Guest contributor: Chris Heberlein, Balluff
Hydraulic actuators can be used to open and close a valve’s position. In automation architectures, a linear position sensor is used within the hydraulic actuator to provide continuous position feedback.
The linear position sensor is installed into the back end of the cylinder. The sensing element resides in a cavity that has been gun-drilled through the piston and cylinder rod, extending the full length of the mechanical stroke. A magnet ring is used as a position marker and mounted on the face of the piston. As the piston (and the position marker) move, the linear position sensor provides a continuous absolute position by way of an analog or digital signal.
In some applications, a cylinder’s position may only be moving across a small portion of the overall stroke or a specific portion of the stroke. The end user could benefit from altering the transducer’s signal based on the application’s specific stroke requirements instead of the entire cylinder’s stroke, thereby maximizing available position resolution. When this situation arises, most transducer manufacturers offer the ability to customize or “teach” a modified output of the stroke via push buttons or from wiring inputs. When this is done, the process does require the cylinder (and position marker) to move to these defined locations for a “teach”.
A more user-friendly and repeatable approach for customized stroke lengths with linear position sensors is to use a graphical software package. The software can be connected
from a PC via USB to a compatible linear position sensor. Starting and ending stroke values can be precisely entered into the software and a graphical representation of the output curve is created. For a more straightforward approach, you can also drag and drop these stroke points by a click of a cursor. The file can be saved on a PC and downloaded to the transducer. In either case, the cylinder’s piston doesn’t need to be actuated.
In projects where multiple, identical actuators and linear position sensors need to be customized, the setup would only need to be done once, the file saved, and simply uploaded to all the sensors for the project. A great time-saver over manually teaching each and every sensor.
Another benefit to using software with linear position sensors is to be able to upload programs for replacement units in a safe user environment (e.g. lab station or office) and shipping them to various job sites. These different locations (or locales) can be in harsh environmental conditions (extreme cold or heat) or areas that contain ignitable or explosive gases or dusts which may be difficult to work in.
Other software features include inverting the output curves, offering position or velocity outputs, and more.
For more information on Balluff’s Magnetostrictive Linear Position Sensors, visit www.balluff.com.
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