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Sourcing and Sinking PLC I/O using a sensor

Steve Brown
Hi I need help as I'm just not getting this..


Sinking - Power externally supplied. Current passes through load, then into sensor and then to ground.

Sourcing - Sensor uses supply voltage to pass current. Sensor drives current out, through the load on to ground.


I really can't picture how this works even using google images!

Does sinking have a constant supply and sourcing doesn't?


Sorry it just isn't making sense to me.
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  • Former Community Member
    0 Former Community Member
    Hi Steven,

    It’s not quite as you described.


    Sourcing, has a power source to the plc card.

    Think of the plc card acting as a relay it switches power to the actuator.

    The power then does the job of energising the actuator and returns to the power source, which may or may not be grounded.

    Akin to a light  switch in the live conductor.


    Now sinking is the same, but the relay is in the neutral line, & the plc is in this case connected to the opposite sude of the piwe supply.


    Next we have inputs, but let’s see if I have explained outputs ok first.
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  • Former Community Member
    0 Former Community Member
    Hi Steven,

    It’s not quite as you described.


    Sourcing, has a power source to the plc card.

    Think of the plc card acting as a relay it switches power to the actuator.

    The power then does the job of energising the actuator and returns to the power source, which may or may not be grounded.

    Akin to a light  switch in the live conductor.


    Now sinking is the same, but the relay is in the neutral line, & the plc is in this case connected to the opposite sude of the piwe supply.


    Next we have inputs, but let’s see if I have explained outputs ok first.
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