AYASKANTA SWAIN for his consistent help and guidance and all faculty members and staff of the Department of. 4.8: Front panel of the LabVIEW window 45 FIG.4.9: Block diagram of the LabVIEW window 45 FIG 4.10 Graph showing reference and output RPM for the observed. A control system seeks to make the output of a physical system track a desired reference input by setting physical system inputs. Control system consists of subsystem and process that are brought together to control the output of the process.
TYPES OF CONTROL SYSTEM
In contrast, digital cameras, video games, and cell phones are not examples of a control system because they do not attempt to track a reference input. Closed-loop control system - A closed-loop control system is one that determines the input forcing function in part by the system response. In this respect, a closed-loop system offers a distinct advantage over an open-loop system.
OBJECTIVES OF CONTROL SYSTEM
CONTROL STRATEGIES
BASIC COMPONENTS OF A CONTROL SYSTEM
So, if a valve needs to be operated, actuators are the device that converts the control signal into the physical action of opening or closing the valve. Decision: Based on the measurement, the controller decides what to do to keep the variable to be controlled at the desired value. Action: Based on the decision made by the controller, the system takes action and this is usually done by the final control element.
PARTS OF A CONTROL SYSTEM
Output or the Controlled Variable: It is the signal or the plant output which we need to control. In our case the speed of the DC Motor is the controlled variable which is
Manipulated Variable: The manipulated variable is used to maintain the controlled variable at the desired set point. In this thesis the output of the controller is the
Delay time: This is the time required to return to the set point after a change has occurred in the variable to be measured by a control system.
Offset: It is the difference between the set point and the measured variable after a new controlled variable level is reached
Disturbance: It is the additional undesirable input to the plant that tries to deviate the controlled variable from its set point and it is the signal which is to be compensated by
PERFORMANCE OF A CONTROL SYSTEM
Peak Time : It is the time required by the response to reach its first peak
Settling Time: It is the time required by the system to settle down within 1% range of the final value
CLASSIFICATION OF A CONTROL SYSTEM
These differences have virtually no impact on control response, although they significantly affect controller selection. The manipulated variable is the most important criterion for determining the control response. Depending on the controller output, the control signal can be continuous or discontinuous. Continuous Controller: In a continuous controller, the output of the controller or the manipulated variable can be any value within the output range of the controller.
Continuous controller: In continuous controller the output of the controller or the Manipulated Variable can have any value within the controller output range. The
Discontinuous controller: In discontinuous controller the manipulated variable can only have discrete values. Depending upon the different states of the manipulated
CONTINUOUS CONTROLLERS
The controller gain determines how much a given change in error changes the output of the controller. In PD Controller, a pure differentiator is added in the forward path of the feedback control system. At this point, the output of the differentiator is much larger than the integral or proportional gain.
The output from the derivative decreases with time and becomes negligible as the error approaches zero. Adding derivative action to a proportional controller increases system stability, reduces % overshoot, reduces rise time and decay time, and improves system transient response. In a PD controller, the output of the controller is the result of the addition of the P and D control elements.
PI controller: As most of the process cannot operate with lag, they need to be controlled at their set points and to achieve this additional intelligence needs to be added to the proportional controller which is achieved by providing integral operation of the original proportional controller. In a PI controller, as long as an error is present, the controller changes its output and when the error is zero or disappears, the controller does not change its output. In a PI controller, the output of the controller changes proportionally to the integral of the error.
The output of the controller or the manipulated variable is obtained by adding P,I and D components and their associated coefficient.
DISCONTINUOUS CONTROLLERS
SELECTING A CONTROLLER
For applications with low requirements for controlling dynamics and where the system does not exhibit large delays, I-controllers are used. If the speed of response is required to be as high as possible, regardless of the large delay, PID controllers are used.
Chapter 2
Data Acquisition System
INTRODUCTION
Data sampling is the process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numerical values that can be manipulated by a computer. Data acquisition systems (abbreviated as DAS or DAQ) typically convert analog waveforms to digital values for processing.
COMPONENTS OF A DATA ACQUISITION SYSTEM
- Transducers
- Signals
Analog signals
Digital signals
- Signal conditioning
- Data Acquisition Hardware
- Driver and Application Software
- DAQ HARDWARE
Sometimes the signals generated are too difficult or too unsafe to measure directly using a data acquisition device. For example, signal conditioning is essential for an effective data acquisition system when dealing with extremely high and low signals, noisy environments, high voltages, or simultaneous signal measurement. Data collection hardware acts as an interface between the computer and the outside world.
It can come in either of two forms - modules that can be plugged into a computer port (parallel, serial, USB, etc.) or cards connected to slots (S-100 bus, ISA, MCA, PCI, PCI-E, etc.) in the motherboard. Driver software: The computer and data acquisition hardware are transformed with software into a complete tool for data acquisition, analysis and presentation. A data acquisition device does not function properly without software to control or drive the hardware.
