Digital Outputs

    Can anyone make me understand why AOD16C is considered sinking and AOD16D is considered sourcing? As I understand, if my outputs are sourcing I send 24V to the PLC input, where 0V is common. If I am using sinking outputs, the PLC inputs float high until I provide 0V when I turn an output on.


    I specified AOD16D output cards for my current project because I wanted to 'source' the PLC with 24V. After all, it says "Source current type" right on the spec sheet. So when I got everything wired, nothing worked right, so I started metering things. Low and behold, all of my outputs are floating, and when I turn them on, they go to 0V - the exact opposite of what I expected.


    I ordered a pair of AOD16C cards assuming they will work for what I am wanting to accomplish, but I still don't understand why. And Fanuc's schematics, especially their I/O specs, confuse the crap out of me...

    It should have worked. I use a lamp holder with leads and a 24V lamp to test outputs. Perhaps the PLC input card is the wrong type.


    See if this helps your understanding:

    Sinking and Sourcing is about conventional current flow where current is considered to flow from positive to negative. If we are providing the 24V, then we are the 'Source' of the current. If we are providing the ground, then we are accepting or 'Sinking' the current.


    The AOD16D is a source. Think of the transistor as a switch, when it is on it connects the 24V at pin 1 to the output.

    Source.png


    The AOD16C is a sinking output. The transistor acts as a switch, when it is on it connects the output to ground at pin 10.

    Sink.png

    Thanks, Skooter. You've at least confirmed what I thought, but this is not what I'm actually seeing.


    I use a DIN-mount solid-state relay to do my testing, with my output circuit firing the relay. The only way I can get this relay to fire is by connecting +24V to A1 with my output wire on A2. This, at least to me, is sinking.


    My AOD16C cards should be here tomorrow. I'll let you know how that turns out, and hopefully this will all start making sense...

    As far as I know...


    +24 on 1 and 11. 0V on 10 and 20.


    The sad thing is, I pretty much go through this every time I install a robot, but I usually have some flexibility when it comes to I/O. Only this time, we've committed to a particular scheme so I can't just flop polarity at the PLC.


    Apologies. I'm just a guy with a degree in Economics who has always worked with and built machines, and is now responsible for a dozen used Fanucs. Very little training other than this forum and what I can read on the interwebs. But like I said, AOD16Cs should be here today. I'll do some testing and post my results. Fanuc, in particular, just really complicates the whole sinking/sourcing thing for me every single time...

    Quote from droth

    Apologies. I'm just a guy with a degree in Economics who has always worked with and built machines, and is now responsible for a dozen used Fanucs. Very little training other than this forum and what I can read on the interwebs. But like I said, AOD16Cs should be here today. I'll do some testing and post my results. Fanuc, in particular, just really complicates the whole sinking/sourcing thing for me every single time...

    My degree is in Film and video production, funny where life takes you.

    Thats strange.

    I would verify all wiring first as HawkME suggested. On a AOD16D verify that you measure +24V between Pin 1 and 10 and between Pin 11 and 20. Make sure to use the correct polarity on the multimeter probes.

    Then choose an output such as Pin 2. With the output off, measure between Pin 2 and 10. There should be no voltage. Turn the output on and you should measure +24V. If any of those checks fail, then there may be a problem with the card.


    Some remote possibilities:

    1.

    Check that the IO Config is correct. I don't know if its possible that it could cause this problem, but check the RACK/SLOT/START number in the IO Config. Verify that you don't have multiple mappings to the same SLOT. For example, in Roboguide I was able to map a DI and a DO to the same SLOT. I'm not sure if thats possible on a real robot though.

    2.

    The card is internally a AOD16C with the wrong cover on it.

    3.

    One improbable cause is that the IO card type is detected incorrectly by the IO Rack.

    OK, thanks all for the replies. As it turns out (which is sadly, too often the case), I missed something yesterday. It is either one of two things: A, I have a few random points on my output cards that are not working correctly, or B, my colleague has wiring issues in his control cabinet. I'm thinking it is the former.


    AOD16Cs showed up today and I isolated the controller, adding my own 24V supply and jumping all of the safety signals. Low and behold, the C-cards are sinkers! I proceeded to put one of 2 D-cards back in, turned on all of the outputs on that card, and found 3 points that did not source any voltage. The other 13 worked like a dream!


    So it turns out, I'm not actually crazy. Just easily confused. So my D cards are sinking inputs (must go high to turn on) and sourcing outputs (supply +24V). Thankfully, that jives with my understanding.

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