CAN with bus length >=1km possible?


Thread Starter

Erwin Torbeyns

hi there

Are there some people here who have experience using CAN (DeviceNet, CANopen, SDS, whatever...) as fieldbus with 1km bus length or more?

I am an electronics engineer and i would like to use CAN to interconnect embedded processing boards (custom designed), based on a
microcontroller with CAN build-in. The application has the following requirements:
- The main purpose is to boadcast relatively short 'strings' (16 to 32 bytes) in a building-automation application.
- Hard real-time performance is not required (<= 50ms is ok)
- Bus load (traffic) is low
- Maximum devices is 32.
- 10 or 20 kbit/s is fast enough
- inter-operability with other manufacures not required
- Total bus lengt can be more that 1km, but never more than 6km

(Don't bother pointing me to LON - it is not an option)

The thing that worries me is the bus lenght of 1km or more. The signal needs to be able to travel twice the distance of the line (+delays in
electronics) within the 'bit time' because of the CSMA-style protocol with arbitration. (using bridges to span the total 6km is acceptable,
but one segment should be able to be 1km). Now, i have found some sources on the web that talk about 1km being ok at 50kbit/s and even 2.5km
at 20kbit/s, 10km at 5kbit/s. But this is all very academic.
So my question is: does anyone have actual experience using CAN with 1km, or more, bus segments? Is it stable or did you experience many