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Comment by contingencies | Hacker News Reader

Interesting. I wasn't aware of any EMI benefit. I wonder if this is true with shielded ethernet cables at lower data rates (eg. 10BaseT)? It seems maximum CAN drop length is far shorter than ethernet, which I guess could become a consideration in industrial deployments.

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yeah, i have seen properly shielded cat5 ethernet based implementations in similar environments. i would have to say that i've seen far more industrial / heavy-commercial applications that used cat5 because "thats whats on the truck" that have had to be re-pulled. in a lot of instances things would "work" for a bit, until the operating environment changed (plant was expanded, circuits re-wired, etc). one of my favorite instances was an electrical submetering system where all the meters would go down at the same time every night. it started happening after the system had been active for a few months. the culprit turned out to be a cell modem the system owner had added. the modem had been mounted inside the NEMA enclosure that housed a datalogger. the datalogger would query values from the submeters over a serial bus (rs485) every minute, aggregate it and upload it to "the cloud"...once a day. the cabling the electricians had used was some generic roll of cat5. it wasn't shielded (and thus the shield wasnt grounded). the modem would broadcast, and that event would "crash" the serial bus, cutting off communication with the submeters. we (not really "me", but the EE i sent to the site) removed the modem relocated it outside of the enclosure so the system could operate while the correct cable was pulled. we had built a number of systems with integrated modems (we had SKUs with that configuration), so the issue really was the wrong cable for the application being used because it was common and on hand (and cheap; legit industrial serial cable can cost you upwards of $1/foot).

The EMI resilience is one of the big reasons why it's used for automotive applications.

Many (all?) CAN standards transmit on redundant copper, in opposing polarities, making it really easy to identify a signal vs noise. https://en.wikipedia.org/wiki/CAN_bus#/media/File:CAN-Bus-fr...

It's like a one-wire serial signal, but redundant.

yeah, differential data lines; common in serial applications where you want to protect from noise. a lot of the higher level dialects are built off something like (if not the) rs485 electrical layer.

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