tailieunhanh - Control Engineering - A guide for beginners - Chapter 2

Tham khảo tài liệu 'control engineering - a guide for beginners - chapter 2', kỹ thuật - công nghệ, tự động hoá phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 2 The process Dynamic action of technical systems The process is the element of a system which has to be controlled in accordance with the application duty. In practice the process represents either an installation or a manufacturing process which requires controlling. Normally the process covers a number of elements within a system. The input is the manipulating variable y received from the control device. The output is represented by the process variable x. As well as these two variables there are the disturbances z which affect the process to some extent through external influences or process-dependent variations. An example of a process is a gas-fired furnace see Fig. 15 . At the start of the process is the valve which has as its input the manipulating variable of the controller. The valve controls the gas flow to the burner. The burner produces heat energy by burning the gas which brings the charge up to a higher temperature. If the temperature in the charge is measured process value this also forms part of the process. The final component of the process here is the sensor which has the job of converting the temperature into an electrical signal. Disturbances here are all the variables in the process which when they change result in a different temperature for the same valve setting. Example If the manipulating variable is just large enough to give the required temperature in the charge and a disturbance occurs due to a fall in outside ambient temperature then if the manipulating variable is not changed the temperature in the charge will also be lower. 635 c . Feed Disturbances pressure value temperature The process system to be controlled Symbolic representation y Fig. 15 Input and output variables of a process When designing a control loop it is important to know how the process responds when there is a change in one of the influencing variables mentioned above. On the one hand it is of interest to know the new process value reached when stable .