36 n SENSORS AND ENCODERS February 2026 www.drivesncontrols.com Linear, rotary or sine encoders: how do you choose? The most common type of industrial feedback device for position and speed sensing is the encoder. These devices are typically selected following, and in addition to, a motor being specified. The variety of encoder designs available means that careful attention is needed in their selection, and the initial factor is their physical measurements. Rotary encoders measure the angular rotation of a motor’s rotor or shaft. They lend themselves to closed-loop control of rotary applications. To achieve this, the sensor signals are converted into digital pulses or sine/cosine waveforms, which the drive or controller interprets to manage speed and position. In applications that involve a straight line of operation – such as a CNC machines or three-axis gantries – a linear encoder may be preferable. These encoders measure true linear position directly, while rotary encoders interpret linear travel by converting shaft rotation. Factors such as mechanical compliance or backlash can affect rotary encoder readings. For straight-line applications that demand the highest-speed operation, or precision down to resolutions of 0.1μm or less, a linear encoder is preferable. Magnetic and optical encoders The main ways an encoder can read changes in speed or position is using magnetic or optical technologies. Magnetic encoders detect changes in a magnetic field according to rotational or linear motion, with the variations converted into signals that provide position and speed information. The presence of dust or moisture doesn’t interfere with these measurements, so magnetic encoders are suitable for use in adverse environments. Optical encoders comprise a light source, a rotating code disc or linear scale divided into lines, and a light detector. They achieve greater precision than magnetic devices because the light sensors can detect higher count numbers than magnetic field changes, which are limited by pole spacing. Optical encoders are also immune from high-noise or electromagnetic interference that could interfere with clean signals and distort data transmission. While modern optical encoders offer better-protected electronics and optics, improving their resilience for lighter applications, magnetic designs, or resolvers, are often better suited to demanding environments. The disc or linear scale in an optical encoder is divided into a number of lines that signify the encoder’s resolution. As the count increases, the accuracy within a specific number of counts increases as well. As the disc in a rotary encoder rotates, the light detector registers the on-off pattern of light passing through it, which a photodiode detector converts into a digital signal. The disc contains two rows of lines, offset by half their width, or a quarter of a complete cycle (90 electrical degrees). This generates two electrical signals known as Channel A and B. The offset enables the drive or controller to determine the direction of the shaft rotation. Additional channels can help to track shaft position and homing, as well as improving noise immunity. This is the operating principle of incremental encoders, which provide positional information relative to their starting points. An incremental encoder’s resolution can be multiplied by four if the counting circuit monitors both the rising and falling edges of Channels A and B – a process known as quadrature detection. Higher resolution improves repeatability and enables faster, higher accuracy control loops. Encoder resolutions of up to 5,000 lines per revolution are standard, although line counts of up to 100,000 are available. When an incremental encoder’s Channels A and B of are output as square waves, the drive or controller reads the edges directly. It’s possible to read these signals as sine waves, enabling much finer gradations of measurement. This increases resolution and reduces truncation errors, resulting in higher loop gains. Sine encoders can achieve more than two million counts per revolution. Thanks to this capability, sine encoders are aimed at applications that demand the highest levels of precision, ranging from high-speed registration, to film coating and web control. These encoders also fit lowspeed operations that demand smooth motion control. Sine encoders can also be used when absolute, rather than relative position sensing, is needed. n Encoders are the most common feedback devices for controlling motors. With numerous technologies to choose from, selecting the right encoder is critical. Gerard Bush, engineering advisor at motion specialist Inmoco, offers some advice. Sine encoders are aimed at applications that demand the highest levels of precision, such as web control
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