Usually the frequency can be displayed on the VFD’s keypad display. You can usually switch between showing rpm speed or frequency. The formula of spindle speed is:
400 Hertz × 2 × 60 seconds / 2 poles = 24,000 rpm vs.
580 Hertz × 2 × 60 seconds / 2 poles = 34,800 rpm,
but the latter is only important for spindles like these. Most spindles have two magnetic poles, which results in a speed range of 6000–24000 rpm by applying 100–400 Hz.
On the VFD output, you should only connect the three-phase spindle. Nothing else.
