What is PID?
PID (Proportional Integral Derivative) is a control loop feedback mechanism widely used in industrial control systems. The PID controller is most commonly used in closed-loop control systems (with feedback). The PID controller calculates the error value as the difference between the variable parameter measured value and the desired set value. The controller will minimize the error by adjusting the input control value. For best results, the PID parameters used in the calculation must be adjusted according to the nature of the system – while the control type is the same, the parameters must depend on the characteristics of the system.
In there:
+ P (Proportional): is a proportional adjustment method, which helps to generate an adjusted signal proportional to the input error according to the sampling time.
+ I (Integral): is the integral of the deviation over the sampling time. Integral control is a tuning method to generate tuning signals so that the error is reduced to zero. This tells us the total instantaneous error over time or the accumulated error in the past. The smaller the time, the stronger the integral adjustment effect, corresponding to the smaller deviation.
+ D (Derivative): is the differential of the error. The differential control generates an adjustment signal that is proportional to the rate of change of the input bias. The larger the time, the stronger the differential tuning range, which corresponds to the faster the regulator responds to input changes.
Types of PID Controllers:
+ Proportional Controller (P).
+ PI (Proportinal and Integral Controller) is called proportional and integral controller.
+ PD (Proportional and Derivative (PD) Controller ) is called the derivative controller.
+ The PID (Proportional, Integral, and Derivative (PID) Controller) is a proportional-integral-derivative (differential) controller.
Why is PID control needed?
In order to understand PID control easily, let’s look at an example: Controlling the temperature of the water discharged from an industrial gas heater.
Case 1: Manual Temperature Control
To control the temperature for the discharge water from an industrial gas heater, the operator must watch the temperature gauge and adjust the fuel gas valve accordingly. If the water temperature exceeds the requirement, the operator must reduce the opening angle of the gas valve (close the valve just enough) to reduce the fuel to reduce the discharge water temperature to the desired value. If the water temperature drops below the required level, the operator must increase the opening angle of the gas valve (open the valve just enough) to put more fuel into the furnace to increase the discharge water temperature to the desired value.
The control task performed by the operator is called feedback control, because the operator changes the combustion rate (fuel feed) based on feedback from the process through the temperature gauge. . The operator, valve, heater and temperature gauge form a control loop. Any operator change to the gas valve affects the temperature, and the results are fed back to the operator via the heat meter, and it is closed loop.
Case 2: Automatic Temperature Control (PID control)
Instead of controlling the temperature manually as above, we can easily control the temperature of the water discharged from the industrial gas heater by an automatic method (using a PID controller). And there is some work that needs to be done to make this system work automatically as follows:
+ Using an electronic temperature measuring device
+ Using electronic control valve (can be integrated with actuator, position locator, ..)
+ Use the controller (PID) and set it up and connect it to the temperature measuring device and the electronic control valve.
The operator sets the setpoint parameter for the PID controller to the desired temperature and the controller output is to set the position of the control valve (set the valve opening angle value). The temperature measured from the temperature sensor, called the process variable, is then transmitted to the PID controller. The controller compares the temperature value received from the sensor with the original setpoint temperature value and calculates the difference or error between the two signals. Based on the error and adjustment constants of the controller, the controller calculates the appropriate output to control the valve opening angle in the correct position to keep the temperature always at the setpoint value. If the temperature rises above its set point, the controller will decrease the valve opening angle and vice versa.
Application of PID controller
1. Application of PID controller in Air Conditioning.
Some heating and air conditioning systems now use a PID controller to regulate the system.
- You have the indoor temperature set to 80 degrees F. This setting is called Setpoint, or SP for short.
- The current reading from the thermostat is 73 degrees F. This term is called the process variable, PV for short.
- The part for heating or cooling is called the control variable, or CV for short. In addition, the control variable is also known as the MV variable.
There are different control actions for indoor temperature control. A direct acting device control means the Setpoint calculation minus the process variable ( SP-PV ). There are many surrounding factors that can affect the parameter adjustment process.
There are different control actions for indoor temperature control. A direct acting device control means the Setpoint calculation minus the process variable ( SP-PV ). There are many surrounding factors that can affect the parameter adjustment process.
2. Application of PID controller in Water Level Control.
This controller runs automatically without human intervention. The following are required:
- The controller receives 4-20mA signal and 4-20mA PID output.
- 4-20mA Water Level Sensor
- Flush output signal control valve 4-20mA
The PID controller will receive the signal from the water level sensor. Then set the display and control water level as required. The controller will operate automatically, without supervision. The PID compares the setting signals and the PID algorithms to maintain the correct water level.
3. Application of PID controller in Inverter.
To perform automatic control of the inverter, it is necessary to prepare:
- Control valve
- Temperature sensor
- PID control inverter for motor
- PID temperature controller for control valve
The temperature sensor controls the inverter speed and water flow as it passes through the control valve. Ensure even mixing and temperature in the tank, increase or decrease the temperature depending on the flow. The evenness of the solution depends on the inverter.
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