PRESENTATION ON THE TOPIC By: Rahul agarwal INTRODUCTION Overload protection circuit are required in inverters and uninterrupted power supplies to make sure that the loads connected to them don’t exceed the maximum power rating. PRINCIPLES MATERIALS USED IN OPC OPTOCOUPLER IC 555 RELAY ( N/C) OPTOCOUPLER The MCT & MCT 2E devices consists of a gallium arsenide infrared emitting diode optically couples to a monolithic silicon phototransistor detector. APPLICATION OF OPTOCOUPLER • General purpose switching circuit • Interfacing and coupling system of different potentials & impedances • I/O interfacing • Solid state relays • Monitor & detection circuit 555 TIMER IC • The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. PINS OF 555 TIMER IC PIN 1 2 NAME GND TRIG PURPOSE Ground, low level (0V) Out rise & interval starts, when this input fall below 1/3Vcc 3 OUT This output is driven to +Vcc or GND 4 RESET 5 6 7 8 A timing interval may be interrupted by driving this input to GND CTRL “Control” access to the internal voltage divider (by default,2/3 Vcc) THR The interval ends when the voltage at THR is greater than at CTRL DIS Open collector ; may discharge a capacitor between interval V+,Vcc Positive supply voltage is usually between Relay • What is a relay? • We know that most of the high end industrial application devices have relays for their effective working. Relays are simple switches which are operated both electrically and mechanically. Relays consist of a n electromagnet and also a set of contacts. The switching mechanism is carried out with the help of the electromagnet. There are also other operating principles for its working. But they differ according to their applications. Most of the devices have the application of relays. • Why is a relay used? • The main operation of a relay comes in places where only a lowpower signal can be used to control a circuit. It is also used in places where only one signal can be used to control a lot of circuits. The application of relays started during the invention of telephones. They played an important role in switching calls in telephone exchanges. They were also used in long distance telegraphy. They were used to switch the signal coming from one source to another destination. After the invention of computers they were also used to perform Boolean and other logical operations. The high end applications of relays require high power to be driven by electric motors and so on. Such relays are called contactors. • This article shows you how to test a relay. A relay will usually have • • • • • • • a coil, pole terminal and a set of contacts. The set of contacts that are open when the relay is not energized are called normally open (N/O) contacts and the set of contacts that are closed when the relay is not energized are called normally closed (N/C) contacts. The following steps can be used to perform the testing of the relay using a multimeter. Keep the multimeter in the continuity check mode. Check for continuity between the N/C contacts and pole. Check for discontinuity between N/O contacts and the pole. Now energise the relay using the rated voltage. For example use a 9V battery for energising a 9V relay. The relay will engage with clicking sound. Now check for continuity between N/O contacts and pole. Also check for discontinuity between N/C contacts and pole. As a final test, measure the resistance of the relay coil using a multimeter and check whether it is matching to the value stated by the manufacture • Relay Applications • Relays are used to realize logic functions. They play a very important role in providing safety critical logic. • Relays are used to provide time delay functions. They are used to time the delay open and delay close of contacts. • Relays are used to control high voltage circuits with the help of low voltage signals. Similarly they are used to control high current circuits with the help of low current signals. • They are also used as protective relays. By this function all the faults during transmission and reception can be detected and isolated.