31-10-2012, 10:59 AM
LDR CONTROLLED ILLUMINATION CONTROLLER
LDR.doc (Size: 33 KB / Downloads: 28)
PRINCIPLE:
The LDR light dependent resistor is varying resistance with light intensity. This will be mostly lenear to the light intensity.
During the darkness the resistance of LDR shoots up to Meg ohm range. When LDR is illuminated by means of the sunlight, the resistance of LDR suddenly decreases (below 10 kilo ohm).
Then the LDR is connected to a wheat stone bridge. There the resistance is converted into differential voltage, then the voltage is amplified and given to the comparator. The comparator compares the light intensity with the required level and it will produce output depends on the intensity. This O/P is connected to the driver circuit which drives the bulb through the triac.
CONTROL SRATEGIES:
The requirements on the motion of the load components determine the performance of the drive. If these requirements are not well defined it is more difficult both to select the control strategy and to dimension the actuator and the power amplifier. More realistic informations can be deduced by characterizing firstly the origin of the load torque and secondly the steady state and dynamic behavior of the moving components. For characterizing the steady state behavior, it is firstly requested to establish if the steady state error of the controlled speed or position should be dependent or independent on the load torque excursions. Secondly it is requested to indicate if the operating conditions of the motor should be fixed in order to optimize the efficiency. For characterizing the dynamic behavior of the moving components, reference will be made to the previously defined classification of the load torques.
SELECTING A DRIVE:
Selection of an electrical drive for a particular application is precisely the choice of a system which provides the required range of speed control most economically with desired accuracy and transient response. The drive must also be reliable requiring least maintenance and having good efficiency. The drive is also characterized by the speed torque curve of the load. The range of speed control of drive is also characterized by the degree of smoothness that can be achieved above and below the base speed. The range of speed control is sometimes required in other direction also. A reversible drive is chosen in this case. A D.C drive can be found to be very efficient having a stable wide range of speed control in either direction of rotation.
CONTROL CIRCUIT:
The control circuit is the final control element of our project. This circuit has an integrator, comparator, optocoupler and a triac.
INVERTING AMPLIFIER:
The inverting amplifier is most widely used of all the opamps. As the name itself indicates this amplifier inverts the input ie, there will be a phase shift of 180 degrees between input and output voltages. As in the circuit shown the output voltage Vout is fed back to the inverting input terminal through the Rf-R1 network ,where Rf is the feedback resistor. Input signal Vi is applied to the inverting input terminal through R1 and the non inverting input terminal of opamp is grounded.
OPTOCOUPLER:
Opt coupler is a internally light operated device. The light is used for the triggering of the elements. The optocoupler which we are using is MOC 3020. It is used for optical coupling. It consists of infrared light emitting doide and a diac sensor. The internal sensing part of MOC is having diac. It actually acts as triac triggering by LED source. The output of the MOC is given to the gate of triac.
TRIAC:
A TRIAC can conduct in both directions and is normally used in ac phase control. It can be considered as two SCRs connected in anti parallel with a common gate connection. Since triac is a bi-directional device, its terminal cannot be designated as anode or cathode. A triac is identified as a three electrode or triode as semiconductor switch. Conduction is triggered by a gate signal. Conduction can be obtained in either direction with a appropriate gate signal. In our project we are using a 40A triac, BTA 21.