Differences between Absolute and Incremental Encoders

Rotary encoders monitor the movement of shafts by outputting pulses when connected. As the shaft rotates, a rotary encoder registers the speed and position of a machine. The mechanical angular position of an axle or shaft transforms into an electronic signal that a control system can process. Encoders are used in various industries, including automotive, chemical food & beverage, packaging, and material handling where precise angular monitoring in necessary. The form factor, resolution and level of ruggedness of a rotary encoder have to be specified for the intended application to enhance the effectiveness of the device. Optical encoders are the most popular designs and feature code discs, light detectors, signals, processors and LED light sources. The calibrated disc and light emitting diode are responsible for generating pulses- as the disc rotates; it gets between the LED and detector, consequently interrupting a light beam. A series of light exposures are formed with each rotation, which the detector tracks and sends the data to the processor. Rotary encoders are available in two examples - the incremental and absolute. Understanding the distinction between these two encoders makes it easy to find the most appropriate one for an intended task. Incremental Rotary Encoders These encoders use two channels, which are out of phase by 90 degrees to generate square wave signals. For every increment of shaft position, there is a one square wave cycle, and this output measures the position. An incremental encoder has the code disc attached to a power transmission shaft while a pickup device is mounted nearby. The pickup device is responsible for monitoring the relative position when the disc turns. Resolution is measured by the number of signals that each turn generates. Another thing about incremental rotary encoders is that, regardless of the location of the shaft radially, the device starts counting from zero when it is powered up. This event happens even when there is power interruption. It is why backup power is recommended to avoid re-homing the device each time the supply is cut off. Incremental rotary encoders are simple to operate, making them suitable for uncomplicated pulse counting and frequency monitoring. Their functioning makes them ideal for direction, position and speed monitoring. Incremental encoders are also very cost-efficient due to their magnetic technology, which results in compact, robust and angular sensing. Absolute Rotary Encoders These types of encoders are designed for more complex or longer positioning tasks compared to incremental. They also have the encoder disc, power transmission and pickup device set up. However, each shaft position triggers a unique code pattern that the encoder disc generates. An absolute encoder can be either single turn where the encoder shaft only turns once to verify position or multi-turn where it takes several turns. Multi-turn encoders are the ones that cater to complex industrial applications while single turns are useful in short travel situations. The output from an absolute encoder can be high or low, depending on the disc pattern of that particular position. An absolute encoder has a resolution of up to 16 bit and can operate on multiple interfaces, including analogue, Fieldbus, Ethernet Serial and Parallel. Absolute encoders not only tell the exact position but also store that information because they have a non-volatile memory. It means that even when power fails, the encoder doesn’t lose track of positioning. In industrial settings where safety is a big concern, absolute encoders are the preferred choices because of their continuous monitoring when there is a power failure and also for their ability to operate point to point. The disadvantage of absolute encoders is that they are quite expensive, though the price has gone down over the years as they become necessary. Manufacturing and production processes have come to rely on encoders for precise positioning. The individual requirements of a machine will determine whether to use absolute or incremental encoders.

For more information on Differences between Absolute and Incremental Encoders talk to Greenbank Machinery Plant Ltd