NPN and PNP sensors function in a similar manner, except the power supply polarities are reversed for each type. NPN inductive sensors are more common in North America, while PNP is more common in Asia and Europe. The HLCP product is delivered with NPN inductive sensors as standard. HLCP cylinders with PNP sensors installed must be ordered as a "Special order" and PNP sensors need to be specifically requested at the time of the order. If PNP is not requested, the cylinders will be delivered with NPN sensors, even for special orders.