Creating a tachometer signal with Mesa 7i77?

I´m converting an old metal mill with analog fanuc servos and apparently it does not have tachometers on the motors but the velocity units need a tachometer signal which is currently created by the fanuc system from the encoder signal.

So what I have figured out so far is that I need to use the encoder velocity feedback, convert it from PPM to RPM and then scale it and send it to an analog output.
I think I even found an example of this a few month ago and have been trying to find it all day with no luck.
So if anyone happends to know were to find an example it would be great, otherwise my first question is:
Do I use a scale in the servo thread or can I somehow do this right in the hardware?

Depending on how you created your original HAL file, its likely you already have a nets for encoder velocity
(PNCCONF makes them for example, and I think the example hostmot2-servo HAL files have these nets as well)
so basically all that is needed is to connect these nets to some spare 7I77 analog outputs
There is no additional scaling needed, as the analog outputs are scalable

If you post your existing HAL file, I can show the required net commands

Hello PCW, dependable as always

Here is part of the hal file and what I have tried to accomplish so far

# encoder feedback
setp hm2_[HOSTMOT2](BOARD).0.encoder.00.counter-mode 0
setp hm2_[HOSTMOT2](BOARD).0.encoder.00.filter 1
setp hm2_[HOSTMOT2](BOARD).0.encoder.00.index-invert 0
setp hm2_[HOSTMOT2](BOARD).0.encoder.00.index-mask 0
setp hm2_[HOSTMOT2](BOARD).0.encoder.00.index-mask-invert 0

#Tachometer generator
setp hm2_[HOSTMOT2](BOARD).0.7i77.0.1.analogout3-scalemax [AXIS_0]OUTPUT_SCALE_TACHO
net encoder.0.velocity <= hm2_[HOSTMOT2](BOARD).0.encoder.00.velocity
net encoder.0.velocity => hm2_[HOSTMOT2](BOARD).0.7i77.0.1.analogout3

Something is not right with the scale though, nothing happens when I change it.

if you change the analog out scalemax parameter
you will also likely have to change the minlimit and maxlimit
parameters for the analog out

jeeybee wrote:

So what I have figured out so far is that I need to use the encoder velocity feedback, convert it from PPM to RPM and then scale it and send it to an analog output.

TxRx Labs in Houston has a Burgmeister powerhawk mill that they did this on, and it is working. You could check with them to get the config file set.

Jon

jmelson: Thanks, that can be a backup plan

Now it seem like it does it right, I can change the value and get different voltages when I turn the MPG I hooked up to test this.
All for now, thank you very much PCW.