[reg.miller]

Hi,

I have a chinese 2kW 3 phase inverter driven spindle, bought as a pair. The VFD takes either manual speed setting or on i/p voltage.

It provides a 10V supply which it seems is intended for a 10k pot. to provide an i/p signal for speed control

I want to control it from software ( GRBL ) via S commands. In principal this works but the output of my circuit is very non linear.

I have a 3V STM ARM board programmed with GRBL, I have added a GPIO port which I'm switching on an internal timer. PMW freq is 2kHz

To protect the uP card I am going through a FOD817 opto isolator.

It's half way there but the non-linearity above 14k rpm makes it a but useless as it is. Can anyone suggest how I should improve the cct?

Sadly , the manufacturer does not provide any info on the nature of the i/p circuit, so it's a bit of guesswork know what to drive it with.

TIA.


PS I don't seem to get the graph I uploaded. Basically it is pretty linear from 0-14k ( 0-9V ) ; then it asymptotes to 10.1V. The range is good but rising too quick then flattening off.