The positioner works according to the force-balance principle. The input signal, coming from the control equipment, acts on a diaphragm chamber. The force produced ing such a way is constanthly compared to the feedback force produced by the stroke scanning lever (204), cam-disc (24) and spring (6). Accrding to the control divergence the valve spindle is forced into the correct position by higher or lower output pressure on the actuator, until the control diver-gence between input force and reset force has become zero.

Looking at the I/P module in the above acheme, the input current I flows through a fixed coil (44.1). There by a soft magnetic system (44.2) ist magnetized. The flux lines of this system being exposed at a gap (44.3) apply a force proportional to the input current to a small magnet (44.4) made of highly coercive alloy. Together with the flapper (44.5) this small magnet forms the moving parts of the system.

The flaper more or less covers a nozzle (44.6), the air flowing from the nozzle forming a restoring force balanced by the force applied to the magnet. The nozzle is supplied with air through a fix orifice (44.7) by the output of a controlling unit (44.8) influenced by the pressure change before the nozzle. Hence a well linear corespondance of clectric input and pneumatic output signal is achieved.

Zero adjustment is made in the pneumatic part of the unit by adjusting the screw (31), the rough range adjustment is performed at the stroke lever (204) and the final adjustment at the adjusting screw(32). The adjustment of the limit switches is made possible by adjustable control flappers (damped and undamped).

The zero and range adjustment of the electronic position transmitter ensue at the marked adjusting screws (0/100%) of the transmitting module.