Process Control in Engineering - Essay Example

The Running Head: Process Control Your name: Course name: Professors’ name: Date: a).Feedback System Feedback system can be defined as a system in which it output is fed back to the input of the system, and depending on the output of the system (Dorato, pg.35), the input of the system is adjusted until a steady-state is reached. In colloquial language, the input is adjusted on the output in the system so as the system can achieve a certain end. When the feedback system act in response to a process, the input signal can be influence in the following ways: an in-phase feedback signal- positive going wave) will make the input signal to be amplified and this will lead to more modification of the signal. While positive-going o the feedback signal will damped the effect of the input signal and this will led to less modifications of the system. The negative feedback mentioned above will help the system to maintain stability despite the external changes experienced by the system to the environment. Consequently, positive feedback will amplify possibilities of divergences. b). Feedback system can be used to minimize disturbance, cancel echo speech systems. a). Cascade System This is a multiple loop-system in which the primary variable inputted is controlled by adjusting the set points of secondary variable controller in the system (Salek, pg.24). The secondary variable is affected by the primary variable through the process. The objective of a cascade system divides control process of a system into two portions, in otherwise, a secondary control loop will be formed around a major disturbance and therefore leaving a minor loop disturbance to be controlled by a primary controller in the system. In the cascading system, it is important for the secondary variable to respond to the disturbance. Some applications in the system can benefit when there is more than one slave controller, however other secondary variable and manipulated variable will be associated with each slave controller in the system and if the slave loops is found to be parallel. b). Cascade system is used to reduce the effective magnitude of a time-lag, or Increase the natural frequency of a system (Salek, pg.25). a). Override System The process involved in an override system will control other process with a single final control element, such as a valve that are from two interdependent process variables and must not exceed acceptable minimum and maximum limit. In the system, the override control will provide protective action against any abnormal operation, also it will incipient any process failure. When we consider control theory, override system can be termed as a logic base switching system, but when it is considered in term of operations, override system will be activated between the softer constraint and the harder constraint. The key element that is found in override control system is a selector switch, and this is usually implemented either in the hardware device or a software function block of the system. Depending on how this selector switched is configured in the system, it will pass high or low several input signals to its output. One way in which a selector switch can control strategy is to select the higher or lower of several measurement signals that is then passed on as the process variable to a feedback controller found on the override system. b). The system can select the highest of several process temperatures to be automatically become the controlling temperature, when the conditions change, the location of the highest temperature will also change regardless of process conditions. a). Auctioneering System This system is adapted to be connected to a thermostat which will be used to control temperature. The thermostat is then modified wherein it will include a temperature sensor which will then provide a sensed temperature signal. The control apparatus that are found in auctioneering will include that for sensing absolute humidity and providing a first output signal corresponding to the sensed absolute humidity. In the system the first comparing apparatus will receive the first output signal and this will then provide a humidity error signal, the predetermined temperature set-point in the system will be responsive to the humidity error signal. The other apparatus will be used to compare the limited temperature set-point signal in the system. In other words, controller will have both the humidity and temperature sensor which will ensure that both temperature and humidity are within comfort levels in the system. b). it is used to as switch to control two variables. a). Feed Forward System Pathway within a system that is used to control signal from the source in the control system’s external environment; controlling signal will anticipates the relation between system and external environment to determine a course of action. This control system is used to avoid the slowness of feedback control, in feedback system; disturbance will be measured and accounted for before they affect the system. Let take an example of feed forward system employed in a house set up, when the door is opened; feed forward will automatically turn on the heater before the house can get cold. The problem with this type of a system is that the effect of the disturbances on the system must be accurately predicted, and at all the time there must be unmeasured disturbance because it will affect the system. For example, the house window was opened and that was not being measured. b). Feedforward system is used in Long distance telephony a). Feedback Feedforward Systems This system or mechanisms