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I have a servo drive with 5 digital outputs. I will be connecting one of the outputs to a 24 V relay to disable the drive if a fault occurs within the drive. The manual gives two schematics using sinking and sourcing.

What should I consider when choosing to sink or source? It seems to me that either way will achieve what I am trying to do.

My CNC controller output enables the servo drive using Di1 out of the 8 digital inputs (Di1 to Di8). This is wired according to the sourcing schematic attached.

I have read all the related posts but can't find anything that explains this or simplifies it enough for me to understand.

Here is a link to the manual if required.

I am using the LXM28AU07M3X servo drives.

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  • \$\begingroup\$ Gustav. Can you please expand on this "in this case you will have to match the input with the proper PLC output connection" \$\endgroup\$
    – Michael
    Commented Nov 17, 2018 at 15:33
  • \$\begingroup\$ It's still a bit confused. I still reckon that the drive can be disabled internally. What would be worth doing is disabling the other drives if a fault occurs in any one of them so that you don't destroy a workpiece. The answers below answer the question about the relay but I suspect that's not the real problem. There's a CircuitLab schematic button on the editor toolbar. Using the Custom Component on that you can draw a high-level block diagram. Double-click to edit. R to rotate. H and V to flip. \$\endgroup\$
    – Transistor
    Commented Nov 17, 2018 at 15:35
  • \$\begingroup\$ OK. Figure 37 shows how to kill AC power to the drive in the event of a fault. If that's all you need then you can wire the output as source or sink. It just depends whether you would prefer the relay connected to +24 V or ground. Generally connecting the relay negative to ground is less confusing when fault finding. \$\endgroup\$
    – Transistor
    Commented Nov 17, 2018 at 16:04
  • \$\begingroup\$ I have attached another image. Do5 is used to disable the power stage if a fault occurs. \$\endgroup\$
    – Michael
    Commented Nov 17, 2018 at 16:04
  • \$\begingroup\$ Transistor. Yes that's all I was planning on doing.Great point regarding disabling the other drives if one faults. I will try and impiment this in the design. \$\endgroup\$
    – Michael
    Commented Nov 17, 2018 at 16:54

2 Answers 2

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If you just want to drive a relay, then it doesn't matter if you choose sourcing or sinking, it will work either way, you just need to have 24 V across the relay's coil to make it switch.

Sinking or sourcing matters only if you try to drive some electronic device with a sinking or sourcing input, in this case you will have to match the input with the proper PLC output connection.

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Sinking (aka low side switching) will provide higher current with less voltage drop, but sourcing (aka high side switching) will allow the load to have a common negative with the rest of the circuit.

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