This is on a machine that has been working fine for years. (and still is
working fine.)
I'm just a little baffled by how the 12v+ is floating right at ground, and the
12v- is -12v below ground. I did a little more poking around, and tried to
check for current between the DC- and ground and the moment I touched the probe
to the DC- to ground Linuxcnc pops up a bunch of errors about the Mesa card
having an over-current, and shutting down. I need to go back and recheck
everything and try to see where i went wrong when I set it up years ago.
However maybe having the DC+ floating at ground level might not be an all bad
thing, I can then connect the 12v+ to the spindle tool clip, and the touch
plate to the input.
With a conventional DC- ground would I need to set up with a 12v pull up
resister to the input and then to the touch plate, and a ground wire clipped to
the tool. (Assuming I can figure out why my 12v is below ground instead of
above it, and fix it.)
- Original Message -
From: "John Thornton" <j...@gnipsel.com>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Sent: Friday, April 7, 2017 4:52:03 PM
Subject: Re: [Emc-users] 7i77 Field Power?
This should clear it up.
http://gnipsel.com/linuxcnc/configs/7i77.html
JT
On 4/7/2017 3:47 PM, Todd Zuercher wrote:
> I was going to start working on putting a tool touch probe on a machine with
> a Mesa 7i77 setup.
> (I was just going to try a wire clipped to the tool and a touch plate for a
> start.)
> I pulled out the multi-meter and started poking around to try to figure out
> what exactly I wanted to do and noticed something odd. I checked the V+ to
> ground and it read 0v and V- showed -12v.
> My field power is suppied by a simple 12v switching power supply (wall wart).
> I don't see any obvious place where the 12v power is referenced to ground
> (positive or negative.) Might this be normal? Would It cause a problem if I
> tried to connect the V- to ground (such as short out the 12v power supply)?
> Is this a symptom of another wiring problem somewhere (a short to ground
> hidden somewhere.)
> Which side should I use for the spindle/tool wire clamp the field power or
> the input pin? (the spindle does show a little resistance to ground)
> Should I put any resistors in line to help protect from short circuits?
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