Bently Nevada 126648-01 Keyphasor I/O Module (External Term.)

Bently Nevada 126648-01 Keyphasor I/O module with external terminations for the 3500/25

The Bently Nevada 126648-01 is the rear-slot Keyphasor I/O module, external-termination version, used with the 3500/25 Enhanced Keyphasor main module in a 3500 machinery protection rack. The manufacturer datasheet lists 126648-01 as the spare “Keyphasor I/O Module (External Terminations)”. It is the non-isolated type, so it is meant for proximity-probe Keyphasor signals, and the field wiring lands on a separate external termination block instead of on the module itself.

In the 3500/25-AA-BB-CC ordering code, 126648-01 corresponds to the B position code 02 (“I/O module with External Terminations”). The sibling parts are 125800-01 (the same non-isolated I/O with internal terminations), 125800-02 (isolated, internal terminations) and 126648-02 (isolated, external terminations). Seven Star LLC supplies 126648-01 in Oman and the GCC as an independent supplier in Muscat.

Decoding 126648-01 within the 3500/25 ordering structure

126648-01 technical specifications

The figures above are taken from the 3500/25 datasheet and describe the module family; values printed on the unit label and in the project documentation take priority for an installed system.

How the Keyphasor channel works with 126648-01

A Keyphasor signal is a once-per-turn pulse, or a multiple-event-per-turn pulse, produced when a notch, key or gear tooth on the shaft passes a proximity probe. The 3500/25 converts that pulse into a digital timing reference that every monitor in the rack can use. With it the rack measures rotative speed, and it can compute vector quantities such as 1X amplitude and phase.

126648-01 is the physical connection point of that chain. It carries the probe signal and the -24 Vdc Proximitor supply between the field and the main module, and it supplies the buffered outputs for external diagnostic equipment. Because it is the external-termination version, a single multipin cable runs from the I/O module to a termination block mounted where wiring is easier, for example on a cabinet wall, and that block carries the field terminals.

Where 126648-01 fits and what it must be paired with

The module installs in the rear of the same rack position as its 3500/25 main module. Each rack may hold no more than two Keyphasor main modules, one in a top half-slot and one in a bottom half-slot, and a system can accept up to four Keyphasor signals in normal configuration or eight in a paired configuration. Redundant (TMR) systems use two Keyphasor modules working in parallel.

• External termination block options listed by the manufacturer: 128718-01 (Euro-style connectors) and 128726-01 (terminal strip connectors).
• Signal cable: the 3500 Keyphasor-to-ET-block cable family 129530-AAAA-BB (lengths from 5 ft / 1.5 m to 100 ft / 30.5 m, supplied assembled or not assembled).
• External termination blocks cannot be used with internal-termination I/O modules, so 126648-01 and 125800-01 are never interchangeable on an installed rack without changing the field wiring arrangement.
• Main module partner: 149369-01 Enhanced Keyphasor Module, which the datasheet states replaces the older 125792-01 module as a direct plug-in.

Selection checklist before ordering 126648-01

• Confirm that the installed I/O module is the external-termination type. A rack wired to terminals on the module itself needs 125800-01 instead.
• Confirm that the Keyphasor transducer is a proximity probe system. For magnetic pickups in shared or isolated service the manufacturer provides the isolated types (125800-02 and 126648-02).
• Check whether the rack uses internal barriers. The internal-barrier I/O is a different assembly and has a narrower operating temperature window (0 to +65 °C).
• Note the agency approval of the existing assembly, since the approval option is selected at the 3500/25 ordering level.
• Count how many external termination blocks and cables the replacement will also need, because they are ordered separately.

Installation, commissioning and maintenance of 126648-01

Treat 126648-01 as a hot-spare item that is changed only with the rack procedures in the 3500 manuals. Use an anti-static wrist strap, keep the module in its antistatic packaging until the moment of installation, and match the new module to the existing external termination cable before powering the Keyphasor channel.

After replacement, verify the following: the OK LED on the 3500/25 front panel is lit, the TX/RX LED flashes, the Keyphasor transducer gap voltage sits in the middle of the threshold window, and the speed reading on the rack display matches the machine tachometer. If the Keyphasor was set to manual threshold, re-check the threshold voltage and hysteresis in the 3500 Rack Configuration Software, because they are programmed in the main module rather than in the I/O module. Good practice for a plant spares store is to hold one external-termination I/O module and one internal-termination module for each rack design in service.

Typical applications in Oman and the GCC

The 3500/25 and its I/O modules sit in the machinery protection racks of gas turbines, steam turbines, centrifugal compressors and large motor-driven pumps found across oil and gas facilities, power stations, desalination plants and petrochemical sites in Oman and the wider GCC. The Keyphasor channel is the speed and phase reference for almost every vibration measurement on those trains, so a failed I/O module often shows up as a loss of speed or phase indication for a whole machine.

Control rooms in the region are air-conditioned, but cabinets near the machine can see high ambient temperature, dust and salt-laden humid air in coastal sites. The external-termination design helps here because field wiring can be moved to a more accessible termination block, and the module itself stays inside the rack. A ready 126648-01 on the shelf shortens the outage window during a turnaround.

Keyphasor I/O module family at a glance

Information to send with your RFQ for 126648-01

• Part number 126648-01 and quantity, plus the full 3500/25 code if known (for example 3500/25-01-02-00).
• Photo of the rear module label, including the serial number and revision.
• Rack type, location (Oman or GCC country) and whether the module is a like-for-like spare or part of a modification.
• Whether external termination blocks (128718-01, 128726-01) or Keyphasor cables are also required.
• Required delivery time and any documents or inspection records needed with the shipment.

Related Bently Nevada products: Bently Nevada 126648-02 Isolated Keyphasor I/O Module, External, Bently Nevada 125800-02 Isolated Keyphasor I/O Module, Internal, Bently Nevada 128718-01 Keyphasor External Termination Block, Bently Nevada 125680-01 3500/40M Proximitor I/O Module, Bently Nevada 125808-01 Proximitor External Termination Block and Bently Nevada 149369-01 3500/25 Enhanced Keyphasor Module.

Documents and quotation

The 3500/25 Enhanced Keyphasor Module datasheet is attached on this page, and the specifications above follow its content. Read it together with the 3500 Rack Installation and Maintenance Manual when planning a change-out.

Send us the part number 126648-01 and the rack details, and Seven Star LLC will confirm condition, quantity and lead time for Oman and the GCC in the quotation.