PWM/frequency signal as input to Mesa card

I'm trying to get the spindle load reading from my VFD to LinuxCNC so that it can displayed in the GUI.

The VFD I'm using to control the spindle motor in my mill is a simplistic Emerson/Nidec M100. While reading the manual for this VFD I noticed that it has one digital output available which can be set to output various different parameters.

 

The output from this pin seems to be frequency or PWM based.

 

Would it be possible to use a PWM signal as input to a Mesa card?

My current setup is a 7i96S and 7i84 and I realize that in order to connect a pin with it's own 24V supply to a normal input I'd probably have to use an optocoupler.

The parameter I'm after in the VFD is called Percentage Load (4.020). The manual for the VFD is available but be aware it's one of the most cryptic manuals I've ever come across: www.nidec-netherlands.nl/media/2019-freq...ss3-0478-0352-03.pdf



 

There is a period measuring firmware module possible for all Mesa FPGA cards
(PeriodM). This may require LinuxCNC master (2.10) to use.  If you use
an OPTO to connect to say a P1 pin, it should be fairly fast to avoid pulse
width distortion.

It does look like you have a choice of PWM or frequency output. Frequency output
can be measured with an encoder input, so its possible to do this with any
relatively current LinuxCNC version, and possibly using a 7I96S isolated input
(as long as you have a spare input and the VFD output gets along with the
sourcing/sinking mode of your other 7I96S inputs) Another advantage of measuring
frequency rather than PWM is that its not so fussy about optocoupler speed.

Thank you PCW for such a quick and detailed response.

The proposed frequency measurement using an isolated input sound very tempting. I'd like to keep the P1 connector free for future expansion and I have two isolated inputs left on the 7i96S.

The 7i96S is setup with the common pin connected to 24v ground. The VFD has it's own internal 24v power supply used for the enable, fwd, rev signals which I have connected to the isolated outputs.

Does this mean that all I would need in order to try out the frequency approach is a decent 24v optocoupler?



Here is schematics of my current 7i96S setup. The serial connector is used for the 7i84 and the analog connector is used for spindle control even though it's not illustrated on the picture.



 

If the VFD output is sourcing or PNP, you don't even need an OPTO
as you could use say INPUT 10 directly.

Firmware with encoder on isolated input 10 (P3 pin 11)
allowing frequency measurement of 24V signals
Suggest 1-2 KHz max:

 
 

Big thanks PCW, the Mesa support on this forum really is amazing!

I'll report back as soon as I've tested this setup.

The VFD doesn't have the most user friendly manual so I'm gonna try and verify the output from the VFD using frequency capable multimeter (UNI-T UT61E) first before I wire anything up.

Just to double check. Do you think connecting a wire straight from the VFD output to the input on the Mesa card is going to work even though my 24v ground is not connected to chassis ground? (I'm suspecting this floating ground setup will not work)

To use the VFD output signal you would need to have the 7I96S
input common (TB3 pin 12) connect to the VFDs input common
(VFD pin 1)

This would connect the drives input common to your 24V supply negative,
which may be undesirable for noise reasons. So it may be better to add an
optocoupler as you first suggested.

I've ordered at set of 24V optocoupler isolation boards from the Aliexpress link below. It's gonna be a month or so before they show up, but when they arrive I'll try the new firmware and see if I can get this working.

 

www.aliexpress.com/item/1005003242672161.html

They are specified to handle a maximum signal frequency of 5KHz so even by Chinese standards they should hopefully be able to handle the 1-2khz rangeI'm planning to use per PCW's advise.

I have a similar inverter. I think we can use the modbus interface.

Is that some hidden feature that needs to be activated?

I can't find anything in the manual regarding modbus.

www.nidec-netherlands.nl/media/2019-freq...ss3-0478-0352-03.pdf

Sorry, my bad . My driver is another series. Your inverter is missing modbus