 independent trip relay outputs (requires external relay module such as 3500/32) |
| Logic Capability | Boolean logic (AND, OR, voting), time delays, start-up inhibit, first-out latching |
| Safety Voting Configuration | 1oo1, 1oo2, 2oo2, 2oo3 (software configurable) |
| Response Time | < 50 ms (typical from alarm detection to trip output) |
| Trip Relay Output Type | Dry contact (requires 3500/32 relay module for field wiring) |
| Indicators | LED: OK, Trip, Inhibit, First Out |
| Redundancy | Yes (dual 3500/91 modules can be configured for redundant ETS) |
| Operating Temperature | -30°C to +65°C (-22°F to +149°F) |
| Storage Temperature | -40°C to +85°C (-40°F to +185°F) |
| Power Consumption | 5.5 W (typical from rack) |
Application Scenarios (use cases)
| Application Area | Description |
|---|---|
| Gas Turbine Overspeed Protection | Logic module receives speed trip signals from 3500/50 speed module; performs 2oo3 voting before overspeed trip. |
| Steam Turbine Emergency Trip | Combines overspeed, high vibration, high bearing temperature, and low oil pressure trip conditions into a single ETS output. |
| Centrifugal Compressor Shutdown | Integrates axial position (thrust), case vibration, and process overpressure trips into one safety logic. |
| Generator Protection System | Combines differential vibration, high winding temperature, and overspeed into a generator trip sequence. |
| Hydro Turbine Overspeed & Bearing Protection | Provides voting logic for overspeed and thrust bearing over-temperature trips. |
| Turboexpander Train (Oil & Gas) | Configures start-up inhibit to bypass low speed vibration trips during machine run-up. |
| API 670 Compliant Machinery Trains | Used as the ETS logic solver in new or retrofitted 3500 racks for critical compressor or turbine trains. |
Notes
The 161204-01 is a logic module only. It does not provide direct relay contacts to field wiring. It must interface with a 3500/32 Relay Module (or similar) for trip output.
Typically used in redundant configurations (two 3500/91 modules) to achieve high SIL level.
Configuration requires 3500 System Configuration Software and a communication processor (e.g., 3500/20 Rack Interface Module).
The module must be placed in the last slot(s) of the 3500 rack (recommended slots 12–14 depending on rack size).
For SIL 2 or SIL 3 applications, additional external safety relays and proof testing may be required per IEC 61508.
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