bombproof RS485 chips?

Hi all,

  I'm working a project where I've got several RS485 nodes cabled together
in about as hostile environment as I can imagine.  High powered vacuum
pumps, high current stepper motors, high static discharge possibilities,
etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
and CMI?  I know that the TI 75176B is right out, but who is in?

thanks,
DLC
-- 
============================================================================
* Dennis Clark         dlc@frii.com                www.techtoystoday.com   * 
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    
============================================================================

Perhaps you need to add some extra static protection measures of your own?


"Dennis Clark" <dlc@io.frii.com> wrote in message
news:406cf412$0$197$75868355@news.frii.net...
> Hi all,
>
>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?
>
> thanks,
> DLC
> -- 
>
============================================================================
> * Dennis Clark         dlc@frii.com                www.techtoystoday.com
*
> * "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003
*
>
============================================================================

Dennis Clark <dlc@io.frii.com> writes:

>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?

Usually in the very hostile environments just selecting a right 
RS485 IC is the usually the solution. TO be able to survive in 
very hostile environment you usually need external protection 
components that stop the spikes and surges so thay don't 
get to the receiver IC. And then you don't that magic IC. 

I work for a company that makes products that are used in 
quite hostile environment (near high power high voltage 
switcgear and power transformers). In those environments 
no single receiver IC is anough, you need external 
protection components. 

For example Maxim seems to have quite a good selection of 
RS485 receivers and protection components. 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/

On 02 Apr 2004 05:03:14 GMT, Dennis Clark <dlc@io.frii.com> wrote:


>  I'm working a project where I've got several RS485 nodes cabled together
>in about as hostile environment as I can imagine.  High powered vacuum
>pumps, high current stepper motors, high static discharge possibilities,
>etc.  

Galvanic isolation takes care of most of the common mode problems and
the twisted pair cables attenuate quite a lot of the differential
voltages. The way cable shields are grounded can also be critical in
some situations. 

Large distances between the PCB tracks are of course needed as well as
suitable optoisolators and power supplies to maintain the isolation
even at discharge voltages of several kilovolts.

Paul
 

"Dennis Clark" <dlc@io.frii.com> wrote in message
news:406cf412$0$197$75868355@news.frii.net...
> Hi all,
>
>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?

Devices like Transguards are very useful for this.

Leon

Dennis Clark wrote:

> Hi all,

>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?

I would use an optoisolator on the receive end, to make it isolated from 
the receive ground.

I don't know what the commercial controllers we use have, but I have 
wires running all over the campus, in hostile envrionments, and they 
never seem to have a problem.  One cable runs into a bldg next to the 
swimming pool, and the juice from the underground conduit wicked up thru 
the wires inside the jacket, and then came out and dried onto the 66 
blocks (for the telephone system).  The juice dried and left a salt 
encrustation over half of the block!  Crazy, but it was still working, 
but not as good as it was supposed to be..

> thanks,
> DLC

think about using shielded / twisted high quality cables/EMI
filters/connectors/housing/PSU

then if you still need bombproof, forget 8 pin parts and design your own
using discrete components.

regards

"Dennis Clark" <dlc@io.frii.com> a &#4294967295;crit dans le message de
news:406cf412$0$197$75868355@news.frii.net...
> Hi all,
>
>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?
>
> thanks,
> DLC
> -- 
>
============================================================================
> * Dennis Clark         dlc@frii.com                www.techtoystoday.com
*
> * "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003
*
>
============================================================================

In article <406cf412$0$197$75868355@news.frii.net>
           dlc@io.frii.com "Dennis Clark" writes:

> Hi all,
> 
>   I'm working a project where I've got several RS485 nodes cabled together
> in about as hostile environment as I can imagine.  High powered vacuum
> pumps, high current stepper motors, high static discharge possibilities,
> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
> and CMI?  I know that the TI 75176B is right out, but who is in?

There are two articles on my website that will give you the merest 
clue about what you are dealing with. The transient figure and the
table are from Railway Industry standards. Equipment I have done for
London Underground deals with that extremely hostile environment very
well. The articles are called "Reading the World" and "Writing the 
World" and are linked from "articles" in my Forth pages (but don't
let that put you off - they are only there as I wrote the articles 
for Forthwrite).

The RS485 chips out there in the commercial domain may even be 
unsuitable when you need to add protection components that will stand
up to the environment you are in. This was the case for the LU 
applications I was dealing with due to the constraints imposed by the
re-use of old auto-couplers. I ended up designing a higher voltage 
version of the RS485 interface in discrete components for the driver
side and a well guarded op-amp for the receiver. That interface, 
during some severe testing, withstood an 18kV directly applied 
transient for 0.1us without even flinching. This was well beyond
the specification it was designed to and was actually an accident 
of test set-up. I ride the line where the systems are installed on 
occassions and will be doing so this Sunday (feeling quite safe).

