The Micro-Desynn System

The Micro-Desynn System


In applications where the movement of a prime mover is small and linear, the use of a basicsystem transmitting element is strictly limited. The micro-Desynn transmitter was therefore developed to permit the magnification of such small movements and to produce, by linear movement of contacts, the same electrical results as the complete rotation of the contact arms of the basic transmitter.

In order to understand the development of this transmitting element, let us imagine that a toroidal resistor has been cut in two, laid out flat with its ends joined together, and three tappings made as before together with positive and negative arms in contact with it. Movement of the contact arms will produce varying potentials at the tapping, but as will be clear from Figure 4.3.10(a), the full range will not be covered because one or other of the arms would run off the resistor. We thus need a second resistor with tappings so arranged that the contact arms can move through equal distances.


If we now take two toroidal resistors and join them in parallel then, by cutting them both in two and laying them out flat, we obtain the circuit arrangement shown at (b). By linking the contact arms together and insulating them from each other, they can now be moved over the whole length of each resistor to produce voltage and current combinations which will rotate the receiver through 3600. Since the contact arms have to traverse a much shorter path, their angular movement can be kept small (usually 450), a feature which helps to reduce the energy required to operate the transmitter.

The resistors are wound on bobbins which may be of round or square section, the latter type being designed to help reduce cyclic and friction errors.

Each resistance bobbin is secured in place against a set of miniature spring contact fingers accurately positioned so as to provide the necessary tapping points.


The contact arms are mounted on a rocker shaft supported between the vertical parts of a Ushaped bracket, and movement of the transmitter's mechanical element is transmitted to the arms via a spring loaded operating pin and crank arm connected to the rocker shaft. Two berylliumcopper hair-springs conduct current to the contact arms and also act together to return the rocker shaft and contact arms to their starting position.