PNP

What is a PNP Transistor?

Sensors are available for many different applications in automation technology. Temperature and pressure can be measured. A distinction can be made between light and dark. Inductive sensors can recognize the proximity of parts, for example in machines with moving parts. The recording of liquid streams and levels is another typical responsibility of sensors. Confirmation to standards of transmission technology is a requirement for the transmission of the sensor signal. This also includes the type of output of the sensor.

Depending on the type, there are sensors with output types PNP and NPN available. In semi conductor technology the letter combinations PNP and NPN equal the three alternating layers which are part of the transistor. There are p endowed and n endowed layers. Endowing is the process of introducing a small amount of foreign atoms into a base material which changes its electric conductivity. In a real transistor further endowed layers are arranged.

How does a PNP transistor switch?

Transistors used in sensors for a signal change work like an electric switch. Depending on the combination of semiconductor layers they are called either PNP switching or NPN switching. The choice for either PNP or NPN depends on the location where it is used. PNP sensors are usually used in Europe, whereas NPN sensors are mainly used in Asia. The PNP sensor is connected to the load via its minus pole. The PNP sensor controls the positive supply voltage. In the set-up of the switch of the NPN sensor the load is connected to the positive supply voltage and the sensor is connected to the minus pole. If the sensor provides a digital PNP signal or an IO-Link signal it has a positive effect on the transmission security. If the sensor is connected via IO-Link lines of up to 20m in length may be used.

PNP Input and Digital PNP Input - The Differences

Typically the signal of a sensor is processed by the control unit (SPS). A PNP input on the SPS is intended for connection of a PNP sensor. Check whether the SPS has a PNP input before selection of the sensor.

If the sensor transmits a digital PNP signal to the superior network component, a digital PNP input is required. A digital PNP input on the control unit may increase transmission security since a digital PNP signal is used instead of an analogue signal. By using a suited adapter, an analogue signal can be translated into a digital signal.