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<br> <br> How to set the PID parameter adjustment <br> PID control introduction <br> Current industrial automation level has become the measure of all modern level of an important symbol. At the same time, the control theory of development has .also experienced a classical control theory, modern control theory and the theory of intelligent control in three stages. Intelligent control of typical instance is fuzzy-automatic washing machine, etc. Automatic control system can be divided into open-loop control systems and closed-loop .control system. A control system including controllers, sensors, transmitters, implementing agencies, input and output interface. Controller output after the output interface, implementing agency, plus to charged systems; control of the amount charged, through sensors, transmitters, and through input .interface to the controller. Different control system and its sensors, transmitters, implementing agencies are not the same. For example, pressure control system uses a pressure sensor. Electric heating control system sensor is a temperature sensor. Currently, PID control and controllers or intelligent .PID controller (meter) has a lot of products are in engineering practice has been widely used, there are all kinds of PID controller products, companies are developed with PID self-tuning features of smart regulator (intelligent regulator), which PID controller to automatically .adjust the parameter is through intelligent adjustment or correction, adaptive algorithm. A use of the PID control for pressure, temperature, flow, liquid-level controller, can realize the PID control function of programmable logic controller (PLC), as well as for PID .control of PC system, etc. Programmable logic controller (PLC) is the use of its closed-loop control module to implement the PID control, and programmable logic controller (PLC) can be connected directly with the ControlNet, such as Rockwell's PLC-5 ., etc. There you can implement a PID control function of the controller, such as Rockwell of Logix product series, it can be directly connected with the ControlNet uses Web to achieve its remote control capability. <br> <br> 1, open- .loop control system <br> Open-loop control systems (open-loop control system) is charged object output (control) on the controller (controller) has no effect on the output. In this kind of control systems, independent of the amount will .be charged against any sent back to form a closed-loop circuit. <br> <br> 2, closed-loop control system <br> Closed-loop control systems (closed-loop control system) features a system of controlled object's output ( .control of) will effect against sent back, the controller output form one or more closed-loop. Closed-loop control systems with positive feedback and negative feedback, if feedback signals and systems given value signal on the contrary, it is called a negative feedback .(Negative Feedback), if the polarity of the same, it is called a positive feedback, closed-loop control system adopts negative feedback, also known as negative feedback control system. Closed-loop control systems with many examples. For example, people is .a closed-loop with negative feedback control system, the eye is the sensor, act as a feedback, human system can last through amendments to make the correct action. If there are no eyes, no feedback loop, also becomes an open loop control system .. Another example, when a real auto washer with continuous checks whether wash clothes and wash afterwards can automatically cut off power supply, it is a closed-loop control system. <br> <br> 3, step response <br> Step response refers .to a step input (step function) added to the system, the system's output. Steady-state error refers to the system's response to the steady state, the system expects the output and actual output. Control system performance can be stable, accurate and fast .three words to describe. Stable refers to system stability (stability), a system to work properly, you first must be stable, step response point should be the convergence of; access refers to the control system accuracy, control, precision, usually with steady .-state error to (Steady-state error) describes that represents the system output steady-state values and expectations of the poor; fast refers to the control system of rapid response, usually with a quantitative description of rise time to. <br> < .br> 4, PID control principles and characteristics <br> In project real, the most widely used regulator control law for proportional, integral, differential control, PID control, also known as PID. PID controller available has been nearly 70-year history, .it is famous for its simple structure, good stability, reliable work, adjust easily and become the main industrial control technology. When the charged object structure and parameters cannot be entirely, or have no access to the exact mathematical model, the control theory of other .techniques are difficult to use, the system controller structure and parameters must rely on experience and field debugging to determine when the application is the most convenient PID control technology. That is, when we don't fully understand how a system and charged object, or .through effective measurement tools to get the system parameters, best used PID control technology. PID control, actual in PI and PD control. PID controller is based on the error, use proportional, integral, derivatives calculated control volume control. <br> (P .) control <br> Proportional control is one of the easiest ways. Its controller output and input error signal proportional relationship. When only a proportional control system output exists when steady-state error (Steady-state error). <br> Points (I .) control <br> In integral controls, the controller output and input error signal proportional relationship of the integral. On an automatic control system, if you enter into steady state after steady-state error, call this control system is a steady-state error .or simply have a worse system (System with Steady-state Error). In order to eliminate the steady-state error, the controller must introduce the "integration". Integration of the error depends on the timeThe integration between, as time increases, integral .term increases. In this way, even if the error is very small, integration will increase over time, it promotes the controller output increases the steady-state error further decrease until equal to zero. Therefore, the ratio + integration (PI) controller, .you can have the system into steady state after steady-state error. <br> <br> Differential (D) control <br> In differential control, controller output and differential input error signal (that is, the error rate) proportional relationship. .Automatic control system to overcome the error of procedure may oscillate or even instability. The reason is because of the larger inertial components (link) or latency (delay) component, with the role of the inhibitor error, its changes