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Answered

CAN Communication Distance

Joe 5 years ago in IQANdesign updated by Justin Wagner 4 weeks ago 14

What is the maximum distance that the IQAN bus can transmit (in terms of cable length)? I can't find it in the documentation and I have a project that requires a display to be away from a hazardous area.

I have not done much with CAN on IQAN. I have some experience with DeviceNet (which is based on a CAN model).

Simply based on the standard, not specific hardware:


Depends on the operating communication rate. Using an industrial cable with shielded wire (in a static noise free area) you should not attempt more than 100 meters at 500kbps and not more than 200 meters at 250Kbps.

Effective length will be reduced where electric noise is present or wiring is susceptible to outside effects. I think many people use coaxial shielded cable when trying to go far.


Be sure to use correctly placed terminating resistors.

Answered

As Neil wrote, 100 m at 500 kbit/s and 200-250 m at 250kbit/s are in some sources given as a theoretical upper limit for CAN.


In brief, a longer bus has a longer the propagation delay (the time for any two nodes to see the same bit). On a bus with a higher bitrate, there is less time for the bit to propagate before the nodes must sample it.


In the IQAN mounting and maintenance instruction book, we give more conservative estimates on CAN bus length, under the assumption it is a 250 kbit/s bus (expansion module or regular J1939), we are stating 100 m as the maximum, but with 40 m as the recommended length.


In both SAE J1939-15 (Physical Layer, 250 Kbps, Un-Shielded Twisted Pair) and SAE J1939-11 (Physical Layer, 250 Kbps, Twisted Shielded Pair), the maximum backbone length is specified as 40 m. This is based on requirements on cabling as well as on the controllers.


By taking controller specific parameters into consideration, and assuming low cable propagation delay per unit length, we have made calculations showing 150 m as upper length for an MD3-XA2 system, and 190 m for an MD3-MC2 system. But given that the cabling is probably going to be less than ideal, I would not advise designing a system with these lengths.

Hello Gustav,  I am having issues with setting up a remote control panel. This panel will use a MD4 and connect to a system using a Md4 and MC43 via J1939. It seems as soon as I connect a cable as long as 40ft my CAN bus fails. If a 15 foot cable is used it works. In the Mounting and maintenance book it states to not use shielded cable for CAN BUS. Have you tested this? I am currently using a shielded cable and wondering if that is my issue.

I'm also curious about this recommendation against using a shielded cable. We've used shielded cable for years on our CAN bus wiring. We have had some sporadic no contact CAN communication issues, but they happen so infrequently that we've never questioned the shielded cable.

I think there is an old post where Gustav covered why they don't recommend shielded. If I remember correctly they stopped recommending shielded because people were frequently using the shield incorrectly and causing issues for themselves. 

I am trying to investigate using the new can routing option as a solution to this - can you tell me which modules support CAN routing?

The CAN routing feature was added in IQANdesign 5, it exists on MC4x modules. If splitting the single bus into two, joined by one module routing the messages actually works will depend on how sensitive the higher layer protocol is to latency of the messages. 

I'm designing a system that will require a bus length of about 750 feet. In the past we've used EKS CAN-FIBER converters and ran fiber optic for buses of this length, but I'd like to eliminate fiber to reduce cost and complexity in the system if possible.


I've found a CANbooster from Proemion that bumps up the voltage to 8V / 16V differential to transmit longer distances.https://www.proemion.com/us/products/hardware/standard-products/canbooster.html


Has anyone had any success with this or similar CAN signal boosters to get more distance on a CAN bus with IQAN?


This specific bus would likely be a HS expansion bus between an MD4 and XC43 or similar.

We tested with CAN to Ethernet bridges and are installing them as we speak. 100m is enough for us, but I understand that if 100m isn't enough, you can install a ethernet switch halfway and then you can go up to 200m, etc.

We use MD4 and MC41. Maybe this is helpfull...

Bridges und Gateways für CAN- und CAN-FD-Netzwerke (ixxat.com)

I have tried to use the CAN@net 420 but was unable to make it work. Did you find success with that device?

Yes, but we used the CAN@net NT200. You need to configure it of course and we have seen that our MC41 starts quicker then the gateways. Maybe something to remember... If you need more information, let me know.

Hey Marcel that would be great. I haven't tried to make it work for about 6 months so I cant recall all my issues at the moment but if I could get your contact and reach out when I get back to it that would be much appreciated. I found their tech services to be completely useless as none of the people I talked to had ever used the device. Very different then Iqan. I do recall some timing issues and the Can Net would fault and would not recover even though I had the faults  turned off. codie@rouseindustries.com

+1

We have used an Anybus CAN Communicator to convert to/from EthernetIP without issue. It wasn't over a long distance, but it worked well with IQAN. FYI - if you go this route, be sure to get the "Communicator" (AB7318). The CANOpen version requires another CANOpen device for setup that couldn't be emulated by the MD4 we were using. Hope this helps.