Hi-Endurance Switching, Sensing
& Linear Position Sensors

Long Stroke Draw Wire Hydraulic Position Sensor Overview

Linear Position Sensors for Long stroke hydraulic cylinders

Its interesting to look at sensor manufacturer’s talk about the “long stroke” version of their hydraulic position sensors. They go on about how their amazing sensors can actually operate on stroke lengths of up to 1.2 meters in some cases! These sensors constitute a variety of technologies, from magnetostrictive to microwave and are billed as highly reliable solutions to a variety of “long stroke” applications.


At CPI, our definition of Long Stroke is a bit different.  When you’re talking about a bore of up to 36” or more and a stroke length of anywhere between 10 and 50 feet, now you’re in our world. You’re talking about a cylinder designed to move some serious equipment in what is likely to be a high power, big dollar, heavy usage, extreme duty environment. Many of these cylinders will go deep into the ocean, in a corrosive salt water environment where they are prohibitively expensive to repair or suffer downtime.

Welcome to the real long stroke hydraulic applications.

Characteristics of Long Stroke and Telescoping Cylinder Position Measurement

Accurate Linear Position Sensing in long stroke, or telescoping hydraulic cylinders is a key component of the overall feature set of the cylinder. As stroke lengths get longer, position sensor technology solutions begin to fall by the wayside. Forget rod-type magnetostrictive sensors past 3 or 4 meters with their core drilling requirement and tendency to fail in horizontal deployments. Forget laser gauges and optical encoders in the dirty, high vibration environment of a long stroke cylinder. Forget finicky microwave technology with its complex resonator placement requirements and control circuitry, for anything but a low intensity, stable environment.

When you consider the requirements of long stroke telescoping cylinders, the list of reliable technologies gets shorter even quicker. You just can’t make a rod dynamically grow with your cylinder so magnetostrictive is out right from the get-go.

Draw Wire Sensors in 2019 for Long Stroke Hydraulics

Despite advances in electro-mechanical design and material science, too many engineers still equate draw wire tech, with grandma’s “string-pots”, a contact based, potentiometer technology. It’s hard to know where to start when explaining how wrong this is…

  1. CPI Draw wire Sensors use a completely non-contacting sensing technology.
  2. There is no string, there is a corrosion proof, stainless steel wire designed to meet spec for up to 50m of stroke length.
  3. CPI draw wire sensors by their very nature can easily accommodate the changing stroke lengths of telescoping cylinders.
  4. Draw wire sensors use absolute position measurement through industry standard connectors and electrical signals. They do not need recalibration.
  5. CPI sensors use an advanced metallurgical design that is impervious to corrosive hydraulic fluid, seawater, and pressure effects up to 10,000 PSI.
  6. CPI sensors are totally waterproof and have been tested for deployment in seawater at depths over 5000 feet or more.
  7. CPI sensors are fully ATEX and IEC-Ex safety rated for deployment in the USA and Europe.

How is this Done?

CPI sensors have evolved for almost 2 decades now into the solution of choice for oilfield hydraulics and other applications. Consider a sensor like our SL-2000. The key to our success is a patented linear-to-rotary-to-linear technology which converts the linear motion of the piston into accurate but reduced linear movement which is then easily measured by a short, hardened magnetostrictive sensor. The overall solution is completely safety rated.

Subsea Hydraulic Piston Linear Position Sensor
The CPI SL2000 Subsea Rated Linear Position Sensor deployed in-cylinder.

Draw wire core component materials are specified for extreme precision, high cycle life, and long-term operation in almost any medium. Virtually any signal output is offered via industry standard signal interfaces.

Both standard and custom mounting are available for your cylinder, including our inside the cylinder mounting which provides the most robust deployment for your solution. There is no other sensor in the world that can operate protected inside a hydraulic cylinder completely immersed in hydraulic fluid at 10,000 psi, with an MTBF of over 1 million cycles.

CPI Linear Positions sensors for Long Stroke Hydraulics are Unique

CPI continues to make what is arguably the only real solution for the harsh duty, long stroke hydraulic cylinder market. After almost 20 years in the field, we know how to do this.

Contact us today to discuss your cylinder application.

Make The "Switch" to CPI

If your momentary switch application demands high performance, we think you should demand CPI. Please call us today to speak with our engineering team about your needs.

(973) 887-9400