An absolute vs incremental encoder choice really becomes a position memory decision. One type of encoder outputs the measured position in "pulses" for the PLC or controller to count. Another reports position as a unique position value for the controller to read. This absolute and incremental comparison affects wiring, homing, downtime, controller selection, and cost.
Quick Specs: Absolute vs Incremental Encoder
- Incremental output is a pulse train (squared wave) producing A/B quadrature signals plus optional Z or index channel.
- Absolute output is a unique code or digital position reading for each measured position.
- A fundamental tradeoff between absolute vs incremental is lower cost and simple speed feedback versus position available at startup.
- Common protocols include SSI, BiSS, quadrature, CANopen, fieldbus, and Ethernet-based serial feedback.
- Before ordering confirm shaft size, bore size, voltage, output, resolution, cable, connector, and desired controller input.
- Absolute vs incremental encoder: the short version
- How incremental encoders work
- How absolute encoders work
- Key differences that affect machine design
- Applications for each encoder type
- The Position Memory Matrix
- Procurement checks before you buy
- FAQ
- References and sources
Absolute vs Incremental Encoder: The Short Version
An incremental encoder measures change in position by sending pulses, signals, or interrupts as the measured shaft or linear position changes, which an intelligent motor controller then gathers and responds to during operation. When the controller has lost count of its pulses, most intelligent systems then need to initiate a homing or reference move to make the system reliable again.
An absolute encoder measures position with an electronic value or code. Each position measures with a different reading than the one before it. Therefore after power-up or power-fail, the system knows where it is and does not need to perform a homing move. That is why absolute encoders are often installed with CNC equipment or other machines that may take a long time to move to a homing or machine reference position again.
| Decision Factor | Incremental Encoder | Absolute Encoder | Why It Matters |
|---|---|---|---|
| Position after power loss | Usually must re-reference | Position value can be read at startup | Controls restart time and recovery risk |
| Output signal | Pulses, often A/B/Z | Digital position word or code | Must match the drive or PLC input |
| Cost tendency | Often lower | Often higher | Budget matters on simple axes |
| Best fit | Speed feedback and counting | Position-critical axes | Wrong fit can add commissioning work |
A quick rule of thumb is to use an absolute encoder on equipment that may require a long time to return to soft or hard reference position, and where knowing absolute position at power-up is critical to the task. Use the incremental encoder when you want good speed control, and seek to use the absolute position data only upon startup or during edge or home finding routines.
How Incremental Encoders Work: Working Principle, Pulses, and Reference Points
An incremental encoder measures change in position by sending a pulse each time the measured shaft or linear scale moves through a small step. Decoder logic translates those pulses into relative position, speed, and direction information about the measured object. In a rotary encoder, the number of pulses per revolution (PPR) abbreviation is often used.
Many types of incremental rotary encoders use a quadrature output mode. In a standard A/B output, the two channels are offset by 90 electrical degrees. In an optical encoder, those signals often come from light passing through a coded disk. Encoder output signals are then routed to the motor drive or PLC so that the direction of travel can be interpreted by phase relationship.
Many incremental encoders also add a third Z, index, or marker channel that can output one pulse per revolution. Once again this does not make the encoder absolute, but can provide a readily repeatable reference signal for programming during a reference, index, or homing routine. On a machine that can run to a safe switch or hard reference, this is often adequate.
The incremental change is what matters here. Incremental encoders generate movement data from the rotation of the shaft, and the controller turns that pulse stream into relative position. When power to the encoder or controller is interrupted, an incremental encoder will need a known reference before the position of the object can be trusted again.
A note on terms: Be cautious when comparing PPR and counts per revolution. Some PLCs count one offset edge per pulse, while others use x2 or x4 decoding modes, so that a 2500 PPR quadrature encoder can produce 10,000 counts per revolution signals, and that count is dependent on signal-to-noise and protocol used.
Incremental encoders are good for machines capable of rapid re-homing, machines that already have quadrature inputs available to the controller, or for axes not always requiring position feedback, only speed. They do require more care when the axis is hidden, vertical, prone to collision, or difficult to move safely after a stop.
