Feature: Industrial
Figure 1: Requirements for accuracy, flexibility and durability will determine whether contact (left) or non- contact potentiometers (right) are a better fit for a given application
M
Improving linear actuator design flexibility with non-contact position sensing
By Thomson Industries’s field application engineers
any linear motion applications that use rod- style electric actuators require information on the position of the load at every point of travel, but because stroke lengths and applications vary so widely, finding the ideal position feedback solution can be
challenging. One of the most common methods for determining where the
actuator is in its stroke uses potentiometers, also called pots, to track changes in electrical resistance or related voltage drops as the actuator extends and retracts. To function as position-recording devices, potentiometers must
maintain an electrical connection to the actuator power circuit. Designers can accomplish this using contact or non-contact potentiometer architectures. Contact-based position measurement has been the simplest and most economical approach, but is limited in resolution, design flexibility and durability. Non- contact architectures overcome many of those drawbacks but have traditionally been too expensive to justify for many mainstream applications. Today, however, the market for non-contact potentiometers
has matured, and prices have dropped. Te benefits of non- contact position measurement are available for a broader range of applications. Understanding the advantages of non-contact potentiometers will help motion system designers determine the most effective way to meet application requirements.
Potentiometer basics Feedback voltage from a potentiometer typically changes from 0.5- 4.5Vdc as the actuator extends. Potentiometers are generally rated in ohms across their entire range and on the shaſt’s number of turns (revolutions) from zero to full coverage. Te most common units are 10k (ohms) 10 turns. As the actuator screw extends or retracts, there is a discrete step
change in resistance, which can be converted into linear position measures. Te more turns the potentiometer takes before it reaches its full resistance range at the end of the stroke, the more precise the position measurement capability it can deliver. A contact-based potentiometer reads these voltage changes by gliding its wiper across wire-round resistance coils, counting
34 March 2024
www.electronicsworld.co.uk
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