[China Transmission Network Industry News] Rotary encoders are important sensors in industry for providing feedback on mechanical position, angle, length, and speed, and participating in control. Rotary encoders are divided into incremental encoders, absolute encoders, and absolute multi-turn encoders.
From the perspective of external receiving devices (such as servo controllers and PLCs), incremental value refers to a change in relative position information, the calculation of the increase or decrease of the signal from point A to point B, also known as "relative value". It requires continuous counting by subsequent devices. Since each data is not independent but depends on the previous reading, it is impossible to judge the error caused by power outages and interference in the previous data, thus causing the error to accumulate.
The "absolute working mode" refers to the determination of an origin point after the device is initialized. All subsequent position information is the absolute position relative to this "origin point". It does not require continuous counting by subsequent devices, but directly reads the current position value. As each reading is independent and unaffected by previous readings, it does not cause error accumulation. This is called the "absolute working mode" of the receiving device.
The definition of "absolute value" within an absolute encoder refers to all position values within the encoder. After the encoder is manufactured, all positions within its range are "absolutely" determined within the encoder. After initializing the origin, each position is independent and unique. Each data refresh and reading, both internally and externally, does not depend on the previous data reading. Neither inside nor outside the encoder should there be any "counting" or accumulation calculation of the previous reading, because such data would not be "independent," "unique," or "all positions within the range have been pre-established absolutely," and would not conform to the meaning of the word "absolute."
Therefore, the true definition of an absolute encoder is an absolute encoding that is independent and unique, with all positions within the range corresponding to the origin position in advance, and does not depend on internal or external counting accumulation.
The "deliberate confusion" and misconceptions surrounding the concept of "absolute" encoders
Many people's understanding of absolute encoders is still limited to the concept of preserving data at a "power outage" location. This is a one-sided and limited view. An "absolute" encoder is not just about power outages. For receiving devices, the true meaning of "absolute" lies in the independence and uniqueness of data refresh and retrieval at each location, whether inside or outside the encoder—an "absolute encoding" that does not depend on previous readings. The definition of this "absolute" is still vague in the market, leading some vendors to deliberately confuse the concept.
Confusion 1: Confusing the "absolute operating mode" of a receiving device with the "absolute" mode of an absolute encoder. The "absolute" mode of a receiving device refers to a working mode where all positions are "absolute" relative to the device's origin, without the need for continuous counting and accumulation. In fact, this mode, through an incremental encoder, its own counting and accumulation device, and battery memory, can also provide the device with "absolute" position information. It is completely different from the "absolute encoding" of an absolute encoder. It carries the potential for counting and accumulation errors, power supply failures in the counting device, and unresponsive counting at high speeds.
Confusion 2: Confusing an absolute single-turn encoder with internal and external counting and accumulation devices with a true absolute multi-turn encoder. An absolute single-turn encoder with a turn counting device is absolute within 360 degrees. However, beyond 360 degrees, its position is no longer "independent" or "unique." It relies on internal or external counting to determine the absolute position information within a certain number of turns. This internal or external "counting device" is the same as an incremental encoder with a counting device and battery memory. Any error in counting, or a momentary power failure during the counting device's operation, will cause errors to accumulate and become unreliable, resulting in deceptive false absolute information.
A true absolute multi-turn encoder, besides having an absolutely unique position within 360 degrees, continues to provide "independent," "unique," and unreliant absolute encoding beyond 360 degrees, driven by a geared mechanical absolute code disk. In fact, based on the definition of "absolute," the aforementioned "pseudo-multi-turn absolute encoder" with a single-turn absolute encoder and a counting accumulation device can no longer be called an "absolute multi-turn encoder," even though it is absolute within 360 degrees. Beyond the 360-degree working range, it is no longer a unique "absolute encoding."
