Sourcing vs Sinking Input and Output

[ColtonDavis]

Hello,

I need help deciding if I need a sourcing or sinking input and output digital card.  I have a snippet from my IAI manual attached. I have the NPN option on the cylinder. Could someone help me decide on which input and output card to get? It appears i should have a sinking digital output card and a sourcing digital input card but I wanted to confirm.

[Bob_Schor]

You do know, don't you, that this is a LabVIEW (software) Forum?  Where is the LabVIEW question?  This looks like something you should ask the company that makes whatever equipment this is, a good Electrical Engineer who can look over the specs of this device and whatever you are using to drive it, but not here ...

Bob Schor

[ikaiser]

Hello Colton,

I agree with Bob. You could potentially get an answer here on your I/O needed, but I'd not rely on it alone before buying expensive equipment.

Regarding your question I agree with your indication after looking at this: What is the Difference Between Sinking and Sourcing Digital I/O?

In case you want to replace the ground connector and switch on the left side of the top-left image with reddish background, then this needs a sinking DO. The image right to it, replacing "load" and "external power 24V" is a sourcing DI. A said, please let someone who guarantees a correct answer verify my indication.

Please note that there are more dimensions to consider: The voltage level (24V) and the current needed / sourced (5mA / 50mA).

[rolfk · Accepted solution]

Actually it is a bit more complicated than this I think. Inputs B3, B4, B5 require a sinking digital 24V output that can sink at least 5mA. B2 however would require a sourcing output if you want to control that through a digital output too instead of a switch.

A2, A3 and A4 require a sourcing 24V digital input. It’s load current can be at most 50 mA but that should be no issue for digital inputs (they have generally a higher input impedance and draw/source at most a few mA of current).

[ikaiser]

Hi Rolf,

Thank you for sharing your thought about the blue diagram. I did not look at if before and I agree: B2 would need an additional, sourcing DO.

[ColtonDavis]

Thank you for the insight here.  I just needed some assurance as to what I'm looking at. I had already contacted the folks that make the cylinders to no avail.  I've also confirmed this with an old EE colleague of mine.  Just making sure I'm buying the correct modules!! 🙂 

[ColtonDavis]

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