1. What is absolute value?
"Absolute value" refers to the absolute position value of a measured location that is independent of the cumulative count of previous measurements and is relative to the measurement origin.
It differs from "relative value," which is a positional value relative to the previous measurement position, while "absolute value" is independent of any other measurement relationship in each normal measurement, hence the name "absolute."
2. What is absolute value encoding?
Absolute value encoding refers to the pre-defined absolute code within a measuring device ( sensor ) that uniquely corresponds to the mechanical position origin within the measurement range for all mechanical positions. Measurements at any time do not need to rely on the history of previous measurements. Even without movement, a unique absolute code can be directly output.
The fundamental advantages of absolute value encoding are: first, it obtains complete position information without relying on movement or comparison with previous history, and each position is unique; second, it is independent of previous readings (including various memory methods) and does not require internal counter accumulation and comparison. It can measure and output a unique signal value without moving the position or needing to know the previous reading position.
3. What is the difference between "absolute encoding" and "absolute value encoding" ?
The fundamental difference is that the term "absolute" emphasizes the measurement receiving device's "absolute" position output mode relative to the external origin, while "absolute value encoding" emphasizes the encoding form within the measurement sensor, providing a unique "absolute code" for all positions relative to the origin within its measurement range. Therefore, the naming convention of an encoder should be determined by the principle of its internal encoding reading.
In reality, anything that relies on counting, whether it's internal battery memory, external battery, or even low-power Wigand effect counting, is still "counting" and can no longer be called "absolute value encoding." It can only be "absolute" relative to the measuring and receiving device.
4. What is an absolute single-turn encoder ?
Within the 360-degree measurement range, the data encoding for each output position is absolutely unique within a single 360-degree rotation, without relying on rotation or previous data to obtain position information. After rotating beyond 360 degrees, the data cycle restarts from 0.
The number of bits in a single-turn absolute encoder represents its position encoding in the power of 2. 8 bits have 256 encoding positions, 10 bits have 1024, 12 bits have 4096, 13 bits have 8192, 14 bits have 16384, and 16 bits have 65536. The highest number of bits currently is found in the 25-bit single-turn absolute encoder from Heidenhain, Germany.
5. What is an absolute multi-turn encoder?
An absolute multi-turn encoder is one that, within its measurement range, not only has "absolute value encoding" within a single 360-degree turn, but also retains a unique absolute encoding for multiple turns of value independent of a counter beyond 360 degrees. Its principle is generally similar to that of the minute and hour hands of a clock.
Multi-turn absolute encoders express their resolution and measurement revolutions by multiplying the number of bits per single turn by the number of bits per multi-turn. The most common multi-turn encoder is 4096 turns, while a few can reach 16384 turns or 65536 turns (16 bits). The GMX425 series of absolute multi-turn encoders can typically reach 4096 turns with 12 bits, and can reach 16384 turns or 65536 turns for special needs.
For example, the absolute multi-turn encoder of the GAX60 series from GEMPLE.
6. What is electronic "absolute"?
While electronic "absolute" sensors can output data in the same absolute value form, they do not pre-encode every position. Instead, they rely on the rotation of the encoder and comparison with the memory of the previous reading to obtain positional information, similar to a magnetic tape recorder or laser CD. The tape or disc must rotate to collect complete information before outputting it. This type of sensor, which requires "movement" or "partial movement" to obtain a similar absolute information output, is called "dynamic" data scanning absolute sensor. On the other hand, some sensors rely on batteries, supercapacitors to store data, or more advanced low- or zero-power Wigand effect readings and capacitors to store the readings. This type of sensor, which can output the memory of positional information without moving, is called "static" electronic absolute sensor.
Whether "static" or "dynamic," electronic "absolute" encoders no longer obtain position information through internal absolute value encoding, so they should not be called "absolute encoders." The name of an encoder should be determined by its internal encoding and reading principles, not just by the similarity of its output signal.
7. What problems arise when comparing an "electronic absolute" encoder with a "true absolute value encoding" encoder?
The internal working principle of an electronic absolute encoder relies on comparing the readings taken during movement with previously stored data to obtain position information. When compared with a "true absolute value encoder," this comparison can lead to errors in three areas:
Firstly, there's the reading accumulation during operation. This part can be affected by various internal and external electrical environmental interference factors or low-probability device failures, leading to incorrect readings. This differs from absolute value encoding, where position information is always present, so even a low-probability reading failure doesn't affect the accuracy of subsequent readings. However, with electronic systems, potential failures in reading accumulation can affect subsequent readings. These errors are difficult to distinguish and continue to be displayed over time and at various positions. Furthermore, readings after power failure rely on battery, capacitor, or energy storage with minimal Wiegand effect power. Due to limited power supply, its anti-interference capability is even worse, and the reading frequency is low. Under conditions of rapid encoder rotation or significant external interference, it's highly likely that the counting and accumulation will be insufficient or disrupted, resulting in reading errors that continue to accumulate.
