February 2021

38 n SENSORS AND ENCODERS February 2021 www.drivesncon trols.com Making sense of encoders T o ensure that a precise volume of insulin is delivered with each pump of a medical infusion device, or that a robot arm used in manufacturing assembly moves to a precise point at the right time, you usually require an electric motor combined with an encoder. Rotary or shaft encoders provide information on the position, count, speed and direction of a motor, and are typically connected to a controlling device, such as a PLC. The PLC uses feedback from the encoder to control the motor precisely. There are two main types of encoder: n Incremental encoders provide real-time feedback and track changes in position and direction, rather than referencing a specific point. They do this by providing feedback on the relative movement between positions with continuous high and low pulses. n Absolute encoders report exact positions, but their increased complexity makes them more expensive. For most applications, incremental encoders are more cost-effective. Adding a suitable interface can give incremental encoders the ability to provide exact position references. Optical or magnetic? Encoders usually operate on optical or magnetic principles. Optical encoders pass infrared light emitted by an LED through a metal code wheel, which has alternating clear and opaque segments. These create distinct light signals that are picked up by optoelectronic sensors. Optical encoders can achieve precise positioning, and their performance is not affected by magnetic interference. Magnetic encoders comprise a magnetised disc with many poles around its circumference. As the disc rotates, sensors such as Hall effect devices, detect the changes in magnetic field. Such encoders – Portescap’s MR2, for example – are ideal for demanding applications that could be subject to possible impact or ingress. They Encoders provide speed and positioning feedback that allows accurate control of motors. Chris Schaefer, an applications engineer at Portescap, examines the technologies involved and explains how to choose the best encoder for your application. Encoders can ensure that drug delivery systems dispense precise amounts of medication at specified rates and that the exact dose is delivered.