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Old May 12th, 2006, 11:51 PM   #1
Eswar
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Post NPN Vs PNP Proximities???

hello all.

I have a diubt regarding the subject (NPN Vs PNP Proximities)...

I learnt from a source that NPN is a sinking and PNP is sourcing..

I like to know whether NPN kind of proximity should be connected to a sourcing input module and the vice versa for PNP???

Also can we connect NPN kind of proximity with a sinking Input module by just interchanging the power terminals (i.e) the + and the - of the proximity...


Thanks in advance

Rgds
Eswar
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Old May 13th, 2006, 01:52 AM   #2
chavak
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Quote:
Originally Posted by Eswar
hello all.

I have a diubt regarding the subject (NPN Vs PNP Proximities)...

I learnt from a source that NPN is a sinking and PNP is sourcing..

I like to know whether NPN kind of proximity should be connected to a sourcing input module and the vice versa for PNP???

Also can we connect NPN kind of proximity with a sinking Input module by just interchanging the power terminals (i.e) the + and the - of the proximity...


Thanks in advance

Rgds
Eswar
You are right about the first question - NPN Proxi -> Sourcing I/P Module.

2nd Question -> I doubt you can convert the proxi by interchanging the + and -.
But I do come across Festo reed switch (3 wire type) can convert from PNP to NPN by interchanging the power cords (Brown and Blue). But for a person who do not know of this will take it as weird, while trouble-shooting.


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Old May 13th, 2006, 09:48 AM   #3
rsdoran
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Maybe this will help; http://www.patchn.com/npnpnp.htm
All these terms are relativistic to how current flows. A PNP device could replace an NPN but if will invert the signal. Example; where an NPN would be ON and provide an input to the PLC the PNP would be OFF and provide no signal.

It depends on the situation but PULL UP or PULL DOWN resistors may be used to change from NPN to PNP or vice versa. This may help understand their use; http://www.seattlerobotics.org/encod...97/basics.html

There are numerous threads available here on this subject;

http://www.plctalk.net/qanda/showthr...&highlight=NPN

http://www.plctalk.net/qanda/showthread.php?t=1615
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Old May 13th, 2006, 09:54 AM   #4
Sergei Troizky
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Quote:
Originally Posted by Eswar
hello all.
I learnt from a source that NPN is a sinking and PNP is sourcing..
Eswar
Yes, as long as you mean a signal source, that is a sensor.

Quote:
Originally Posted by Eswar
I like to know whether NPN kind of proximity should be connected to a sourcing input module and the vice versa for PNP???
Eswar
Yes for Allen Bradley. No for Mitsubishi.
For other brands it may be yes or no, you need to see the specs and sample diagrams.

Quote:
Originally Posted by Eswar
Also can we connect NPN kind of proximity with a sinking Input module by just interchanging the power terminals (i.e) the + and the - of the proximity...
Eswar
No, do not even try this.
Never reverse the power polarity for electronic circuits.
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