Digital systems
Thermal and mechanical systems

There are thermal systems, which are approximately astatic. They can be approached by a space, insulated thermally as well as possible, with minimum heat losses (polystyrene box, vacuum bottle, experimental chamber with ideal insulation) and with a hard source of heating, independent on temperature difference (e.g. a light bulb, heater, heating without thermal protection).

In mechanics, there are a lot of systems of purely astatic character. All systems, having a linear or angular velocity as an input and position or angle as an output, are astatic, e.g. vehicles, trains, slide rests and turntables of machine tools, movable parts of manipulators, elevators and cranes (heading angle, trolley position or length of wound rope).

The astatism is contained also in systems, where the input is acceleration and output value is a velocity. But if a position is regarded as an output value, while having the acceleration as the input, the system would have second order astatism (consisting in double integration). Free fall is not a common phenomenon in mechanical designs, but systems with constant acceleration and deceleration are often implemented. They can be realized e.g. in elevators, because this kind of take off is comfortable for passengers. At some level of simplification, the takeoff can be regarded as having constant acceleration at some aircraft motors, vehicles, trains or rockets.

For demonstration clarity, only the step changes at the input (valve opening and closing, switching a pump on or off, constant current of directions, constant acceleration or deceleration) are considered. Step changes at the input are also often used in practice in system (plant) identification and model creation, i.e. determination of its structure and parameters from measured response. System properties (e.g. that it is a first order astatic), however, do not depend on an input value time behavior. If we can (and want to) actuate continuous values at the input and measure continuous values at the output, we would observe the very same properties of the system, as if we actuate it by step input values – only the behaviors would be more complicated and less comprehensible. For example, the water level will be still an integral of flux over time, even if the flux will be varied by arbitrary continuous opening and closing of the valve.