Position-sensing hydraulic cylinder

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

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Internal LDT

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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]

 
Hydraulic cylinder with a Hall effect sensor mounted along its barrel to sense position of a magnetic piston inside. The sensor is mounted without having to gun drill the piston rod, yet its size and location protect it from potential environmental damage.

External LDT

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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.

References

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  1. ^ Herceg, Edward. "Position Sensor Technology Comparison for Hydraulic Cylinder Feedback" (PDF). Archived (PDF) from the original on 2024-04-25. Retrieved 2024-04-25.
  2. ^ Hydraulics & Pneumatics Magazine Archived 2011-07-18 at the Wayback Machine
  3. ^ Journal, Fluid Power (2019-01-10). "Strong, Tough, and Reliable: Linear Displacement Transducers Take on the Most-Demanding Applications". Fluid Power Journal. Retrieved 2024-04-25.
  4. ^ "Electronic Position-Sensing Hydraulic Cylinders.(Energy Manufacturing Company Inc introduces cylinders having electronic position-sensing option)(Brief article) - Design News - HighBeam Research". 2012-10-23. Archived from the original on 2012-10-23. Retrieved 2023-12-09.
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