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Sink V/S Source Inputs - Which is better

Created by: Navnag at: 7/16/2013 8:36 PM (14 Replies)

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7/16/2013 8:36 PM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 9/25/2024 Posts: 2325 Rating: (308)	Hello all We are replacing an existing automation system ( Non Siemens ) for one of our customers. The DIs ( apprx 200 DIs ) in the existing system are of Source type. We would prefer to use Standard Sink modules for the reason that these are normal stock items in our country and easy to procure. Alsoall Other S7 systems installed in customer's plant are of Sink Type. ( Although it would require us to do a little more work in wiring ) While disussing with the customer, the following questions arose and there were no clear answers : a) What are the Technical advantages / disadvantages of Sink Modules vis-a-vis Source Modules ? b) Why some manufacturers prefer Sink while others prefer Source Inputs ? Can someone shed more light on these points. Thanks Navnag
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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7/17/2013 10:21 AM	Rate (0)
N. Vijay Silver Member Joined: 3/17/2013 Last visit: 8/25/2024 Posts: 481 Rating: (43)	Hi Navnag One of the advantages of sourcing is that it is more fail-safe to have a signal that doesnt turn into a True signal when the wire is shorted to GND, which was almost universally the case with old sinking (NPN) I/O. Sinking is easier to connect sensors in parallel, especially if they have different power sources. Regards, Vijay.

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7/17/2013 2:04 PM	Rate (0)
viralpatel Silver Member Joined: 11/18/2010 Last visit: 8/5/2022 Posts: 523 Rating: (32)	N. Vijay Hi Navnag One of the advantages of sourcing is that it is more fail-safe to have a signal that doesnt turn into a True signal when the wire is shorted to GND, which was almost universally the case with old sinking (NPN) I/O. Sinking is easier to connect sensors in parallel, especially if they have different power sources. Regards, Vijay. Hi , Vijay, i don't think any advantage of Source i/p then sink i/p,we have two option/facility from it we can choose any option ,as you said source i/p is better then why we are using many time sink type i/p Vp

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7/17/2013 2:27 PM	Rate (1)
William_B Posts: 5225 Rating: (1196)	Most would understand if you state NPN vs PNP. This describes the transistors used in the circuit. It also known as negative switching and positive switching. You will find that it is more to do with region. Eastern countries like Japan and Taiwan, as well as the USA prefer NPN. Europe and probebly many of their old colonies mostly PNP. It reminds me of the debate of 60Hz vs 50Hz on AC power. When using common emittor circuit, it is possible to use to change it to positive switching by using a pull-up resistor to 24Vdc.. provided the transistor can handle the voltage drop. For me it is handy to convert Taiwanese instruments to PNP. When you have switches in the field, NPN has the advantage that you do not need to carry voltage there. BUT a wire short is seen as ON, as stated. I have been told that NPN technology is less likely to carry noise. I do not know this as fact. NPN can be difficult to understand for some.. The power level is low for "on" signal. That makes logic a bit troublesome. PNP should be using higher power thresholds (opinion, not fact) to represent a off and a on. Distortion of 24V logic on high frequency pulsing signals is a real problem. I think NPN has less issues.. but it is better to use 5V in this case. It is my advice to stay with the logic standard that the client/factory understands. In most cases this will do fine.. regardless on the choice. w
William_B Posts: 5225 Rating: (1196)
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7/17/2013 2:40 PM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 9/25/2024 Posts: 2325 Rating: (308)	Thanks William B.for your take on the issue. I would agree with you on most issues. We were in two minds here as customer had both types of systems in the same plant ( Some Machines from europe, some from east asia ) He has left the decision upto us as long we provide him with a valid explaination. I guess we will go ahead with standard Siemens Hardware ( Sink ) as all other Siemens PLCs in his plant are of this type, Cheers Navnag
	Last edited by: Navnag at: 7/17/2013 2:40 PM There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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7/17/2013 3:02 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	No worries there my friend, Be careful to say NPN is Siemens standard. Probably PNP should be the "standard" as Siemens is European. I thought came up.. can you connect the S7-1200 as NPN? w
William_B Posts: 5225 Rating: (1196)	Last edited by: William B. at: 7/17/2013 3:30 PM Apologies, I had singing and sourcing swapped around. As per S7-1200 -- one instrument can do either, it depends how it is connected: M connected to + or -.
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7/17/2013 3:03 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 11/18/2024 Posts: 12296 Rating: (2691)	Hello Navnag; If you open chapter 3 of the following manual, you will see that Siemens DI and DO modules offer a variety of sink/source options. SIMATIC S7-300 S7-300 Module data For example, look at the attached schematic of a 64-point DImodule that can be setup as sinking or sourcing, depending only on the selected wiring. There are also 64-point DO sinking (1BP50-)and sourcing (-1BP00)modules that can be selected for your project. Hope this helps, Daniel Chartier Attachment sink-source DI.jpg (749 Downloads)

