1. General Information

• Manufacturer: Bently Nevada (Baker Hughes)

• Model Number: 3500/20

• Main Board Part Number: 125744-02

• Rear I/O Board: 125745-01 (Exclusive Communication Terminal Board)

• Product Name: Standard Rack Interface Communication Module

• Series: 3500 Machinery Protection System

• Module Type: Full-height legacy serial communication module

• Application: Early-generation rack communication gateway; realizes serial data transmission, rack configuration and alarm data upload; widely used in old-version power plant and petrochemical monitoring system; replaced by 3500/22M TDI Ethernet module.

• Installation Rule: Must be installed in the last slot of the rack

• Compliance: API 670

2. Functional Description

• Communication Interface: RS232 + RS422 Dual Serial Port

• Transmission Protocol: Proprietary Bently serial communication protocol

• Baud Rate: Fixed 38.4 kbps high-speed serial transmission

• System OK Relay: Built-in rack health diagnostic relay output

• Configuration Function: Local software configuration via serial cable

3. Electrical Specifications

• Backplane Power: +5 VDC from rack backplane

• Power Consumption: 4.75 W typical (Low power consumption)

• Serial Port Standard: RS232 (Short distance) / RS422 (Long distance)

• Relay Contact Rating: 30 VDC / 5 A Normally Closed dry contact

• Transmission Distance: Max 1200 meters (RS422)

• Isolation Voltage: 1500 VAC channel-to-system isolation

4. Environmental Specifications

• Operating Temperature: -30 °C ~ +65 °C (-22 °F ~ +149 °F)

• Storage Temperature: -40 °C ~ +85 °C (-40 °F ~ +185 °F)

• Relative Humidity: 5% ~ 95% (Non-condensing)

• Anti-vibration: Compliant with API 670 industrial vibration standard

5. Mechanical Specifications

• Structure: Full-height single slot legacy communication module

• Dimensions (H × W × D): 241.3 × 24.4 × 170 mm

• Weight: Approximately 0.63 kg

• Mounting: Hot-swap capable, tail slot mandatory installation

6. Compatible Devices

• Matching Rear Board: 125745-01 (Serial port terminal board)

• Upper Software: Legacy System 1 Serial Monitoring Software

• Rack Chassis: Early version 3500 rack chassis

7. Key Features

• Dual serial port design for short & long-distance communication

• Low power consumption, stable operation for long-term monitoring

• Independent system OK relay for rack fault alarm

• Simple serial wiring suitable for old industrial control system

• API 670 compliance for critical rotating machinery protection

8. Critical Difference (20 VS 22M)

• 3500/20 (125744-02): Old version, Serial port(RS232/422), No waveform, slow transmission.

• 3500/22M (288055-01): New version, Ethernet+USB, Waveform/Spectrum, high-speed TDI.