If you must have it as small as possible then look at the App-Notes
from Linear Technology, which were a good read on the subject. I 
think you may have to look at proper galvanic isolation to ensure you
protect the microprocessor/controller and may even have to consider
whether the interface chips become sacrificial in exceptional 
circumstances.

As a quicky clue (I suggest you still read up on transient energy 
managemnent though) you will end up clamping and sinking transient 
energy spikes that would otherwise destroy your circuits. The energy 
has to go somewhere and either a Transorb Diode or big resistor is 
going to have to take the brunt of this energy surge. Capacitance in 
parallel with the Transorb but in series with some resistance will 
help to slow down the transient energy groth in your circuits. However, 
you may also need to PSPICE* your interfaces to understand what this 
may do to the signal you wish to get through.

Naturally, you will have to decide where your trade-offs are within 
your system. Only you can do that though. PSPICE can become a very 
good friend in such circumstances (but do not think you can hurry it).
In doing the interfaces for the LU job I ran hundreds of PSPICE 
simulations for each and every interface type. I usually ended up 
building and testing two or three versions of each to confirm what
I saw in PSPICE.

I suspect that when you have gone through this quite arduous mill 
once you should be better set to tackle even greater challenges like
when you get asked to design and build systems that are guaranteed
to run for 30 years with very little or no maintenance and will only
require rapid fault-finding to an LRU* replacement if they do fail.

*PSPICE is a circuit analysis tool that will run all the normal set
of calculations for your circuit. This is often attached to packages
like OrCAD, UltiCAP and Proteus schematic capture tools. This can be
an enourous amount of work if you have to enter models of the components
you are using (although many manufacturers have these models available
ready to use.

*LRU Line Replaceable Unit. Essentially a plug in module of the 
system.

-- 
********************************************************************
Paul E. Bennett ....................<email://peb@amleth.demon.co.uk>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

CWatters <colin.watters@pandorabox.be> wrote:
: Perhaps you need to add some extra static protection measures of your own?

OK,

  I didn't make myself clear enough.  I know that other features will
be needed to make a good system, not just a "magic" driver.  But, a 
chain is only as strong as its weakest link.  I'm looking for a driver
chip that won't be that weakest link.  I'm already planning on shielded
cabling, twisted pairs, cabled common line, transorbs, etc.  No stone is
being left unturned.  

With that all in mind...
DLC


: "Dennis Clark" <dlc@io.frii.com> wrote in message
: news:406cf412$0$197$75868355@news.frii.net...
:> Hi all,
:>
:>   I'm working a project where I've got several RS485 nodes cabled together
:> in about as hostile environment as I can imagine.  High powered vacuum
:> pumps, high current stepper motors, high static discharge possibilities,
:> etc.  Can anyone suggest an 8 pin part that is REALLY bombproof to static
:> and CMI?  I know that the TI 75176B is right out, but who is in?
:>
:> thanks,
:> DLC
:> -- 
:>
: ============================================================================
:> * Dennis Clark         dlc@frii.com                www.techtoystoday.com
: *
:> * "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003
: *
:>
: ============================================================================



-- 
============================================================================
* Dennis Clark         dlc@frii.com                www.techtoystoday.com   * 
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    
============================================================================

Paul Keinanen <keinanen@sci.fi> wrote:
: On 02 Apr 2004 05:03:14 GMT, Dennis Clark <dlc@io.frii.com> wrote:

Paul,

  I've read the app notes on total galvanic isolation and have a question
for those who may have more experience than I in that area.  My network
will be quite short (less than three meters total) and all of the nodes
as well as the cabling will be on the same supply, in the same box and
near the same noise.  In those circumstances it seems to me that total
galvanic isolation is a pretty elaborate design, and not really useful
since the board is as likely to be "hit" as the cable by any static
blast or motor CMI.  Am I off base with that thinking or with total
isolation actually be of value in this environment?

DLC

:>  I'm working a project where I've got several RS485 nodes cabled together
:>in about as hostile environment as I can imagine.  High powered vacuum
:>pumps, high current stepper motors, high static discharge possibilities,
:>etc.  

: Galvanic isolation takes care of most of the common mode problems and
: the twisted pair cables attenuate quite a lot of the differential
: voltages. The way cable shields are grounded can also be critical in
: some situations. 

: Large distances between the PCB tracks are of course needed as well as
: suitable optoisolators and power supplies to maintain the isolation
: even at discharge voltages of several kilovolts.

: Paul
: 

-- 
============================================================================
* Dennis Clark         dlc@frii.com                www.techtoystoday.com   * 
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    
============================================================================