How Absolute Rotary Encoders Work: Unique Codes, Single-Turn, and Multi-Turn Position
An absolute encoder outputs a position value, rather than only reporting motion. Instead of sending pulses that a controller must count from a starting point, it assigns a digital code or value to every measurable position. When the controller asks for position, it gets that value back and does not have to build it up from pulsed input.
Single-turn absolute encoders identify position within one revolution between 0 and 360 degrees. Multi-turn encoders record how many revolutions have passed. For a rotary table that only requires the accurate angle within 360 degrees, single-turn feedback may be sufficient. If a lift axis, ball screw, or robot joint needs the turn count as well as the angle, multi-turn feedback may be required.
Absolute encoders report absolute position information as a digital signal. Absolute encoders retain that value differently by design family, but the buyer's question is simple: can the controller determine the exact position before the machine moves?
Several interface families support absolute encoders. CAN in Automation's CiA 406 profile, for example, defines an application profile for absolute linear and rotary encoders and includes process data including position and velocity. BiSS, an open interface used in motion-control sensor and actuator systems, also supports absolute encoder applications.
Startup certainty is the practical value. With an absolute encoder, the machine can know the axis position even before motion is started, as long as the drive, controller, encoder, wiring, and parameter setup are all correct. One condition still applies: an absolute encoder is not a plug-in cure for every lost-position problem. Every part of the feedback chain needs to support the protocol and position format.
Absolute Encoders vs Incremental Encoders: Key Differences That Affect Machine Design
It's fine to understand the basic definitions, but a design choice is nearly always driven by the machine's behavior in a stop condition. Ask about things like power loss, E-stop, product jam, cable fault, or drive replacement. If the machine can readily re-home in seconds, incremental feedback may be acceptable. When movement before position recovery could cause tooling or scrap parts, absolute feedback deserves a thorough evaluation.
The difference between absolute and incremental feedback is often described as memory versus counting. The difference between incremental and absolute selection, though, is usually found in the restart sequence, controller input, and downtime tolerance. Those differences between the two encoder families are where the purchase decision becomes clearer.
| Difference | Incremental Encoder | Absolute Encoder | Selection Impact |
|---|---|---|---|
| Power-loss behavior | Position count may be lost | Position can be available at startup | Absolute is stronger when restart position matters |
| Reference point | Needs home switch, index pulse, or known start | Usually no homing move needed for position read | Incremental is fine if homing is safe and fast |
| Direction | Quadrature A/B phase relationship | Direction inferred from position change or drive data | Both can support bidirectional motion |
| Resolution language | PPR, CPR, or counts after decoding | Bits, positions per turn, or digital value length | Do not compare raw numbers without units |
| Controller input | High-speed counter or encoder input | Serial, fieldbus, or drive feedback interface | Protocol support can decide the project |
| Wiring | Often simpler, but pulse signals can be noise-sensitive | May need shielded digital interface wiring | Check cable length and electrical environment |
| Commissioning | Homing logic must be tested | Protocol, scaling, and zero offset must be set | Both need setup, just in different places |
| Maintenance | Easier to replace in many simple systems | May require parameter backup and drive matching | Document part number and controller settings |
| Typical cost | Often lower | Often higher | Compare cost against downtime and scrap risk |
Incremental and Absolute Encoders: Applications Where Each Type Usually Wins
Incremental encoders generally apply to machines where the main function is pulse counting, speed feedback, or simple position tracking from a known start. Machines of this type include conveyors, roll-feed lines, inexpensive relays/Timers rack systems, simple machine-vision indexers, motor speed feedback, and retrofits with value-based redesigns. For a conveyor that can jog to a sensor and re-establish the track without damaging product, incremental feedback is likely appropriate.
Incremental rotary encoders and incremental optical encoders are widely used in motion control applications where speed and direction matter more than saved absolute position. A capacitive encoder or magnetic encoder may be considered when dust, oil, vibration, or packaging constraints make optical sensing less attractive.
