CANBus compatibility and CANBus Repeater

[Michel Osso]

Hello, I have got a product which has got a CANBus with 5 wires and speed at 125KB/s. The CANBus is used to have remote I/O modules which are used for the HVAC control. In total, I can have up-to max 15 modules I/O on the CANBus. The length of the CANBus is max of 10 meters when it is installed outside the electrical cabinet. For some projects, I need to have a CANBus longer (up-to 40 meters). To do so, I need a CANBus repeater. I am not used to the CANBus as I am used to TCPIP network. Then, I would like to ask some questions which will help me to make the correct choice:
1) Is it possible to use a CANBus repeater for a CANBus with 125 KB/s at 5 wires?
2) If we can use a CANBus repeater, what could be the problems? delay of the signal? voltage ?
3) What do I have to look when I will choose a CANBus repeater?
4) Do you have any CANBus repeater that I could use ?
Thank you for your help - Kind regards - Michel  

[Michel Osso]

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Hello,

I have got a product which has got a CANBus with 5 wires and speed at 125KB/s. The CANBus is used to have remote I/O modules which are used for the HVAC control. In total, I can have up-to max 15 modules I/O on the CANBus. The length of the CANBus is max of 10 meters when it is installed outside the electrical cabinet. For some projects, I need to have a CANBus longer (up-to 40 meters). To do so, I need a CANBus repeater. I am not used to the CANBus as I am used to TCPIP network.

Then, I would like to ask some questions which will help me to make the correct choice:

1) Is it possible to use a CANBus repeater for a CANBus with 125 KB/s at

5 wires?

2) If we can use a CANBus repeater, what could be the problems? delay of the signal? voltage ?

3) What do I have to look when I will choose a CANBus repeater?

4) Do you have any CANBus repeater that I could use ?

 

Thank you for your help

 

Kind regards

 

Michel  

 

 

[Funny N.]

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Hi, Michel,
If you only run CAN network up to 40 meter, you don't need a repeater.
The SAE J1939 runs at 250K bps and its backbone can work up to max. 40 meters.
I also see some CAN network runs at 1 M bps with 40 meters backbone.
So you don't have to worry anything but concentrate on your detail design.

 

Funny N.
Au Group Electronics, New Bedford, MA, http://www.AuElectronics.com

----- Original Message ----
From: "Osso, Michel" <Michel.Osso@...>
To: canlist@...
Cc: Andreas.Neubauer@...
Sent: Friday, July 25, 2008 6:53:25 AM
Subject: [CANLIST] CANBus compatibility and CANBus Repeater

Hello,

I have got a product which has got a CANBus with 5 wires and speed at 125KB/s. The CANBus is used to have remote I/O modules which are used for the HVAC control. In total, I can have up-to max 15 modules I/O on the CANBus. The length of the CANBus is max of 10 meters when it is installed outside the electrical cabinet. For some projects, I need to have a CANBus longer (up-to 40 meters). To do so, I need a CANBus repeater. I am not used to the CANBus as I am used to TCPIP network.

Then, I would like to ask some questions which will help me to make the correct choice:

1) Is it possible to use a CANBus repeater for a CANBus with 125 KB/s at

5 wires?

2) If we can use a CANBus repeater, what could be the problems? delay of the signal? voltage ?

3) What do I have to look when I will choose a CANBus repeater?

4) Do you have any CANBus repeater that I could use ?

 

Thank you for your help

 

Kind regards

 

Michel  

 

 

[Steve Letkeman-3]

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My messages don't seem to be making it through...trying again...


Steve Letkeman wrote:

Hi Michel, With CAN, the slower the data rate the longer your bus can be.  For 1Mbps the maximum
network length would be 40m but for 125kbps the length increases to 500m so it doesn't sound like
a repeater would be necessary, but, having said that, there might be another reason the manufacturer
has put a 10m limit.  One example might be that your 5 wires are carrying DC power to the
remote nodes and that there is sufficient draw as to create too much voltage drop by going over 10m.
The other reason might be their choice of CAN transceivers that might limit this (this would seem
unlikely but you never know)
  You'll have to try and find out what the 5 wires do but the first 4 are likely DC power, ground, CAN
high and CAN low.  The 5th wire might be a spare, might be an extra power lead or might have some
other function like a synchronizing signal or diagnostic line etc.
  If you do use a CAN repeater it will delay the CAN messages going back and forth across the
repeater but it shouldn't have any effect on the system as the delay should only be one message
length (plus a bit) in each direction.  Most times a system won't expect a response that fast because
you have to account for other traffic on the bus.
Steve
www.zanthic.com

