On Wed, Jun 04, 2008 at 09:57:53PM -0600, [EMAIL PROTECTED] wrote:
> Hi
> Servo Dynamic told me that have encoder with too much resolution is not
> help because drive will not be able to process or use too much pulses from
> encoder. Are there a MAXIMUM limits of pulses from encoder?
Typically there are limits in the maximum speed of the quadrature waveform at
both the encoder and at the receiving end.
For instance, in the documentation that mesa provides for the 7i33:
In TTL mode, the input RC filter limits the maximum encoder input frequency
to approximately 1 MHz. This corresponds to 4 million counts per second with
most quadrature counters (4X mode). The maximum input frequency may be lower
with encoders that have high value (>1K Ohm) pull-up resistors on open
collector outputs.
In RS-422 mode, maximum encoder input frequency is 10 MHz, giving a maximum
count rate of 40 million counts per second
http://mesanet.com/pdf/motion/7i33man.pdf page 7
In emc2 there are practical limits on the precision of position values due to
the use of "float" as the fundamental type for "analog" values such as
encoder positions. For instance, the values 1.0 and 1.0 + 0.5**23
(approximately 1.0000001) are both exactly representable, but no values
in between those two can be represented. Similarly, 2.0 and
2.0 + 0.5**22 (approximately 2.0000002) are both exactly representable,
but no values in between those two can be represented.
http://en.wikipedia.org/wiki/Floating_Point#Implementation_in_actual_computers:_IEEE_floating-point
Jeff
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