On Sat, 15 Nov 2008 10:42:02 -0600, "Karl Townsend"
wrote:

OK, I think I want NPN but I'm easilyconfused. The PLC input is at +12
volt, then a resistor (5.5K), then the switch (photo eye in this case), then
common(0V). Correct?


If this is a 12VDC control system, and jumpering the input to 0V turns
the input on, then an NPN is what you want. Unless there's something
unusual about the PLC input or wiring you shouldn't need an external
resistor.

--
Ned Simmons