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How to Choose Between Wet Source or Dry Source

What is a sourcing output?

In a sourcing configuration, the sensor is the source of the current required to power the load. Current supplied by the sensor passes through the load second and then to ground. A sensor with a sourcing output switches the positive leg of the circuit. With a sourcing sensor, your input voltage powers the load.

Do I want a sourcing output for my sensor? 

If you want to see the supplied voltage as well as the transistor logic on the output wire when on, you want sourcing.  

A common application for a PNP output sensor is to connect to a relay or contactor.


OK, looks like sourcing is for me. Now how do I choose wet or dry source? 

Imagine your sensor is connected to a light bulb. Do you want the light bulb to turn on when the unit is wet, or when it is dry?  

Dry source = “When dry, light is on.” 

Gives transistor logic when dry, along with the voltage you are putting into it. 

Wet source = “When wet, light is on.”  

Gives transistor logic when wet, along with the voltage you are putting into it. 

Some considerations: 

If a PNP cable is damaged there is a chance the signal could short to ground and damage the sensor. 

For inductive loads use diode suppression. 

Models using sourcing output: