3-wire sensors are sourcing, type "PNP", or sinking, type "NPN", with separate connections for the power supply and for the output. These sensors are protected against overload, short circuit, and reverse polarity. The residual current is negligible. For sensor type PNP, the load is connected between the output and ground potential (L-) For sensor type NPN, the load is connected between the output and L+.
Depending on the type of output-stage transistor used, sinking output stages are often referred to as NPN output stages. Sourcing end stages are referred to as PNP output stages.
A special type of switching 3-wire sensor is the sensor with a digital current output. In its standard version, the 3-wire sensor represents the switch state by the voltage level at the switching output. The special type with digital current output sees the sensor represent the switch state by an applied current. The output thus acts as a current source. When not switched on, the switching output drives an applied current of approximately 5 mA through the connected load. When switched on, this current increases to approximately 10 mA.
A lower sensitivity to external electromagnetic interference is typical and considered a benefit of this output type. Another benefit is the diagnostic capability. Lead breakages and lead short circuits can be detected and evaluated.
The connection of a sensor with a digital current output is the same as for a sensor with PNP and normally-open output. The load is between the output connection and the ground potential.
Sensors with push-pull output combine the characteristics of a PNP output and an NPN output. These sensors correspond to sensor type E (3-wire), in which the switching output is equipped with a PNP and an NPN transistor. This allows the load to be connected between the output cable and L+ or L-.
Sensors with push-pull output are used by Pepperl+Fuchs in the following technologies:
These sensors are usually marked with the following in the third block of the Pepperl+Fuchs order designation:
–EI = special type with digital current output
–EP = sensors with push-pull output
Sensors of type –E are available in the following switching element functions:
These sensors have separate connections for the power supply and the analog output. An analog signal proportional to the measured variable can be tapped at the output. The most common analog signals are 4 mA ... 20 mA and 0 V ... 10 V. The measured variable can be the object distance, an inclination angle, a fill level, a valve position, an acceleration value, etc. Many inductive analog sensors can be parameterized so that the output can be optimally adapted to the conditions of the application. Inductive analog sensors often additionally have switching outputs for signaling limit values; see 3-wire sensors with frequency output for direct-current voltage operation.
Sensors of this type are marked with the following in the Pepperl+Fuchs order designation:
–I = sensor with current output or
–U = sensor with voltage output
Such sensors are available in the following versions:
Take a look at the range of Pepperl+Fuchs inductive sensors.