A keyphasor is the once-per-revolution pulse that gives every measurement in the rack a phase reference. With it, the system can sort vibration into orders, track shaft orbit direction, trigger steady snapshots of the waveform, and protect against overspeed reliably. Without a healthy keyphasor the monitors still alarm, but diagnostics degrade — filters and order tracking lose their anchor. The 3500/25 module serves the whole rack from one input, which is why we recommend a configured spare.
