7i76 spindle control with Sherline speed control

Hi,

I am having an issue with controlling spindle speed of a Sherline lathe using the spindle output from 7i76.

I am not able to get full spindle speed. The main problem seems to be the 7i76 loading down the speed control input.
The min pot is turned all the way down, max turned all the way up. P1 to P3 voltage is around 7 volts with 0 rpm commanded.
P2 to P1 reads 0 volts. When spindle speed is increased P2 to P1 will increase and P3 to P1 as well. At max speed P3 and P2 are at the same volts.
P3 to P1 is down to 3.7 volts.
Is the Sherline speed control not compatible or could there be another problem?

Settings in Pncconf are:
analog min limit = -20 <- had to have a negative value here otherwise would not work
analog max limit = 2000
analog max scale = 2000

Thanks,
Kevin

The 7I76 analog output is mainly intended for interfaces that have a fixed 10V supplies like VFDs
and can draw up to 8 mA or so when at full scale. If the power circuit cannot supply this current it will droop
In this case probably the easiest option is a isolated 10 or 12V supply. A Wall adapter can be used for this function

Thanks,

That did the trick, spindle speed tracks with what is commanded as it should.

I had wondered if an external supply could be used. I had a 7.5 volt wall pack. Supply voltage came out at 9.3 volts.

There is still one oddity. If I set min analog limit to 0, the spindle will not come on. Currently it is set at -1.