With the integration of electronics in modern hydraulic systems growing
stronger every day, modern hydrostatic transmissions very often rely on
"them circuit chips", which, in their turn, "make their decisions" on
the basis of information supplied by the speed sensors, mounted in
motors and sometimes in pumps.
In Sauer Danfoss series 90 pumps and motors, for
example, these small hall sensor based devices pick up the barrel
rotation speed by sensing the alternative magnetic field, created by
the moving magnetized ring, mounted on the barrel. These sensors DO NOT
require physical contact with the ring to pick up speed. If you look at
the pictures to the left, you'll see what happens when the contact
occurs - both the magnetic ring and the speed sensor usually end up in
scrap - and those do not come cheap!
you will find some technical information and mounting instructions on
Sauer Danfoss speed sensors. Under any circumstances remember - when in
doubt - too much out is better than too much in!