Secondly, there is the issue of the memory used for cumulative counting. This type of memory is affected by various factors, such as limited electrical energy or problems with memory energy components, including battery depletion, the limited capacity of capacitors and the Wigand effect, data distortion caused by interference coupling of the capacitor storing data, data distortion when data is re-acquired, battery failure at low temperatures, battery explosion at high temperatures, and the lifespan of the memory energy and data memory. These factors can all affect the memory's ability to store data and whether it may become distorted or fail when re-acquired.
Thirdly, the speed response is limited and the data is reprocessed and decoded for output. Since it relies on the integration and decoding of two parts of data, namely the readings during movement and the comparison of internally stored data, the speed response is limited. Under various conditions such as carry synchronization processing, rapid movement reading and processing, and interference, the reprocessing, decoding and output of the two sets of data may still result in errors. Moreover, this kind of error is different from that of true absolute encoding. Once an error occurs, it cannot be judged (or it needs to be judged by comparison with auxiliary sensors), and the error in time and position continues.
In summary, electronic absolute encoders, in principle, are not absolute encoders because they do not encode every position absolutely. If an error occurs, it will affect the accuracy of subsequent readings, and this possibility of error always exists; the only difference is the probability, which reflects the manufacturer's technical level. Therefore, in principle, it is not an "absolute value encoding" encoder. Its application should be carefully avoided in situations where errors could cause greater losses, such as security monitoring.
8. What is a clock gear-type absolute multi-turn encoder?
A single-turn absolute encoder measures each code track on the optical code disk during rotation to obtain a unique set of codes. When the rotation exceeds 360 degrees, the code returns to the origin, which does not conform to the principle of unique absolute coding. Such an encoder can only be used for measurements within a rotation range of 360 degrees and is called a single-turn absolute encoder.
True multi-turn absolute encoder: Encoder manufacturers utilize the mechanical principle of clock gears, adding a set of mechanical gears to the code disk. When the central code disk rotates, it drives another set of gears (or multiple sets of gears and code disks) through gear transmission, adding more turns of encoding on top of the single-turn encoding to expand the encoder's measurement range. This method is similar to the seconds, minutes, and hours of a mechanical clock, and is also called an absolute encoder, or clock gear-type absolute multi-turn encoder. In this true multi-turn absolute encoder, the values for multiple turns are also determined by the mechanical position, with each position encoding being unique and non-repeating, eliminating the need for memorization.
9. What is an electronic multi-turn "absolute encoder"?
Single-turn code disks use the principle of absolute value, such as optical multi-track absolute single-turn encoders or magneto-electric absolute single-turn encoders. Multi-turn measurement uses electronic counting accumulation and registering, which is called "electronic multi-turn absolute encoder". However, calling it "absolute value encoding" is not serious and is deceptive. This is partial absolute value encoding. The complete full-stroke measurement range cannot be considered absolute value encoding, but rather partial incremental counting.
Electronic multi-turn absolute encoders include those that use the previous reading to determine the number of turns without a battery, but have a limited range of movement angles after a power outage; others use built-in or external batteries to record the number of turns, and can remember the number of turns when the battery capacity is limited and the power is off; currently there is also a type that uses the Wiegand effect (no power consumption pulse generation and counting) to record the number of turns without a battery, but it still belongs to electronic multi-turn encoders.
Electronic multi-turn encoders still have the potential for errors in reading, registering, and rereading. Once this possibility occurs, it cannot be detected and remedied, and other auxiliary sensors need to be used for comparison and correction. In addition, electronic multi-turn encoders have limitations on rotation angle and speed after power failure.
10. What is a Wiegand effect encoder?
Some electronic multi-turn encoders use the Wiegand effect to count the number of turns.
In the 1960s, John Wiegand discovered that a significant difference exists between the inner core and outer layer of a properly treated magnetic metal wire, allowing for a transition between the two states under certain conditions. This effect is known as the Wiegand effect, and wires exhibiting similar characteristics are called Wiegand wires. Magnetic sensors made from these wires can generate power-free spike pulses when subjected to changes in the N-S magnetic field. Wiegand sensors feature high operating temperatures (up to 200°C), the ability to output high pulse voltages (5-6V) without any external power supply, and direct computer interfacing. Therefore, they have found applications in many fields. Sensors made using this principle are called "Wiegand sensors." These sensors require almost no power supply, and the spikes they generate can even be stored in capacitors. Encoders that count internally in Wiegand sensors and store the tiny energy of spikes in capacitors were first produced in the 1990s. However, due to the technological limitations at the time, their performance was very unstable. In recent years, the emergence of low-power electronic components has allowed this product to gradually mature and enter the market. However, its reliability is limited, and it can currently only be used for counting revolutions (because the number of revolutions counted is small and the frequency is low, the reliability factor reflects the low probability of occurrence). Single-revolution code disks use absolute value code disks (such as those based on magnetoelectric principles).
