Re: [CAD_CAM_EDM_DRO] Re: Position counter stop updating....Still there....

Well if you have seen that before then it well could be it.
I have never had that problem, but my computer and
breakout boards are all in a well shielded case. As mentioned
the ribbon cable to the card is a twisted pair type. My star ground
point is right next to the breakout board and digital and analog
ground is hooked there.

The servo amps are also in that box about a foot away. They are all
bypassed right at the terminals with a couple hundred mf.

So filters on encoder lines would do nothing unless that was a noise
path to the card internals.
What about ferrite beads on the card grounds?

If the computer case was the star ground point that might help.
It is earthed through the power plug. Or it is on mine.... hmmm
I'll bet Babar is using something other than 120v 60 Hz power.
Actually on high power audio gear I have sometimes floated
the units to remove hum from loops through rack panels.
Not the best thing to do, but it did work well sometimes
in desperate situations. Good way to get shocked.

Les
Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, September 15, 2002 12:59 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Position counter stop updating....Still
there....


> Babar wrote:
>
> > although the stg2diag shows big errornous values
> > following is the respone of stg2diag utility:
> >
> > [root@localhost bin]# stg2diag
> > Servo To Go Board IO address = 0x200
> > +1.000 +1.000 -2.000
> > +1.000 +1.000 -65538.000
> > +1.000 +1.000 -2.000
> > +1.000 +1.000 -65538.000
> > +1.000 +1.000 -2.000
> > +65537.000 +65537.000 -65538.000
> > +1.000 +1.000 -2.000
> > +65537.000 +65537.000 -65538.000
> > +1.000 +1.000 -2.000
> > +65537.000 +65537.000 -258.000
>
> Bingo! This is the same horrible behavior seen with the STG-I
> card! This is not encoder noise, this is noise on the digital position
> reading coming OUT of the 7166 encoder chips. NIST put in a filtering
> routine to throw away any samples that were too far away from the last
> sample. but, notice, these jumping values are almost always jumping ONE
BIT
> in the middle-most-significant byte! The first bit of that middle byte is
changing
> from sample to sample, causing a jump of 65536 counts in the total
position
> value. Since the STG-II is a significant rework of the STG card, I
suspect this
> is an inherent defect in the 7166 chip, at least in the mode that STG and
EMC
> use it.
>
> Are these lines sequential samples recorded to memory, or does the
computer only
> print out a position reading whenever it detects a change from the
previous one?
> In other words, do these wildly jumping reading pour out of the computer,
or do
> they come out every now and then?
>
> I noteced the problem was most severe in the STG-I when the encoder
position moved
> acrosss the boundary from 0 to -1, ie. when all 24 bits changed value at
once. This
> could be expected to cause noise in the system.
>
> I don't know what to tell you about this, but from previous info you've
supplied, it
> is a problem of noise getting into the STG card, and upsetting its logic.
If you have those
> cable shields connected to terminals on your STG breakout board, try
grounding them to
> the computer's CASE, instead. You don't want to force interference
currents through the
> board's logic, or through the logic's ground traces.
>
> But, this info you provide here makes it look very clear it is NOT,
specifically, noisy
> encoder signals causing false counts in the encoder counters.
>
> Jon
>
>
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