THERMODYNAMIC STABILITY OF THE OPERATION OF SENSORS

Different thermodynamic states can develop during the operation of sen sors, namely, static equilibrium, stationary non-equilibrium and time- dependent ones, which can be caused by reversible or irreversible proc esses, namely, spontaneous, generated and fast ones. From the point of view of stability these states can be divided into three categories, stable, unstable and indifferent. (The strong instabilities, such as d issipation, singularities, catastrophes, bifurcation and chaos, may al so be investigated by specific apparatus originating from the fundamen tal thermodynamics.) Certain stability problems can be solved by the m ethod of negative or sometimes positive feedback. The disturbance of a n equilibrium state can be described unambiguously by designating new parameters corresponding to the disturbed state. It is shown that the new state is characterized by series of inequalities, the terms of whi ch can be extensive and intensive quantities, non-equilibrium deviatio ns and thermodynamic forces or forces and currents, depending on the c haracter of the given problem. The genuine dynamic stabilization mecha nism is connected to the equalization process. It is shown that the ac tual decay of an external disturbance is not necessarily a monotonic p rocess in time. Some characteristic parameters decrease, while others increase, producing the so-called oscillatory cross effects. Starting from the derivation of the entropy and conductivity matrixes, their an alogous properties and role in the conservation of stability are deter mined. The stability of the stationary or general non-equilibrium stat es is investigated by variational principles, leading directly to the stability criteria. The possible applicability of the methods presente d is demonstrated by various types of examples.