Check Application To Specify Sensors

但在选择归纳或电容性代理时，材料的选择是最大的问题，建议自动化供应商Turck USA Inc.的Automation Vitale，Applications Engineering Manager（www.turck.com），也在 Minneapolis 。“更重要的是，是铁丝素或有色金属？”他说，参考要感应的材料。如果金属，选择incuctives，建议Wayne Meyer，产品经理，工业传感器集团，病士Inc.（www.sickusa.com) another Minneapolis vendor. “That also assumes you can get extremely close, about 25 millimeters (mm) away [from objects to be sensed].” But target size has to be at least three times nominal sensing distance, recommends Thurston Horton, product and technology training manager for Balluff USA Inc. (www.balluff.com), a Florence, ky. , components vendor.

Typical applications for inductives include sensing bottles with metal caps, cans of food or liquids, or other metallic objects on conveyor belts, Vitale explains. But beyond metallics, Meyer says you must ask: “What am I trying to detect? Are there size, shape, color and/or surface irregularities?”

答案可能指向使用电容性能，可以将目标从50到60 mm距离。“但是传感范围不是决定因素，”Vitale说。它的电容灵活性地看到金属和非金属。但是，可以反射。“如果传感器设置为看木头，并且你把手放在那里[在光束中]，它不知道手和木材之间的差异，”霍顿解释说。这可能导致安全或运营相关的问题。

电容器也唯一地检测容器中的液体水平。“他们可以看到杯子，牛奶纸箱，洗发水瓶等内部，”霍顿笔记。调整它们以实现最佳效果意味着首先调整到容器，然后将传感器设置为忽略该信号并仅看到液体。他说，随着油箱，例如，必须通过壳体和电容器安装瞄准镜，并忽略玻璃。

Dusty or wet environments may require inductives or capacitives, depending on the application, Meyer adds. So where do photoelectric sensors, including fiber optic ones, fit? When the sensor needs to be farther away from the object and where proxes don’t work, such as inside machines or underneath a carriage, he explains. “Photoelectrics can see wood, metal or other materials,” notes Horton.

Retro look

But how they see differs. With thru-beam and retro-reflective sensors, the beam is interrupted; with diffuse sensors, the beam is reflected. “Thru-beam is best for conveyors. It only has to look once across them,” Horton says. Thru-beams are better for dusty environments, he also says, though retro-reflectives are cheaper and easier to install. With diffuse photoelectrics, the brighter the target, the greater the sensing distance, Horton notes. Regardless, “with photoelectrics, you have to pay more attention to color, surface and reflectivity, and also ambient lighting,” cautions Meyer.

遥感或恶劣环境决定纤维optic sensors, a photoelectrics subset. Knutson notes that with these, “you can get 20 to 30 feet or more” away from targets. Inside ovens is one high-temperature environment in which these sensors are used, because they are rated to at least 600 to 1,000 degrees Fahrenheit. “Maybe I need to detect if the part is in the proper place,” Horton says. For example, end-users might set the light beam along the conveyor’s sides in a bakery’s continuous oven to determine pans’ lateral positions, explains Knutson.

So whether the technology is inductive or capacitive proxes, or photoelectrics such as fiber optics, discrete sensors can cover a wide range of applications for automation end-users. As Meyer puts it, “There’s something for everyone.”

C. Kenna Amos.,ckamosjr@earthlink.net,is an自动化世界Contributing Editor.