Bently Nevada 125800-02 Isolated Keyphasor I/O Module, Internal

An isolated rear I/O module for magnetic pickup Keyphasor inputs

The 125800-02 is the Isolated Keyphasor I/O Module with internal terminations for the Bently Nevada 3500/25 Keyphasor Module. It sits in the full-height rear slot behind the half-height Keyphasor main card and brings the two transducer channels and the buffered Keyphasor outputs onto pluggable terminal connectors on the module itself.

Bently Nevada designed the isolated I/O for applications where the Keyphasor signal is wired in parallel to several devices and must be isolated from other systems, such as a turbine control system. It was created for magnetic pickups, and it can also isolate Proximitor inputs if an external power supply is provided. Its main purpose is speed measurement: it can deliver phase, but it adds a slightly higher phase shift than the non-isolated version, and the datasheet plots that shift against machine speed.

Technical specifications

Choosing between isolated and non-isolated I/O

The 3500/25 offers five rear module types. The standard Keyphasor I/O (125800-01 internal, 126648-01 external) gives the lowest phase shift and suits proximity probe Keyphasor channels used for 1X and 2X vector data. The isolated I/O (125800-02 internal, 126648-02 external) is the choice where a magnetic pickup signal is shared with a control system or a separate speed device. An internal barrier I/O module (135473-01) is listed for intrinsically safe field wiring.

As a general installation note, an internal-termination module cannot be used with an external termination block; the field cables land directly on the connectors of the I/O module.

Documents and quotation

The 3500/25 Enhanced Keyphasor Module datasheet, which lists this module in its spares section, is attached. Browse Vibration Monitoring for related 3500 modules.

For a quotation, send the part number, quantity and the Keyphasor main module installed in the rack.

What a Keyphasor Signal Does in a 3500 System

A Keyphasor is a once-per-turn reference signal taken from a notch or projection on a rotating shaft. Each time the mark passes the transducer, a pulse is generated. The 3500 rack uses this pulse in two ways. First, the time between pulses gives shaft speed. Second, the pulse is a phase reference: by comparing the timing of each vibration waveform with the Keyphasor pulse, the monitoring system can calculate the phase angle of the vibration at running speed and its harmonics. Phase and amplitude together form the vibration vectors used for balancing, critical speed analysis and machine diagnostics.

The 3500/25 Keyphasor Module conditions these signals and distributes them across the rack backplane to other monitors that need a speed or phase reference. The I/O module behind it is the field interface: it takes the transducer wiring and brings out buffered outputs for portable analysers and other equipment.

Magnetic Pickups and Isolation

A magnetic pickup produces a voltage when a ferromagnetic target passes in front of it, without needing an external power supply. The amplitude of the signal increases with speed. When the same pickup also feeds a turbine governor, overspeed device or control system, a direct parallel connection can create ground loops or let a fault in one system affect another. The isolated I/O module 125800-02 places isolation between the field signal and the 3500 rack, so the shared signal can be used by the monitoring system while keeping the systems electrically separate.

Installation and Maintenance of the 125800-02

• Confirm that the main module installed in the slot is a 3500/25 ordered for isolated I/O before fitting the 125800-02.
• Follow the Bently Nevada field wiring diagrams for the terminals and shields.
• Configure the channels in the 3500 Rack Configuration Software to match the transducer type and the Keyphasor event ratio.
• Observe electrostatic discharge precautions when handling modules, and follow site procedures for work on live racks.
• After installation, check speed and phase readings against a known reference or a portable instrument.

Spare Parts Strategy

Rack I/O modules are usually kept as critical spares because a failed Keyphasor channel can affect speed and phase information for several monitors in the rack. Record the exact part number of each installed I/O module, since the internal-termination, external-termination and barrier versions are not interchangeable without changes to wiring or configuration.

Typical Applications in Oman & the GCC

3500 systems protect steam and gas turbines, centrifugal compressors, large pumps and generators in oil and gas production, refining, petrochemical, LNG, power and desalination plants across the region. The 125800-02 is used where a magnetic pickup is shared with a turbine control or overspeed system.

Why Source the Bently Nevada 125800-02 I/O module from Seven Star LLC

Seven Star LLC supplies Bently Nevada equipment and spare parts to industrial, laboratory and project customers across Oman and the GCC. Our team works from the complete ordering code rather than a short description, because many manufacturers sell several closely related variants under similar names. When you request a quote, we compare the requested code with the manufacturer’s published data and, for a replacement, with the label of the installed unit, so that differences in version, accessories or scope of supply are raised before the order is placed.

Our team can help confirm the correct ordering code, list the accessories and consumables that are ordered separately, and collect the documentation your project or maintenance department needs for its records. To start, request a quote with the model, quantity, application and any site or project specification that applies.