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7/17/2013 3:13 PM	Rate (0)
N. Vijay Silver Member Joined: 3/17/2013 Last visit: 8/25/2024 Posts: 481 Rating: (43)	Dear Viral I never saidmajor advantage, but can you explain the possiblity of wire shroting to GND will be read as wrong in sourcing or sinking? That's the point I mentioned like normally stop or ESTOP should be NC, I know some plants use as NO upto them, but Option as NC is fail safe. Regards, Vijay

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7/17/2013 3:42 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	N. Vijay Dear Viral I never saidmajor advantage, but can you explain the possiblity of wire shroting to GND will be read as wrong in sourcing or sinking? That's the point I mentioned like normally stop or ESTOP should be NC, I know some plants use as NO upto them, but Option as NC is fail safe. Regards, Vijay May I try explain? NPN connection registers an ON when pulled down to negative/power ground. OFF is if the pin is pulled a bit higher than negative ground (it does not need to be 24V!) When using NPN and a wire cut occurs shorting to ground, the system can see it as ON. If the circuit is normally closed, the state is seen as good (ON) even if the circuit is switched. If the circuit is normally open and the wire cut makes no contact.. the input never reads a signal too. In the case of PNP and normally closed circuit.. the system will know if there is a break in the line. Shorting to ground causes a fuse to blow or your power supply's protection circuit to come in play. If the two lines however short to each other.. oops problem again. There is a good reason why protection circuitry has rules to follow to try and avoid these. BUT that is a lecture for another thread. (no disrespect, just being playful) Also for homework think about "new" safety circuits that use communication instead -- communicating regularly "here I am".. maybe? [wink] Start a new thread for experts to explain if you wish to know more. w
William_B Posts: 5225 Rating: (1196)
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7/17/2013 5:18 PM	Rate (1)
BhaPraJ Silver Member Joined: 1/28/2012 Last visit: 7/23/2024 Posts: 519 Rating: (83)	Navnag Hello allWe are replacing an existing automation system ( Non Siemens ) for one of our customers.The DIs ( apprx 200 DIs ) in the existing system are of Source type. We would prefer to use Standard Sink modules for the reason that these are normal stock items in our country and easy to procure. Alsoall Other S7 systems installed in customer's plant are of Sink Type. ( Although it would require us to do a little more work in wiring )While disussing with the customer, the following questions arose and there were no clear answers :a) What are the Technical advantages / disadvantages of Sink Modules vis-a-vis Source Modules ?b) Why some manufacturers prefer Sink while others prefer Source Inputs ?Can someone shed more light on these points.ThanksNavnag Durin GOOGLING about this topic, found very good explanation on NI website. . Hope you like this post. . http://digital.ni.com/public.nsf/allkb/A10122C63A7F5CFE86256B4C007491DD
	Regards, BhaPraJ
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