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Author Topic: Spindle Motor is the cause of all my problems  (Read 6355 times)

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Offline Hood

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Re: Spindle Motor is the cause of all my problems
« Reply #10 on: August 06, 2012, 02:11:11 PM »
Current thinking on shielding is to bring all shields at the control end to a single point  and ground there.
Hood

Offline Hal

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Re: Spindle Motor is the cause of all my problems
« Reply #11 on: August 08, 2012, 08:57:10 PM »
Ground only one side of the shield. I use the control box side. I would enclose the power supply and speed control inside the main box if you have trouble.

No wireless for me. Garage door may open if one of the jets fly to low. The battery in my wireless keyboard and mouse loves to die when I need to finish.

Hal
Re: Spindle Motor is the cause of all my problems
« Reply #12 on: August 11, 2012, 02:04:31 PM »
Single end grounding of shields is the standard for most (all?) low voltage signals wires these days.  I have seen all kinds of weird things caused by ground loop when somebody mistakenly gets a second ground point.  Audible noise on audio cables.  Rolling bar distortion on video cables, etc etc ... 

Trust me.  Ground shields on only one end at a common central point. 

Offline Hood

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Re: Spindle Motor is the cause of all my problems
« Reply #13 on: August 11, 2012, 04:13:59 PM »
Not always true that grounding at one end is the way to go. For most things Mach related it is but I can assure you that only grounding the shield at one end of the encoder cable on the motors that utilise sick stegmann  sine/cosine smart encoders will not work, they need the shield grounded at both ends.
Hood
Re: Spindle Motor is the cause of all my problems
« Reply #14 on: August 11, 2012, 04:52:28 PM »
Not always true that grounding at one end is the way to go. For most things Mach related it is but I can assure you that only grounding the shield at one end of the encoder cable on the motors that utilise sick stegmann  sine/cosine smart encoders will not work, they need the shield grounded at both ends.
Hood

Then they are using the shield as part of the signal circuit or using an electrical charachteristic of the shield for some purpose other than just shielding if it actually must be "grounded" at both ends.  Alternatively they may require it be "connected" at both ends, but it might still only actually be grounded at one end.  Not being familiar with that particular piece of equipment of course you can argue the actual application more effectively than I could.  

An example I am more familiar with:
I know in fire alarm signal circuits often the shield must be connected through from device to device and often connected to the device (depending on the application), but its still only connected to ground at the control panel.  Accidental mechanical grounds are avoided by make the body of the device out of plastic.  

P.S. The main reason for the use of plastic is price.  Avoidance of accidental mechanical grounds is incidental. 

« Last Edit: August 11, 2012, 04:54:05 PM by Bob La Londe »

Offline Hood

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Re: Spindle Motor is the cause of all my problems
« Reply #15 on: August 11, 2012, 05:36:09 PM »

Then they are using the shield as part of the signal circuit or using an electrical charachteristic of the shield for some purpose other than just shielding if it actually must be "grounded" at both ends.  Alternatively they may require it be "connected" at both ends, but it might still only actually be grounded at one end.  Not being familiar with that particular piece of equipment of course you can argue the actual application more effectively than I could. 

An example I am more familiar with:
I know in fire alarm signal circuits often the shield must be connected through from device to device and often connected to the device (depending on the application), but its still only connected to ground at the control panel.  Accidental mechanical grounds are avoided by make the body of the device out of plastic. 

P.S. The main reason for the use of plastic is price.  Avoidance of accidental mechanical grounds is incidental. 



Dont think they are, its simply a shield as far as I can see, below is a pic of the signal and power wires and shield is additional to them. The motor is grounded via  the Earth wire, the drive is also grounded so both ends are, In fact Allen Bradley recommend the shield be connected at both ends even on standard encoders. On the cables I have made up myself I have on some and not on others and they seem fine either way but the smart encoders need to be, if you attempt to run the motor with only one end connected it faults almost right away. The first cable I made up for a smart encoder only had the sheld grounded at the control end and I couldnt even get it running, in fact it faulted out as soon as I enabled the drives. I ended up swapping out the encoder for a standard one and it was only later that I discovered, by chance, that the shield needs connected at both ends.

