Machsupport Forum
Third party software and hardware support forums. => dspMC/IP Motion Controller => Topic started by: habituralcnc on March 30, 2020, 10:10:55 PM
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Hi all,
Ive owned my dspmc for about 4 years running stepper motors,
sadly it is discontinued,
now i have dmm servos running on +/- 10V analog torque mode
but im still confused about star grounding multiple drives please if any one is still running a dspmc a little help to understand
would be much appreciated!
is my real world ground wiring interoperation of star grounding multiple servo drives with dspmc correct ?
things that I'm most confused with are:
should my signal (com) ground bus be bonded to my earth ground power bus?
how to test if my switch mode power supply is already internally got com bonded to earth ground creating a ground loop?
ground symbols in AnalogDriveConections.pdf from vital systems don't seam to match standards eg, attached image
taken from the dspmc manual :
in order to filter the electrical noise from motors, drives and vfds, the GND (common)pins on j2....j7 should be tied to the
earth ground at multiple points.
the following example shows GND pins on j2 tied to earth ground.
in addition, the power supply negative terminal should also be connected to any of the j2..j7 GND pins at two or more
terminals
trying to achieve this without creating ground loops not so easy
best regards
Amyl
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UPDATED INTERPERTION STAR GROUND
to include j7
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or should it be done this way?
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EDIT3
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Anyone know how this works ? :o
cheers
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normaly you put all chasis grounds to your earth potential.
for a anlaog Signal you use a two wire (twisted) shielded cable from the
source to the Destination and shield should be wired to the GND of the source
(of cource i hear all the voices witch say do no do this), but for a good start
it was the best soluition for me for the last 35 jears.
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hello, thanks for your reply,
I understand the cable shielding should be grounded only at the analog source end of a shielded cable,
what i'm having trouble understanding is interpreting the schematic for properly grounding the entire system
in this instance should i keep common from dc power supply isolated from service earth ground
and then run multiple earth returns from j2..j7 to earth ground and separately to common ground?
Best Regards
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i would prefer to run AIN- and AIN+ directly via 2 wire shielded / twisted cable to the Motion Controller and
put shield on Motion Controller side to GND. the analog Input of your dmn dyn4 is isolated so do not connect
AIN- to Signal ground bus.
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hi,
Thanks a lot for you feedback got me thinking
are you sure AIN- on dyn4 is isolated ? looks like its an opamp?
Com pin 5 on dyn4 is opto isolated so shouldn't connect to signal Gnd ?
have attached a simplified version is this what you mean ?
cheers
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if you have a quick look to the dyn4 Manual it says clearly that all Input signals are isolated.
also the example wiring diagram of the analog Input Shows nothing to connect AIN- to somewhere else
as the analog out ground of the source.
so why are you trying to create Problems ?
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the Mayor Problem is to get all those different wires and calbes onto this 25pole Sub D connector.
i have used on all my machines those Interface modules.
then you can use a Standard 25pole cable from controler to the module and connect at the Interface
module all your different single wires cables and so on.
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Thank you for taking the time to reply.
I'm not trying to create problems, i'm trying to understand.
i not trying to offend you ether.
yes the dmm manual Shows nothing to connect AIN- to somewhere else.
it also shows the shield of ain+ and ain- connected to JP4 shell
but like you have already mentioned connecting the shield to ground at the output side makes a lot more sense
its what i will do.
The dspmc manual shows otherwise please see attached pdf, any thoughts on this ?
it also says relating to this attachment:
in order to filter the electrical noise from motors, drives and vfds, the GND (common)pins on j2....j7 should be tied to the
earth ground at multiple points.
the following example shows GND pins on j2 tied to earth ground.
in addition, the power supply negative terminal should also be connected to any of the j2..j7 GND pins at two or more
terminals
yes those interface modules are great!! i have a few already in use
Best Regards
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Voltage is the difference in potential between two points.
The analog output found at the DSPMC breakout board is referenced to its analog ground.
The servo uses the difference between AIN- and AIN+. These should be connected to the breakout board.
If AIN- were to be grounded at the servo any noise on the interconnecting grounds will be seen by the servo.
The servos control high power. It is inevitable that some noise will be developed on their ground wires.
No connection to the breakout board ground from the signal ground bus or the power ground bus is needed. The breakout board sees ground from the DSPMC.
Yes, there will be noise between the the breakout board ground and the servo ground. Connecting AIN- to the breakout board gives the servo the reference to cancel that noise.
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hi,
Sorry been away from computer
Thank you for taking the time to reply!
just a note this is a hobby so far for me so electronics this is not my career
I plan to get a qualified electrician to look over my work
To MN300,
I value the information provided it makes perfect sense to me thank you
its now how i have it wired,
but can you explain what the example in the dspmc Manual analog servo drive connection is all about
because it contradicts what your saying ?
is it for connecting older style simple servo amplifiers ?
My dspmc has analog inputs also if they are temporally unused is it ok to leave them floating?
will they introduce noise ?
Thanks again
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I will need more information to answer your questions. Can you show more about the info in the DSPMC manual.
You could copy and paste the pertinent images or a link to the manual(s) and page numbers would be good.
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hi,
Here is a link the the manual
http://www.vitalsystem.com/portal/motion/dspmc/DSPMC.pdf
page 24
cheers
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The diagram on page 24 has symbols for both Earth-Gnd and GND. I don't know what physical connections, if any, the GND symbols imply. If you ignore them you can see a star ground system.
The wire from Signal Ground to the Earth-Gnd will carry any noise current induced into that ground by the drive. In a well designed Drive, with the analog circuit properly isolated from the power section, that current will be small and not disrupt the speed signal. Still it would be best to connect the INV input closer to the DSPMC analog ground. I guess they suggest their wiring method because it's easier and adequate for most cases.
The manual says very little about the analog inputs. I hope the manual would mention grounding unused inputs it if it is mandatory. it's probably safest to do that anyway. I wish CNC manuals would have more detail about the circuity so we could make more informed decisions.
As TPS said using shielded twisted pair is very good practice.
There is a lot you can get away with in a system with short wiring runs but when trouble starts you'll really wish you had done it correctly.
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hi,
So i had this crazy idea! I've got this old hitachi 20MHz oscilloscope pulled it out of the cupboard wiped off the dust and fired it up
connected THE main oscilloscope lead to +/-10V analog0 and alligator clip to analog GND on controller this what i got:
image1 = controller powered only , thinking this is strange doesn't look right
image2 = servo drives powered,not enabled, thinking looks like high voltage lightning at the top and bottom of the weird square wave, looks cool but very wrong
image3 = servo drives powered, enabled, and jogging servo one direction continuously, if you look closely you can see little teeth on the square wave
see next post
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image4 = controller powered only, 24V power supply -com connected to earth ground
image5 = servo drives powered, enabled, and jogging servo one direction continuously,24V power supply -com connected to earth ground, wow looks better! i can see how the signal works now the amplitude of the square wave increases as speed increases.
image6 = servo drives powered, enabled, and jogging servo one direction continuously,24V power supply -com connected to earth ground,higher rpm jogging distorts the signal like a wave, also the entire signal moves up and down slightly some other noise issues i suspect! DC offset?? but could be PID adjusting the signal not sure that works.
On this old CRT oscilloscope you cant see vertical lines,
by the way I'm only measuring dc signals staying clear of ac high power!
edit: sorry last pic is blurry chose the wrong picture