are always behind the error changes .. The solution is the role of the inhibitor error "ahead" of change, that is in error is close to zero, the role of the inhibitor errors should be zero. This means that the controller is only the introduction of "proportion" which often .is not enough, the proportion of role only amplify the amplitude of the error, and is currently a need to increase the "differential", it can forecast error trends, thus, with the proportion + differential controller, can lead to suppress error control equal .to zero or even negative, thus avoiding the accused of a serious overshoot. So on a large inertia or lag charged objects, proportional derivative (PD) + controller can improve the system in the adjustment process of dynamic properties. <br> 5, PID .controller tuning <br> PID controller tuning is the control system at the core of the design. It is based on the characteristics of the accused process determines the PID controller scaling factors, integration time and the size of the differential time. PID controller tuning methods ., summed up in two major categories: the first is theoretical calculation setting method. It is largely based on mathematical model of the system, after calculation to determine the controller parameters. This method of calculation of the data may not be able to directly use, .must also be adjusted by project real and modified. The second is project setting method, it relies primarily on engineering experience, direct control system with the test, and the method is simple, easy to grasp, in engineering practices widely adopted. PID controller parameter .tuning method of works, notably the critical ratio method, the response curve and decay method. Three of these methods has its characteristics, its common ground through test, and then follow the engineering experience formula on the controller parameters setting. But either way the controller .parameters, you need to actually run in the last adjustment and improvement. Now generally use is critical ratio method. Use this method for PID controller parameter tuning steps are as follows: (1) first pre-selection a sufficiently short sampling period for the system .to work; (2) only joined the proportional control link until the system is entered step response is critical when the oscillation, note the magnification factor and critical oscillation cycle; (3) to a certain degree of control over the formula evaluates to the PID .controller parameters. <br> PID parameter setting: depends on experience and technology of familiar reference measurement tracking and set the value curve, thereby adjusting the size of the P \ I \ D. <br> PID controller tuning parameters in the project, various .regulation systems experience data in pid parameter can refer to the following: <br> Temperature T: P = 20 ~ 60%, T = 180 ~ 600s, D = 3-180s <br> Pressure P: P = 30 ~ 70%, .T = 24 ~ 180s, <br> Level L: P = 20 ~ 80%, T = 60 ~ 300s, <br> Flow rate L: P = 40 ~ 100%, T = 6 ~ 60s. <br> Book of .the commonly used formula: <br> Parameter setting to find the best, from small to large order enquiries <br> After the first proportional integral differential, and finally put together <br> Curve is frequent, the proportion of oscillation dial to zoom < .br> Curves floating around the big Bay, the ratio of up to the small wrench <br> Curve deviates from the reply to slow down the integration time to <br> Long curved wave period, integration time to lengthen <br> Curve oscillation frequency .quickly, down the differential <br> Dynamic difference to volatility slow. Differential time should be extended <br> The ideal curve two waves, descending 4-1 <br> A look at the second tune analysis, adjust quality does low here an empirical .method. This approach is essentially a try to scrape together, that it is in production summed up proven methods, and in the scene has been widely used. <br> <br> This approach is the basic procedures in accordance with operating experience, determine .a set of controller parameter, and set the system into closed-loop operation, and then to join the step disturbances (such as changing the regulator of the given value), the observation was transferred amount or regulator output of step response curve. If the .control is not satisfied with the quality, according to the setting of parameters to control the process of changing the controller parameters. This trial until satisfied. <br> <br> Experience simple and reliable method, but require a certain field operating experience, the .whole timing is easy with subjective and one-sided. When a PID controller, there are multiple tuning parameters, repeatedly try to scrape together more often and hard to get the best tuning parameters. The following example with PID regulator, specific description of the experience .of setting step £ º ¡ .¾ 1 ¡ .¿ .let regulator parameter integral coefficient S0 = 0, the actual differential coefficient k = 0, the control system put into closed-loop operation, from light to change the scaling factors S1, let the disturbance signal for step-change, observation control process until satisfactory .control of the process. <br> 【2】 take proportional coefficient S1 is the current value by 0.83 from light to increase the integral coefficient S0, also let the disturbance signal for the step change until achieving satisfactory control of the process. <br> .【3】 integral coefficient S0 remains unchanged, changes the scale coefficient S1, observation control procedure has not improved, continue to improve the adjusted until satisfied. Otherwise, the original scale coefficient increased number, then S1 adjustment integral coefficient S0, seeks to improve the .control of the process. So repeatedly try to scrape together until you find satisfactory ratio coefficient S0, S1 and integral coefficients. <br> 【4】 introduce appropriate practical and differential coefficient kActual differential time TD, this may be appropriate to increase the scale coefficient .S0, S1 and integral coefficients. And the aforementioned steps are the same, differential time setting also repeatedly adjusted until the control process is satisfied. <br> <br> Note: simulation system used by the PID regulator and traditional industrial PID regulator differs between .the various parameters, mutual non-isolated, with its very convenient adjustment rule. <br> <br> PID parameters are based on the inertia control object. Large inertia as: big oven temperature control, generally in more than 10 P, I = .3-10, D = 1 cent. Small inertia if: a small motor with a pump pressure closed loop control, generally only PI control. P = 1-10, I = 0.1-1, D = 0, these must be corrected when .debugging. <br> I provide an incremental PID for your reference <br> △ U (k) = Ae (k)-Be (k-1) + Ce (k-2) <br> A = Kp (1 + T ./ Ti + Td / T) <br> B = Kp (1 +2 Td / T) <br> C = KpTd / T <br> T sampling cycle Td differential time Ti integration time using the above algorithm can construct your own PID algorithm .. <br> U (K) = U (K-1) + △ U (K).