Re: J1939-11 physical connection on IEC terminal blocks?

Hello Vincent,

Unfortunately I have earlier experienced solutions you described. The use of terminal strips
is not a good idea, because of some reasons:
1: First and major issue is impedance mismatch of the transmission line. If you are using
   terminal strips for connecting several nodes into a single location or locations too
   close to each other, the lumped impedance of the connected nodes will change too much
   the line impedance and thus introduce impedance transition point, introducing reflections.
   By using the T-pieces etc. there will be anyway longer distance between the nodes and
   much smaller risk for significant mismatch.
2: Material and geometry of the terminal strip connectors also cause impedance mismatch and
   decreasing the signal quality.
3: Connection work efficiency and quality will be collapsed when you change well polarized
   standard connectors/cables into cables with flying leads, which have to be connected
   manually, wire-by-wire. The risk may even be higher, if there is plain wires available
   and installation are occasionally made without proper, impedance-matched, twisted-pair or
   cable.
4: Shield should exist 360deg around the signal pair. By using terminal strips with bridges,
   the shield will be just a single line in parallel with the signal lines, not anymore
   providing EMI protection.

I have found serious problems with as low bit rates as 250kbps, which is mainly used in J1939
systems.

Merry Christmas,

-H

Heikki Saha, CTO
  M.Sc. Automation
  Dr.Tech. Electronics
TK Engineering Oy
Mail address:  P.O. box 810, FIN-65101 VAASA
Visit address: Yrittäjänkatu 17, FIN-65380 VAASA
+358 (0)50 588 6894
[email protected]
http://www.tke.fi/
http://www.canopen.fi/

----- Original Message -----
From: "Vincent Royer" <[email protected]>
To: [email protected]
Sent: Monday, December 22, 2014 11:26:57 PM
Subject: [CANLIST] J1939-11 physical connection on IEC terminal blocks?



Hi all, 


At my shop, we have standardized using the Deutsch 3 way splitter and connector parts for doing all our J1939 connections on our commercial truck chassis. 


However, we are doing very complex systems involving several nodes in a small area. To facilitate wire interfacing for the input / output and power signals, we have started using IEC Din-Rail terminal blocks. However, to date, we have not used these terminals for the J1939 connections. 


My technician asked if he could use 3-level signal/signal/shield IEC din rail terminal blocks, in which the shield terminal is connected right down to the din rail. The idea is that when there are several J1939 nodes being installed in near proximity, we could use several of these 3-level terminal blocks, and simply insert jumpers to interconnect them. Then, connected to the last terminal would be a typical 120 ohm resistor. 


Here's an image of this type of connector. We have jumpers which push in to interconnect any level to the terminal next to it. 


http://www.connectwell.com/media/2836181-CDLG2_5.gif 



This will allow us to bring the backbone into the panel, terminating it only once at the first terminal rail. the "jumpers" would now become the backbone, with the nodes each only a couple mm apart. 


Does anyone see any potential issues with this arrangement? 


Thank you! 







-- 
Vincent Royer 
Electrical Project Coordinator 
Intercontinental Truck Body 
email: [email protected] 
phone: (604) 576-2971 
mobile: (604) 861-1057
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