Hi,
I have a Delta Model B VFD. It, like almost all VFDs has several programmable digital outputs. These outputs, depending on the manufacturer can tell you current say, or temperature and
various other parameters. There is one available output on my VFD that produces a pulse every revolution, ie an index pulse, or rather a synthesized index pulse.
I've never used it so I cant tell you whether it is sufficientlty accurate to use for rigid tapping say but it certainly is good enough for Mach to use to work out how fast the spindle is going.
The top end of my highspeed spindle (24000 rpm max) is enclosed so I can't readily attach a pulse generator and I don't want to take the top off it. I paid big bucks for a German made one
and I do NOT want to bugger it up!
Mach, or more technically correctly your ESS, measures the time between index pulses and then calculates how many rpm. Mach can display that figure and it is a VERY accurate measure of
the actual speed of the spindle.
I seldom find that I need a really accurate spindle speed, within 5-10% is adequate for most things, rigid tapping however is a specialized procedure and requires an accurate measurement.
My highspeed spindle is very low torque and so I don't even try to use it for rigid tapping, consequently I don't really care about accurate speed. If however you are interested or have a specific need
then you may want to think about attaching a pulse generator to your spindle. If its not practical maybe your VFD has a synthesized index signal as mine does.
Can you post the manual for your drive?
Craig