Position-critical axes tend toward absolute encoders. Axis position needs to be known during machine power-up in robot joints, multi-axis machines, tool changers, lift axes, packaging changeover systems, and servo axes inside guarded cells. A small difference in encoder price can be dwarfed by a long re-homing sequence, tooling crash, or wasted batch of parts.
Absolute encoders are available as single-turn and multi-turn encoders, and absolute rotary encoders can be used where many rotations must be tracked. The advantages and disadvantages of absolute feedback should be judged against the machine's downtime cost, not only against the encoder line item.
Robotics is one reason this option continues to become more prominent. According to the International Federation of Robotics, 542,000 industrial robots were installed in 2024 and 4,664,000 industrial robots were in operational use worldwide. IFR predicts 575,000 installations in 2025 and more than 700,000 by 2028. As factories add more robot and servo axes, position memory becomes a larger part of uptime planning.
The 10-Row Position Memory Matrix: Choose the Right Encoder Type
Consult the Position Memory Matrix to determine if the machine requires position memory or movement feedback. Scan through each row, viewing from the axis side, not the encoder side.
| Machine Condition | Usually Choose | Reason |
|---|---|---|
| Axis can safely re-home after every restart | Incremental | Reference recovery is acceptable |
| Axis must know position before any movement | Absolute | Position memory reduces unsafe startup moves |
| Job is only speed feedback | Incremental | Pulse frequency is often enough |
| Axis is vertical or can fall under load | Absolute | Startup position matters more than encoder price |
| PLC has only high-speed counter inputs | Incremental or controller upgrade | Absolute protocol support may be missing |
| Servo drive already supports BiSS, SSI, or CANopen encoder feedback | Absolute | Integration path is already available |
| Environment has long cable runs and electrical noise | Evaluate both | Signal driver, shielding, and protocol matter |
| Downtime costs more than the feedback device | Absolute | Faster recovery can outweigh purchase cost |
| Replacement must match an old machine with fixed wiring | Match existing type | Compatibility beats theoretical improvement |
| Buyer is comparing surplus or refurbished options | Verify exact part data first | Similar encoder names can hide different outputs |
Pro Tip: Don't begin with "absolute is better" or "incremental is cheaper." Begin with the restart sequence. When a machine cannot move safely until it knows exactly where it is, the choice moves closer to absolute feedback.
Cost, Integration, and Procurement Checks Before You Buy
Even the better encoder type becomes the wrong part if the mechanical and electrical details do not match. Procurement teams should save the full nameplate and application data before asking for a quote or buying a replacement.
- Mechanical fit includes shaft diameter, hollow-bore diameter, flange and mounting hole pattern and dimensions, available space, and coupling.
- Electrical fit includes supply voltage, output signal, current draw, cable length, connector type, and shielding needs.
- Resolution should be confirmed as PPR, CPR, counts after decoding, bits, positions per turn and multi-turn data.
- Protocol should be compatible with quadrature, SSI, BiSS, CANopen, EtherCAT feedback from the drive or other interface specific to the controller.
- Environment checks include IP rating, temperature range, oil, dust, vibration, washdown, and electrical noise.
- Controller setup consists of: scaling, zero offset, homing routine, direction, diagnostic bits, parameter backup.
- Source condition should state whether the part is new, surplus, pre-owned, or refurbished, plus the warranty and return terms.
iTrustbot sources industrial automation hardware such as PLCs, servo systems, sensors, control cards, and encoders through independent channels. In this article, the provided encoder collection URL returned 404, so no product or collection link is included. For replacement sourcing help, use the iTrustbot quote process from the store navigation rather than an outdated collection URL.
Encoder Selection Trends for 2026
Networked servo and robotics systems are increasing the use of absolute encoder interfaces, but incremental encoders are not disappearing. Increasing robotic and multi-axis automation deployment increases the benefit of position data during startup, diagnostics and fast recovery. In parallel, simple speed loops and counting applications still benefit from the lower cost and wiring simplicity of incremental feedback.
