Reinventing Draw Wire Sensors – Part 2
Draw Wire Sensor Measurement Electronics
In our first segment on reinventing draw wire sensors, we discussed the tremendous amount of mechanical design and materials science innovation that went into the creation of an entirely new, high endurance draw wire position measurement system. In part 2 of this series, we discuss the types of transducer electronics available for the CPI draw wire position sensor and the relative advantages of each.
CPI currently offers two options for sensor measurement electronics: one is an LVDT-based measurement system which can provide a sealed, non-contacting solution that can be completely enclosed within a hydraulic cylinder or hydraulic accumulator. In this case, signal conditioning electronics are remotely located, so the sensor can operate in higher temperatures, and is highly tolerant of temperature induced error. The other option is an extremely short magnetostrictive sensor probe which can be mounted through the cylinder wall. This approach leverages all of the technology advances behind magnetostrictive sensors, including intrinsic safety ratings, redundancy, and suitability for subsea deployments.
A comparison of the two transducer solutions follows:
| LVDT | Magnetostrictive | |
| Accuracy | Excellent | Excellent |
| Repeatability | Excellent | Excellent |
| temperature range | -40 to 105C | -40 to 85C |
| Operate in high pressure | Yes | Yes |
| Subsea ready | No | Yes |
| Water submersible | No | Yes |
| Cylinder mounting | completely internal or external | internal with lateral probe, or external |
| Redundancy available | No | Yes |
| Intrinsic Safety ratings | No | Yes |
| Analog outputs | Yes | Yes |
| RS485 output | Yes | Yes |
| SSI output | No | Yes |
| Ethernet / Fieldbus | No | Yes |
| Pushbutton calibration | Yes | Yes |
| Signal conditioner | Remote | integral or remote |
| Temperature effects | Minimal | moderate |
Choosing a CPI Position Sensor Measurement Technology for Your Application
LVDT Position Sensor Technology – The LVDT based solutions for our position sensors Include a wide variety of designs each meant for various applications and price points. In general the LVDT based sensors are an excellent choice for large construction hydraulics, heavy EMI environments, or high vibration deployments. Their minimal control electronics, and sealed enclosure allow them a high degree of immunity to fluids allowing them to be mounted on the oil or the gas side of a cylinder, or outside the cylinder entirely.
Magnetostrictive Position Sensor Implementation – This is the technology to choose if you need an Intrinsic Safety rated solution due to proximity to explosion risk or other safety concerns. Likewise if you need to deploy on the drilling platform or at the well head on hydraulic accumulator systems deployed at or near the ocean floor (ie. Blow out preventers…). Our SL2000 system is completely waterproof and runs without issue under pressure, fully submerged in 5000 feet of seawater.
For more information on the use of our unique sensor technology in your hydraulic cylinder position measurement application, contact our engineering team today.
