Re: [CAD_CAM_EDM_DRO] Filters, and a ? for Mariss was Re: Rotor inertia.

Mariss Freimanis wrote:

>Jon,
>
>Not true.
>
>The encoder input chain / channel is:
>
>1) 1K pullup resistor to +5VDC, input to schmitt NAND gate (CD4093).
>2) Output of NAND to 47K / 100pF low-pass (5uS RC delay).
>

OK, well a 5 uS filter is all you can have on a drive spec'd for 200 K
steps/counts per second.

>3) Output of low-pass filter into 2nd schmitt NAND gate.
>4) Output of 2nd NAND to quadrature decoder.
>
>This filter will not pass any signal artifact narrower than 5uS and
>squares-up slow rising/falling encoder edges. The low-pass bandwidth
>matches the expected encoder roll-off frequency of 100kHz.
>
>This filter has been tested with a 20' foot motor cable bundled with
>unsheilded encoder cable in a common harness. The behavior and
>accuracy of the servo was unaffected.
>

Well, that is interesting. Some users reported they needed shielded
encoder cables to make their system work. But, I must admit, I was not
there, and didn't see shielded cable fix the problem.

Jon