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 combined) 4. PNP-NO (normally open) 5. PNP-NC (normally closed) 6. PNP-NC+NO (normally open and normally closed combined)
PNP and NPN type sensors generally have three leads: a power supply line (VCC), a 0V line, and an 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, effectively outputting a high-level power supply. For NPN-NO type, when no signal is triggered, the output line is floating, meaning the VCC power supply line and the OUT line are disconnected. When a signal is triggered, it outputs the same voltage as the VCC power supply line, meaning the OUT line is connected to the VCC power supply line, outputting a high-level VCC. For NPN-NC type, when no signal is triggered, it outputs the same voltage as the VCC power supply line, meaning the OUT line is connected to the VCC power supply line, outputting a high-level VCC. When a signal is triggered, the output line is floating, meaning the VCC power supply line and the OUT line are disconnected. For NPN-NC+NO type, it simply adds an extra output line OUT, which can be used 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, 0V. For PNP-NO type, when no signal is triggered, the output line is floating, that is, the 0V line and the OUT line are disconnected. When a signal is triggered, it outputs the same voltage as 0V, that is, the OUT line and the 0V line are connected, and the output is a low level, 0V. For PNP-NC type, when no signal is triggered, it outputs the same voltage as the 0V line, that is, the OUT line and the 0V line are connected, and the output is a low level, 0V. When a signal is triggered, the output line is floating, that is, the 0V line and the 0V line are connected. When the output current is suitable, PNP and NPN can be used in any PLC.
In fact, regardless of whether the sensor outputs PNP or NPN, as long as the output current meets the requirements of the PLC , it can be used with any type of PLC. It all depends on how the programmer programs it. The following example uses the FX-1S series PLC:
1. The FX1S requires a low-level active condition. When using an N-type output sensor, the program detection can be set to be triggered by a rising pulse. When the sensor is in position, it can detect normally and execute the corresponding instructions.
2. When using a P-type sensor, the output is high. In this case, as long as the sensor output current reaches the PLC's requirement of 4mA, simply change the program detection to a rising pulse trigger. When the sensor outputs a signal, it's equivalent to a sudden change from 0V to 24V, i.e., a falling pulse. The PLC can then detect this normally and execute the corresponding instructions. In reality, when selecting a sensor, we should consider the input current of the PLC's input terminals. (Siemens sensors are generally around 2mA, while Mitsubishi FX series sensors are around 7mA. As long as the sensor's pull-in or pull-out current meets the requirements, either P-type or N-type sensors can be used.)
The Mitsubishi FX uses an internal circuit board with a common anode optocoupler, so it can only use NPN type PLCs such as Siemens or Delta. The COM terminal is floating, allowing you to choose between common anode or common cathode connection. The type is determined by the choice. Common anode connection can only use NPN, and common cathode connection can only use PNP. However, some PLCs have multiple COM terminals, and each terminal can have either common anode or common cathode to accommodate all types of PLCs.
