The three phases are typically labled ABC and the rotation is determined by the phase sequence...A-B-C. If you swap two (any two, just two)the sequence reverses...C-B-A.
Masking ambient noise is often difficult if not impossible. You can take background measurements first to help separate them from your measurements of interest later.
Rich L.
The connection from the shaft brush to ground is a second path shunting current away from the bearing path to ground, therefore it does not measure shaft current thru the bearing, but helps reduce it. One thing the measurement will tell you is if there is a problem with the insulation on the...
While you say precise position control is not needed, a stepper motor should still be an option for your quick reversal and position holding application. Better yet, for smooth motion (variable speed and torque) I would go with Brushless DC in the form of a 3-phase Permanent Magnet motor driven...
Typical Variable Frequency Drives (VFD) are made up of 3 sections. A rectifier on the input (sounds like a 3-ph rectifier in your case), a DC link, and an inverter that switches the DC to synthisize AC at other frequences and voltages. Voltage imbalance on the 3-phase source may cause...