The FX-311P is a manually set fiber sensor from the FX-311 series featuring a red LED emitting element and PNP open-collector transistor output. It incorporates a 12-turn potentiometer with visible red backlight indicator for precise sensitivity tuning and detection of very fine differences. The sensor employs a four-chemical LED technology that greatly reduces adverse influences on emission performance, resulting in stable operation that requires minimal adjustment over time. An integrated "assist function" provides rapid flashing feedback to indicate the optimum sensitivity position, enabling easy and reliable adjustment for narrow sensing ranges. The amplifier is suitable for 35 mm width DIN rail mounting and includes features such as timer selection, mode selection, and operation mode switches. This design is ideal for applications requiring highly sensitive manual tuning with long-term stability and reduced maintenance requirements.