Unit 45 Industrial Systems : Assignment

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Unit 45 Industrial Systems: - Assignment 3IntroductionMeasuring systems and closed loop systems are used in many applications that we take for granted inday to day objects. In order for a feedback loop to be complete back to the central processor there mustfirst be some form of measuring device to provide the signal input to the PID controller allowing for thechange in the output to be monitored and changed.Practical Measurement SystemAn AC supply from mains is input into the electrical power unit and is then converted into a DC output tothe motor control unit, PE482A, mounted below, this is done through the bridge rectifier that can beseen on the power electronics control unit PE483. A load can be applied to the DC motor in the form of amagnet surrounding the metal disk coupled to the output shaft of the motor. The motor control unitreceives a feedback signal from the motor via a tachogenerator mounted on the opposite end of theshaft. This can then alter the performance depending on how much of the load is applied, the PID shouldensure the motor maintains a constant speed. On this particular set up the speed can be adjusteddepending on different variables such as speed or torque.The three black potentiometers are all connected to a summation point and they can be used to select aset parameter value for the motor to achieve. This could be a variety of different values such as; voltage,current or armature speed.CharacteristicsThe inverter circuit in the motor control system has a continuous AC supply from the socket on the desk.The motor in the system requires a constant DC supply and as such the full bridge rectifier in theinverter circuit will supply this. The DC voltage generated from the rectifier is then supplied to thecontrol circuit seen below the inverter. The control circuit enables the user to adjust the performance ofthe motor by making it run at a higher speed or with more torque. The control circuit is a closed loopsystem that has and input, process and an output then with a feedback signal, which in this case issupplied by a reference from the motor as described previouslyThe main use for the tachogenerator is to feedback information from the motor thus allowing thecontrol circuit to supply a calculated voltage that will allow it to reach and maintain a set speed. Anincrease in the voltage will increase the speed and a decrease in voltage will do the opposite. Thelimitation of this setup is that only voltage can be changed from the control circuit, other parameterscannot be changed.2
Advantages/ disadvantagesThe equipment used in this test is old and obsolete and so spare parts are difficult to get hold of andmay need to be specially made in order to carry out a repair. There would also be further costs shouldany of these components not be suitable for the circuit and need replacing with others. The running ofthe hardware may also come at a cost, along with a rig in which it is safe for the testing to take place.The wiring and set up of the rig is not so accurate or intuitive as it is selected by potentiometers thatshould fail or drift.The equipment is useful in the fact that, if testing is successful, the rig can eb placed straight into anapplication and run as designed and tested. There will be no error and 100% guarantee of a workingproduct. Extensive testing can take place manipulating many variables to produce just as many differingresults. These kits can also be measured electronically and shown on an oscilloscope, these could also berecorded and printed for records.Computer-based Measurement SystemUsing a simulator will show graphical results based on circuits built within the simulation. Componentsand parameters in the circuit can be changed quickly and easily in order to achieve the desired output.Should this designed circuit then be replicated in real life the exact same results should be achieved dueto the accuracy of the results.3
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