Position sensors for hydraulic cylinders must meet one central requirement: they should not negatively affect the compactness of a hydraulic cylinder. This means that when a position sensor is fitted, the length of the cylinder should not grow if possible and the extended installation length should be as short as possible.
Position sensors with an innovative functional principle
To satisfy this requirement, SIKO applies an innovative functional principle that achieves a previously unknown degree of compactness. The SGH cylinder stroke measuring technology has a completely different technical approach than conventional measuring systems that work with magnetostrictive, inductive or Hall-based technology.
SGH systems employ a wire-actuated mechanism
SGH systems use a wire-actuated mechanism that is integrated directly into the cylinder to measure the stroke. The wire of the wire-actuated mechanism is attached to the piston head. When the cylinder extends, the wire wound on a wire drum is pulled out. The resulting rotation of the wire drum is detected without contact by the sensor electronics and converted to a linear path. This means that precise and absolute position tracking of the cylinder is possible at any time. The magnets used to measure the rotation are scanned through the pressure-resistant base plate of the SGH systems. The electronic components are fully encapsulated on the non-pressurised side of the system. The entire measuring system is therefore incorporated into the cylinder and optimally protected against external environmental influences. Clear advantage: in contrast to measuring systems mounted externally on the cylinder, the sensor system cannot be damaged, negatively affected or even destroyed by environmental conditions..
Resistant to shock and vibration
Another advantage of the SGH technology is its resistance to shock and vibration. Very strong shocks and vibration occur in particular in utility vehicles such as construction machines and agricultural machinery, for example when an excavator bucket hits the ground with a high impact when it is lowered. This results in a strong shock wave that reaches both the hydraulic cylinder and the sensors. Wire-actuated encoder sensors that are run on the basis of a flexible wire absorb this effect (as there is no lever effect that can occur as in rod-based sensors).
In-house durability tests and design of all sensor components
With regard to development and design, SIKO profits from 30 years of wire-actuated encoder know-how. No other competitor can tap such a wide-ranging wealth of experience. SIKO development and product design engineers also profit from this know-how. The wire-actuated encoders systems of the latest of the SGH25 and SGH50 ranges also benefit from this competence.
These SGH sensors are also fully developed by SIKO. As this is one of the core competencies of the company, all sensor components are also fully designed on the companyís premises. This also applies to wire-actuated encoder components such as the spring, which is a very important component. The spring can be loosely regarded as the motor of a wire-actuated position sensor. When the wire is retracted, the spring is responsible for moving the drum backwards and rewinding the wire. Force ratios, spring characteristic curve and the rotational speed are all specified and defined by SIKO for each product. For this reason SGH position sensors set standards, especially with regard to the durability and long service life, as they are designed and tested both electronically (contactless, magnetic measuring principle) as well as mechanically over the service life of a hydraulic cylinder, and also satisfy the quality requirements of renowned manufacturers and OEMs.
Hollow-drilling of the piston unnecessary
As the sensor rod has to be integrated into the piston over the entire measurement path in magnetostrictive measuring systems, it was often necessary to carry out long and high-precision drilling operations on the piston. This is not only expensive, but also weakens the piston structure. With the stroke measuring system based on the SGH technology, only a small thread is necessary in the piston to attach the wire. As a result the system achieves a high savings potential. This means a significant reduction in the production time as well as the overall costs when manufacturing the hydraulic cylinders. The longer the stroke length, the greater the potential financial savings, also with regard to logistic costs. This benefits cylinder manufacturers, machine builders and end customers at the same time - a true win-win situation for all sides.
SGH sensors and electronics with the protection class IP69K
To survive the tough conditions in the mobile world, the sensor system is fully integrated into the cylinder and therefore given maximum protection against external influences.. For this reason the SGH sensors are included in protection class IP69K. They ensure the very greatest protection against environmental influences such as dirt, dust and water.
Modular KV1H plug-in system ensures flexibility in design and construction
Position sensors of the SGH range feature KV1H plug connections. This modular plug-in connection system has protection class IP69K and is also fully integrated into the cylinder interior. A M12 connector serves as an interface and establishes the connection to the power supply or controller.
From the viewpoint of cylinder manufacturers, the modular character of the KV1H plug-in system enhances the flexibility of design and construction. In comparison to the products of competitors, during the development of different or new cylinders it is not necessary to replace the entire sensor system, which often features fixed cables, but attention must only be paid to a KV1H plug-in connection which is adapted to the cylinder design. Reduction of the variety on the design side therefore streamlines downstream processes such as development, production and maintenance on the manufacturerís side.
In addition, SGH sensors and electronics also have the very highest electromagnetic compatibility (EMC), especially in mobile machines as in comparison to stationary machine systems, mobile machines are not grounded, but are at the same time exposed to a wide range of external voltage pulses. For this reason the SGH sensor has an extremely high EMC and is designed to meet the statutory EMC requirements and is protected against defects and failure
Redundancy, interfaces and safety
The sensors of the SGH range are available with the conventional analogue interfaces, CANopen and also with SAE J1939. Redundant versions (CAT3, PLd) are available for safety-critical applications to meet the requirements of EN13849. There is therefore a choice available for the safety versions between a redundant analogue interface, redundant CANopen, redundant SAE J1939 or CANopen Safety.
The standard-feature teach-in function of the SIKO wire-actuated position sensors enables OEMs and cylinder manufacturers to significantly reduce the number of different versions in comparison to many conventional measuring systems. With the variable specification of the measuring length of the sensor (teach-in), a sensor can cover a wide range of measuring lengths. In addition to the number of different versions, the storage requirements for any spare parts are also lower.