The Wiegand principle counting is still a type of electronic multi-turn encoder, and it has its own limitations. Because the signal generated by its own power source is relatively weak, it is easily interfered with by surrounding electrical noise. The counting and registering processes are still susceptible to interference and errors, and once an error occurs, the original position is lost and cannot be recovered. It must be used with caution in relatively clean electrical environments and is not suitable for hoisting, engineering, or other applications with complex electrical environments. Furthermore, it has limited energy storage, poor anti-interference performance after power outages, slow counting response, and poor anti-interference during power-off and power-on switching. In short, it is not a complete absolute value encoder and cannot be called an "absolute multi-turn encoder." Foreign sample materials clearly state that it is a single-turn absolute encoder with a multi-turn Wiegand effect, "electronic" multi-turn. Intentionally omitting the "electronic" aspect of the Wiegand effect and directly calling it an "absolute multi-turn encoder" deliberately confuses it with the more expensive and reliable mechanical absolute encoders, which is suspected of being unserious commercial deception.
11. What is a full-stroke multi-turn absolute encoder?
Throughout the entire measurement stroke, the internal encoder of the measuring sensor uses absolute value encoding. This differs from some measurements that are partially absolute value encoded and rely on cumulative counting, or measurements that require refreshing the starting point and restarting as absolute values after exceeding a certain stroke. Because the measurement range of geared absolute multi-turn encoders is limited by the internal mechanical gear set, the number of turns for absolute value encoding is finite, such as 4096 turns (12 bits), 16384 turns (14 bits), or economical 64 turns or 16 turns. This type of encoder, which specifies the measurement stroke and confirms that absolute value encoding is used within this measurement stroke, is called a full-stroke absolute encoder. Using full-stroke multi-turn encoding requires using it within this range according to the provided encoder turn count. The sensor restarts from the starting point after exceeding the stroke.
12. What are some examples of absolute single-turn encoders?
GEMPLE offers optical and magnetoelectric absolute single-turn encoders;
As needed, GEMPLE will offer the market higher-end hybrid absolute encoders that combine optical and magnetoelectric technologies.
13. What are some examples of absolute multi-turn encoders?
GEMPLE's multi-turn absolute encoders currently on the market are all mechanical full-stroke absolute encoders, without internal electronic counting principles or batteries.
(In the future, GEMPLE will also provide some encoders with absolute value encoding and electronic counting based on market needs, but will always indicate their electronic counting characteristics.)
14. What is an intelligent encoder?
The intelligent encoder is a patented invention of GEMPLE. Its encoder incorporates a 32-bit intelligent MCU chip and Easypro software for computer configuration. Each intelligent encoder integrates digital RS485 output and analog current output (4-20mA). For various applications, such as angle, length, and speed measurement, electronic cam switch output, and overspeed/low-speed output switching, the output can be directly applied through intelligent settings. For RS485 signals, baud rate, address, and resolution can be set; for 4-20mA signals, zero point, full-scale point, rotation direction, and current calibration can be set. Furthermore, the digital signal can be converted to various fieldbuses, Ethernet, wireless, etc., as needed. This marks the beginning of the intelligent era for encoders, providing the sensor foundation for angle, length, and speed measurement for intelligent factory equipment management and the Internet of Things.
Easypro software interface
15. What is the analog signal output of an absolute encoder?
Absolute encoders internally use digital encoding, but their output can be converted to analog signals using a digital-to-analog converter (ADC), such as 4-20mA current or 1-5V voltage. Examples include the GMS412 LB (single-turn absolute 4-20mA output) and the GAX60 LB (multi-turn absolute 4-20mA output), etc.
16. Why can't the analog signal value of an absolute encoder start from "0"?
The analog signal values of an absolute encoder cannot start from 0. If the output is 0, it's impossible to determine whether the signal is on or the encoder is working properly. Furthermore, a 0 signal is easily affected by external interference, causing slight fluctuations that make it impossible to determine whether the position value is changing or due to interference. Therefore, current signals (4-20mA) start from 4mA, voltage signals (1-5V) start from 1V, and outputs (0-10V) start from 2V for the position reference point.
17. What absolute encoders with signal outputs are available from GEMPLE?
For other output signal requirements, please contact GEMPLE to discuss collaborative production.
