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DC output modules with output protection

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  • DC output modules with output protection

    Last week, I had a tech install a flyback diode on a relay backwards. When the panel was powered up and the output energized, that wee little diode managed to crowbar the power supply, and short out the PLC output before letting the magic smoke out. The pre-powerup check by a second tech didn't catch it, and I didn't catch it either though I should have. That particular output on the card is now permanently shorted on, regardless of what the programming tells it to do.

    I was using a BX16-TD1 module.

    I reassigned the output to a spare after replacing the diode, and moved on. But it got me thinking: is there any hope for DC output cards (or even BRX PLCs) with protected outputs? I know that other PLC lines have that feature. Something like a polyswitch PTC thermister "resettable" fuse? I'd happily pay more to not worry about blowing up an output MOSFET, especially when I'm in the field doing an install, and I'm short on spare outputs. Bonus if it reports somehow to the PLC that the output is shorted.

    BobO, if you're listening, please tell Santa that's on my wishlist for Christmas this year


    Thanks!



    Ryan Poethke



  • #2
    We built a protected output module for Terminator and sold almost none of them for years until one customer started buying a few. It generally isn’t hard, and we don’t mind building them, but folks tend to not buy them. I’ll mention it to the hardware team to see what it would take in practice.

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