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Author Topic: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES  (Read 4962 times)

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Offline TPS

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Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #10 on: April 01, 2020, 02:25:13 PM »
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.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #11 on: April 01, 2020, 05:06:15 PM »
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:
Quote
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

Offline MN300

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Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #12 on: April 01, 2020, 09:30:30 PM »
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.
Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #13 on: April 03, 2020, 10:03:30 PM »
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


Offline MN300

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Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #14 on: April 03, 2020, 10:38:15 PM »
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.
Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #15 on: April 03, 2020, 11:11:22 PM »
hi,

Here is a link the the manual
http://www.vitalsystem.com/portal/motion/dspmc/DSPMC.pdf

page 24

cheers

Offline MN300

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Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #16 on: April 04, 2020, 12:30:42 AM »
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.
Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #17 on: April 04, 2020, 10:57:08 PM »
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
Re: DSPMC SIGNAL STAR GROUNDNG FOR ANALOG DRIVES
« Reply #18 on: April 04, 2020, 11:17:43 PM »
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
« Last Edit: April 04, 2020, 11:31:06 PM by habituralcnc »