For buyers, the clearest trend is to confirm controller support early. BiSS, SSI, CANopen, or fieldbus encoder feedback can be a strong technical fit only when the drive and PLC can read, scale, and diagnose that signal. Without that support, the project may need a drive card, gateway, or a different encoder type.
Encoder Terminology Checklist for Comparing Absolute and Incremental Encoders
Terminology causes many bad encoder purchases. Use this checklist when comparing absolute encoder vs incremental encoder options, especially when datasheets mix PPR, bits, output type, and sensing technology in the same table.
| Term to Check | What It Means in Selection |
|---|---|
| Incremental encoder is an electromechanical device | This phrase normally means the encoder converts mechanical motion into pulse feedback for a controller. |
| Encoder is an electromechanical device | Both incremental and absolute encoders turn mechanical motion into electrical position or speed information. |
| Incremental encoders measure change in position | The controller still needs a reference if the application requires stored absolute position. |
| Absolute encoders report a digital signal | The drive must support the protocol and scaling, not just the mechanical encoder body. |
| Incremental encoders and absolute encoders | Compare them as feedback systems, including wiring, controller card, homing sequence, and maintenance plan. |
| Incremental encoders can also provide information | They can provide speed, direction, and relative position when the controller count is valid. |
| Encoders provide position of the shaft | Check whether the datasheet means shaft angle, linear travel, relative movement, or saved position after power loss. |
| Produce an output signal | Match that signal to the receiving input: high-speed counter, drive feedback port, fieldbus card, or serial interface. |
| Encoder components | Disk, sensor, bearings, housing, connector, and electronics all affect service life and replacement fit. |
| Optical absolute, magnetic, or capacitive encoder | Sensing technology can matter when oil, dust, vibration, or installation space is the real constraint. |
| Like an incremental encoder | If a device only outputs pulses and loses reference after shutdown, treat it as incremental in the machine sequence. |
| Encoders can use Synchronous Serial Interface | SSI-style feedback may fit older drives, while BiSS or CANopen may fit newer motion control architectures. |
FAQ
Q: What is the difference between an absolute and an incremental encoder?
An incremental encoder reports movement as pulses, and controller logic counts those pulses to track relative position. An absolute encoder reports a unique position value, so the controller can read exact position directly. In practical terms, the difference is whether the machine must re-home after power loss or can know position at startup.
Q: What are the disadvantages of absolute encoders?
Typical absolute encoder negatives are higher cost, protocol support, and setup time. They may also be harder to troubleshoot or replace when the original drive parameters, zero position, or communication defaults were not recorded.
Q: What are the 4 types of encoders?
A common grouping is incremental rotary, absolute rotary, incremental linear, and absolute linear encoders. Another common grouping is optical, magnetic, capacitive, and inductive sensing technologies. When purchasing, clarify both the measurement format and sensing technology.
Q: Do incremental encoders lose position after power loss?
Controller logic may lose the counted position even if the hardware remains mechanically intact after power is removed. Many incremental systems use a home switch, index pulse, or predetermined startup sequence to reconstruct position after power returns.
Q: Is an absolute encoder always more accurate than an incremental encoder?
No. Position reporting format is not the whole accuracy story. Accuracy relies upon sensor design, mechanical mounting, resolution, signal quality, controller decoding, and calibration.
Q: Can rotary and linear encoders both be absolute or incremental?
Yes. Rotary encoders measure shaft angle or rotation. Linear encoders measure linear travel distance. Both formats are selectable as absolute or incremental depending on how they report position information.
Q: Which encoder type is better for a servo motor?
It depends on the servo drive, application risk, and startup behavior. Many speed and position loops function fine using incremental encoders. Drive-supported absolute encoders are often chosen when the axis must recover position without a homing move.
About This Encoder Comparison
This article compares absolute encoder and incremental encoder selection for industrial automation buyers rather than hobby motion projects. Decision factors are manufacturer-neutral and tied to visible interface references, so readers can move toward a safer replacement or quote request.
References & Sources
- CiA 406: Encoder profile - CAN in Automation
- BiSS - The High Performance Interface - BiSS Association e.V.
- World Robotics 2025 report - Industrial Robots - International Federation of Robotics
