Re: [CAD_CAM_EDM_DRO] Major encoder trouble, need advice.

Hi Jon,
Thank you for taking the time to read it all AND answer, I appreciate it!

>Well, that's 14400 * 541 / 60 = 129840 counts per second. What is the
>software sampling rate of the (PIC ?) CPU there? I'll bet it is about
>130,000/second, or every 7.7 us.

It's an AVR chip and I think it's interrupt driven. The stated
max-frequency is 100-150kHz depending on step-multiplier settings etc so
I think the tests with the 3600 lines encoder prooves that it works to
specs.

>Well, it IS the encoder, period. Have you tested the US Digital encoder
>when it is CONNECTED to the UHU? That is what matters. Is there a mode
>to measure position through the UHU with the drive not "driving"? My
>guess is the switching transients of the power stage of the UHU are
>upsetting the US Digital encoder. If it is OK when the power stage is
>off, but goes haywire when the drive is active, you have a major piece
>of information. One thing to try is a significant capacitor, like 4.7
>uF across the DC input pins of the encoder, RIGHT at the encoder.
> Is the 5 V power for the encoder coming from the UHU, or some other
>power supply?

I agree, it 'has' to be the encoder, but of course USDigital
disagrees.... Yes, all measurements on the encoder has been done with it
connected TO and powered BY the UHU drive. I can't see the encoder
count but I can see if it detects invalid counts and I have tried, with
the motor power supply turned off, spinning the motor shaft "by hand"
from very slow to as fast as I can and I don't see any reports of
invalid transitions then. I'll try to rig something up so I can spin it
with a cordless drill or whatever.

After solving another issue with the drive I tried it with the AMT
encoder and 15m of unshielded cable lying in a ring right on top of the
motor and drive and run it for over 90 minutes without trouble. So if it
is noice - which it indeed looks like - the USDigital encoder must be
overly sensitive.

USDigital recomends the 26C32 receiver while the HP-UHU has the
SN75115... big difference?

I'll definetly try with a 4.7uF at the encoder. Also, on the drive PCB
the low voltage GND and the motor supply GND is separated but connected
to each other at one single point. I wonder if cutting this trace and
connecting the -ive of both supplies outside the board will help or make
it worse...

Again, thank you Jon, it's much appreciated!
/Henrik.