Position-sensing hydraulic cylinder

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 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.