Position Sensing in Long Stroke Hydraulic Cylinders

Linear Position Sensor use in long stroke hydraulic cylinder

Long stroke hydraulic cylinders commonly find use in equipment that is subject to extreme environments.  This includes heavy duty industrial equipment of the sort found in power plants, oil and gas exploration, deep sea applications, and high-end mobile hydraulics such as mining and construction equipment.

In the past, rod-type magnetostrictive sensors were the dominant implementation for stroke lengths up to 23 feet. For those who are familiar with this technology the inherent deficiencies of needing to use a long narrow rod inserted into a perfectly drilled center bore are obvious.

  1. The rods are highly susceptible to vibration and temperature changes.
  2. The rods are give to “sag over” after use and must be replaced.
  3. Their limited temperature range of 185F is easily exceeded in many applications.
  4. Drilling a long center bore that is straight and within tolerances can be highly problematic, the longer the cylinder.
Linear Position Sensor by CPI

CPI’s SL Series LVDT Based Linear Position Sensor

Instead a new long stroke linear position sensor offers superior performance over magnetostrictive technology in harsh environment applications. Our product uses LVDT technology to provide a completely non-contacting solution to linear position sensing.  CPI’s SL Series Linear Position Sensors  are built to be drop in replacements for rod-type magnetostrictive sensors.

Unlike the rod based design of magnetostrictive sensors, the SL Series Sensor is based on a unique implementation of draw-wire sensor technology. The sensor is enclosed in a pressure vessel with a cable that passes through a high-pressure conduit made from standard hydraulic hose. A compact LVDT is used which can operate either in or out of the hydraulic fluid, and is highly resistant to harsh environments. Then using CPI’s highly developed sensor core, our sensor converts the relatively long stroke of hydraulic cylinders to the short stroke of the LVDT via a patented linear to rotary to linear mechanism that is unique in the industry.

Some advantages of the SL series LVDT based linear position sensor include:

  • Completely non-contacting measurement technology (LVDT).
  • One SL series part number can drop-in replace rod sensors of many different lengths.
  • Inherent vibration immunity.
  • Absolutely no core drilling is required.
  • Greatly extended operating temperature range.
  • Absolute position measurement, no startup calibration or “zeroing out” required.

For those who really understand hydraulic cylinder design, we think you’ll see that our position sensor technology is really a game changer.

Please call our engineering team to discuss your application today.  

For more information also see our discussion of LVDT based Linear Position Sensors.