At present, the level of industrial automation has become an important indicator to measure the level of modernization in all walks of life. At the same time, the development of control theory has also experienced three stages of classical control theory, modern control theory and intelligent control theory. A typical example of intelligent control is a fuzzy fully automatic washing machine or the like. The automatic control system can be divided into an open loop control system and a closed loop control system. A control system includes a controller, a sensor, a transmitter, an actuator, and an input and output interface. The output of the controller is added to the controlled system through the output interface and the actuator; the controlled quantity of the control system is sent to the controller through the input interface through the sensor and the transmitter.
Different control systems have different sensors, transmitters and actuators. For example, pressure control systems use pressure sensors. The sensor of the electric heating control system is a temperature sensor.
At present, there are many PID controllers and their controllers or intelligent PID controllers (meters). The products have been widely used in engineering practice. There are various PID controller products, and all major companies have developed PIDs. The intelligent regulator of the parameter self-tuning function, wherein the automatic adjustment of the PID controller parameters is realized by intelligent adjustment or self-correction, adaptive algorithm. There are pressure, temperature, flow, and liquid level controllers that use PID control, programmable logic controllers (PLCs) that can implement PID control functions, and PC systems that can implement PID control. The programmable controller (PLC) uses its closed-loop control module to implement PID control, while the programmable controller (PLC) can be directly connected to ControlNet, such as Rockwell's PLC-5. There are also controllers that implement PID control functions, such as Rockwell's Logix product line, which can be directly connected to ControlNet and utilize the network for remote control.
Parameter tuning of PID controllerThe parameter tuning of the PID controller is the core content of the control system design. It determines the scale factor, integration time and derivative time of the PID controller according to the characteristics of the controlled process. There are many methods for PID controller parameter tuning. There are two general categories:
The first is the theoretical calculation tuning method. It is mainly based on the mathematical model of the system, and the controller parameters are determined through theoretical calculations. The calculation data obtained by this method may not be directly usable, and must be adjusted and modified through engineering practice.
The second is the engineering setting method, which relies mainly on engineering experience and is directly carried out in the test of the control system. The method is simple and easy to grasp, and is widely used in engineering practice.
The engineering tuning method of PID controller parameters mainly includes critical ratio method, reaction curve method and attenuation method.
Each of the three methods has its own characteristics, and the common point is to pass the test, and then adjust the controller parameters according to the engineering experience formula. However, no matter which method is used, the controller parameters need to be adjusted and improved in actual operation. The critical ratio method is generally used now.
The tuning steps of the PID controller parameters using this method are as follows:
(1) First pre-select a sampling period that is short enough for the system to work;
(2) Add only the proportional control link until the system has a critical oscillation in the step response of the input, and record the proportional amplification factor and the critical oscillation period at this time;
(3) Calculate the parameters of the PID controller by a formula under a certain degree of control.
The engineering tuning of PID controller parameters, the empirical data of PID parameters in various adjustment systems can be referred to below:
Temperature T: P=20~60%, T=180~600s, D=3-180s
Pressure P: P=30~70%, T=24~180s,
Liquid level L: P=20~80%, T=60~300s,
Flow rate L: P=40~100%, T=6~60s.
PID common port:Parameter tuning to find the best, from small to large
First, the ratio is post-integrated, and finally the differential is added.
The curve oscillates frequently, and the proportional disk is enlarged.
The curve floats around the big bay, and the proportional disk is small
The curve deviates slowly and the integration time decreases.
The curve has a long fluctuation period and the integration time is longer.
The curve oscillates at a fast frequency, first lowering the differential
The momentum is large and the fluctuations are slow. Derivative time should be lengthened
Ideal curve two waves, front high and low 4 to 1
A look at the second adjustment and multi-analysis, the adjustment quality will not be low
PID parameter setting: It is based on the familiarity of experience and technology, and the measurement value tracking and set value curve are referenced to adjust the size of P\I\D.
PID regulation experienceKp: Proportional coefficient ----- Proportional band (proportionality) P: Percentage of the ratio of the relative value of the input deviation signal change to the relative value of the output signal change (reciprocal of the proportional coefficient)
T: sampling time
Ti: integration time
Td: differential time
Temperature T: P=20~60%, Ti=180~600s, Td=3-180s
Pressure P: P=30~70%, Ti=24~180s,
Liquid level L: P=20~80%, Ti=60~300s,
Flow rate L: P=40~100%, Ti=6~60s.
(1) Generally speaking, in the tuning, it is observed that the curve oscillation is very frequent, and the proportional band needs to be increased to reduce the oscillation; when the maximum deviation of the curve is large and tends to be a non-periodic process, the proportional band needs to be reduced.
(2) When the curve fluctuates greatly, the integration time should be increased; if the curve deviates from the given value and does not come back for a long time, the integration time needs to be reduced to speed up the elimination of the residual.
(3) If the curve is oscillating, the differential action should be minimized, or temporarily not differentiated; the maximum deviation of the curve is large and the attenuation is slow, and the differential time needs to be lengthened to increase the effect.
