# Sinking and Sourcing



## McClary’s Electrical (Feb 21, 2009)

CanadianSparky said:


> Is there an easy way to remember what sinking and sourcing inputs/outputs mean? For the life of me I just can't wrap my head around the concept.


 
Picture sinking as flushing a toilet. The signal is derived at the source of the flush and leaves there to somewhere else


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## DriveGuru (Jul 29, 2012)

Think of it as though you have a relay, sinking is putting the switch on the neutral/ground side, sourcing is applying voltage from the line side.


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## McClary’s Electrical (Feb 21, 2009)

DriveGuru said:


> Think of it as though you have a relay, sinking is putting the switch on the neutral/ground side, sourcing is applying voltage from the line side.


 
True, but the current flow in sinking is flowing AWAY from the load and the current flow in sourcing is flowing TOWARDS the load. So I remember it as sinking "flushing a toilet."


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## DriveGuru (Jul 29, 2012)

Depends wether you are talking about hole flow or electron flow


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## newbi (Dec 17, 2011)

DriveGuru said:


> Depends wether you are talking about hole flow or electron flow


 I wouldn't even throw that other variable into something that I have a hard time remembering. I think most guys like the conventional theory better including myself. I drive myself crazy sometimes just thinking about electron theory.


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## DriveGuru (Jul 29, 2012)

I guess I'm showing my age,lmao


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## CanadianSparky (May 10, 2011)

Now aren't inputs and outputs different?


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## DriveGuru (Jul 29, 2012)

The difference is in an output, the output device is either (sinking) making the connection to ground or (sourcing) making the connection to the voltage supply. Where in an input you are making the connections to control an internal device.


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## DriveGuru (Jul 29, 2012)

That's why I say think of it like a relay coil. My instructors would always tell me "KISS".... Keep It Simple Stupid . Always try to simplify it


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## MDShunk (Jan 7, 2007)

FWIW- sourcing sensors and outputs are mostly on American machines, and sinking is mostly used on European machines.


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## CanadianSparky (May 10, 2011)

DriveGuru said:


> That's why I say think of it like a relay coil. My instructors would always tell me "KISS".... Keep It Simple Stupid . Always try to simplify it


Funny my theory instructor used to say the same thing.


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## DriveGuru (Jul 29, 2012)

Not sure I'd agree with that MD, I've seen allot of machines built in the states that use sinking, at one time it may have been like that. It's not my personal preference, I prefer sourcing, too many issues such as induced noise or simply a grounded wire causing a false input can happen


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## CanadianSparky (May 10, 2011)

DriveGuru said:


> Not sure I'd agree with that MD, I've seen allot of machines built in the states that use sinking, at one time it may have been like that. It's not my personal preference, I prefer sourcing, too many issues such as induced noise or simply a grounded wire causing a false input can happen


I have actuyally heard what MD said before as well as it says it on multiple online sites......but then again websites aren't always true haha.


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## MDShunk (Jan 7, 2007)

DriveGuru said:


> Not sure I'd agree with that MD, I've seen allot of machines built in the states that use sinking, at one time it may have been like that. It's not my personal preference, I prefer sourcing, too many issues such as induced noise or simply a grounded wire causing a false input can happen


Depends on whether the machine was made to DIN and ISO standards or not, but I can 100% guarantee that sourcing is the predominant standard in the US. Just look at an American sensor company catalog, and see what part numbers are quick ship and which are not. The flip side is that you'd be hard pressed to find an overseas machine that is anything but sinking, unless it was ordered that way.


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## A Little Short (Nov 11, 2010)

MDShunk said:


> FWIW- sourcing sensors and outputs are mostly on American machines, and sinking is mostly used on European machines.





DriveGuru said:


> Not sure I'd agree with that MD, I've seen allot of machines built in the states that use sinking, at one time it may have been like that. It's not my personal preference, I prefer sourcing, too many issues such as induced noise or simply a grounded wire causing a false input can happen


My dealings with sinking/sourcing was with prox switches and zero sensors. They were on French made machines. The first time I had to change one I put it on, wired it just like it came off and it didn't work. Actually blew a fuse and popped the sensor.
Turns out the original sensor was sinking and the new one was sourcing.
The company didn't put that little bit of info in with the new sensor.
They were famous for making you figure something out or have to call one of their techs in.
You couldn't tell by looking/comparing some of their parts either as they were constantly changing mfg. for their replacement parts.


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## DriveGuru (Jul 29, 2012)

Hmmm... I don't know...there's allot of foreign **** in the states now,lol. Most of the sensors I deal with can be wired sourcing or sinking thankfully. But I will agree that 99% of the crap coming from across the pond is sinking


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## Frank Mc (Nov 7, 2010)

Most machines i have worked on here in Oz use Sourcing inputs....The Jap,s tend to use sinking inputs.....Im wondering if its something that was carried on from electronic,s design...All the old microprocessors used active low control signals...???

Frank


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## A Little Short (Nov 11, 2010)

Little-Lectric said:


> My dealings with sinking/sourcing was with prox switches and zero sensors. They were on French made machines. The first time I had to change one I put it on, wired it just like it came off and it didn't work. Actually blew a fuse and popped the sensor.
> Turns out the original sensor was sinking and the new one was sourcing.
> The company didn't put that little bit of info in with the new sensor.
> They were famous for making you figure something out or have to call one of their techs in.
> You couldn't tell by looking/comparing some of their parts either as they were constantly changing mfg. for their replacement parts.





