PLC input

joaco1993 · Nov 30, 2015

the input will be a pushbutton. Should I fuse it or no ?

I cant see why some people say that you can fuse it or not, what would i protect in this case ? the powersource ?? because when i press the pushbutton. The circuit would be the same as if i had a short dead..

Bullzi · Nov 30, 2015

I normally fuse the main power that is used for the inputs. Depending on the how large the power supply is I may segregate the power into several fuses to be able to isolate the inputs and outputs. This gives more protection and makes a short much easier to find if a problem happens.

James Mcquade · Nov 30, 2015

We normally put a fuse or cb for the inputs and outputs.
Depending on the application, I have even seen a fuse for (4) inputs on a card for a total of four fuses per input card.
We sometimes put a fuse on each output card and even on each group of 8 outputs. Again, this depends on the application and the risk analysis done if we loose all the inputs / outputs.

The reason behind fusing is to not loose the main power.
If the main power fuse blows, you may loose the plc, hmi, mmi, and damage the machine and produce versus loosing the power to all inputs or even a single card. Less chance of machine damage / product damage.

regards,
james

joaco1993 · Nov 30, 2015

Thanks for answering, does anybody has a wire diagram ?? in .cad or .pdf ??

I cant still figure out the exact position where to put the fuses.. in my example if before the PB or after..

With many IO`s also the same.. if someone has any diagram would be usefull

thanks!

osmanmom · Dec 1, 2015

hope this help,modify it to meet your application.

geniusintraining · Dec 1, 2015

joaco1993 said:
because when i press the pushbutton. The circuit would be the same as if i had a short dead..

Dead short would only be true if you did not have the PLC in the loop... the fuse would be protecting the power supply feeding the inputs

You can also want to read up on Sink and Source inputs, see link below

https://www.automationdirect.com/static/specs/sinksource.pdf

joaco1993 · Dec 2, 2015

Hi thank you all for answering.

I have just recieved my CLICk Plc and started doing some things.

I looked at the sink and source input and outputs, but cant understand when should I use one or the other.. it seems the same to me , as both closes the circuit.

geniusintraining · Dec 4, 2015

joaco1993 said:
I looked at the sink and source input and outputs, but cant understand when should I use one or the other.. it seems the same to me , as both closes the circuit.

Correct... it seams like Asia uses more sink and US uses more sourcing, I like sourcing for my builds, I have seen a few shorts over the years and a couple of these would of made the input on (true) with sinking so for me the logical wiring is sourcing and having positive going into the PLC should be on not negative ... that said they both do the same thing so learn both

More so if your plant/customer is using one way stick with that way and dont change it up

Handcraftedsince87 · Dec 4, 2015

You're either providing a source, say 24v+ to complete the circuit, or you're sinking the 24v+ back to the negative side of the power supply. Either way your completing the circuit, it just depends on "which side". Some VFD's require a sinking signal when being controlled with discrete I/O. So maybe all you have is a sourcing output card and maybe you have to put an interposing relay to give the drive what it needs to run/stop. you apply 24v+ to the common of the drive inputs, and then switch the individual run/stop/fwd/rev commands to the negative of the power supply.

joaco1993 · Dec 7, 2015

Okay, got it, thanks both !

John Morris · Dec 7, 2015

On our builds, all the inputs( just before the PLC ) and all the outputs ( just after the PLC ) have micro mini C/b. 1 amp. ($9.50 ea )

Better to trip a C/b then wipe out a $300 I/O card

Gives the customer added protection for their investment.

Perception.

PLC input

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