Pnp/npn

What actually happens when you use a PNP sensor with a NPN cable? I had an electrician do this on the floor, and I know they don't work together, but I guess I'm not sure why.
thanks

In most cases.....

PNP
Brown +
Blue -
Black PNP OUTPUT

NPN
Brown +
Blue -
White NPN OUTPUT

The wires/terminals have to match the correct sensor type (pnp/npn).

This is an excerpt from this page:

http://www.physlink.com/Education/AskExperts/ae430.cfm

JUNCTION TRANSISTORS

A junction transistor consists of a thin piece of one type of semiconductor material between two thicker layers of the opposite type. For example, if the middle layer is p-type, the outside layers must be n-type. Such a transistor is an NPN transistor. One of the outside layers is called the emitter, and the other is known as the collector. The middle layer is the base. The places where the emitter joins the base and the base joins the collector are called junctions.

The layers of an NPN transistor must have the proper voltage connected across them. The voltage of the base must be more positive than that of the emitter. The voltage of the collector, in turn, must be more positive than that of the base. The voltages are supplied by a battery or some other source of direct current. The emitter supplies electrons. The base pulls these electrons from the emitter because it has a more positive voltage than does the emitter. This movement of electrons creates a flow of electricity through the transistor.

The current passes from the emitter to the collector through the base. Changes in the voltage connected to the base modify the flow of the current by changing the number of electrons in the base. In this way, small changes in the base voltage can cause large changes in the current flowing out of the collector.

Manufacturers also make PNP junction transistors. In these devices, the emitter and collector are both a p-type semiconductor material and the base is n-type. A PNP junction transistor works on the same principle as an NPN transistor. But it differs in one respect. The main flow of current in a PNP transistor is controlled by altering the number of holes rather than the number of electrons in the base. Also, this type of transistor works properly only if the negative and positive connections to it are the reverse of those of the NPN transistor.

Rodrigo, try THIS LINK for a less technical (and more "to the point") explanation...

Mike, I disagree with your "In most cases..." statement. Maybe true for you, but not for me. Banner is the only one I can think of that uses the white wire for NPN, so I'll say:

In SOME cases, it's as Mike described, in other cases, it's

Brown: +
Blue: -
Black: Output (PNP or NPN, depending on the sensor)

And there are others as well!

This European color code seems to be becoming the "standard", but occasionally you still run across the Asian color code, which is:

Red: +
Black: -
White: Output

beerchug

-Eric

OK Rodrigo, you let us know which explains it better. I followed that link and have to disagree with Eric on this one.

What actually happens when you use a PNP sensor with a NPN cable? I had an electrician do this on the floor, and I know they don't work together, but I guess I'm not sure why.

Click to expand...

The original question asks nothing about HOW PNP/NPN devices work. The question refered to cables used, I assume on quick disconnect type devices.

The simple answer is it doesnt matter what cable is used as long as the connections match and the person making the wiring connections know what wire is what and what they are doing. All 3/4 wires can be purple as long as you know which wire is +, - and output.

Personally I have never heard of a NPN or PNP cable. I use many brands and the Quick disconnect cables may work on multiple devices. I have in some cases used cables from a different manufacturer.

It just happens that when I read this I was also looking up a proximity sensor in a Pepperl+Fuchs catalog, I want quick disconnect. The catalog shows my connection as type V1, this is a micro DC 4 wire, 4 pin cable that is used on both NPN and PNP devices.

Eric, You are right, SOME cases would have been better. I guess the best thing to do is read the documentation with your devices.

I wrote this up earlier this morning and then got side-tracked. Ron posted while I was... doing other things...

Any way... Ron is right.

Rodrigo...

Here's a little story... in terms of the question... as you asked it..

So... I'm making a new input run. I'm installing a sensor. I find that all I have is the sensor (the sensor has a quick-disconnect). I forgot to bring the mini-euro-quick-disconnect-cable-thingee with me.

I call down to the shop. You pick up the phone. I explain the situation. You say, "Sure, I'll bring up the cable... Do you want the 'PNP' kind or the 'NPN' kind?"

After a pregnant pause... I say... "Yes.... bring one of each... and then you can show me which one I should use."

While I'm waiting, I wonder if you keep the "NPN-Cables" stored near the spools of DC-Wire and the "PNP-Cables" stored near the spools of AC-Wire... or, vice-versa?
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Rodrigo...

I've got a box with a couple of dozen sensor cables. Some are 3-pin/3-wire, 4-pin/4-wire, 5-pin/5-wire. None of the cables are marked as being "NPN" or "PNP" specific.

They are simply, multi-conductor cables with a 3-, 4- or 5-pin connector on one end.

If the connector fits the sensor, there ya go.

Now all you need to know is...

• the identity of the pins AT the sensor (function - sensor pin#)
• the identity of the pins/wires IN the connector (connector pin# - wire color)

Example:

SENSOR SENSOR    PIN     CONNECTOR   WIRE    

 TYPE   PIN#   FUNCTION     PIN#     COLOR      DESTINATION

------+------+----------+----------+-------+--------------------+

 NPN     1      PS(+)         1       BRN          PS (+)

         2     NotUsed        2       YEL          ------

         3      PS(-)         3       BLU          PS (-)

         4      Output        4       BLK    Sourcing PLC Input   

------+------+----------+----------+-------+--------------------+

 PNP     1      PS(+)         1       BRN          PS (+)

         2     NotUsed        2       YEL          ------

         3      PS(-)         3       BLU          PS (-)

         4      Output        4       BLK    Sinking PLC Input   

------+------+----------+----------+-------+--------------------+

Each Sensor-Pin corresponds to a "function".
Each Sensor-Pin/Function corresponds to a Connector-Pin.
Each Connector-Pin corresponds to a Wire Color.
Each Wire-Color corresponds to a particular destination.

Notice that the only difference is in the destination. In the chart above, the destination is determined by the configuration of the field device (NPN or PNP). ACTUALLY... the destination type determines the required field device type!

There are other possible configuration combinations. The drawings that Eric pointed to indicate all of the possible NPN & PNP sensor connections.

The question, as posed, has nothing to do with the way NPN works versus how PNP works.

Now... if what you are actually talking about is installing a cable (with molded connectors on both ends) between a sensor and something like a profibus I/O Module and that module "expects" an "NPN" sensor... but you have a "PNP" in the field... Now we're talking about a horse of a different color! We might actually be talking about Zerbas.

In case anyone is wondering... A "Zerba" is just a Zebra with the stripes reversed...

Actually, there ARE PNP and NPN cables... They're the ones with the LED indicators in them...

And if you use a lighted NPN cable with a PNP sensor, the little LED that indicates that the output is on won't light (and, depending on the cable/sensor brand, sometimes it will illuminate when the output is OFF)

beerchug

-Eric

In response to the original question--it all depends on how you connect it!!!

Another question--What happens if you connect an NPN cable to an NPN device incorrectly???