▪ Control Objective: maintain house temperature at SP in spite of disturbances The important elements of a home heating control system can be organized like any commercial application: As an aside, note that there also must be a safety interlock to ensure that the furnace burner switches on and off as the fuel flow valve opens and closes.Īs the energy output of the furnace rises or falls, the temperature of our house increases or decreases and a feedback loop is complete. If e(t) = SP – PV < 0, it signals to close the valve. So in this example, if e(t) = SP – PV > 0, the controller signals to open the valve. In our home heating system, the controller output (CO) signal is limited to open/close for the fuel flow solenoid valve (our FCE). The action of the controller is based on this error, e(t). The measured temperature PV signal is subtracted from set point to compute controller error, e(t) = SP – PV. A sensor, such as a thermistor in a modern digital thermostat, measures temperature and transmits a signal to the controller. Starting from the far right in the diagram above, our process variable of interest is house temperature. Nevertheless, we introduce the idea of control loop diagrams by presenting a home heating system in the same way we would a more sophisticated commercial control application. Block diagrams help us visualize the components of a loop and see how the pieces are connected.Ī home heating system is simple on/off control with many of the components contained in a small box mounted on our wall. Have a final control element (FCE) that can receive the controller output (CO) signal, react in some fashion to impact the process (e.g., a valve moves), and as a result cause the process variable to respond in a consistent and predictable fashion.Īs shown below ( click for a large view), the home heating control system described in this article can be organized as a traditional control loop block diagram. Have identified a process variable we seek to regulate, be able to measure it (or something directly related to it) with a sensor, and be able to transmit that measurement as an electrical signal back to our controller, and To design and implement a controller, we must: 1) The major components of a control system include a sensor, a controller and a final control element. A controller seeks to maintain the measured process variable (PV) at set point (SP) in spite of unmeasured disturbances (D).

Loop half of a key