Hood
Re: Spindle Motor is the cause of all my problems
« Reply #16 on: August 11, 2012, 05:41:29 PM »
Perhaps there is some internal shielding that needs to be connected.  At the encoder end something would have to be connected to the body of the machine for it to be "grounded." I guess the easy way to tell is disconnected the controller end and put a meter on it between the shield and ground.  

I am not saying its impossible that they are creating a ground loop, just that its more likely they are connecting the shield to the device.

We may be quibbling over the difference between connected and grounded, but there is a difference.  On a device if there is a place to connect the shield or ground wire that does not mean its grounded at that point.  
« Last Edit: August 11, 2012, 05:43:30 PM by Bob La Londe »

Offline Hood

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Re: Spindle Motor is the cause of all my problems
« Reply #17 on: August 11, 2012, 05:55:07 PM »
The shield connects to either the metal body of the encoders cover or  bolted the motor body itself. The motor power cable  has the three phases and an Gnd wire the Gnd wire connects to the motor body and at the drive end it is connected  to the Earth connection on the drive.

It was something I found unusual after all the talk of only grounding the shield at one end but as it turned out it was the exception to the standard practice. I do remember reading a bit about low voltage high frequency signals need the shield grounded at both ends but it was a long time ago and I dont recall any details.

As has been said though it is normal just to connect the one end and this for some reason seems to be the exception.
Hood
Re: Spindle Motor is the cause of all my problems
« Reply #18 on: August 11, 2012, 06:43:16 PM »
Shielding on both ends works fine as long as EVERYTHING is grounded properly.  There is no room for error.  I know that the newer versions of the ProMotion, Burny and Hypertherm controls ground on both ends.  There are closed loop AC servo systems with high voltage signals.  Grounding on one end DOES seem to work best on Mach systems though.

Offline RICH

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Re: Spindle Motor is the cause of all my problems
« Reply #19 on: August 11, 2012, 07:27:17 PM »
Shielding is a rather diffcult to put in simple terms but I will try and confuse .....
 
The shield is nothing more than an barrier to keep something out, something in, or take something away.
The barrier can be solid, like a metal wall, or it can be open, like a fence and still act as barrier. Thus electrically
it can be 100% or less. It can be open, and be effective, but the actual opening size is frequency related.
The best shield is 100% as it totally shields what is inside from what is outside and vise versa. Additionally it can can conduct.
So what happens to the shield at the ends is important.

If one end is connected to ground and the other not connected, then it acts as shield along it's path but additionally it conducts
and provides a path for signals to the ground. It won't  transmit all signals since depending on it's length is acts as a short to
transmission.

Shields are normally taken to a single point and that point goes to ground. Ground is not ground. Ground is just a reference.
In the case of shielding, ground is taken to a single / common point and usually that single point continues to a specific point not
associated with other points of an electrical device. Simple said, the shielding is run to a point which provides almost no resistance to
the signal and separate from any other grounds.  If grounds are connected then signals can can travel along to what that other ground
are connected to.

BTW, you twist wire pairs as the signals running on the outside of the conductors have difficulty mixing or traveling since an inductance is
seen by the signal.  

Now it gets more interesting as one must consider how signals are received, mixed, transmitted, etc, etc.
A conductor can receive a signal via conductance or inductance. Any conductor which cuts an electrical field will acquire a  signal.
The shield will keep that signal out from combining with or riding on the inside wires.

I have used signal rather loosely. The unwanted signal is usually some kind of field  created by say a motor, vfd, etc. and that field is
made up of numerous signals of varying frequencies. Noise as it is called, because we can't understand the meaning as compared
to speech or represent it as a simple wave.

How intense a field is rather difficult to envision as you can't see it,but, for description purposes  just envision the field as a balloon
filed with signals and the source of the signals is at the center of the balloon. The noise weakens in intensity as the distance increases.

So use the above to understand how shielding is used when running wires to a motor or whatever.

FWIW,
RICH