Infrared phototach - The 404B Infrared Phototach is a self-contained, reflective sensor. The phototach is relatively immune to ambient light sources, making it ideal for outdoor use in areas where reflected light and glare cause conventional phototachs to malfunction. It provides direct readings up to 20,000 RPM at distances up to 3 feet. Distance may vary with RPM. The phototach's small effective beam makes it a good choice for sensing relatively small objects, while its visible red light makes it extremely easy to align.