Cross channel phase is a process of using a two-channel instrument to determine the phase relationship between two measurement locations without using a fixed reference tachometer. The cross channel phase uses two time waveform signals: Using channel “A” as a reference it takes one cycle in the time waveform as one revolution of the shaft and plots the “B” channel time waveform against channel “A” to determine the relative phase. This process is useful for confirming angular or offset misalignment, unbalance, loose parts, and problems such as soft foot (machine frame distortion), etc.
Cross channel phase cannot be used for performing a dynamic balance on a rotating component as it refers to relative phase while dynamic balancing requires absolute phase data.
Vibration Analysis by Gary James CRL