Position-sensing hydraulic cylinder explained
A position-sensing hydraulic cylinder is a hydraulic cylinder with an integrated position feedback sensor to determine its current position.
Position-sensing hydraulic cylinders may be found in heavy industry, subsea, and mobile heavy equipment applications.[1]
Linear Displacement Transducers
Internal LDT
With In-cylinder Linear Displacement Transducers (LDTs), the hydraulic cylinder’s piston rod must be bored through its center to accommodate certain elements of the LDT — usually the waveguide tube of a magnetostrictive transducer.[2] The machining and additional production steps associated with “gun drilling” the piston rod can add cost to the finished cylinder. Magnetostrictive LDTs provide extremely high accuracy, down to one micron.[3]
External LDT
External linear displacement transducers (LDTs) eliminate the need for a hollow hydraulic cylinder rod. Instead, an external sensing “bar” utilizing Hall-Effect technology senses the position of the hydraulic cylinder piston. This is accomplished by the placement of a permanent magnet within the piston.[4]
An external Linear Displacement Transducer (LDT) utilizes a magnet that generates a magnetic field, which passes through the steel wall of a hydraulic cylinder. This magnetic field provides a locating signal to an external sensor.
Advantages of external LDTs include:
- Preservation of Rod Strength: The full buckling strength of the rod is maintained.
- Ease of Maintenance: The cylinder design simplifies assembly, installation, and servicing.
- Versatility in Connectivity: There is a wide range of sensor inputs and outputs available.
- Accessibility: The external sensor is easily accessible and can be replaced if necessary without the need for recalibration.
- Durability: The small sensing bar is positioned along the exterior of the hydraulic cylinder, reducing the risk of environmental damage.
- Accuracy: The positioning accuracy is +/- 0.5 mm, which is sufficient for most mobile equipment applications.
External links
Notes and References
- Web site: Herceg . Edward . Position Sensor Technology Comparison for Hydraulic Cylinder Feedback . live . https://web.archive.org/web/20240425230515/https://cisp.cachefly.net/assets/articles/attachments/55123_position_sensor_technology_comparison_for_hydraulic_cylinder_feedback.pdf . 2024-04-25 . 2024-04-25.
- http://www.hydraulicspneumatics.com/Classes/Article/ArticleDraw.aspx?CID=84767&HBC=TechZone/Cylinders&OAS=&NIL=False Hydraulics & Pneumatics Magazine
- Web site: Journal . Fluid Power . 2019-01-10 . Strong, Tough, and Reliable: Linear Displacement Transducers Take on the Most-Demanding Applications . 2024-04-25 . Fluid Power Journal . en-US.
- Web site: 2012-10-23 . Electronic Position-Sensing Hydraulic Cylinders.(Energy Manufacturing Company Inc introduces cylinders having electronic position-sensing option)(Brief article) - Design News - HighBeam Research . 2023-12-09 . https://web.archive.org/web/20121023071523/http://www.highbeam.com/doc/1G1-149350858.html . 2012-10-23 .