THE IMPACT OF FEEDBACK ON THE DETERMINATION OF MASSES AND FORCES IN CONTROLLED ATMOSPHERES

Examples of various developments are shown which have led to the prese nt balances used for application in controlled atmospheres. The develo pment started from the beam balance and the spring balance. The geomet rical configuration, selection of materials and choice of indication r esulted in a diversity of balances, adapted to physicochemical experim ents in vacuo or in gases and vapours under predetermined temperatures and pressures. The introduction of feedback control, applicable to al l basic modifications of mechanical balances, resulted in improved per formance with reduced demands on mechanical design. It has facilitated the simultaneous observation of different variables, e.g. mass and to rque or force components. The elements of automatic weight compensatio n in a closed loop are discussed. Feedback control represents the basi s of free magnetic suspension which enables the weighing of an object in a closed container with an external balance and the measuring of fo rces on a body in controlled motion. It also enables signals for sampl e temperature and gas pressure to be transmitted through the wall of t he reaction chamber. New developments in this special field are briefl y discussed.