Design News, February 2013

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Non-Contact Precision Measurment KD-2306 Applications range from lab work, to production/process automation. The DIN rail mount interface makes it ideal for integration into OEM equipment and industrial control applications. It is a cost-effective replacement for LVDTs, air gauges, dial indicators and micrometers. n Position/Displacement n Shaft Vibration/Runout n Component Alignment n Measuring Dimensions n Part Sorting n Check our Applications Handbook for more. Call for an on-site seminar. 800-552-6276 principle to implement and the most frequently used. It utilizes the geometry of optics to determine if an object is closer than a defined distance. For example, if cookies on a conveyor belt must be counted with- The closer an object is to the sensor, the larger the reflected light angle. The farther away an object is, the smaller the reflected light angle. out detecting the belt or if the level of molded plastic parts in a hopper must be monitored without sensing the hopper surface, then SPT is the best sensing solution. SPT sensors emit a beam of light, typically infrared or visible red, which is reflected by an object back to the sensor's receiver. The angle of that reflected light beam relative to the emitted light beam axis varies based on the distance to the sensed object. The closer an object is to the sensor, the larger the reflected light angle. The farther away an object is, the smaller the reflected light angle. So when the reflected light shines on one segment of the single pixel, the sensor recognizes that the detected object is in the near field. But when the reflected light shines on the other segment of the pixel, it is recognized as being in the far field and is ignored. SPT is ideal for ignoring objects in the background and for consistent detection of objects in the near field, regardless of their color or reflectivity. The older alternative to this technology is diffuse mode sensing in which objects are detected based on the amount of reflected light energy. But diffuse mode sensing is prone to detecting background objects and has starkly different sensing distances depending on the object's attributes. Multi-Pixel Technology also uses the principle of optical triangulation that is utilized with SPT sensors. However, MPT sensors make use of not a single threshold between receiver elements, but many more, even up to 128 thresholds. While SPT sensing detects up to a certain distance but not beyond that, MPT sensing can also define sensing windows within which objects are sensed. MPT sensors are flexible enough that multiple distances can correspond to multiple outputs of the same sensor. For example, an SPT device could detect pill bottles or medical syringes closer than 65 mm. But an MPT device could also detect those bottles at a distance between 48 mm and 65 mm, or it could trigger one discrete output when something is closer than 48 mm and another output when something is closer than 65 mm. Pulse Ranging Technology is a method of distance measurement. PRT offers continuous information on the distance from the sensor to the observed object. It utilizes very highintensity bursts of light that leave the sensor's emitter, are reflected by the sensed object, and are detected by the sensor's receiver. Based on the amount of time for the light to be emitted and to be picked up by the sensor's receiver and using the speed of light in air as a constant, the distance to the object can be accurately calculated by the sensor. PRT is used not only to measure distance along a line of sight, but also to calculate dimensions of an object. Or it can act in the same capacity as an SRT or PRT sensor and detect objects within a certain distance or range. An alternative to PRT is one based on phase-correlation, in which the emitter sends light continuously and measures the distance to an object based on the phase angle of the reflected light. Phase correlation sensors have weaker optical signals, and are thus more prone to interference from ambient lighting. They can detect different colored objects at difference distances and can also detect "phantom objects" when a background object is out of phase by 360 degrees. When an application calls for T14 T r e n d waT ch : s e ns o r s / mach ine v is io n / a s up p le me n T To de s ign ne ws

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