Presence sensing is a broad topic that entails both object detection and machine guarding. Choosing the right device always entails some forethought, especially when installing it in difficult-to-reach or hazardous areas. Our panel of experts tells you what you need to know. Tim Kelly, vice president of U.S. sales, Tri-Tronics: The reason there are different technologies is that each application is unique and may require the best solution. Obviously, there are applications that are extremely easy, repeatable and unchallenging. These types of applications require very little technical expertise and can be solved with almost any kind of low-cost sensing technology. But the more difficult applications require some level of expertise from the supplier, as well as the best technology to solve the problem. Ultrasonic sensors are good for ignoring color, texture and material differences, but they may have issues with angle of incidence or speed or limited space between objects. Photoelectric sensors are great for either tolerating differences in colors, as infrared LEDs are often utilized, or detecting the difference in colors, like white LEDs do. Polarized photoelectric sensors can be...