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Guest steve28

sink or source

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just started on plcs and sink or source is becoming a bit confusing anybody out there explain in simple plain english please

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Sink or source IS confusing specially when all manufacturers are not using same terminology. It is better to talk PNP and NPN because this is common to all brands. Since you posted question in Mitsubishi forum you can consider sink to be NPN and source to be PNP. There are plenty of treads in this forum explaining the difference (check the download section for example).

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Hi, There is really only one circuit, i.e. #1, a power source - 24vdc etc. #2, a load - could be a relay, a resistor inside a plc module etc. #3, 0vdc COM. The three parts to this one circuit are not located in one place, they can be separated by cables, junction boxes, external relays, PLC modules etc. As for SINK/SOURCE, think of it as where the energy or current originates from. SINK = meaning that the switchable source of the energy/current originates from elsewhere and your PLC is receiving it. Usually the PLC is providing as #2 and #3. SOURCE = Your PLC is the source of the energy/current and is outputting a switchable energy/current to an external device. Usually the PLC is providing as #1 .....um, hope that helps! It's hard not to talk in electrical terms! Ian.

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The definition of Sink/Source gets a lot of people in trouble. The trouble is that the original confusion-free definition as defined by the electronics industry has been improperly used by some of the plc manufacturers such as Mitsubishi. The following quotes are from my article Industrial Control Safety: Definition of Source/Sink: Example: Let's say you have a relay with the negative side of the coil connected directly to the negative of your power supply. Then you have a switch which connects the positive side of the supply to the positive side of the relay coil. That switch is going to supply positive charges to the relay coil when you turn the switch on. That makes the switch a "sourcing" device because it is a "source" of positive charges as far as the relay is concerned. The relay coil is a "sinking" device because it accepts or "sinks" the positive charges from the switch. If you instead connected the positive side of the coil directly to the supply and switched the negative line to the coil, then the coil would be a source and the switch would be a sink. Jim Rowell Edited by JimRowell

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There is also a couple of downloads you can read: http://forums.mrplc.com/index.php?act=Downl...&CODE=02&id=150 http://forums.mrplc.com/index.php?act=Downl...&CODE=02&id=141

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just checked in to see if you kind people out there answered my plea for help with sink or source and was overwhelmed at the response. thanks one and all for the help and thanks to you i now understand it. expect to be pestered by me for some time to come!!!!!!

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How about this for simple Input or Output Connections.... If the current goes IN to the PLC it is SINK If the current goes OUT of the PLC it is SOURCE

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Not so fast.... I would like to ask everyone to avoid sink/source terminology because it will only get more people confused. This is not good way to describe interface because interpretations differ. Example: If you have NPN sensor(s) wired to PLC input, when sensor is on, current will flow from PLC input (positive common) into sensor output (negative). According to Mitsubishi this PLC input module is SINK type. Regards, panic mode

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Actually, understanging the difference between NPN(Sinking) and PNP(Sourcing) outputs is something different from how different manufacturers classify their hardware. Without going in deep electronic details: 1. The output transistor with open collector (a.k.a. solid state switch) is used as the standard output in industrial hardware, both for sensors and PLC outputs. Such output can distrubute (N)egative if it is NPN or (P)ositive if it is PNP. 2. Since the standard logic ground is the negative pole of the DC power, the NPN output is sinking the load to the logic ground and PNP is sourcing it to the logic power (usually +24VDC). There is no problem in understandig the PLC outputs definition. Concerning the inputs, Mitsubishi classifies them from the point of view of sinking or sourcing sensors connected. Allen Bradley does exactly opposite- it judges the inputs themselves as sinking or sourcing load for sensors. Hard to say what is more correct. Well, gramatically the AB definition seems more correct, because we are classifying the inputs, not the sensors connected. On another hand, people with good experience in electronics, but new in automation, intuitively support the Mitsubishi definition. I agree: the best way is to specify NPN or PNP sensors for a project. Omron and Aromat do exactly this.

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One analogie is that WATER FLOWS IN THE SINK. Just like electricity flows toward zero through the SINK device from the SOURCE device.

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I agree with everything you say, Sergei, except it's rather easy to say which is more correct. IMHO (always), Mitsubishi is just plain wrong. Incorrect. Mistaken. AB is right. The terms are not specifically PLC terms. They are general electronics terms and I've never seen this kind of confused usage except from a couple of PLC related manufacturers. It's confusing because it goes against the entire rest of the electronics industry. Since it was the rest of the industry that invented and defined the terms, I'll run with them. It's similar to the way the security industry for years used to mix up the terms N.O. and N.C. regarding sensor contacts. Don't think for a second that just because Mitsubishi is a large multi-million dollar company that they are always correct. Large companies (same as small companies or you or me) do many brilliant things but sometimes they make very basic mistakes. This is one of their very basic mistakes. I'll give you another example... The entire air handling industry seems to think that one should feed the bottom of contactors and switches. They almost universally adhere to this. They are wrong. Everyone else since the beginning of time has done the opposite. They started down that road by picking their own standard, not even aware that a standard was already in place. A standard that was older than the entire air handling industry. I'm sure it had more to do with a lack of knowledge and experience on their part than anything else. It was a good old fashioned screw-up. Or how about all those instruments that check motor rotation and printed right on the label it explains that rotation should be viewed from the shaft end of the motor.... did they let the new graduate write that or what? Heck, I can give you dozens of examples. By the way, I really like Mitsubishi and the way they do things in general. But they did drop the ball. Jim Rowell

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I agree with you, Jim. The AB definition is more correct as they are both formulated. If Mitsubishi said "Inputs for Sinking sensors" then they would be more correct and more logical. As I said, many electronicians instinctively feel Mitsubishi definition to be more correct. I think, the reason is that saying Sinking or Sourcing we should judge the signal source (sensor output or switch), not the load (PLC input). Still, the best way is to specify PNP or NPN sensors.

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here is a great example npn/pnp

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