Re: reliable CAN connection

thanks for the quick response. 
I know its possible to build more redundancy into systems. What I wanted to see if projects use CAN as a single channel to communicate with only one device, and them have  a CAN channel for each device. 
In our application each device has a CAN-In (M12 male ) and an a CAN-out (M12 female), if any of these connections fails, the CANbus is down.

Peter


> On Jun 4, 2016, at 11:33 AM, John Dammeyer <[email protected]> wrote:
> 
> There are systems that use dual CAN systems for fault redundancy.  The Space
> Shuttle used 5 computers, 4 of one type and a 5th of a different and
> programmed by a different group.  I believe each control surface etc. had 3
> actuators and used a voting system to determine if one of the
> cumputers/actuators/sensors would be disabled.
> 
> So needless to say fault tolerance can be built into anything and it all
> comes with a cost.
> 
> Generally any system is only as strong as the weakest part and a CAN bus
> failure could be a weak link.  But if the system is designed to be optimal
> for price/size/functionality it's unlikely you'd have multiple sensors or
> actuators to do the same thing.  
> 
> Let's look at a simple example.  A multi-panel solar panel with multiple
> MPPT chargers and a dual axis servo motor system that tracks the sun.  If
> the CAN bus connecting it all fails then the system fails since the goal of
> such a system is to optimize each charger on a solar panel to operate in
> its' MPPT point for a given output voltage.
> 
> If there is a master controller and each MPPT charger was Ethernet Enabled
> you could use a hub or switch and run a star network from the controller to
> all the MPPT chargers.  Now the weak link is the hub and a single failure
> there also takes down the system.  Or use an RS485 system with a repeater in
> each MPPT Charger so data goes in but is also sent out again with the second
> driver.  Disconnecting the bad unit requires a small jumper module to
> connect the now separated bus.  But wait, for CAN just unplug the bad MPPT
> charger.  No plug needed.
> 
> Take it one step further with CAN and bring the CAN bus into the module with
> a DPDT relay controlled by the module or by a star network f wires from the
> master controller.  Now you can mechanically disconnect any module without
> impacting the rest of the system.  
> 
> Each of those scenarios increases the price and complexity.  In the case of
> solar farms that might be useful since losing one unit isn't a big deal.
> But on a system that loses the end travel limit switch because the CAN bus
> failed likely loses the ability to operate anyway.   That means the CAN bus
> isn't the weak point.  The missing sensor would be.
> 
> So I think a generalization that CAN bus needs to be dual or more depends
> totally on the application.  Where it's needed it's already done.  Notice
> many of the embedded micro-processors have dual controllers.
> 
> John Dammeyer
> Automation Artisans Inc.
> http://www.autoartisans.com
> Ph. 1 250 544 4950
> 
> 
> 
> 
> 
> 
> 
> 
>> -----Original Message-----
>> From: [email protected] [mailto:[email protected]] On
>> Behalf Of Peter Lauer
>> Sent: June-04-16 8:05 AM
>> To: [email protected]
>> Subject: [CANLIST] reliable CAN connection
>> 
>> 
>> Hi,
>> we recently reviewed a study that showed that the reliability of a system
>> goes down when you use one CAN bus instead of discrete connections. lets
>> say you have 3 actuators and 3 sensors on one bus, the bus goes down, you
>> loose all actuators and all sensors.
>> 
>> instead of going back to all discrete wiring, what about staying with CAN
> on
>> the actuator and sensor side but have a separate CAN channel on the
>> controller? Basically like the switch from BNC Ethernet to 10BaseT. Than
>> only one channel can go down at a time, and you still have control over
> the
>> rest.
>> 
>> Peter--
>> Archives and useful links: http://groups.yahoo.com/group/CANbus
>> Subscribe and unsubscribe at www.vector.com/canlist/
>> Report any problems to <[email protected]>
> 
> --
> Archives and useful links: http://groups.yahoo.com/group/CANbus
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> Report any problems to <[email protected]>

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