Output Control Methods

The simplest form of control mechanism is an open-loop output. “Open loop” means that there is no feedback from the controlled device back to whatever is controlling it. Microprocessor-based control systems work the same way as the opamp. They control some real-world device, such as a heater or a motor, which attempts to make something (position or temperature) match a desired value. One fact that sets microprocessor-based control systems apart from linear systems is that the microprocessor system is always a sampled system. This means that the microprocessor samples the output of the sensors at regular intervals. Any changes that happen between samples are lost. The disadvantage to this system is that the furnace is sized to the house and has limited ability to raise the temperature. The next step up in complexity from an on-off design is proportional control. The concept behind proportional control is that the amount of control signal varies, based on the size of the difference between the actual condition and the desired condition.