Simple cranes used in truck beds or simple lifting applications can use electric or diesel powered motors to deliver the required lifting force. Indeed many of these cranes use our waterproof limit switches for everything from anti-two-block prevention, to proximity sensors, to operator control panels.
But it gets really interesting when you begin to talk about hydraulic cranes, especially those used in large construction or oil & gas applications where the forces involved are tremendous, and the cost of failure potentially tragic in terms of both machine and man.
Many of the largest, most powerful cranes in the world use huge bore, telescoping hydraulics of some kind in both fixed and mobile configurations. A great example of this is the Liebherr LTM, currently considered the largest, most powerful mobile hydraulic crane in the world. With a lifting capacity of 1200 Metric Tons and a telescopic boom which extends to 100 meters, this crane on wheels can lift the equivalent of 700 cars.
Stationary cranes or crawler cranes like those used at shipping ports, mounted on barges, or installed on long term construction projects can lift even more weight though not all of these are hydraulic based. Consider “Big Carl” one of the worlds largest land based cranes, currently hard at work in the UK building a nuclear power plant. The crane was shipped from Ghent, Belgium to the Hinkley Point C project location in Somerset, UK on over 250 trucks over a period of months. The crane can manage up to 3000 metric tons and has over 5200 Tons of counterweights.
Linear Position Measurement in Crane Design
Large crane designs take many forms but a couple of applications for Linear Position Sensors are common
- Load-Torque Transducers – In this application, draw wire sensors are commonly used to measure overall load torque to prevent cranes from turning over. Calculations made from the sensor inputs and other inputs insure compliance with operational limits. This safety system is so important that often redundant draw wire sensors are employed for fail safe operation.
- Piston Position Measurement – For long stroke and telescoping hydraulics used on many cranes, and understanding of the piston position is critical for safe operation of the crane. Draw wire sensors are one of the only technologies that have the potential to handle both the stroke length and the robustness requirements here.
For cranes using telescoping hydraulics, there are very few robust solutions to hydraulic cylinder piston position measurement in the marketplace. Consider some of the high level requirements of such a solution:
- Sensor must be capable of extremely long stroke length measurement (10m – 30m)
- Sensor must withstand extreme shock and vibration
- Sensor must be impervious to adverse weather elements.
- In certain applications, sensor will need to be safety rated to prevent explosion risk when working in flammable component areas.
- Sensor must work in telescoping applications where the cylinder may be multi-stage.
CPI makes an entire line of high endurance draw wire sensors designed from the ground up for maximum life and durability in the harshest environments inside hydraulic cylinders and accumulators, and below the ocean.
CPI Draw Wire Sensors for Crane Applications.
While other draw wire sensors claim to be hardened for harsh duty construction applications, CPI sensors were designed and built from scratch with that in mind. From the material science used in our parts, to our patented transduction approach, our sensors have the most robust operating characteristics of any draw wire sensor in the world today. Furthermore, many other draw wire manufacturers still use rotary encoders or even potentiometers in their design. CPI’s SL Series sensors are non-contacting technologies using either LVDT based transducers, or an ultra-short magnetostrictive sensor. We achieve contactless operation by virtue of a patented linear to rotary to linear conversion mechanism that effectively scales down linear piston movement to small increments readable by a short magnetostrictive sensor or an LVDT.
Many characteristics of the CPI SL series sensor make it perfect for both external or internal deployment inside the hydraulic cylinders used on hydraulic cranes:
- These sensors are impervious to temperature and pressure effects and can be deployed completely immersed in hydraulic fluid without compromising mechanical operation.
- The Sensor’s cable retraction mechanism is over designed to allow for significant speed and improved lifetime even for double-acting telescoping cylinders.
- Stroke Lengths for the Product line go up to 30m (SL-6000)
- The sensor is sealed and completely waterproof. Our sensors have been deployed in open seawater close to 1 mile down.
- Electro-mechanical endurance of over 1 million cycles.
- Sensor is by design, highly impervious to vibration, and thermal conditions.
- Sensor can be fully safety rated for deployment in hazardous areas such as drilling platforms. Sensor is fully ATEX and IEC-EX Certified.
- CANBUS or virtually any other analog output available.
For Crane designers looking for draw wire solutions outside the cylinder, CPI offers external mounting for all our hardened sensors in stroke lengths from 10M to 30M.
For more information on how CPI sensors can lift crane design to new heights, call our engineering sales team today.