diamond: RE: [DIY-CNC] What kind of wire are you using to

Hi Steve

You describe areas below where you had problems in RF installations and
comms systems. A whole new set of problems come in here and different
concepts to control the problems.

Often comms systems use signalling like a differential encoder system, you
can now screen both ends since any noise on one cable is the same on the
other and the difference between them remains the same. The screen on both
ends also becomes necessary since the cable distances are generally that
great that a large voltage exists between systems and needs to be
normalised, without it the noise voltage gets so large that the signals can
saturate the input stage and become unreadable.

RF is another issue where current travels internally which is OK, but also
externally on the cable screen. Simple applying some inductance to the
screen with an external ferrite ring, or just coil the cable makes it harder
for the RF to travel on the outside. This is also often applied in certain
signal cable situations. We also sometimes double screen an RF cable, or
signal cable, with signal cable the internal screen is connected at one end
only, but the external screen can be connected at the one or both ends.

So nowadays you can do better than best if you understand where noise issues
are occurring from, this is often though a lot more than just connecting a
cable, the protocol is important as well.

Trouble is now we are starting to really complicate things for the
newcomers.

As to Telemech, seems their documents in this case are reasonable, but there
are errors and misunderstandings within telemechs documentation system they
are now aware of, some of them very serious. I have been working with
several directors and their development offices in France to correct some of
these, but some of these will take 5 years to correct, and others just
relate to important work they had claimed to do but not actually done.

Regs Mark

Dr. Mark Vaughan Ph'D., B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd., reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH UK.

Phone/Fax 44 (0) 1872 561288

RSGB DRM111 (Cornwall)

_____

From: DIY-CNC@yahoogroups.com [mailto:DIY-CNC@yahoogroups.com] On Behalf Of
Steve Blackmore
Sent: 25 February 2008 00:58
To: DIY-CNC@yahoogroups.com
Subject: Re: [DIY-CNC] What kind of wire are you using to

On Sun, 24 Feb 2008 20:49:18 -0000, you wrote:

>Yes Harko
>
>Connecting screens at one end is for signal cables and totally correct
>procedure.

Not necessarily! For instance,

Download the Telemanique Altivar 31 VFD manual

It says...

Power supply, non shielded.

Non shielded wires for relays.

Shielded cable for motor connections, grounded at both ends.

Shielded cable for control/signal wiring, grounded at both ends.
Intermediate connections must be in EMC shielded boxes.

Shielded cable for braking resistor. (If fitted) Shielding must be
continuous, Intermediate connections must be in EMC shielded boxes.

I agree that what you are saying is a good generalisation, but it
certainly isn't written in stone! You need to heed the manufacturers
recommendation and/or experiment a bit ;)

In a past life I installed comms and computer equipment in high RF areas
in "government facilities", and grounding cables at one end often
doesn't work in that situation. You've just made an antenna.

Closing the holes and making a Faraday shield works, but it's difficult
and sometimes impossible to achieve because of ground loops or non
commoned grounds, you just have to do the best you can to get a
satisfactory performance.

Steve Blackmore
--

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