On Wed, 2011-03-16 at 21:05 +0000, andy pugh wrote:
> On 16 March 2011 20:50, Michael Jones <[email protected]> wrote:
>
> > And yes, the pot is isolated as you've said.
> >
> > Does this mean that this upgrade is a "not recommended" or possibly
> > hazardous direction, or just that there's more I need to do besides just
> > hooking up the VFD output pins from the G540 to make it work
> > correctly/safely without breaking something?
>
> It should be fine, but you need to know how "isolated" the VFD output is.
> I had a KBIC speed controller and the low side of the pot was held at
> +Motor voltage (100V)
> The VFD output has it's own GND terminal, which is a good sign.
>
> http://www.cnczone.com/forums/gecko_drives/88165-g540_vfd_output_floating.html
> Has a comment from Mariss (who is Mr Gecko) saying that it will be OK.
>
"The analog output is optically isolated from both the G540 and the PC.
- Mariss"
This quote doesn't instill much confidence, but it seems that the G540
terminals 7 Ground, 8 Output, 9 +10V are isolated from the Gecko circuit
and float. I am guessing these terminals are implying a potentiometer
like function in the G540. The +10V terminal is were you would connect
the +10V output from the KBIC to a potentiometer. Ground connects to the
ground from KBIC potentiometer terminal for the far end of the
potentiometer from the +10V. Then the output terminal (8) and an EMC2
digital PWM signal go to the potentiometer wiper.
Current
KBIC
---------------
GND Wiper +10
| | |
| V |
+-----------+
Potentiometer
New
KBIC
---------------
GND Wiper +10
| | |
| | |
GND OutP +10V
7 8 9
G540
^
|
Parport 14
The wiper will be controlled by the EMC2 PWM on parallel port pin 14 VFD
PMW (50Hz). See here for the EMC2 HAL setup:
http://linuxcnc.org/docs/html/examples_spindle.html#r1_2
The PWM frequency will be determined by the thread rate that the PWM
component is loaded in - usually the servo thread or 1kHz (?). The G540
doc hints at 50Hz, but I think it will work anyway. This is off the top
of my head, so check the above for yourself.
I suspect you could wire the terminals directly, but there is a
possibility that current limit resistors might be needed somewhere.
--
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/index.html
California, USA
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