Encoder Selection Guide

Encoder Selection Guide

Encoder selection is a comprehensive decision-making process that integrates three core dimensions: mechanical structure, control requirements, and environmental conditions. Improper selection may result in insufficient positioning accuracy, equipment failure, or cost waste. Below is a complete selection guide covering core parameters to practical scenarios, designed to help accurately match your needs.

I. Clarify Core Needs First: What Problem Do You Need the Encoder to Solve?

Before selection, you need to define the core objectives of the application scenario to avoid blindly pursuing high parameters. Common application scenarios and key focus points are listed below:

Application Scenario	Core Requirement	Key Selection Parameters
Motor speed/rotation direction monitoring	Real-time speed feedback and direction identification	Resolution (number of pulses), output signal type
Robotic arm joint positioning	High-precision position control and multi-turn memory	Resolution (high bit count), multi-turn technology
Conveyor line displacement measurement	Linear distance conversion and anti-interference	Resolution (number of lines), protection level
Servo system closed-loop control	High-speed response and low latency	Signal frequency, output interface (e.g., HTL/TTL)
Harsh environments (dust/oil contamination)	Equipment durability and damage prevention	Protection level (IP), installation method

II. Core Parameter Selection: 6 Key Indicators Determining Encoder Performance

Type Selection: Incremental vs. Absolute (The Most Basic Decision)

The core difference between the two lies in whether they can 'memorize position'. This should be determined based on whether position information needs to be retained after a power outage.

Comparison Dimension	Incremental Encoder	Absolute Encoder
Working Principle	Outputs continuous pulses, and position/speed is derived through counting	Each position corresponds to a unique 'code value', and the position is output directly
Power-off Memory	None (the count resets after a power outage, requiring re-zeroing)	Yes (a built-in memory chip retains the position after a power outage)
Accuracy and Resolution	Depends on counting accuracy, making it suitable for medium and low-precision scenarios	Higher resolution (typically 13-25 bits), making it suitable for high-precision applications
Cost	Low (simple structure)	High (complex chips and algorithms are required)
Typical Applications	Motor speed monitoring, conveyor line speed control	Robotic arms, CNC machine tools, elevator positioning

Selection Suggestions:- If only 'speed/relative displacement' is needed (e.g., fan speed, conveyor belt speed) → Choose an incremental type;
- If 'absolute position' is required (e.g., robotic arm joints, machine tool coordinates) or re-zeroing after a power outage is not feasible → Choose an absolute type.

2. Resolution: Core Indicator Determining 'Positioning Accuracy'

Resolution refers to the number of 'minimum units' output by the encoder per full rotation, and its expression varies by type:

Incremental type: Expressed as 'Pulses Per Revolution (PPR)' or 'Lines Per Revolution (LPR)' (e.g., 1000 PPR = 1000 pulses output per revolution). Note: If A/B phase quadrature signals are used, accuracy can be improved through '4x frequency multiplication' (1000 PPR → 4000 counts per revolution).
Absolute type: Expressed as 'Bits' (e.g., 16 bits = 2¹⁶ = 65536 unique positions per revolution). If 'multi-turn positioning' is required (e.g., the motor remains accurate after rotating 100 turns), a 'multi-turn absolute encoder' is necessary. The multi-turn bit count is typically 12-20 bits (e.g., 16-bit single-turn + 12-bit multi-turn = a maximum of 4096 turns × 65536 positions per turn).

Selection Formula:Required Resolution = 1 / Maximum Allowable Positioning Error (radian/angle)
Example: If the allowable error ≤ 0.18° (i.e., the maximum error per revolution is 0.18°), the resolution must be ≥ 360° / 0.18° = 2000 PPR (incremental type) or ≥ 11 bits (2¹¹ = 2048, absolute type).

3. Output Signal and Interface: Matching the Controller (PLC/Microcontroller/Driver)

The output signal of the encoder must be compatible with the interface of the backend control equipment. Common types are as follows:

Signal Type	Interface Form	Characteristics and Application Scenarios
Voltage Signal (HTL/TTL)	Differential Signals (A/A-, B/B-, Z/Z-)	Strong anti-interference capability (transmission distance ≤ 100m), suitable for industrial sites (e.g., servo drivers, PLCs)
Open Collector (OC)	Single-ended Signals (A, B, Z)	Requires an external pull-up resistor, weak anti-interference capability (≤ 10m), suitable for short-distance control (e.g., microcontrollers)
Serial Communication	RS485 (Modbus-RTU), SSI, EtherCAT	Long transmission distance (RS485 ≤ 1200m), capable of transmitting multi-turn data, suitable for multi-device networking (e.g., large production lines)
Parallel Communication	Multi-bit Parallel Lines (e.g., 16 bits)	High speed but complex wiring (a large number of lines), suitable for short-distance high-precision scenarios (e.g., CNC machine tools)

Selection Notes:- If there are strong interference devices such as frequency converters and motors on-site → Prioritize differential signals (HTL/TTL) to avoid counting errors caused by signal interference;
- If remote monitoring is required (e.g., the control room is more than 100 meters away from the equipment) → Choose RS485 or EtherCAT serial interfaces.

