Technical Support

An inductive encoder is a non-contact, high-precision position sensor based on the principle of electromagnetic induction. It measures angle or displacement by detecting changes in the magnetic field between the stator and rotor. It features high accuracy, high resolution, resistance to dust and oil, and strong anti-interference capabilities, and is widely used in industrial automation, robot joints, automotive manufacturing, and medical equipment.

I. Inductive encoders typically consist of two main parts:

① Stator (stationary part): Contains one or more excitation coils (transmitting signals) and receiving coils (receiving signals).

② Rotor (moving part): Usually a metal (such as copper or aluminum) disc or ruler with special tooth or slot shapes, called an inductive scale.

II. Its working process can be summarized in three steps:

① Excitation (transmitting): High-frequency alternating current is passed through the excitation coil on the stator, generating a high-frequency alternating magnetic field.

② Modulation (induction): When the metal teeth or slots on the rotor/moving coil pass through this magnetic field, eddy currents are generated in the metal, like a transformer. These eddy currents, in turn, change the original magnetic field distribution, thereby modulating (changing) the signal induced by the receiving coil.

③Decoding (Reception): The receiving coil on the stator receives the modulated signal. The amplitude and phase of the signal change regularly with minute changes in the rotor/moving position.

Through complex electronic circuits to process and decode these signals, the current position can be accurately determined, and a digital signal (such as an absolute position value) or a pulse signal (used for incremental counting) can be output.

I. Superior Anti-interference Capability:

Photoelectric encoders are susceptible to environmental contamination such as dust and oil, while magnetic encoders are highly sensitive to stray magnetic fields generated by motors. Inductive encoders, operating on the principle of electromagnetic induction, are naturally insensitive to magnetic field interference, making them ideal for compact joint spaces with strong motor magnetic fields.

II. Superior Mechanical Robustness and Vibration/Shock Resistance:

The sensing component (rotor) is typically made of simple ferromagnetic materials or a substrate with layers or patterns of conductive materials such as copper, without the fragile glass grating disk. The air gap requirement between the stator and rotor is less stringent than that of optical encoders.

III. Wide Temperature Adaptability:

The performance of the LED light source and photodetector in optical encoders is significantly affected by temperature; accuracy and stability decrease at extreme temperatures. In contrast, the core of an inductive encoder is copper wire and magnetic materials, allowing for a typically wide operating temperature range (e.g., -40°C to +125°C).

I. For rotary encoders: Resolution is usually expressed as the number of pulses per revolution or the number of positions per revolution.

① Incremental encoders: Commonly represented by PPR. For example, a 2500 PPR encoder generates 2500 electrical pulses per revolution. Therefore, its minimum angular resolution is 360° / 2500 = 0.144°.

② Absolute encoders: Commonly represented by bit depth. For example, a 16-bit single-turn absolute encoder can generate 2^16 = 65,536 unique position codes per revolution. Its minimum angular resolution is 360° / 65,536 ≈ 0.0055°.

II. Note the difference between "resolution" and "accuracy":

① Resolution: The smallest change that the encoder can "report". (How "fine"?)

② Accuracy: The error between the encoder's "reported position" and the "actual physical position". (How "accurate"?)

III. When selecting an encoder, resolution is a parameter that needs to be carefully considered:

① Higher is not always better: Excessively high resolution means higher costs and generates a huge amount of data, placing higher demands on subsequent signal processing circuits and controller communication bandwidth.

② Matching principle: The choice of resolution should match your final accuracy requirements, the accuracy of the mechanical transmission system (such as the lead screw pitch), and the processing capacity of the control system. A rule of thumb is that the encoder resolution should be 5 to 10 times higher than the positioning accuracy required by the system to ensure that the controller has sufficient data for smooth and precise control.

I. Incremental Encoder:

Relative positioning, no fixed position encoding, only outputs A/B quadrature pulses + Z zero-position pulse. Position/velocity detection is achieved by the controller counting/distinguishing the pulses. Current position information is lost after power failure; recalibration to zero is required upon restart.

II. Absolute Encoder:

Absolute positioning, each physical position corresponds to a unique digital code (binary/Gray code). The position value is directly output. The current position is permanently remembered after power failure; recalibration to zero is not required upon restart; the current position can be directly read.

I. Core Definition of Linearity Accuracy:

Linearity accuracy refers to the maximum deviation between the actual position value detected by the encoder and the theoretical linear position value. It reflects the degree to which the position detection result of an absolute encoder closely matches the "ideal linear scale" across the entire range. It is a core indicator for measuring the positioning accuracy of an absolute encoder (lack of linearity indicates non-linear deviation in position detection, leading to inaccurate positioning).

II. Core Definition of Pulse Accuracy:

Pulse accuracy refers to the consistency and accuracy of the A/B quadrature pulses output by the encoder in terms of waveform, phase, spacing, and duty cycle. It reflects the "quality" of the pulse output of an incremental encoder and is a core indicator for measuring the reliability of pulse counting in an incremental encoder (poor pulse accuracy can lead to controller counting errors and speed regulation jitter).