Dec 28, 2021 
As is known to us, rotary encoders consist of incremental encoders and absolute encoders. And absolute encoders are much more expensive than incremental encoders. In fact, both two types of encoders are used for position measurement. So what’s the point of using an absolute encoder?
For distance measurement applications, both incremental and absolute encoders can be chosen - from a technical point of view. The advantages of absolute encoders are reflected in accuracy and performance, while incremental encoders seem more economical and practical.
When an incremental encoder is used for position measurement, the signal input system of the equipment is required to count the position based on the continuous repetitive pulses fed back from the encoder. There may be various unexpected situations during the operation of the equipment, which must require initialization of the position axis to restore the system. Therefore, this undoubtedly prolongs the downtime of the equipment.
But if an absolute encoder (single-turn or multi-turn) is used, as long as its target range is within the encoder's turn range, the equipment system can eliminate process of position counting and turn accumulation. Users directly refer to the feedback data output by the encoder, which will help save the complicated origin calibration initialization operations when the equipment is restored to operation. Besides, the downtime of the equipment will be shortened and the overall operating efficiency of the production line improves.
Figure 1: HENGSTLER Encoder AC59/0013EQ.72SBB
Single-turn and multi-turn absolute encoders
Broad temperature range: -40 to +100 Celsius degree
Resolution: up to 34 bits (22 bits in single-turn, 12 bits in multi-turn, depending upon interface)
Compact construction: 50 mm long
High EMC compatibility
Housing Option: Aluminium
Various bus connections: SSI, BiSS, EtherCAT, Profinet, Profibus, CANopen, CANlayer2, DeviceNet, Interbus and SUCOnet
1. Synthetic Binary Encoder
The resistor of the synthetic binary encoder is made by mixing carbon film, graphite, quartz powder and organic powder into a suspension, and then coating it on glass glaze fiberboard or adhesive paper. With simple production process, it is the most widely used absolute encoder now.
Figure 2: YL001XJ Synthetic binary encoder
Pros Cons
Wide resistance range Lower power
High resolution Poor high-temperature resistance
Long service life Poor humidity resistance
Low cost Difficult to make absolute encoder with low resistance
Multiple models
Made into various types of absolute encoders
Table 1: Pros and cons of synthetic binary encoders.
2. Organic Solid Core Absolute Encoder
It is a new type of absolute encoder that press the organic resistance powder into the groove of the insulator through heating and plastic pressing. Organic solid core absolute encoder is made with carbon brushes and its solid resistor body is thick, so it serves a longer mechanical life than a binary encoder.
Pros Cons
Good heat resistance Large temperature coefficient
Higher power Much dynamic noise
High reliability Poor moisture resistance
Good wear resistance Complicated manufacturing process
Longer mechanical life Poor accuracy (precision)
Table 2: Pros and cons of organic solid core absolute encoders.
It is used to adjust voltage and current in miniaturized, highly reliable, high wear resistance equipment, AC and DC circuits.
3. Metal Glaze Absolute Encoder
It is a new type of absolute encoder developed after the 1960s. Its matrix composition is ceramic, while the resistor body is made of sintered metallic glass glaze.
Metal glaze absolute encoder is made by vacuum technology depositing several materials such as metal composite film, metal oxide film, metal alloy film and button oxide film on a ceramic substrate (non-metallic mineral as raw material).
Pros Cons
Good heat resistance Poor wear resistance
Higher resolution Small resistor value, ranging from 10 Ω to 100 KΩ
Small distributed inductance and capacitors
Shortest mechanical life (no more than 10 thousand times)
Low noise electromotive force
Table 3:Pros and cons of metal glaze absolute encoders.
4. Winding Absolute Encoder
Constantan wire or nickel-chromium alloy wire is used as a resistor and wound on an insulating frame to make a winding absolute encoder.
If you need to measure a range of rotation exceeding 360 degrees, you should choose a multi-turn absolute encoder. It is made following the principle of clock gear mechanism.
When the center code wheel rotates, another set of code discs (multiple sets of gears or code discs) are driven by gears, adding the turns of encoding. The measuring range is expanded, so it is called a multi-turn absolute encoder. Its code is determined by the mechanical position, and each position code is unique.
This type of encoders is mainly used as a voltage divider and transformer. Also, it is used for zero adjustment and adjustment of working points.
Pros Cons
Small contact resistance Poor resolution
High precision Lower resistance
Small temperature coefficient Poor high-frequency characteristics
Table 4:Pros and cons of winding absolute encoders.
5. Digital Absolute Encoder
The digital absolute encoder is a semiconductor integrated circuit. The single-turn absolute encoder measures each engraved line of the optical code disc during rotation and obtains a unique code. When the rotation exceeds 360 degrees, the code returns to the original point.
This does not comply with the principle of unique code. This kind of encoder can only be used for measurement within 360 degrees of rotation, which is called a single-turn absolute encoder. It is suitable for home theater system, audio surround control, audio amplifier and cable TV equipment.
Pros Cons
High adjustment accuracy (precision)
Not fit for use in outdoor and harsh environment.
No noise
There's error caused by mechanical clearance
when measuring linear displacement.
Extremely long working life
Difficult to overcome the slip when measuring objects in orbit.
No mechanical wear (a basic type of component failure)
Data read/write
With configuration registers and data registers
More power flat storage function
Easy software control
Small size
Easy to assemble
Table 5: Pros and cons of digital absolute encoders.
It is very important to choose the right type of encoders for your product design, so it is necessary to understand the key differences between various encoders. With the narrowing of the price gap and the continuous change of technology, absolute encoders have many unique advantages compared with incremental encoders. And they are becoming the first choice to meet different location measurement requirements.
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