On Fri, 29 May 2020, andrew beck wrote:
Date: Fri, 29 May 2020 10:36:10 +1200
From: andrew beck <andrewbeck0...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] mesa 7i76 spindle encoder not counting suddenly
hey gene
sorry for the slow reply
just getting to this grounding thing now.
currently I have single large copper block with a lot of holes in it for
terminals, this is connected to the earth(ground) wire that goes back to
the whole shed main ground wire rod in the dirt
all my servo drives and vfd main grounds go back to this point as do all
motor grounds etc. this is how heidenhain set up the machine originally
and they have a whole grounding schematic showing how it all works. I have
basically copied that.
I have 2 meanwell 24v powersupplies that have the ground wire on the input
side also connected to ground. the output side (phase and neutral) are
floating relative to ground and not connected to ground at all I think. as
the meanwell switching powersupply output should be isolated from the
input. I think this is correct
the computer cord ground wire is currently connected to this same large
copper block.
my computer via the 5i25 currently supplies 5v logic power to the 7i76
and one of the 24v meanwell powersupplys supplies the 24v field io for the
7i76
my encoder problems started when I connected up the servo drive simulated
encoder output to the 7i76 encoder counter. I haven't connected the 5v and
24 v grounds together. they did work for awhile but don't now
I have a 7i89 and 7i84 coming soon and will need a external 5v powersupply
anyway i think so will change when they arrive here from america.
anyway I read your reply and got a bit confused could you read my email
here and let me know what I need to change and why I should do it this way
just so I understand.
regards
Andrew
From your symptoms (no signal from A, /A wires) the issue is not likely to be
on the interface side but on the drive or wiring side. One other possibility
is a A, /A short on the 7I76E. This can be ruled out by unplugging the encoder
connector from the 7I76E and re-checking for those signals.
On Thu, May 21, 2020 at 9:31 PM Gene Heskett <ghesk...@shentel.net> wrote:
On Thursday 21 May 2020 01:57:06 andrew beck wrote:
hey peter
I had a look and the unless there is a shorted out pin in the servo
drive connector itself I think the wiring is all good.
and I highly doubt the servo drive has problems all I did was connect
the 24v back into the servo on pin which is how it has been running
for the last ages.
anyway how do you recommend commoning the grounds?
it is as simple as connecting the field power 0v ground with a wire to
the logic power 0v ground?
Yes, but how you do it can be very important.
In your control box, install a longer bolt, #6 or #8-32 to the chassis.
4mm if metric.
Connect all grounds to this bolt, checking that they are not grounded at
the far end. By doing this, you are establishing a single point ground
that is the zero volt reference for the whole system. Connect this bolt
to the building static ground, the bare wire in most power cabling.
Connect the machines frame to this bolt.
Connect the - rails of all supplies to this bolt.
Connect the - terminals of all cards to this bolt.
Break the 3rd pin off the computers supply cable and connect the
computers chassis to this bolt. Power the computer not from the wall,
but from the same power feeding this box.
Connect the shielding of all shielded cabling to this bolt. Do not
connect the far end of this shielding to anything that is otherwise
grounded.
By making sure these grounds are not connected anyplace else you are
breaking any ground loops which can and will act as antennas to insert
noise into your control signals.
By having this single point ground, a nearby lightning strike can inject
a 100k volt pulse into the system ground as what would be called
a "ground bounce", but the system will not see it as noise nor be
damaged, because everything is bouncing in unison.
Regardless of what that bolt does during the strike, the 5 volt supply
remains at 5 volts to this bolt, and the 24 volt supply remains at 24
volts to this bolt.
And when the storm is done, your chances of having anything damaged is
reduced to the vanishing point.
Stay well Andrew.
[...]
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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Peter Wallace
Mesa Electronics
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