PNP to NPN Information

Brad

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B
I've read the information on this site as how to convert these outputs. Now how about some information that even I can understand. I have a pnp sensor and need to convert it to npn. The brown wire is 24vdc, blue is 0v and the black is the load. Now, between which 2 wires do I connect the resistor?
 
Brad,

No matter with your sensor polarity : you can't change it !
That's why nothing changes : your resistor should always be wired
between output and 0V (charge for PNP output).

What you have to understand is how a PNP output (your sensor)
can be wired to an NPN input (PLC, counter, ...) and activate it
properly. Assuming that your sensor is PNP / NO type :

Test your input (PLC - NPN type, meaning there is usually a common point with 24V wired on it) : you can activate this input when
grounded (strap to 0V). Replace the strap by a 2,2k resistor : your
input is activated too, with a current flow through the resistor.

Keep the resistor wired from NPN input to 0V, and add your sensor's output (PNP) to your input : when the sensor is activated (outputting
24V), your PLC's input is at 24V too. So, the COM point is at 24V, the input at 24V too, no current is flowing through your input : your input is not activated. In this case, the resistor becomes the charge of your sensor's output. Current flows through the sensor, and reaches 0V through the reistor.

If your sensor does not detect anymore, its output is high (not connected). This way the current flows from input's COM to 0V via
the resistor (the input becomes activated).

Conclusion : PNP sensor's output wired to an NPN input + resistor between input and 0V = runs with reverse INPUT's polarity (and not
reverse sensor's output polarity)

Determine the necessary resistor's wattage by U=RI and W=RIxI formulas.

Regards
 

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