Bulletin 42KF PTFE Coated Miniature Photoelectric Sensors are designed for liquid level detection applications typically found in the semiconductor wafer manufacturing and handling industry. The PTFE (polytetrafluoroetheylene) casing protects both the sensor and the connecting cable from many caustic solutions which would normally damage other sensors. These sensors are DC operated and provide a sinking (NPN) output. You can connect an optional output module in-line with the sensors to convert this signal to a sourcing PNP output.