Re: CAN Inspector: a CAN node to sample the CAN bus waveforms

Am Sonntag, 13. März 2016, 10:47:24 schrieb Michael Ashley:
> Dear CAN bus gurus,
> 
> I've been thinking of a design for a CAN node that is able to digitize the waveform on CANH and CANL and then transmit the waveform as multiple CAN messages. The device would also be able to report the CAN power supply voltage. I'm interested in your opinions on this concept.
> 
> The design is based around the Texas Instruments ADC08B200 ADC, which digitizes to 8-bits at up to 200 Msps. Its key feature is a 1 kB data buffer that can be read out slowly, so there is no need for the MCU to keep up with the data in realtime.
> 
> The motivation for wanting such a device is that I'm using a CAN bus for some remote experiments in Antarctica, and there have been several cases recently where the bus has operated in a degraded mode (CANL shorted to ground, missing terminator - this is on a 70m long bus running at 100 kbps) without anyone being awareof it. The people who are servicing the equipment do not have the expertise or the time to connect up TDRs or oscilloscopes or even multimeters to diagnose problems. The physical environment can be very tough, e.g,. -40C in summer (-80C in winter) and high altitude (over 4000m), so asking someone to connect an oscilloscope and make measurements is asking a lot. The personnel are only on-site for betwen 5 and 21 days over summer each year; the rest of the time the equipment is entirely remote.
> 
> A "CAN Inspector" node that could be simply placed on the bus would be very valuable. I could remotely monitor the bus, recognise when problems occur, and give repair instructions. An alternative approach could be a small USB-accessible oscilloscope.
> 
> One of the big advantages of CAN is its fault tolerance. However, if the fault occurred some years ago, and you are already running in a degraded mode, then you have already used up all your tolerance.
> 
> I will post a link to a draft schematic for the CAN Inspector in a subsequent message.
> 
> Regards, Michael

Hello Michael,

I know of a device which at least does the measurement you like to have.
http://www.ems-wuensche.com/product/datasheet/html/can-physical-layer-analyzer-error-diagnostics-canwatch.html
As you can see, problem/error signaling is done by LEDs.
Your Idea to transfer the data by the CAN bus itself is good as long as the bus is able to be used by the can nodes and not totally disturbed.

Another approach is building some error recognition in the CAN nodes itself. Each of the nodes should at least be able to read out the CAN controller error counters. In case of CANopen devices the error counters can be available in the object dictionary to be requested by SDOs or to be transmitted by an PDO. Cyclic or by a change, whatever PDO mechanism is implemented.

-- 
mit freundlichen Grüßen / Regards
  Heinz
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