which will loop back the signal to the system itself; the system has both the input and the output, part of the output will be fed back to the inputs so as to increase the input (positive feedback). Feedforward will anticipate the relationship that is there between the system and environment and it determines the course of action, and feedback will monitor the discrepancies which will be used to refine the actions. Problem to be controlled will be chosen in the input in some system in such a way it will cause the output to behave in some desired way; it will either stay near the reference value-regulator problem, or it will follow a close desired trajectory- tracking problem. b). Feedback and feedforward control are used together in dead time and inverse response compensation. In dead time compensation is used when device take time to show any changes to an input, while inverse response compensation is used in controlling systems where when change is put it will affect the measure variable in one way but later it will affects it in the opposite way. a). Split Range System This is a control scheme in which the output of a system is split into two or more control valves; the dual situation in the system is employed when there is one measured variable and several control variables (Buckbee, pg.34). In a split range system, a flare valve will need to open quickly and this is as a result of high pressures going though the flare valve, consequently, the compressor suction valve will be at all time move slowly and this is because it will prevent instability in the compressors found in the system. When the flare valve is turned slower to stabilize the split range system compressor, the valve will be slower as the pressure in the system rises and this will bring a problem; flare route will differ to the process of the route to the compressors, so both routes in the system will require different tuning for optimal control to prevent this problem from happening. The solution for this problem with pressure is to replace split range controller with two independent controllers, which will read the same pressure transmitter, but one controller will control the flare valve, and the other controller will control the suction valve, not only each valve will be turned correctly, but different set-points will prevent flare valve from ‘popping’ unnecessarily. b). Split range system is commonly used in heating and ventilation systems, to avoid heating and cooling in the system at same time, there is not often a small where heating nor cooling is supplied into the system (Buckbee, pg.35). a).  Ratio System Ratio control is usually used in a system to maintain the flow rate of one stream in a process at a specified proportion relative to another stream (Luo, pg.27). An application for this type of a system is whereby a combine or blend of two feed streams are used to produce a mixed flow with a desired physical property such as gases, liquids, powders, slurries or melts. The flow rate in the system can change and this will depend on product demand, limitations in maintenance, feedstock variations and energy availability to the system. There are various types of ratio systems: Linear Flow Signals Required, Flow Fraction (Ratio) Controller, Ratio Relay or Flow Fraction Controller, and Multiplying Relay with Remote Input (Luo, pg.28). a). Adaptive System This is a physical system that will change its behavior in response to environmental change; this adaptive change is necessary for the system to achieve its goals or objectives (Kalouptsidis,Pg.45). This system is usually contrasted with a static system, but there is difference because a static system does not have any self-repair abilities and it usually remain in a single non-adaptive state until the system is terminated, on the other hand an adaptive system is able to self modify itself into different system-states so it will be able to navigate, different functions, also it will succeed within different environments. These systems are always built to engage and respond to environmental changes. It not easy to differentiate between static systems and adaptive systems, because both system types come with degrees, and some static systems have primitive monitoring devices that work in a specific context such as thermostat. Similarly, those devices which have adaptive systems come with functionality constraints and limitations because radical changes to the environment will make the device lose its functionality, therefore it’s unlikely adaptive system to have a global adaptability. b). Adaptive systems nowadays are widely used in microwave ovens to regulate the power output bases of microwave oven on various sensor readings of the food being warmed by the equipment (Kalouptsidis,Pg.46). Works Cited Buckbee, George. Mastering Split-range Control. London: Booksurge Llc Publisher, 2009. Print. Dorato, Peter. Analytic feedback system design: an interpolation approach. London: Brooks/Cole Publisher, 2000. Print. Kalouptsidis, N. Adaptive system identification and signal processing algorithms. London: Prentice Hall Publisher, 1993. Print. Lipták, Béla. Instrument engineers' handbook: supplement one of the Instrument engineers' handbook, volumes I and II. Michigan: Chilton Publisher, 1972.Print. Luo, Juon. Peak-to-average power ratio reduced parallel interference cancellation Multicarrier-Code Division Multiple Access system with anti-interference property. London: ProQuest Publisher, 2008. Print. Salek, Mark. Cascade system: a universal method of solving fluid power sequence circuits. New York: National Fluid Power Association Publisher, 1964. Print. Read More