The BENTLY 3500/25 125792-01 is a fundamental component of the 3500 Machinery Protection System. It serves as a specialized tachometer module that processes signals from proximity probes or magnetic pickups to determine shaft rotational speed and phase angle. Without a Keyphasor signal, synchronized vibration analysis—such as identifying specific 1X or 2X vibration components—would be impossible. The module provides a once-per-turn pulse that acts as a timing reference for all other monitoring modules in the rack.
The 3500/25 module is a two-channel device, meaning it can accept inputs from two independent Keyphasor transducers. In high-criticality applications, these two channels can be used to monitor two separate shafts or provide redundant sensing for a single shaft. The 125792-01 hardware is designed to ensure that if one transducer fails, the system can automatically switch or provide an alarm, maintaining the integrity of the phase-locked data required by System 1 software.

The 125792-01 module is engineered to handle a wide range of input frequencies, supporting machines ranging from low-speed hydroelectric turbines to high-speed centrifugal compressors. It features sophisticated signal conditioning that filters out mechanical runout and electrical noise from the raw transducer signal. The module can be configured to trigger on the leading or trailing edge of a notch or a projection on the shaft, providing flexibility for various mechanical mounting scenarios.
Information processed by the 3500/25 is distributed across the 3500 rack backplane. This allows every vibration monitor in the system to "see" the timing pulse. By correlating vibration amplitude with the Keyphasor pulse, the system can generate Bode plots, Polar plots, and shaft centerlines. The 125792-01 ensures that this timing data is transmitted with microsecond-level accuracy, which is vital for detecting subtle changes in machinery health.
The 125792-01 module includes built-in self-diagnostics that monitor the health of the connected transducers and the internal circuitry. Front-panel LEDs provide immediate feedback on "OK" status and pulse activity. During installation, the module is configured via the 3500 Rack Configuration Software, where thresholds and hysteresis are set to ensure stable pulse triggering even in the presence of shaft surface irregularities.