Driver software can be defined as the layer of software for easy communication with the hardware. Application Software: Application software allows full control and visibility of various data operations that can be performed on the input signals. An electronic component found in many data acquisition devices that produces an analog output signal.
Data acquisition devices have single or differential input, many devices support both configurations.
2.3.1 Resolution
- Sampling rate
- DAQ Hardware Used
- DAQ software used
- Chapter 3
The sampling theorem ensures that band-limited signals (i.e., signals limited by the maximum frequency) if sampled at a sampling rate greater than twice the maximum frequency, can be completely reconstructed from their sampled version. A phenomenon known as aliasing occurs when the sampling rate is lower than the Nyquist sampling rate (undersampling). NI LabVIEW is used as application software to control all processes and system operation.
It provides integration with thousands of hardware devices and offers hundreds of built-in libraries for advanced analysis and data visualization for creating virtual instruments. In the block diagram, you develop graphical code to retrieve and analyze your measurement data, branch and repeat the code, and interface with elements on the front panel. Data acquisition applications typically involve acquiring signals, displaying the data in a front panel graph or chart, and saving the data to a file.
CONTROLLER , ACTUATOR AND SENSOR
- INTRODUCTION
- PID CONTROLLER
- Proportional term : The proportional gain changes the output in such a way that the change is proportional to the current error
- Integral term: The integral term makes a change to the output that is proportional to both the error magnitude and the error duration. The error is accumulated over the time and this
- Derivative term: The derivative term is calculated by determining the slope of the error with respect to time and multiplying the derivative gain Kd with the rate of change of error
- PWM GENERATOR
- SENSOR
- Chapter 4
PID controller is basically designed to control the output of the process to a fixed value called the set point or the reference. In the above block diagram, control element is the controller used to control the output of the process. In this thesis we used an infrared reflector sensor to sense the speed of the car and NI PCI 6221 configured in a computer as a transducer to provide the digital output to the controller input.
The output of the controller is used by the PWM Generator to produce the PWM waveform which will be the input to the system which in our case is a DC Motor. The PID controller (which is actually configured as a P controller for an open-loop system) gives output as the duty cycle of the PWM waveform generated by the PWM generator. The following figure shows how the output of the proportional controller changes with a change in gain of the controller.
As shown in Figure 3.4, when the value of the proportional gain increases the sensitivity of the system with respect to the change in the error value increases, i.e. The integral reduces or even completely eliminates the steady-state error and shortens the response time to change the error, but may cause the controller output to exceed the set value. To calculate the output power of the PID controller, the proportional, integral and derivative terms are added.
The IR reflector sensor detects the speed of the DC motor and provides series of on/off pulses according to the speed of the DC motor.
IMPLEMENTATION OF LABVIEW BASED CONTROLLER
- INTRODUCTION
- DC MOTOR - AN OVERVIEW
- DC MOTOR SPEED CONTROLLER
- DC motor speed control using PWM
- DC MOTOR INTERFACING WITH DAQ CARD: IC L293D
- OPEN LOOP SYSTEM FOR DC MOTOR SPEED CONTROL
- EXPERIMENTAL SETUP .1 DC motor hardware setup
- Software setup in LabVIEW
- RESULTS AND DISCUSSION
Therefore, the speed of the DC motor can be controlled by varying the field current. The controller may or may not measure the speed of the motor to use as feedback for error reduction purposes. In this thesis we implemented an open loop system without feeding the sensor output to the controller input.
So how to change the speed of the motor with fixed input voltage led to the development of systems known as speed controllers. Basically, the output of the PWM Generator is given to the EN1 pin of the L293D. In open loop system, the speed of the DC motor can be changed by changing the duty cycle of the PWM which depends on PID input.
In our case of a DC motor, the equilibrium condition is the desired or reference value speed of the motor. The other two terminals of the sensor are used to supply power to the sensor (0 and 5V). The output signal is a square waveform whose frequency varies proportionally to the speed of the motor.
This signal is observed in a CRO to measure the engine RPM by doing the calculation as. The controller (P controller) is implemented in LabVIEW with a setpoint control as the desired motor RPM. The output of the controller which is the duty cycle of the required PWM is fed into the input of the PWM generator.
CONCLUSION AND FUTURE WORK
- Design and FPGA implementation of PID controller by Sonali Gupta
- Design and FPGA implementation of PID controller for dc motor control by Rajesh Garg and Gourav Kumar
- Pulse width modulation by atmel
- Control systems engineering by Norman S Nise (California State Polytechnic University,Pomona)
- Embedded system design A unified hardware/software introduction by Frank Vahid
- Application of a LabVIEW for Real-Time Control of Ball and Beam System by “Basil Hamed”
Design and FPGA Implementation of PID Controller for DC Motor Control by Rajesh Garg and Gourav Kumar Rajesh Garg and Gourav Kumar. Kamoun, “A digital PID controller for real-time and multi-loop control: A comparative study,” in controller for real-time and multi-loop control: A comparative study,” in Proc.
