ABSTRACT
The simplest kind of electronic control system comprises three stages: input, processing, output. Examples are given on p. 13. A general diagram is drawn below. These are called open-loop systems.
There are also closed-loop systems, in which part of the signal from the output stage is fed back to the input stage. For example, in a thermostat, see next page, a small part of the heat from the heater warms the thermistor sensor.
