Comparison of Hydraulic Cylinder Position Sensing Technologies.

In the field of hydraulic cylinder position sensing, the same basic technologies have dominated the landscape for the last decade. Recently a hybrid solution developed by Control Products Inc of East Hanover NJ, has solidly entered the field providing increased reliability and robustness in harsh environmental deployments, and ease of retrofit for existing rod-based sensor types.

A comparison of basic sensor types with their relative strengths and weaknesses shows how this new sensor compares to the major Linear Position Sensor Technologies.

Properties	Poten-tiometer	Magneto-strictive	LVDT	Draw Wire (Optical Encoder)	Pure Optical Encoder	CPI SL Series
Electronics Complexity	Low	Moderate	Moderate	High	High	Moderate
Non-Contacting	No	Yes	Yes	Yes	Yes	Yes
Accuracy	Fair	Excellent	Excellent	Very Good	Excellent	Very Good
Resolution	Fair	Excellent	Excellent	Excellent	Excellent	Excellent
Temp. Range	Fair	Very Good	Excellent	Excellent	Excellent	Excellent
Vibration Immunity	Fair	Good	Excellent	Fair	Fair	Excellent
Magnetic Field Immunity	Excellent	FAIR	Very Good	Very Good	Very Good	Very Good
Temp Range	Fair	Good	Excellent	Excellent	Excellent	Excellent
Linearity	Moderate	Very Good	Good	Very Good	Very Good	Very Good
Cost	Low	High	Moderate	Moderate	High	High
Max Stroke Length	20”	120”	20”	120”	60 in	275”
Telescoping Cylinders	No	No	No	Yes	No	Yes

This new hydraulic cylinder position sensor technology fits in the class of draw wire sensors but replaces the electronics with a patented LVDT implementation for reliable position measurement in harsh environments. Using a unique linear to rotary to linear mechanism the LVDT can detect displacement at the spool on either the oil or the gas side of the cylinder without the need for the transformer to encapsulate the cylinder. Using an LVDT that is completely sealed, this combination yields a solution that is immune to vibration, magnetic field interference and has an extended operating temperature range up to 125C. The system is very accurate and has high MTBF, while being easy to field retrofit in a wide array of cylinders and stroke lengths including telescoping cylinders. CPI’s SL series LVDT based Linear Position Sensors are commonly used in long stroke hydraulic cylinders and accumulators where harsh operating environments must be tolerated.

This technology is a game changer for applications like heavy duty Construction equipment, non-automotive vehicular applications, Oil and Gas Mining equipment, even steel Mills.  Anywhere that hydraulic position sensing encounters high temperature, high vibration, and long periods of continued use.  With the wide variety of mounting configurations available and our ability to drop-in replace rod-type sensors, our total cost when considering the improved MTBF in these applications makes us a superior choice in almost every application.

To learn more about our technology please see our website at http://www.cpi-nj.com/lvdt-sensor-technology