Re: Agilent Encoder Pull-up resistor

Looking at the datasheets for both the encoder and the drive, it looks
like it should work even though the rutex has a differential input.
The input circuit for the Rutex is in the setup guide and shows an
simple comparitor with an AC terminator (bad design but we can work
with it).

Put recommended pullups on all three encoder outputs at the encoder.
Put 10 ohm series drive resistors in right after the pullups (just in
case). Use 100ohm twisted pair cable over to your drive on all three
lines, where common is ground (use Cat 5). At the rutex, bias the
negative (inverted) inputs at 2.5V using a divider made of two 1K
resistors. Connect the commons from the twisted pair to the drive's
ground.

Just in case: AC terminators are bad signal design practice for
anything but clocks of a known frequency. I would personnaly snip the
100 ohm terminator resistors and use a 100 ohm series drive resistor
into the cable. This would get you a cable that could go at least 100m
and several MHz.

This will work -- signal integrity is one of my areas of expertise,
although admittedly I'm usually trying to get 2 GHz signals to go
across a backplane.

Realistically, you could probably get your existing setup to work by
simply biasing the negative inputs at 2.5V, but I tend to like doing
things right anyway.

On 8/14/06, shadi_salhab_78 <salhab@...> wrote:
> Hi all ,
> I've installed an Agilent Encoder HEDS 5500 on a servo motor to
> conunnicate with rutex drive , the problem is that it only read pulses
> on very low RPM , if I rise RPM it stops reading , I have put a
> pull-up resistor mentioned in Agilent data sheet, the result is drive
> reads at a higher RPM, I kept increasing the pull-up resistor value
> until I reached 4K ohm each but no more then 600 RPM , which is not
> sufficient , is it supposed to be the situation with Agilent encoders
> ? or there is some problem with the encoder? Should I try to use
> differential encoders?