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
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
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
Although this initial application is on a tractor the TLI is equally well
suited to applications on any form of mobile hydraulic machinery.
more information, click here :-
Variohm - Tel: +44(0) 1327 351004