What is "absolute value encoding" and what is "pseudo-absolute encoder "?
In the automation industry, most of us know that industrial rotary encoders are divided into absolute encoders and relative encoders (also known as incremental encoders). Most of us are also familiar with incremental encoders, as PLCs and servo controllers have integrated high-speed counters to collect and count the AB phase signals of the incremental encoder. However, most people seem to have a vague understanding of the definition of "absolute encoders," and there seem to be many misconceptions about why absolute encoders should be used. As a result, "pseudo-absolute encoders" have been able to swagger into the market.
First, let's talk about "incremental encoding" and "absolute value encoding".
The concepts of incremental encoding with a time axis and counting process, and absolute value encoding without a counting process:
1. Relative encoding, also known as incremental encoding, requires only a small number of bits for encoding on the encoder's internal code disk. For example, in an orthogonal AB-phase incremental encoder, regardless of its resolution or the number of square wave pulse output lines, the internal encoding is only 2 bits, with 1/0 encoding for both A and B phases. However, the angle or position to be measured often exceeds two bits, such as 0~16383. Where does this large amount of data information come from? The receiving end needs to accumulate or decrease the data based on the relative changes on the time axis, using a counter to count and store this large amount of data encoding information.
The incremental encoded data is actually very limited, with only 2 bits of valid data! The 0/1 pulse signals of phase A and phase B.
Incremental encoders accumulate large amounts of data at the receiving end through a counting process. This counting process harbors many unpredictable errors and also incurs uncertain costs later on.
2. Absolute value encoding
The encoder's internal code disk already contains large-scale encoded data, which is unique throughout the entire specified measurement stroke. It is independent of the time axis and requires no counting process. Whether data is read or not, it can directly output large-scale encoded data, independent of the time axis, based on downstream data instructions. Being independent of the counting process means there's no need to consider the counting start point, power outages, or whether there's further movement after a power outage. There's also no need to worry about interference or whether the encoder can recover the true encoded angle information after interference.
2. What is a "pseudo-absolute encoder"?
There are three levels of understanding of absolute value encoding in the market, from beginners to experts. The first two are relatively vague understandings of absolute value encoding, which has led to the emergence of two pseudo-absolute encoders based on this vague understanding.
1. The first level of beginner's understanding: treating absolute data output as an absolute encoder—Absolute data refers to determining the coordinates of an origin and outputting multiple bits of data for these coordinates (usually serial output, not pulse counting). It only refers to the form of the data output. It does not mean that the internal encoding is absolute encoding; it is very likely that there is already incremental encoding using counters and registers internally.
2. The second level is the realm of half-understanding. Is saving data without loss the same as "absolute value encoding"?
Another vague and erroneous understanding is that "absolute encoders can save data even when power is off," which led to the second type of pseudo-absolute encoder.
Using a single-turn absolute value encoding (a limited encoding of about ten bits) and a multi-turn counter, regardless of whether there is a battery, it is still an electronic multi-turn counting process. The original encoding is only about ten bits, but it can output more than twenty or thirty bits of data. Where does the extra data come from? There is a counter! Non-unique encoding—this is not absolute value encoding!
3. The third level, the realm of true absolute value encoding, has no counter! All mechanical original positions are uniquely pre-existing with absolute value codes. The output is the same as the original mechanical position code in bits; this is sometimes called a mechanical absolute value encoder.
The core significance of absolute value encoding: From a physics perspective, the counting process in non-absolute value encoding is related to the time axis. It is a hybrid data combination of position encoding and time axis, representing a multi-physical variable event. There is always another physical variable with a low probability of uncertainty within a certain time period; the only questions are when, under what circumstances, and with what probability it will occur. Relative quantity encoding is a bivariate encoding of angle change plus time variable. Absolute value encoding, on the other hand, is a single large data encoding without a time axis; the output information is only related to the original encoding of the actual angle position. Any encoding that requires a counter to introduce time axis information, either internally or externally, is not absolute value encoding.
The fundamentals of absolute value encoding without a timeline, without a counter, and in mechanical in-situ are: first, it can obtain complete location information of a large dataset without relying on movement, and each location code is unique; second, it is unrelated to previous historical readings (including various memory methods), which means it has no timeline and no historical events.
Third, let's expose the two major pitfalls of "pseudo-absolute encoders" in the market:
1. Battery-powered pseudo-absolute multi-turn encoder:
The earliest Wiegand inductive sensors were used for water meter counting, and the earliest Wiegand counter encoders originated around 2005. Here's what they looked like initially:
After more than a decade in operation, Weigen multi-turn encoders have made significant progress. The biggest progress, however, is that after the market gradually recognized them, under the discerning eyes of the public, they no longer dared to directly claim to be "absolute encoders" and instead called them "multi-turn encoders." The word "absolute" has been quietly removed.
