Long Stroke Hydraulic Cylinders Part 2 – Replacing Failed Rod-Type Sensors.

Replace rod type magnetostrictive position sensor

Rod based magnetostrictive position sensors are historically one of the primary types of feedback sensors used on hydraulic or pneumatic cylinders where high accuracy was of primary concern.  The sensor (often called an “LDT” or “MLDT”) incorporates a stainless steel tubular probe (ie. “the Rod”) and is surrounded by a short toroidal magnet installed in a counterbore in the piston. Magnetostrictive sensors can consume a fair amount of power and are not the most mechanically rugged sensor technology.  They are subject to shock and vibration issues, and present challenges for installation and field replacement.

The CPI SL series picks up where traditional magnetostrictive sensors leave off.  The sensor technology is completely non-contacting, and is a drop-in replacement for existing rod-type sensors in long stroke applications. No core drilling of the piston rod is required at all. The video below documents just how easy it is to replace a rod type sensor in our applications. It can be done in essentially three steps:

  1. Unscrew the existing Rod Sensor from the sensor port and remove the rod.
  2. Insert our patented self locking cable connector using our special slotted hex wrench. The sensor port is typically 18mm or a #8 SAE O ring port.
  3. Fasten the high pressure hydraulic hose to the sensor port with a standard 7/8″ wrench.
  4. Done.

CPI’s LVDT based Linear Position Sensors

CPI’s hydraulic sensor solution is a game changer for position sensing in mobile hydraulics and long stroke piston accumulators.  Other advantages include:

  1. A completely non-contacting measurement technology.
  2. One part for all stroke lengths.
  3. Can be used in telescoping cylinders and piston accumulators.
  4. Field retrofittable for rod-type sensors with no modifications.
  5. Robust to shock & vibration where rod-type sensors do not survive.
  6. Will operate in high temperatures (300F) where rod-type sensors do not.

External Hydraulic Cylinder Position Sensor Mounting

To make the entire assembly work perfectly for external mount simply add an external Linear Position Sensor for Long Stroke Hydraulicscable guide.  With this addition the entire assembly works perfectly for typical mobile cylinder applications like a backhoe loader stick cylinder.  See the illustration.

These components also excel at sensing piston position in hydraulic piston accumulators and do not require extensive design modifications.  They can be mounted on either the gas or the oil side.

About CPI

CPI is a US based manufacturer of precision waterproof switches, electro-mechancial thermal switches and linear position sensors. Heavy duty materials and robust performance characterize all of CPI’s products. Custom designed and off the shelf products in each category satisfy the most demanding operational environments. Industries served include Military, Aviation, Oil & Gas Exploration, Mining, Safety, and Construction Vehicle manufacturers as well as dozens of others.