8051 microcontrollers

Power Control and Switching Introduction Control of electric power, or power conditioning, requires the conversion of electric power from one form to another, that is, DC to AC, one voltage level to another, and so on, by the switching characteristics of various electronic power devices. Some of these devices, such as silicon controlled rectifiers (SCRs), can be operated as switches by applying control voltages to their controlling input (gate terminal of gate- turn-off thyristor (GTO)). Others, such as triggered vacuum and gas gap switches rely on over-voltages or triggering. For large power systems, control is exercised by supervisory control and data acquisition (SCADA) computer systems located at a central location. This master station communicates with remote stations in the system to acquire data and system status and to transmit control information. These centers support the two main objectives of power system control, that is, (1) stable (voltage and frequency) power and (...

Servo Systems Introduction During the past 60 years, many methods have been developed for accurately controlling dynamic systems. The vast majority of these systems employ sensors to measure what the system is actually doing. Then, based on these measurements, the input to the system is modified. These concepts were initially used in applications where only a single output was measured, and that measurement was used to modify a single input. For instance, position sensors measured the actual position of a motor, and the current or voltage put into the motor windings was modified based on these position readings. An early definition of these systems is the following: A servosystem is defined as a combination of elements for the control of a source of power in which the output of the system, or some function of the output, is fed back for comparison with the input and the difference between these quantities is used in controlling the power (James, Nichols, and Phillips, 1947). T...

Computer Control Systems Distributed Control Systems (DCS) Microcomputer-based subsystems are standard in most computer control systems available today. The digital subsystems are interconnected through a digital communications network. Such systems are referred to as distributed digital instrumentation and control systems because of the network approach used to monitor and control the progress. Figure 18.63 depicts a representative distributed control system (Seborg, Edgar, and Mellichamp, 2004). The DCS system consists of many commonly used DCS components, including multiplexers (MUXs), single-loop and multiple-loop controllers, PLCs, and smart devices. A system includes some or all of the following components: 1. Control network. The control network is the communication link between the individual com- ponents of a network. Coaxial cable and, more recently, fiber-optic cable have often been used. A redundant pair of cables (dual redundant highway) is normally supplied to red...

Advanced Control Techniques Although the single-loop PID controller is satisfactory in many process applications, it does not perform well for processes with slow dynamics, time delays, frequent disturbances, or multivariable interactions. We discuss several advanced control methods next, which can be implemented via computer control. One of the disadvantages of using conventional feedback control for processes with large time lags or delays is that disturbances are not recognized until after the controlled variable deviates from its setpoint. One way to improve the dynamic response to disturbances is by using a secondary measurement point and a secondary controller; the secondary measurement point is located so that it recognizes the upset condition before the primary controlled variable is affected. One such approach is called cascade control , which is routinely used in most modern computer control systems. Consider a chemical reactor, where reactor temperature is to be contr...