SD series is an optical level switch line that emit a beam of infrared light into the tip (prism) of the sensor. In the absence of the liquid at the sensor tip the light is reflected back to the sensor’s receiver. When the target liquid is present surrounding the sensor tip, the light is refracted into the liquid and away from the SD series level switch receiving component thus how liquid presence and absence is determined. The SD series output will be activated accordingly. These optical level switch devices are compact, cost-effective and ideal for a wide variety of fluids.