APPLICATION STORY


 In-Cylinder Transducer upgrades three point linkage.


The TLI contactless position transducer from Variohm Components has recently been used to upgrade the three point linkage system on farm tractors. The traditional three point linkage system hasn't altered much since it was introduced in the 1920's. it forms the bridge between the tractor and the agricultural implement allowing some degree of positional adjustment whilst maintaining a constant operating force. The exact selling of the linkage was always something of a compromise. GKN Walterscheid have recently introduced a hydraulic top linkage arm which is designed to automatically optimise the position of the implement to suit the task being performed. The device utilises a linear position sensor which is integrated into the hydraulic cylinder which forms the body of the top linkage.
The operator uses a "Teach In" principle to find the best possible selling for the implement which he is using. The system then remembers this selling and automatically adopts it whenever that particular implement is used. In the GKN Waterscheid application the position sensor is a special non-contacting device with a stroke length of 250 mm, it sits directly in the hydraulic oil inside the cylinder. This arrangement has a number of advantages the prime ones being that there are no additional projections around the cylinder, which can get damaged or take up space, and that the cylinder acts as a protective housing and keeps the sensor free from dirt, sand, water or any other environmental effects. The sensor itself is an extremely clever device which employs a combination of resistive and capacitive technologies. It utilises a conductive plastic resistance track like a conventional potentiometnc transducer but in conjunction with a capacitive pickup rather than a conventional wiper. Because it has no sliding contact the life expectancy is obviously much higher than a comparable potentiometric device. In order for the capacitive pickup to work properly the resistance track has to be supplied from an alternating source which is obviously a problem on tractors. The new sensor, designated the TL1, overcomes this problem by having an integral electronics package which converts the battery supply into an ac. source then evaluates the output from the capacitive pickup before returning it to a d.c. output. In effect the TLI is as easy to use as a conventional potentiometer. Long term accuracy under even the most arduous conditions is guaranteed as the TLI offers a linearity of 0.15%, a resolution of 0.01 mm and a life expectancy of 200 million cycles, It is available in stroke lengths of between 50 and 1000 mm. Although this initial application is on a tractor the TLI is equally well suited to applications on any form of mobile hydraulic machinery.



For more information, click here :-
Variohm -
Tel: +44(0) 1327 351004

January 2001

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