Osso, Michel wrote:

Hello,

I have got a product which has got a CANBus with 5 wires and speed at 125KB/s. The CANBus is used to have remote I/O modules which are used for the HVAC control. In total, I can have up-to max 15 modules I/O on the CANBus. The length of the CANBus is max of 10 meters when it is installed outside the electrical cabinet. For some projects, I need to have a CANBus longer (up-to 40 meters). To do so, I need a CANBus repeater. I am not used to the CANBus as I am used to TCPIP network.

Then, I would like to ask some questions which will help me to make the correct choice:

1) Is it possible to use a CANBus repeater for a CANBus with 125 KB/s at

5 wires?

2) If we can use a CANBus repeater, what could be the problems? delay of the signal? voltage ?

3) What do I have to look when I will choose a CANBus repeater?

4) Do you have any CANBus repeater that I could use ?

 

Thank you for your help

 

Kind regards

 

Michel  

 

 

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[Thilo Schumann-2]

Dear Michel,

first, CAN itself only has two wires, which are called CAN high (CAN_H)
and CAN low (CAN_L). All the other wires are Ground, Power and
I-dont-know. Thta means, If you would need a CAN repeater, that would be
only of the two wires.

 From the timing point of view, your CAN, you do not need any CAN
repeater. It is even worse. CAN repeaters limit you much more, from the
timing point of view. Because repeaters are time delays.

Normally, if CAN is run at 1 Mbps a network length of about 30m to 40m
is possible. At 125 kbps a CAN network length of 500 m is possible. But
with CAN repeaters the possible network length is much more limited.

CAN repeaters are only need, if you have physical problem to guarantee
the required voltage levels. Normally, this is required if you go over
1000 m.

Best regards

Thilo

Osso, Michel schrieb:

>
> Hello,
>
> I have got a product which has got a CANBus with 5 wires and speed at
> 125KB/s. The CANBus is used to have remote I/O modules which are used
> for the HVAC control. In total, I can have up-to max 15 modules I/O on
> the CANBus. The length of the CANBus is max of 10 meters when it is
> installed outside the electrical cabinet. For some projects, I need to
> have a CANBus longer (up-to 40 meters). To do so, I need a CANBus
> repeater. I am not used to the CANBus as I am used to TCPIP network.
>
> Then, I would like to ask some questions which will help me to make
> the correct choice:
>
> 1) Is it possible to use a CANBus repeater for a CANBus with 125 KB/s at
>
> 5 wires?
>
> 2) If we can use a CANBus repeater, what could be the problems? delay
> of the signal? voltage ?
>
> 3) What do I have to look when I will choose a CANBus repeater?
>
> 4) Do you have any CANBus repeater that I could use ?
>
>  
>
> Thank you for your help
>
>  
>
> Kind regards
>
>  
>
> Michel  
>
>  
>
>  
>

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|  Kontumazgarten 3
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|
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[Ram-12]

Hi all,

I have 4 CAN nodes (sensors) on a bus and my software monitors and gets
data from the sensors at 500kbps, Std CAN. If any of the sensor quit
sending me the data, based on the ID i can identify the faulty node. I
tried to detect a short to ground fault on a CANH pin with one
particular node and still have all the other nodes on the bus. It seems
the software randomly picks up fault on all the nodes and reports them
instead reporting the node whose CANH pin is short to ground. Is it
possible to detect the short to ground fault on a CANH or CANL on a
particular node when multiple CAN nodes are connected on the bus. Please
need advice

Thanks
Ram
>
>  
>
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[Geoff Field]

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Hi Ram,

Unless you have series resistance and analogue voltage sensing, there is no way to do this.  If CANH (or any line at all, really) is shorted to ground at any point, it's going to register as shorted to ground on all other connected devices that have a ground line of similar value.


Bottom line: You cannot change the laws of physics.