(4) If the proportional band is too small, the integration time is too small or the differential time is too large, and periodic periodic shocks will occur. The integration time is too small, the oscillation period is long; the proportional band is too small, the oscillation period is short; the differential time is too large, and the oscillation period is the shortest
(5) If the proportional band is too large or the integration time is too long, the transition process will change slowly. The proportional band is too large, and the curve, such as an irregular wave, deviates significantly from the given value. If the integration time is too long, the curve will slowly return to the given value through an aperiodic abnormal path.
Note: When the integration time is too long or the derivative time is too large, beyond the allowable range, no matter if the proportional band is changed, it cannot be remedied.
PID debugging stepsNo control algorithm is more efficient and convenient than the PID adjustment rule. Now some of the funky point regulators are basically derived from the PID. It can even be said that the PID regulator is the other control adjustment algorithm.
Why is the PID application so extensive and long-lasting?
Because PID solves the most basic problem that automatic control theory has to solve, it is the stability, rapidity and accuracy of the system. Adjusting the PID parameters can achieve the system's load capacity and anti-interference ability under the premise of system stability. At the same time, the integral term is introduced in the PID regulator, and the system adds a zero point to make it a first order or For systems above the first order, the steady-state error of the system step response is zero.
Due to the wide variety of controlled objects in the automatic control system, the parameters of the PID must also change to meet the performance requirements of the system. This brings considerable trouble to the user, especially for beginners. The following is a brief introduction to the general steps to debug PID parameters:
1. Negative feedback
Automatic control theory is also known as negative feedback control theory. First check the system wiring and make sure the feedback from the system is negative feedback. For example, the motor speed control system, the input signal is positive, when the motor is required to rotate forward, the feedback signal is also positive (PID algorithm, error = input - feedback), and the higher the motor speed, the larger the feedback signal. The rest of the system is the same as this method.
2. General principles of PID debugging
a. Increase the proportional gain P when the output does not oscillate.
b. When the output does not oscillate, reduce the integral time constant Ti.
c. Increase the differential time constant Td when the output does not oscillate.
3. General procedure
a. Determine the proportional gain P
When determining the proportional gain P, first remove the integral term and the derivative term of the PID, generally let Ti=0, Td=0 (see the parameter setting description of PID for details), so that the PID is pure proportional adjustment. The input is set to 60%~70% of the maximum allowed by the system, and the proportional gain P is gradually increased by 0 until the system oscillates; in turn, the proportional gain P from this time gradually decreases until the system oscillation disappears, recording At this time, the proportional gain P sets the proportional gain P of the PID to 60% to 70% of the current value. Proportional gain P debugging is completed.
b. Determine the integral time constant Ti
After the proportional gain P is determined, the initial value of a larger integral time constant Ti is set, and then Ti is gradually decreased until the system oscillates, and then, in turn, Ti is gradually increased until the system oscillation disappears. Record Ti at this time, and set the integration time constant Ti of the PID to 150% to 180% of the current value. The integration time constant Ti is completed.
c. Determine the differential time constant Td
The integral time constant Td is generally not required to be set and is 0. To set, as in the method of determining P and Ti, take 30% of the oscillation.
d. The system is unloaded and loaded and coordinated, and the PID parameters are fine-tuned until the requirements are met.
Toggle switches
Toggle switches, also called On Off Toggle Switches, is often used as the switching device of the equipment stalls. Meanwhile, we are also offer our customers Key Switches, Metal Switches, Automotive Switches, Push Button Switches, etc.
The Electrical Toggle Switches is a manually controlled Toggle Switches similar to the dial switch. Most of this Latching Toggle Switches are widely used in on-off control of AC and DC power circuits, and are less commonly used in circuits of several kilohertz or up to 1 megahertz. Let's take a look at the following.
1. Splash-proof knob button switch
The panel is installed with a splash-proof `O` ring seal, and the knob is a ball. It is a splash-proof ball button knob switch. Its terminals are in a straight line and the bottom of the terminals is sealed with epoxy resin. Strong corrosion resistance, suitable for automotive parts
2. Vertical Mount Right Angle Toggle Switch
The vertical mounting of the terminals and the terminal pins are right-angled, so it is a vertically mounted right-angled toggle switch. Its contacts are gold-plated and highly reliable. Mostly used in anti-theft devices, alert system.
3. Bipolar single toggle switch
At the same time, the switch breaks the phase line and the N line and controls one branch. Therefore, it is a bipolar single toggle switches. The contacts are in 3PDT form and are used for multimedia speakers and stereos.
4. Standard surface mount unthreaded toggle switches
The terminal adopts the standard mounting mode. Its sleeve has no thread. It is called a standard surface mount screw-less switch. The contacts are SPDT and its electrical life is as high as 55,000. Used for medical equipment
5. Horizontally mounted right-angle toggle switch
Compared to the vertical switch, it only changes direction to horizontal, so it is horizontally mounted right-angle toggle switch. The contacts are double-pole double-throw and the bottom of the terminal is Epoxy Seal. Mostly used for computer peripherals.
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