Many engineers still specify incremental position sensors because they believe absolute versions are too complex and/or costly. Darran Kreit, technical manager at Zettlex, compares the two approaches. Understanding the difference between incremental and absolute measurement techniques can be challenging. As well tackling the terminology, engineers also have to deal with confusing statements from sensor manufacturers who claim they provide absolute measurement sensors, when what they are really offering is incremental. In this article, I will use the term "sensor" to cover encoders, transducers and detectors. The distinguishing feature of an incremental position sensor is that it reports an incremental change in position. In other words, when an incremental sensor is powered up, it does not report its position until it is provided with a reference point from which it can measure. An absolute sensor unambiguously reports its position within a scale or range. When an absolute sensor is powered up, it will report its position, without needing any reference information. "What happens on power up?" is a good acid test to differentiate between the two types of sensor. If the sensor has to go through some form of calibration step - it's incremental. If it doesn't - it's absolute.
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