Geoff

----- Original Message ----
From: Ram <rams@...>
To: canlist_NOT@...
Cc: canlist@...
Sent: Thursday, 31 July, 2008 4:46:12 AM
Subject: [CANLIST] Short to ground fault


Hi all,

I have 4 CAN nodes (sensors) on a bus and my software monitors and gets
data from the sensors at 500kbps, Std CAN. If any of the sensor quit
sending me the data, based on the ID i can identify the faulty node. I
tried to detect a short to ground fault on a CANH pin with one
particular node and still have all the other nodes on the bus. It seems
the software randomly picks up fault on all the nodes and reports them
instead reporting the node whose CANH pin is short to ground. Is it
possible to detect the short to ground fault on a CANH or CANL on a
particular node when multiple CAN nodes are connected on the bus. Please
need advice

Thanks
Ram
>
> 
>
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---

Find a better answer, faster with the new Yahoo!7 Search - Start Here.

[Thilo Schumann-2]

Hi Ram,

that is how CAN is working. If a bit is different than expected it will
be detected as an error by everybody.

For example, if there is a short to ground (it does not matter where)
and someone wants to transmit a message, it will be detected by
everybody as an error for two reasons. First, because at least the
checksum of the message will be wrong -> error.
Second, if someone detects an error the message will be destroyed at all
with an error frame. At least that will be detected by everybody as an
error.
Then the message is going to be retransmitted. That will lead to an
error again and the message is retransmitted again and so on. That will
lead possibly lead to the situation that the sending node will switch
into the CAN state BUS-OFF and the other nodes into the CAN state ERROR
PASSIVE.
Presumably another node will send in between a message as well then the
story described above will repeat.

What you can do to isolate the faulty node? AFAIK, nothing. Maybe Steve
can give us some more insights on this topic.

You can use a different physical layer. Instead of the high-speed
physical layer according to ISO11898-2 you can use the fault-tolerant
physical layer according to ISO11898-3. But this one has different
issues. For example, the maximum transmission rate is limited to 125
kbps. If a certain fault is detected and you still want to communicate,
then the maximum transmission rate is limited even more.

Greetings

Thilo

Ram schrieb:

>
> Hi all,
>
> I have 4 CAN nodes (sensors) on a bus and my software monitors and
> gets data from the sensors at 500kbps, Std CAN. If any of the sensor
> quit sending me the data, based on the ID i can identify the faulty
> node. I tried to detect a short to ground fault on a CANH pin with one
> particular node and still have all the other nodes on the bus. It
> seems the software randomly picks up fault on all the nodes and
> reports them instead reporting the node whose CANH pin is short to
> ground. Is it possible to detect the short to ground fault on a CANH
> or CANL on a particular node when multiple CAN nodes are connected on
> the bus. Please need advice
>
> Thanks
> Ram
> --
> Archives and useful links: http://groups.yahoo.com/group/CANbus
> Subscribe and unsubscribe at www.vector-informatik.com/canlist/
> Report any problems to <canlist-owner@...>
>
>
>

--
+--------------------------------------------------------------------
|                                                                    
|  CAN in Automation (CiA) GmbH                                        
|  Kontumazgarten 3                                              
|  DE-90429 Nuremberg                                                  
|                                                                    
|  phone: [phone]           http://www.can-cia.org         
|  fax:   [phone]          mailto:headquarters@...
|  CEO Holger Zeltwanger             AG Nuernberg HRB 24338                                                                  
+--------------------------------------------------------------------


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[Ram-12]

Hi all,

Thankyou very much. Now i have a clear picture. Appreciate all your help.

Thanks
Ram

Thilo Schumann wrote:

