I have this sorted

The Heiz controller has been configured for a Mechatron VFD. The manual is not very clear as to the 25pin port functions. The Heiz Zero3 port 'LPT2' connects to a second port on the PC (I am just using the standard printer port for LPT2 and a PCI parallel card for the more important LPT1). The port '0-10V' does then serve to supply the voltage & switching functions.

To avoid joining the ACM & DCM grounds of the VFD, I have configured for the Huanyung as follows:

Port 0-10V, pin 14 (constant 3.25V) connected to the 5V coil of a reed relay which is operated through switching (to ground) pin1. The switched terminals of the relay open & close FOR & DCM of the VFD

Port 0-10V, pin 18 (+ve 0-10V) and pin 25 (ground) then supply the variable voltage to control the spindle speed between VI & ACM of the VFD.

Configure port input I222 hood - query ready signal cabinet HF spindle LPT2 PIN 12 (for WINPC-NC)

The Huanyung is then good to go. The only thing wrong at the moment is the spindle speed is running at +30% across the speed range but I will add a trimmer to adjust this.

Thank you Boyan for saving me from smoking the VFD at the outset

Gavin