DriveGuru said:


> Hmmm... I don't know...there's allot of foreign **** in the states now,lol. Most of the sensors I deal with can be wired sourcing or sinking thankfully. But I will agree that 99% of the crap coming from across the pond is sinking


The sensors I received could be wired both ways too. But with no info with them at all you had no way of knowing that at all. I had to call them and they said..."oh, you have to wire them for the other kind." Well, thanks for that info, now send me another sensor to replace the one I just popped because of your lack of [email protected]!!:hammer:


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## DriveGuru (Jul 29, 2012)

Ya gotta love that,lol. I would have been cussing too


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## zawala (Jul 30, 2009)

Its Been a while since I've had to deal with these. But The way i used to remeber it was a pnp device (p for positive) was a sourcing or positive switching. While a npn (N for negitive) was a sinking or negitive Switching. That was just the "trick" I used to remember it.


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## piperunner (Aug 22, 2009)

Well sinking and sourcing I/O cabinet with logic boards inputs and outputs .
There basic power input points maybe positive + sinking input or negative - sourcing input so the positive flows npn and the negative flows pnp which is current flow direction . Its the way current flows into a transistor basic theory . Sorry but its the other way around on outputs so sinking output is npn sourcing output is pnp .


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## mikey383 (May 21, 2012)

The way I try to remember it is:

A sinking input receives positive (+) voltage, a sourcing input receives negative (-) voltage. 

A sinking output "looks for" negative voltage, and a sourcing output "puts out" positive voltage. 

With that, you want your input device to be PNP on a sinking input (devices put out + voltage, and PLC input receives it), or NPN on a sourcing input (PLC puts out (+) voltage, and devices sends (-) back to PLC).


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## DriveGuru (Jul 29, 2012)

PNP or NPN each can be configured for sinking or sourcing, just depends how you wire it, and at worst case you add a resistor for pull up or pull down. Another way of saying sinking or sourcing is active low or active high, active high you apply voltage to the input, active low you apply the return path I may be showing my age, but I still like electron flow;p


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## PLCatLATTC (Oct 23, 2011)

Think Positive!!!!!!!!

If the positive current flows through switch first the switch is a PNP (sourcing) and the PLC input module is a (sinking) module.

If the positive current flows to the input module first the PLC input card is of the (sourcing) type and the switch has to be a (sinking) type NPN.

PNP wiring can be safer for devices because if a cable is cut or faults to ground its possible that a fuse will blow. 

NPN wiring can turn on a input/output if faulted to ground in certain situations. 

Many PLC manufactures follow the theory that current flows from the positive to negative. (conventional theory)


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## tyrone3340 (Apr 14, 2010)

CanadianSparky said:


> Is there an easy way to remember what sinking and sourcing inputs/outputs mean? For the life of me I just can't wrap my head around the concept.


sink = negative
source = positive
sink switching negative
source switching positive


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## Del (Feb 10, 2011)

Oh the joy of automation. The pleasant discourse of being positive or negative on the subject.

Zawala beat me to the punch on PNP, and NPN.

Let us say they there are many machines on both sides of the pond that cause false inputs on an earthed neutral.

Consider the common nema practice of the overload contact on the neutral side of a contactor/relay coil circuit, for simplicity of fault finding, shouldnt the control contacts all be on the hot leg.

Regards


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## DriveGuru (Jul 29, 2012)

"Any fool can know.....the point is to understand. " - Albert Einstein


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## AJMOORE (Sep 20, 2012)

*Sinking and sourcing*

Also trying to understand sinking and sourcing. For example if i have a 2 wire 4-20ma flow meter for a bar graph would sinking or sourcing be of any concern for quality of signal. The flow meter actually has an external means of grounding the flow meter to earth ground or am i off on a totally different subject. Thanks


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## greenman (Apr 20, 2012)

npn or pnp? 
http://www.automationdirect.com/static/specs/sinksource.pdf
will this help?


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## greenman (Apr 20, 2012)

Wonder why we have npn or pnp, 
Here is why you have the two types!
NPN transistors are more "tough" than PNP for the same physical size the are cheaper to make and therefore more widely used.
When I say "tough" what I mean is they (NPN) can handle those transistor killers like spikes and over currents way beter than PNP for proof look at the spec sheets.
The main advantage is that NPN switches on and off a lot faster than PNP.​


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## John (Jan 22, 2007)

Try this.....
NPN is for cars and PNP is for houses which is the *source* of our income?

Something like the saying for resistor color codes.....Bad Boys Rape Our Young Girls But Violet Gives Willingly......Get Some Now


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## Peewee0413 (Oct 18, 2012)

http://letsmakerobots.com/node/3474


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## 123 (Oct 28, 2012)

The term for sensors is PNP and NPN. 
PLC inputs are mostly sinking, and use PNP sensors, outputs are sourcing.
Old machines used to use NPN sensors and sourcing inputs, because PLC’s replaced gate
logic, and it was all negative logic. The Europeans use now the same thing as we do.


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