> Hi Ram,
>
> that is how CAN is working. If a bit is different than expected it
> will be detected as an error by everybody.
>
> For example, if there is a short to ground (it does not matter where)
> and someone wants to transmit a message, it will be detected by
> everybody as an error for two reasons. First, because at least the
> checksum of the message will be wrong -> error.
> Second, if someone detects an error the message will be destroyed at
> all with an error frame. At least that will be detected by everybody
> as an error.
> Then the message is going to be retransmitted. That will lead to an
> error again and the message is retransmitted again and so on. That
> will lead possibly lead to the situation that the sending node will
> switch into the CAN state BUS-OFF and the other nodes into the CAN
> state ERROR PASSIVE.
> Presumably another node will send in between a message as well then
> the story described above will repeat.
>
> What you can do to isolate the faulty node? AFAIK, nothing. Maybe
> Steve can give us some more insights on this topic.
>
> You can use a different physical layer. Instead of the high-speed
> physical layer according to ISO11898-2 you can use the fault-tolerant
> physical layer according to ISO11898-3. But this one has different
> issues. For example, the maximum transmission rate is limited to 125
> kbps. If a certain fault is detected and you still want to
> communicate, then the maximum transmission rate is limited even more.
>
> Greetings
>
> Thilo
>
> Ram schrieb:
>>
>> Hi all,
>>
>> I have 4 CAN nodes (sensors) on a bus and my software monitors and
>> gets data from the sensors at 500kbps, Std CAN. If any of the sensor
>> quit sending me the data, based on the ID i can identify the faulty
>> node. I tried to detect a short to ground fault on a CANH pin with
>> one particular node and still have all the other nodes on the bus. It
>> seems the software randomly picks up fault on all the nodes and
>> reports them instead reporting the node whose CANH pin is short to
>> ground. Is it possible to detect the short to ground fault on a CANH
>> or CANL on a particular node when multiple CAN nodes are connected on
>> the bus. Please need advice
>>
>> Thanks
>> Ram
>> --
>> Archives and useful links: http://groups.yahoo.com/group/CANbus
>> Subscribe and unsubscribe at www.vector-informatik.com/canlist/
>> Report any problems to <canlist-owner@...>
>>
>>
>>
>
>

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[Corrigan, Steve]

Ram,

First, how is this short happening?

Second, a short of CANH to ground should halt all data transmission on the bus.  Please check the short closely.

Cheers,
Steve C.

-----Original Message-----
From: canlist-owner@... [mailto:canlist-owner@...] On Behalf Of Ram
Sent: Wednesday, July 30, 2008 1:46 PM
To: canlist_NOT@...
Cc: canlist@...
Subject: [CANLIST] Short to ground fault


Hi all,

I have 4 CAN nodes (sensors) on a bus and my software monitors and gets data from the sensors at 500kbps, Std CAN. If any of the sensor quit sending me the data, based on the ID i can identify the faulty node. I tried to detect a short to ground fault on a CANH pin with one particular node and still have all the other nodes on the bus. It seems the software randomly picks up fault on all the nodes and reports them instead reporting the node whose CANH pin is short to ground. Is it possible to detect the short to ground fault on a CANH or CANL on a particular node when multiple CAN nodes are connected on the bus. Please need advice

Thanks
Ram
>
>
>
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[Ram-12]

Hi Steve,

We are working on all possible FMEA for our system and the short to
ground fault was one among that. Yes i did the see the whole bus go down
and bus load was 0% with all four nodes. Thanks for your reply.

Ram

Corrigan, Steve wrote:

> Ram,
>
> First, how is this short happening?
>
> Second, a short of CANH to ground should halt all data transmission on the bus.  Please check the short closely.
>
> Cheers,
> Steve C.
>
> -----Original Message-----
> From: canlist-owner@... [mailto:canlist-owner@...] On Behalf Of Ram
> Sent: Wednesday, July 30, 2008 1:46 PM
> To: canlist_NOT@...
> Cc: canlist@...
> Subject: [CANLIST] Short to ground fault
>
>
> Hi all,
>
> I have 4 CAN nodes (sensors) on a bus and my software monitors and gets data from the sensors at 500kbps, Std CAN. If any of the sensor quit sending me the data, based on the ID i can identify the faulty node. I tried to detect a short to ground fault on a CANH pin with one particular node and still have all the other nodes on the bus. It seems the software randomly picks up fault on all the nodes and reports them instead reporting the node whose CANH pin is short to ground. Is it possible to detect the short to ground fault on a CANH or CANL on a particular node when multiple CAN nodes are connected on the bus. Please need advice
>
> Thanks
> Ram
>  
>>
>>    
> --
> Archives and useful links: http://groups.yahoo.com/group/CANbus
> Subscribe and unsubscribe at www.vector-informatik.com/canlist/
> Report any problems to <canlist-owner@...>
> --
> Archives and useful links: http://groups.yahoo.com/group/CANbus
> Subscribe and unsubscribe at www.vector-informatik.com/canlist/
> Report any problems to <canlist-owner@...>
>
>
>
>
>  

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