Position sensing in mobile applications can be tricky, especially on large machines with long boom cylinders. Such machines often rely on cable reels and string pots, but these devices are not always reliable. They can stretch, thus require recalibration. And the elements—winds causing erratic readings and dither in the hydraulics, ice buildup preventing the wire from retracting and tree limb interference, for example—can wreak havoc with these measurement devices.
Enter a new linear transducer, the ML model from Rota Engineering Ltd., Manchester, UK. This new modular sensor can be built up to 130 ft long, for external mounting on standard boom cylinders, said Mark Hoffman, Vice President of Sales and Marketing for Rota.
Like all Rota transducer designs, the ML uses the company’s patented external design, which eliminates the need for a gun-drilled piston rod. A transducer is mounted on the cylinder barrel and detects the position of the cylinder’s piston by sensing a magnetic field formed by a permanent magnet embedded in the piston. As the piston rod extends or retracts, the magnetic field propagates through the standard carbon steel cylinder wall to communicate with the linear transducer.
The new ML design is modular in nature and it can be built in 1.5, 3, 7, and 10 ft sections, and assembled on-site. This eliminates production, test, shipping, storage, installation, and maintenance issues, said Hoffman.
For example, internal transducers in long-stroke cylinders can encounter a number of issues, mostly due to their size. Storage and shipping can be a problem with anything over 7 ft, but because the ML is modular in nature and can be easily snapped together for a quick and easy fit, it eliminates these problems. In addition, the cylinder tube supports the sensor, so sagging is not a problem, unlike in internal designs.
The ML sensor operates in temperatures down to –40°F and is a non-contact/frictionless design with no external parts that can wear. Accuracy of Rota’s external transducers is typically ± 0.5 mm, which is more than adequate for most mobile equipment.
Rota Engineering Ltd.
Filed Under: Design World articles, Sensors (proximity)