PNP and NPN type sensors essentially utilize the saturation and cutoff states of transistors to output two states, classifying them as switching sensors. However, their output signals are diametrically opposed: high and low levels. A PNP outputs a low level (0), while an NPN outputs a high level (1).
PNP and NPN type sensors (switching type) are divided into six categories:
1. NPN-NO (Normally Open)
2. NPN-NC (Normally Closed)
3. NPN-NC+NO (normally open and normally closed common type)
4. PNP-NO (Normally Open)
5. PNP-NC (normally closed type)
6. PNP-NC+NO (normally open and normally closed common type)
PNP and NPN type sensors generally have three leads: the power supply line VCC, the 0V line, and the out signal output line.
1. NPN type
NPN means that when a signal is triggered, the signal output line OUT is connected to the power supply line VCC, which is equivalent to a power supply line that outputs a high level.
For NPN-NO type, the output line is floating when there is no signal trigger, meaning the VCC power line and the out line are disconnected. When a signal triggers, it outputs the same voltage as the VCC power line, meaning the out line is connected to the VCC power line, and the output is a high-level VCC.
For the NPN-NC type, when there is no signal trigger, it outputs the same voltage as the VCC power supply line, meaning the out line is connected to the VCC power supply line, resulting in a high-level VCC output. When a signal triggers, the output line is left floating, meaning the VCC power supply line and the out line are disconnected.
For the NPN-NC+NO type, it simply means there is an extra output line OUT, which can be used or discarded as needed.
2. PNP type
PNP means that when a signal is triggered, the signal output line OUT and the 0V line are connected, which is equivalent to outputting a low level, OV.
For PNP-NO type, the output line is floating when there is no signal trigger, meaning the 0V line and the out line are disconnected. When a signal triggers, it outputs the same voltage as 0V, meaning the out line and the 0V line are connected, and the output is a low level 0V.
For the PNP-NC type, when there is no signal trigger, it outputs the same voltage as the 0V line, meaning the out line and the 0V line are connected, resulting in a low level of 0V. When a signal triggers, the output line is left floating, meaning the 0V line and the out line are disconnected.
For the PNP-NC+NO type, similar to the NPN-NC+NO type, there is an additional output line OUT and two output lines with inverted signals, which can be selected as needed.
We generally use the NPN type, which is active high. PNP is rarely used.
