The Bently Nevada 125704-01 is the TMR Relay I/O Module for the 3500/34 Triple Modular Redundant Relay Module in the 3500 Machinery Protection System. It contains 12 epoxy-sealed relays arranged in four channel groups of three, providing 2-out-of-3 voting for each of the four relay output channels.
Item No :
125704-01Order(MOQ) :
1 PiecePayment :
EXW/CIFProduct Origin :
USAShipping Port :
WuhanLead Time :
3-5daysWeight :
3kg| Specification | Description |
|---|---|
| Manufacturer | Bently Nevada (Baker Hughes) |
| Model | 125704-01 |
| Product Family | 3500/34 TMR Relay Module |
| Product Type | TMR Relay I/O Module (Full-Height) |
| Compatible Main Module | 125696-01 (TMR Relay Module) |
| Number of Relays | 12 total (4 channel groups × 3 relays) |
| Relay Type | DPDT connected as SPST per channel |
| Voting Logic | 2-out-of-3 (2oo3) per channel |
| Contact Life | 100,000 cycles @ 1.5 A, 24 Vdc or 1 A, 120 Vac |
| Relay Operation | Normally Energized (NE) |
| Arc Suppressor | Not supported |
| Sealing | Epoxy-sealed relay construction |
| Power Consumption | 9.6 W typical |
| Diagnostic LEDs | OK, TX/RX, CH ALARM |
| Rack Position | Rear slot directly behind the 3500/34 TMR Relay modules |
| Rack Space | 1 full-height rear slot |
| Dimensions (H x W x D) | 241 mm x 24.4 mm x 99.1 mm |
| Weight | 0.5 kg (1.0 lb) |
| Operating Temperature | -30°C to +65°C (-22°F to +150°F) |
| Storage Temperature | -40°C to +85°C (-40°F to +185°F) |
| Humidity | 95%, non-condensing |
| Country of Origin | USA |
| Lifecycle Status | Active / Available as New Surplus |
| Model | Description | Typical Application |
|---|---|---|
| 125704-01 (this model) | TMR Relay I/O Module (12 relays, 2oo3 voting) | 3500/34 TMR Relay output execution |
| 125696-01 | TMR Relay Module (half-height, main card) | Companion front card for 125704-01 |
| 3500/34-01-00 | Complete TMR Relay Module assembly | Safety-critical TMR protection systems |
| 125720-02 | Spare 4-Channel Relay I/O Module (hazardous/SIL) | 3500/32M hazardous area applications |
| 149986-02 | Spare 4-Channel Relay Control Module | 3500/32M relay logic and voting |
| 129771-01 | 3500/34 TMR Relay Module User Guide | Documentation for TMR configuration |
Q1: What is the primary function of the 125704-01?
It is the TMR Relay I/O Module for the 3500/34 Triple Modular Redundant Relay Module. It contains 12 relays arranged in four channel groups of three, providing 2-out-of-3 voting for each of the four relay output channels. It receives three independent Alarm Contact Signals per channel from the 125696-01 TMR Relay Module and determines the final relay output state by majority vote .
Q2: How does the 2-out-of-3 voting work?
For each relay channel, the TMR Relay Module (125696-01) generates three independent Alarm Contact Signals from three separate data paths. These signals are fed to three separate relays within the channel group on the I/O module. The output is determined by 2-out-of-3 voting — at least two of the three relays must agree for the output to change state. If a data path's OK status is NOT OK, the associated alarm contact signal is invalidated .
Q3: What is the difference between the 125704-01 and the 125720-02?
The 125704-01 is the TMR version with 12 relays and 2oo3 voting, designed for the highest availability applications. The 125720-02 is the standard 4-channel relay I/O module for the 3500/32M, with voltage-restricted contacts for hazardous area and SIL applications. They are not interchangeable and serve different system architectures .
Q4: Can the 125704-01 be hot-swapped?
No. The field wiring terminal blocks must be disconnected and the slot area de-energized before extraction. Removing this hardware under active load can disrupt the safety voting loops and trigger false emergency trips. Always follow proper ESD precautions and verify the replacement module's configuration matches the original .
Q5: What are the common diagnostic alerts for this module?
Common alerts include:
Module Not OK: Internal self-diagnostic failure, often due to aging relay coils
Relay Fault: Channel fails to actuate, often from external wiring shorts or contact wear
Relay Readback Mismatch: Contact welding (often caused by inductive load kickback without surge suppression) or coil degradation
Watchdog Timeout: Backplane communication break, often from firmware version mismatches
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