4. Mechanical Installation: Matching Shaft Diameter, Connection Method and Space

Improper mechanical installation will cause encoder wear and reduced accuracy. Pay attention to the following 3 key parameters:

Shaft Diameter: The encoder shaft diameter must match the motor/load shaft diameter. Common specifications are 6mm, 8mm, 10mm, and 12mm (e.g., if the motor shaft diameter is 8mm → select an encoder with an 8mm shaft diameter); if the shaft diameters do not match, a coupling (an elastic coupling is preferred to avoid radial/axial deviation) is required.
Connection Method:- Sleeve Type (Hollow Shaft): Fits directly on the load shaft without a coupling, saving space (suitable for small-volume equipment); - Shaft Extension Type (Solid Shaft): Connected to the load shaft via a coupling, ensuring coaxiality (radial deviation ≤ 0.1mm, axial deviation ≤ 0.5mm).
Installation Space: Select the 'outer diameter' (e.g., 38mm, 58mm, 80mm) based on the internal dimensions of the equipment. For small equipment (e.g., UAV motors), choose micro encoders smaller than 25mm.

5. Environmental Adaptability: Coping with Harsh Conditions Such as Temperature, Dust and Humidity

Environmental parameters directly determine the service life of the encoder. Focus on the following core indicators:

Protection Level (IP Code):- IP54: Dust-proof (cannot completely prevent dust ingress but does not affect normal operation), splash-proof (suitable for dry workshops); - IP65: Fully dust-proof and water-jet resistant (suitable for outdoor or dusty scenarios, such as mining machinery); - IP67: Fully dust-proof and resistant to short-term water immersion (suitable for humid or occasionally waterlogged scenarios, such as cleaning equipment); - IP68: Fully dust-proof and resistant to long-term water immersion (suitable for underwater equipment, such as underwater robots).
Operating Temperature:- Standard Type: -10℃ ~ 60℃ (indoor equipment); - Wide-Temperature Type: -40℃ ~ 85℃ (outdoor, high-temperature equipment, such as metallurgical machinery and automobile engines).
Anti-Vibration/Shock:- Vibration: Standard ≤ 500Hz/20G, Industrial Grade ≤ 1000Hz/50G (e.g., motors, machine tools); - Shock: Standard ≤ 100G (0.1ms), Industrial Grade ≤ 500G (0.1ms) (e.g., construction machinery, transportation equipment).

6. Other Key Parameters

Maximum Rotational Speed: The maximum rotational speed allowed by the encoder (e.g., 6000rpm, 10000rpm) must be ≥ the maximum rotational speed in practical applications (e.g., if the motor rated speed is 3000rpm → select an encoder with a maximum speed ≥ 3000rpm).
Power Supply Voltage: Common values are 12V ~ 24V DC (industrial equipment) and 5V DC (microcontrollers), which must be consistent with the power supply of the control equipment.
Output Phase Difference: The phase difference of A/B phase quadrature signals is 90°, which is used to determine the direction of rotation (A phase leads B phase → forward rotation; vice versa → reverse rotation). All incremental and absolute encoders support this function, so no additional selection is required.

III. Summary of Selection Process: 5 Steps to Quick Matching

Define the Scenario: Clarify whether the requirement is for 'speed monitoring', 'absolute positioning', or 'relative displacement' → Select an incremental or absolute type;
Calculate Accuracy: Calculate the required resolution (PPR/Bit) based on the allowable error;
Match the Interface: Select the output signal (e.g., HTL/RS485) based on the controller (PLC/driver);
Fit the Mechanics: Confirm the shaft diameter, installation method, and space dimensions;
Adapt to the Environment: Select the protection level and operating temperature range based on temperature, dust, and vibration conditions.

IV. Common Selection Mistakes

Blindly Pursuing High Resolution: Excessively high resolution will result in an excessively high signal frequency (e.g., an encoder with 10000 PPR operating at 1000rpm has a signal frequency = 10000 × 1000 / 60 ≈ 166kHz). If the controller processing speed is insufficient, it will cause 'pulse loss', which will instead reduce accuracy.
Ignoring the Protection Level: Selecting IP54 in a dusty/oily environment will cause internal dust ingress, reducing the encoder's service life from more than 5 years to less than 1 year.
Interface Incompatibility: Selecting an encoder with an RS485 interface when the controller only has a TTL interface requires an additional signal converter, increasing costs and potential failure points.

Through the above steps, the selection goal of 'performance matching, optimal cost, and longest service life' for the encoder can be achieved. For further precise selection, you can provide specific application scenarios (e.g., 'servo motor positioning, allowable error 0.1°, controller is a Siemens PLC, ambient temperature -20~50℃') to further narrow down the selection range.