The BENTLY 128085-01 is a specialized I/O module that facilitates the input of Keyphasor signals into the 3500 system. A Keyphasor signal is a once-per-turn voltage pulse that provides a timing reference for the rotation of the machine shaft. This is vital for calculating shaft speed and, more importantly, for determining the phase angle of vibration signals. The 128085-01 ensures that this pulse is captured with microsecond precision, enabling accurate Bode and Polar plots in System 1 software.
The 128085-01 supports two independent channels of Keyphasor input. This allows a single I/O module to monitor two different machine trains or to provide redundant phase references for a single high-speed shaft. The module is compatible with both proximity probes and magnetic pickups, automatically adjusting its threshold logic to accommodate the different signal profiles produced by these sensors.

Reliable tachometer readings require robust signal conditioning to prevent false triggering from mechanical runout or electrical noise. The 128085-01 employs sophisticated hysteresis and threshold logic to ensure that only the intentional once-per-turn event is counted. This level of signal integrity is essential for maintaining a stable speed reading and a consistent phase reference during machine startup and coast-down phases.
Designed for internal termination, the 128085-01 features high-quality terminal blocks that accept shielded twisted-pair wiring. The module’s design ensures that the cable shields are correctly grounded to prevent noise ingress. Because the Keyphasor signal is distributed across the entire 3500 rack backplane, the reliability of the 128085-01 is paramount—a failure here could impact the phase-locked data of every other vibration monitor in the rack.
As with all modern 3500 series hardware, the 128085-01 is hot-swappable. This allows maintenance teams to replace the I/O module without shutting down the entire machinery protection system, provided that appropriate safety procedures are followed. Its rugged construction ensures a long service life in environments ranging from offshore platforms to large-scale utility power plants.



