Proper grounding of 7i77 and cables

More
25 Aug 2021 19:24 - 25 Aug 2021 19:29 #218726 by kimachren
tommylight: If I translate that correctly, I should connect the shield to the back plate near mesa, since that is the machine ground.

PCW: Actually they should be the same ground potential, or at least very close.
i have built a big sheet metal enclosure around the headstock. Inside this enclosure there are several compartments; on the back side, behind the machine is the "power compartment" where the contactors, breakers and drives are. On the front side is a separate compartment for the electronics and a touchscreen. All sheet metal plates are screwed together.

edit: I tried to put a 1nF cap across the AOUT and AGND on the mesa and the noise went down to 1/4. At least in that end. I'm not sure if that is a wise thing to do..?
Last edit: 25 Aug 2021 19:29 by kimachren.

Please Log in or Create an account to join the conversation.

More
25 Aug 2021 22:27 #218739 by tommylight

tommylight: If I translate that correctly, I should connect the shield to the back plate near mesa, since that is the machine ground.


--
A:
-Normal coaxial cable = a single center wire plus the screen/shield wire = center wire from AOUT on Mesa to AIN on the drive (also named REF sometimes), screen wire to AGND on Mesa and AGND on drive. Nothing else, never connect AGND to machine ground!!!
--
B:
-Shielded/screened cable with 2 or more INSIDE wires OR CAT6 STP cable = one wire from AOUT on Mesa to AIN/REF on drive, the other wire (from the same pair) from Mesa AGND to drive AGND = ONLY in this case the shield/screen should be tied to machine ground near the mesa board and left UNCONNECTED on the drive side.
-
Sorry for using all caps, but this has to be done as described for "A" OR "B" above depending on type of cable used. There is no translation.
The following user(s) said Thank You: kimachren

Please Log in or Create an account to join the conversation.

More
25 Aug 2021 23:42 #218742 by kimachren
Translated maybe was the wrong word. I meant as in your explanation applied to my particular setup/case. Sorry.

Please Log in or Create an account to join the conversation.

More
26 Aug 2021 00:19 #218746 by tommylight
Nothing to be sorry about, that was meant for me as i always assume i did not explain it properly, so hopefully the last post was clearer.

Please Log in or Create an account to join the conversation.

More
02 Sep 2021 23:45 #219474 by EricKeller
No idea about those drives, but I have some older drives that have all isolated i/o except the analog in. The analog ground was directly connected to the power ground. Which I thought was a bit rude. I ended up connecting the power supply ground for the mesa to the power ground back at the point where the power comes into the cabined. My guess is that Chinese drives are somewhat sloppy on that front. Most industrial power supplies have floating outputs, so there shouldn't be any problem doing this. It's best to check.

The signals you posted look like they probably come from a similar issue to me.

Please Log in or Create an account to join the conversation.

More
03 Sep 2021 06:58 #219493 by kimachren
The analog ground is isolated from power ground in these drives, but the ground is shared between analog in and analog out (monitor). On the 7i77 side the analog in (inputs 0..3) are referenced to "power" ground and hence the analog ground has to be connected to power ground in order for the monitor signal to work.

I followed tommylight's advice and changed to coaxial cable (RG58 to be specific), but have not been able to put the scope on yet. The motors seem to be quieter, but I'm not sure. I also grounded the encoder cables to the back plate instead of GND at the 7i77 terminal.


Products - Servo Systems - AC Servo Motors and Drives - Delta (deltaww.com)

Please Log in or Create an account to join the conversation.

Moderators: PCWjmelson
Time to create page: 0.124 seconds
Powered by Kunena Forum