On 11/19/24 12:18, Viesturs Lācis wrote:
Hello!
First thing is that there is Commander CD750 VFD for the spindle motor
that I have (almost) under control with 2 output pins on 7i37 board
and an analog output of 7i36 board. The thing is that I do not
understand why is the analog output voltage fluctuating. I did a short
video here:
https://www.youtube.com/shorts/no8-CHsCggc
What I have there is pwmgen scale set to 100 and value at 30 so that
should be 3V on the analog output. There is slightly more. With pwmgen
value equal to 0 I still have 0.3V so I would gladly fix that offset
but have no idea how. But the main problem is the fluctuation because
then VFD also is adjusting the motor speed. For demonstration purposes
I did turn the spindle on and it can be heard easily that motor speed
is not steady. Those numbers on VFD are output frequency as an
additional indication that input voltage is fluctuating.
I would appreciate any ideas where to look further.
The second question is about Yaskawa encoders and decoding rotor
position from C channel pulses as described here:
https://forum.linuxcnc.org/27-driver-boards/53321-yaskawa-incremental-encoder-and-mesa-7i48?start=0#305997
Is it possible to implement it? So far I have been circumventing it by
keeping the old drives in the cabinet for treating the encoder signal
and export "standard" ABZ signal for LinuxCNC, but now the thing is
that I have a first case of the encoder signal output being unreadible
any more.
Viesturs
The first thing I'd look for is a ground loop.
Somewhere a doubled up ground seems to be modulating things by introing
a power line frequency hum into the feedback loop. That can be
maddeningly difficult to find. Probably addressed by a single ground
bolt where all grounds terminate, lift one wire at a time and ohmeter to
the frame, if it still has ground continuity, find the short and remove
it. Then put that wire back on the bolt and test again. All grounds
including the powerline static ground should go to this single bolt,
/no/ place else.
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Cheers, Gene Heskett, CET.
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