Difference between PLC output options: Sourcing/Relay

[JJ1234]

I have a Automation Direct Click Plus that you can buy option CPU slot modules for input/outputs.

The slot modules have the options of sinking, sourcing or relay. I know what sinking/sourcing is and relays but what is the difference on a PLC?

I've not bought a plc before only work on the ones we already have which are all AB.

What is most common to use? Relays?

My current project is just going to be using push buttons, some lighted push buttons, a pneumatic solenoid, a pressure switch and a little 24v led light.

Not sure what I should buy.

 

[geniusintraining]

Try this https://library.automationdirect.com/sinking-sourcing-concepts/

Also on the AD website you can look at the different wiring ways in the manual and that should help.

 

[JJ1234]

I think i understand a little more. Only the output has the option for relay.

 

[I_Automation]

One thing to consider about relay outputs if you do any home projects:


Relays are NOISY. The first control I did for Christmas lights was a SLC 5/03 rack and used relay outputs. The noise of the relays clicking in the living room was terrible. Shut them down and replaced them all with DC outputs.

 

[ojz0r]

Also the relay outputs have FAR less lifespan than transistor outputs. Usually its better to use transistor outputs and external interface relays that are easier to swap one by one rather than a whole I/O card.

 

[JJ1234]

Generally its easier for the card to source the power right? Then you dont need an external power source?

 

[plvlce]

Generally its easier for the card to source the power right? Then you dont need an external power source?

So where do you think the card is getting the power it is sourcing?

 

[JJ1234]

From a power supply that powers the plc if its 24v or just a wall plug if is 120v but for simple things ive always just ran power off of the plc for outputs and inputs. Ive mostly used the 1400s.

 

[plvlce]

From a power supply that powers the plc if its 24v or just a wall plug if is 120v but for simple things ive always just ran power off of the plc for outputs and inputs. Ive mostly used the 1400s.

Generally an output card will require its own power connection(s). If the PLC has its own integrated power supply you can tap off that or whatever provides the PLC's own power (at the expense of losing electrical isolation). Regardless, wherever you're getting power from you can equally well get it there for a relay output as for a sinking or sourcing output.

 

[I_Automation]

Generally its easier for the card to source the power right? Then you dont need an external power source?

SOURCING does NOT mean the card provide the power. Some analog cards have the option of providing internal power or selecting external power, but not discreet outputs.



Sourcing is controlling the Positive polarity.
Sinking is controlling the Negative polarity. (Often considered grounding out the controlled coil or light)



All output cards on all PLC's (maybe excluding some micro-PLC or smart relay) have a common terminal for the output. SLC cards have 2 commons - 1 for /0 to /7 and another for /8 to /15. MicroLogic, Mitsubishi and other have a common for anywhere from one to 6 outputs.