Sensor Type

[Tom749]

I want to know the concept of Sensor Type, exactly. I know the PNP/NPN type of the sensors, well. But what is the main difference between NPN N.O. and NPN N.C / PNP N.O and PNP N.C? is there no hardware difference in the N.O and N.C inside of the sensor circuit? Just the difference of the active line signal at normal situation? Thanks for your help in advance.

[dmargineau]

A NPN sensor contains a solid state Negative/Positive/Negative semiconductor junction switch (transistor); when "commanded" (gate "minus" polarized-NNN), it will "switch minus", allowing DC current flow between the DC power supply and a "source" input device. When a N.O. NPN sensor is "not-active", the Signal pin does not carry any potential; when "triggered", the N.O. NPN sensor "polarizes" the Signal pin with the (-) potential of the DC supply power. When a N.C. NPN sensor is "not-active", the Signal pin carries the (-) potential of the DC supply power. ; when "triggered", the N.C. NPN sensor Signal pin does not carry any potential. A PNP sensor contains a solid state Positive/Negative/Positive semiconductor junction switch (transistor); when "commanded" (gate "plus" polarized-PPP), it will "switch plus", allowing DC current flow between the DC power supply and a "sink" input device. When a N.O. PNP sensor is "not-active", the Signal pin does not carry any potential; when "triggered", the N.O. PNP sensor "polarizes" the Signal pin with the (+) potential of the DC supply power. When a N.C. PNP sensor is "not-active", the Signal pin carries the (+) potential of the DC supply power. ; when "triggered", the N.C. PNP sensor Signal pin does not carry any potential. Edited August 17, 2011 by dmargineau

[Ken Moore]

Great explanation

[TimWilborne]

Here is a good visual that Terry Woods did some years ago explaining the differences between NPN and PNP http://www.wikiplc.com/index.php?option=com_content&view=article&id=57:npn-pnp-devices-and-connections&catid=20:plc&Itemid=118