Bently Nevada 128718-01 Keyphasor External Termination Block

Bently Nevada 128718-01 Keyphasor external termination block

The Bently Nevada 128718-01 is the Keyphasor External Termination (ET) Block with Euro style connectors for the 3500/25 Enhanced Keyphasor Module. It provides a remote landing point for the once-per-turn reference transducers of a 3500 machinery protection rack and connects to the module’s external-termination I/O through a dedicated cable. The block is listed as an accessory in the 3500/25 datasheet.

Overview

A Keyphasor signal is a once-per-revolution pulse, usually produced by a proximity probe observing a notch or projection on the shaft. The 3500 rack uses it to measure shaft speed and to provide the phase reference needed for 1X and 2X vector data, slow-roll compensation and machinery diagnostics. The 3500/25 module conditions these signals and distributes them to the monitors in the rack over the backplane.

When the 3500/25 is ordered with external-termination I/O, the field wiring from the Keyphasor transducers lands on an ET block such as the 128718-01 instead of on the I/O module itself. Seven Star LLC supplies this block on request for customers in Oman and the GCC; availability, condition and lead time are confirmed at quotation, with technical support for selection and cross-checking of the reference against the rack configuration.

Key features

• External termination block for the 3500/25 Enhanced Keyphasor Module.
• Euro style plug-in connectors; the terminal-strip equivalent is 128726-01.
• Works only with external-termination I/O modules (standard or isolated).
• Connects to the rack through the 129530 KPH signal to ET block cable.
• Lets Keyphasor field wiring be terminated in a marshalling cabinet away from the rack.

Technical specifications

Operating principle

The ET block is passive. Each Keyphasor transducer’s supply, signal and common conductors are landed on its Euro style connectors, and the 129530 cable carries them to the external-termination I/O module at the rear of the rack. The 3500/25 module supplies −24 Vdc to the transducer, detects the once-per-turn event and passes the conditioned Keyphasor signal to the other monitors. Buffered outputs are provided at the front of the module (coaxial connectors) and at the rear through Euro style connectors, for portable analysers and diagnostic systems.

Typical applications

• Speed and phase reference for steam and gas turbines, compressors and generators.
• Machines with several shafts or gearboxes needing more than one Keyphasor input; a rack supports up to four Keyphasor signals, or eight in paired configuration.
• Magnetic pickup speed inputs using isolated I/O; magnetic pickups need shaft speeds above 200 rpm.
• Installations where all transducer wiring is marshalled in separate field termination cabinets.

For Triple Modular Redundant (TMR) racks, the 3500/25 datasheet calls for two Keyphasor modules, so a TMR installation using external terminations needs an ET block and cable set for each module’s external I/O. In a standard rack, one half-height module handles two transducers; adding a second card (option A02) raises this to four, and paired configuration allows up to eight Keyphasor signals per rack.

Selection and ordering notes for the Bently Nevada 128718-01

The 3500/25 ordering code is 3500/25-AA-BB-CC. Option A01 is one half-height two-channel card and A02 is two cards (four channels). The B option selects the I/O: B01 internal terminations, B02 external terminations, B03 internal barrier, B04 isolated internal and B05 isolated external. The C option defines approvals: C00 none, C01 cNRTLus Class 1 Div 2, C02 ATEX/IECEx/CSA Zone 2.

• ET blocks cannot be used with internal-termination I/O, so the module must have option B02 or B05.
• ET blocks and cables are ordered separately from the module.
• Choose 128718-01 for Euro style connectors or 128726-01 for terminal strips.
• Spares in the same family: Enhanced Keyphasor module 149369-01 (a direct replacement for 125792-01), internal I/O 125800-01, external I/O 126648-01, isolated internal I/O 125800-02, isolated external I/O 126648-02, barrier I/O 135473-01 and user guide 129770.

Installation and commissioning

• Mount the block in the field termination cabinet following the 3500 installation documentation.
• Connect the 129530 cable between the block and the external-termination I/O module.
• Land each Keyphasor transducer, keeping shields continuous and grounded at a single point.
• Confirm the probe gap voltage and the speed reading in the 3500 configuration software, then check the once-per-turn pulse on the buffered output with an oscilloscope or analyser.

Maintenance and troubleshooting

If the speed reading drops out or phase readings jump, check the probe gap and the condition of the shaft notch first, then the connectors on the ET block and the 129530 cable. A missing transducer supply at the block indicates a cable or I/O module problem. Isolated I/O adds a slight phase shift, so do not mix isolated and non-isolated reference channels when comparing phase data between machines without accounting for it.

Quotation enquiries for Oman and the GCC

Seven Star LLC supplies the Bently Nevada 128718-01 on request; availability, condition and lead time are confirmed at quotation. Please send:

• the exact part number 128718-01 and the 129530 cable code with length and assembly option;
• quantity;
• a photo of the block label or of the 3500/25 module and I/O labels;
• the machine and application, for example compressor speed and phase reference.