Flipping Spindle Signal

I discovered that my spindle driver has a reversed speed signal. I.e. 10 volts = 0 speed, 0 volts = full speed.
In a programming language the fix could be as simple as: Required Output = 10 - Normal Output.

Is there a way to do this in Hal?
My other alternative is to use an inverting opamp but to get full range I will need a single supply rail to rail opamp capable of running at the required voltage range.

Hi Sadlers,
I don't know how to do that in hal. But I'm sure you can adjust it on your amplifier. Paramter called maybe
Frequency command resource setting
or
Running command resource setting

Do you have a manual for your amplifier?
Chris

You can certainly do this in hal (say with the scale component)
But as crhis@cnc said it would be better to setup the drive to act
in a standard way.

Are you sure the drive is really running at full speed with 0V applied?

A hal or hardware setup error could cause this kind of behaviour:
0 commanded RPM = maximum VFD RPM

It definitely works this way. I connected a pot and measured the voltage. Not too much I can do about the drive settings. The controller (and motor) were salvaged from a treadmill. It replaces the original lathe single speed motor with more power (and variable speed), at the great price of free.

Some more information: This is a DC drive/motor combo with a 90 V dc motor and PWM controller.. I have speed control from near zero to just under 6000 rpm with pretty good torque right down to the low end. When I need more torque, I can move the pulleys around. Bottom line, the arrangement serves me well (other than the quirky control voltage)

So the way I see this working is adding the following lines to my Hal file:
Loadrt scale count =1
addf scale.0 servo-thread
setp scale.0.gain -1
setp scale.0.offset=10
net spindle-speed-scale spindle.0.speed-out => scale.0.in
net spindle-speed-DAC scale.0.out => ??

Is this the right way to do this? Where should the out go to?

Just a stab in the dark, but what about inverting the PWM pin?

Yeah, I tried that. I doesn’t do what is needed.

What board/controller?

I am using a mesa 5i25/7i76