Bently Nevada 126648-02 Isolated Keyphasor I/O Module, External

Isolated Keyphasor I/O with wiring taken out to a termination block

The 126648-02 is the Isolated Keyphasor I/O Module with external terminations for the Bently Nevada 3500/25 Keyphasor system. Instead of terminal plugs for each channel, both transducer channels leave the module on a single multi-pin connector marked TRANSDUCERS, which connects by cable to an external termination block. The buffered Keyphasor outputs remain on a small pluggable connector on the module.

Like the internal-termination version 125800-02, it is designed for magnetic pickups and for signals that are shared in parallel with other systems, such as a control system, where isolation is required. It also works with Proximitor inputs if an external power supply is provided. Bently Nevada notes that the isolated I/O is intended mainly for speed and adds a little more phase shift than the non-isolated module.

Technical specifications

What to order with an external-termination module

Bently Nevada states that when I/O modules with external terminations are ordered, the external termination block and the cable must be ordered separately. For the 3500/25 that means one Keyphasor ET block, either 128718-01 with Euro style connectors or 128726-01 with terminal strip connectors, and one 129530 cable. The cable code sets the length (0005 to 0100 feet) and whether it comes assembled (02) or not assembled (01).

External termination is generally used where field cables are marshalled in a separate termination cabinet rather than brought to the back of the rack.

Documents and quotation

The 3500/25 datasheet with the spares and cable codes is attached. Browse Vibration Monitoring for the main module and other 3500 parts.

For a quotation, send the part number and quantity, and say whether you also need the ET block and the 129530 cable with its length.

What a Keyphasor Signal Does

A Keyphasor signal is a once-per-turn (or multiple-event-per-turn) pulse taken from a notch or projection on the machine shaft. In a Bently Nevada 3500 system it is the timing reference for the whole rack. Monitors use it to measure shaft rotative speed, to calculate the phase angle of the 1× and 2× vibration vectors, and to synchronise waveform sampling for diagnostic software. Without a healthy Keyphasor signal, many of the diagnostic and filtered vibration values in the rack cannot be produced.

The 3500/25 Keyphasor module receives the transducer signals through its I/O module, conditions them into clean digital timing pulses and distributes them over the rack backplane to the monitor modules. The I/O module selected, such as the 126648-02, defines how the field wiring connects and whether the inputs are isolated.

Why Choose the Isolated 126648-02

Isolation becomes important when the same transducer signal is shared with another system, for example a turbine control system or an overspeed device that also reads a magnetic pickup. If both systems are connected to the transducer without isolation, ground potential differences can create ground loops that distort the signal or inject noise. The isolated I/O module breaks this path, so the 3500 system can share the signal without interfering with the other equipment. As noted above, Bently Nevada positions the isolated module mainly for speed measurement because it introduces slightly more phase shift than the non-isolated version.

Magnetic Pickups and Proximity Probes

A magnetic (passive) pickup generates a voltage when ferrous teeth or a notch pass its pole piece; its output amplitude rises with speed and it needs no power. A proximity probe system measures the gap to the shaft and needs a supply voltage from the monitor or an external source. The 126648-02 is designed for magnetic pickups, and it can be used with Proximitor inputs only when an external power supply is provided.

Selection & Ordering Guide for the 126648-02

When replacing a module in an existing rack, match the part number on the installed module and check the rack configuration so that the 3500/25 settings remain valid.

Installation & Maintenance

• The I/O module occupies the rear slot behind its Keyphasor module; make sure the front and rear modules are the matching pair for the configuration.
• Route the 129530 cable between the rack and the ET block away from power cables, and secure the multi-pin TRANSDUCERS connector.
• Follow the shield and grounding guidance in the 3500 installation manual to avoid introducing a new ground loop at the termination cabinet.
• Because the Keyphasor feeds other monitors, follow site permit and bypass procedures before working on the module.
• After replacement, confirm the speed reading and phase values against a known reference or historical data.

Typical Applications in Oman & the GCC

3500 racks with Keyphasor modules protect gas turbines, steam turbines, centrifugal compressors, large pumps and generators in oil and gas production, gas processing, refining, petrochemical and power plants across the region. The external-termination 126648-02 is common where plant standards require all field wiring to land in a dedicated marshalling cabinet.

Why Source from Seven Star LLC

Seven Star LLC supplies Bently Nevada 3500 modules and accessories across Oman and the GCC. Our team can help confirm the correct I/O module, ET block and cable codes before a quotation is issued.