FW: J1939/11 SHIELD GROUND

Good Day Bram,

 

Thank you for that information.  You seemed to sum it up pretty easily.

Unfortunately I do not have a copy of J1939/11 to reference.  My resources
are limited and I do not have the funding to purchase such document from
SAE.. my company does not really see the point in 'investing' in such
documents at the moment.  I chose J1939/11 as our business is in the
off-highway fluid power sector.  So a majority of our customers use J1939. 

I am looking to follow best practices from the very beginning, rather than
making things work.. then realizing it didn't follow requirements and it be
a mess down the line or doesn't communicate with other CAN networks on a
machine.

We (and that, I mean, 'I') are hoping to expand from a hydraulic supplier
into a systems integrator using electronics/hydraulics.  Is there any other
source for J1939/11?.. 

[email protected] <mailto:[email protected]> 

 

Thank you for your time,

-Cain

 

 

From: [email protected]
<mailto:[email protected]>
[mailto:[email protected]] On Behalf Of Bram
Kerkhof
Sent: Tuesday, June 09, 2015 8:25 AM
To: [email protected] <mailto:[email protected]> 
Subject: RE: [CANLIST] J1939/11 SHIELD GROUND

 

Oh yeah... Lock a bunch of EE engineers in the same (virtual) room, utter
the words "cable shielding" and "ground loop", grab some popcorn and sit
back to enjoy the spectacle of nerd wars being waged... ;-)

 

J1939-11 is pretty clear:

-          Shield should be connected (using the drain wire) to *all*
connectors/nodes. Each node should ground the shielding using a resistor and
capacitor in series to the best possible ground point.

-          Shield should additionally be grounded directly to vehicle
ground, using wire conductor to one single point, with lowest impedance
connection possible, preferably close to the center of the network.

 

My 2 cents: if you are using shielded cables, the shield should always be
connected on all nodes. Without a ground loop there is no shield, but rather
a (potential) antenna that might introduce really fun problems to diagnose.

 

As you are referring to J1939 and each node is connected to the same power
supply with a shared ground, there *should* be no issues with (high) ground
potential differences. The nodes *should* be designed to be able to deal
with ground potential differences gracefully. Although I've been bitten more
than once by bad design in that department. Cable shielding and ground
loops/isolation are (apparently) hard to design for.

 

A second question: do you really need shielded cabling? CAN differential
signaling is pretty robust, and introducing shielding often introduces more
complexity (and hence errors) than it aims to fix.

 

The shielded cable should have a braided shield or a drain wire that you can
connect to the shield pin. The standard prescribes using a solder sleeve or
specific socket with extended contact area for the drain wire.

 

cheers,

Bram

From: [email protected]
<mailto:[email protected]>
[mailto:[email protected]] On Behalf Of Cain
Shultz
Sent: dinsdag 9 juni 2015 12:39
To: [email protected] <mailto:[email protected]> 
Subject: [CANLIST] J1939/11 SHIELD GROUND

 

Hello,

 

I have a question about proper grounding for CAN SHIELD.  I am sure other
protocols talk about CAN shield, however I suppose my question is specific
to J1939/11.

Where do you ground the shield to?

 

Lets say I have a very basic CAN network, 3 nodes total.  All of which has a
CAN SHIELD pin on their boards.  Do I connect each one, just one?  Every
forum I see, it says to ground your shield only one time.  And most images I
see, show that you ground it directly to battery.  However if the CAN SHD
pins on my micro controllers are grounded internally.. wouldn't that do the
same?

The controllers are Danfoss MC012 or MC024 versions.

I do not think the API is available online however I have their Plus+1
software which all the APIs are loaded internally.

 

With shielded cable, is there an actual wire I will crimp to my DT04-3S
deutcsch 3 pin connector?  Or do I literally take the foil wrapping and get
it in the pin.

Very novice so I apologize for my ignorance.

No worries, this project is for training only.

 

This forum has been very educating and I have learned a lot just sitting in
the background reading the past year.

 

Thank you for your time!

-Cain