PRESENTATION ON THE PRESENTATION ON THE TOPICTOPIC

By: Rahul By: Rahul agarwalagarwal

INTRODUCTIONINTRODUCTIONOverload protection circuit are Overload protection circuit are

required in inverters and required in inverters and uninterrupted power supplies to uninterrupted power supplies to make sure that the loads connected make sure that the loads connected to them don’t exceed the maximum to them don’t exceed the maximum power rating. power rating.

PRINCIPLES PRINCIPLES

MATERIALS USED IN OPCMATERIALS USED IN OPC OPTOCOUPLEROPTOCOUPLER

IC 555IC 555

RELAY ( N/C)RELAY ( N/C)

OPTOCOUPLER OPTOCOUPLER The MCT & MCT 2E devices consists The MCT & MCT 2E devices consists

of a gallium arsenide infrared of a gallium arsenide infrared emitting diode optically couples to a emitting diode optically couples to a monolithic silicon phototransistor monolithic silicon phototransistor detector. detector.

APPLICATION OF APPLICATION OF OPTOCOUPLEROPTOCOUPLER• General purpose switching circuit General purpose switching circuit • Interfacing and coupling system of Interfacing and coupling system of

different potentials & impedancesdifferent potentials & impedances• I/O interfacing I/O interfacing • Solid state relaysSolid state relays• Monitor & detection circuitMonitor & detection circuit

555 TIMER IC555 TIMER IC• The 555 timer IC is an integrated The 555 timer IC is an integrated

circuit (chip) used in a variety of circuit (chip) used in a variety of timer, pulse generation and oscillator timer, pulse generation and oscillator applications.applications.

PINS OF 555 TIMER IC PINS OF 555 TIMER IC PINPIN NAME NAME PURPOSEPURPOSE11 GND GND Ground, low level (0V)Ground, low level (0V)22 TRIGTRIG Out rise & interval starts, when this Out rise & interval starts, when this

input fall below 1/3Vccinput fall below 1/3Vcc33 OUTOUT This output is driven to +Vcc or GNDThis output is driven to +Vcc or GND44 RESETRESET A timing interval may be interrupted A timing interval may be interrupted

by driving this input to GNDby driving this input to GND55 CTRLCTRL ““Control” access to the internal Control” access to the internal

voltage divider (by default,2/3 Vcc)voltage divider (by default,2/3 Vcc)66 THRTHR The interval ends when the voltage The interval ends when the voltage

at THR is greater than at CTRLat THR is greater than at CTRL77 DISDIS Open collector ; may discharge a Open collector ; may discharge a

capacitor between intervalcapacitor between interval88 V+,VcV+,Vc

ccPositive supply voltage is usually Positive supply voltage is usually between 3 & 1between 3 & 1

RelayRelay• What is a relay?What is a relay?• We know that most of the high end industrial application We know that most of the high end industrial application

devices have relays for their effective working. Relays are devices have relays for their effective working. Relays are simple switches which are operated both electrically and simple switches which are operated both electrically and mechanically. Relays consist of a n electromagnet and also mechanically. Relays consist of a n electromagnet and also a set of contacts. The switching mechanism is carried out a set of contacts. The switching mechanism is carried out with the help of the electromagnet. There are also other with the help of the electromagnet. There are also other operating principles for its working. But they differ operating principles for its working. But they differ according to their applications. Most of the devices have according to their applications. Most of the devices have the application of relays.the application of relays.

• Why is a relay used?Why is a relay used?• The main operation of a relay comes in places where only a The main operation of a relay comes in places where only a

low-power signal can be used to control a circuit. It is also low-power signal can be used to control a circuit. It is also used in places where only one signal can be used to control used in places where only one signal can be used to control a lot of circuits. The application of relays started during the a lot of circuits. The application of relays started during the invention of telephones. They played an important role in invention of telephones. They played an important role in switching calls in telephone exchanges. They were also switching calls in telephone exchanges. They were also used in long distance telegraphy. They were used to switch used in long distance telegraphy. They were used to switch the signal coming from one source to another destination. the signal coming from one source to another destination. After the invention of computers they were also used to After the invention of computers they were also used to perform Boolean and other logical operations. The high end perform Boolean and other logical operations. The high end applications of relays require high power to be driven by applications of relays require high power to be driven by electric motors and so on. Such relays are called electric motors and so on. Such relays are called contactors.contactors.

• This article shows you how to test a relay. A relay will This article shows you how to test a relay. A relay will usually have a coil, pole terminal and a set of contacts. The usually have a coil, pole terminal and a set of contacts. The set of contacts that are open when the relay is not set of contacts that are open when the relay is not energized are called normally open (N/O) contacts and the energized are called normally open (N/O) contacts and the set of contacts that are closed when the relay is not set of contacts that are closed when the relay is not energized are called normally closed (N/C) contacts. The energized are called normally closed (N/C) contacts. The following steps can be used to perform the testing of the following steps can be used to perform the testing of the relay using a multimeter.relay using a multimeter.

• Keep the multimeter in the continuity check mode.Keep the multimeter in the continuity check mode.• Check for continuity between the N/C contacts and pole.Check for continuity between the N/C contacts and pole.• Check for discontinuity between N/O contacts and the pole.Check for discontinuity between N/O contacts and the pole.• Now energise the relay using the rated voltage. For Now energise the relay using the rated voltage. For

example use a 9V battery for energising a 9V relay. The example use a 9V battery for energising a 9V relay. The relay will engage with clicking sound.relay will engage with clicking sound.

• Now check for continuity between N/O contacts and pole.Now check for continuity between N/O contacts and pole.• Also check for discontinuity between N/C contacts and pole.Also check for discontinuity between N/C contacts and pole.• As a final test, measure the resistance of the relay coil As a final test, measure the resistance of the relay coil

using a multimeter and check whether it is matching to the using a multimeter and check whether it is matching to the value stated by the manufacturevalue stated by the manufacture

• Relay ApplicationsRelay Applications• Relays are used to realize logic functions. They play a very Relays are used to realize logic functions. They play a very

important role in providing safety critical logic.important role in providing safety critical logic.• Relays are used to provide time delay functions. They are Relays are used to provide time delay functions. They are

used to time the delay open and delay close of contacts.used to time the delay open and delay close of contacts.• Relays are used to control high voltage circuits with the Relays are used to control high voltage circuits with the

help of low voltage signals. Similarly they are used to help of low voltage signals. Similarly they are used to control high current circuits with the help of low current control high current circuits with the help of low current signals.signals.

• They are also used as protective relays. By this function all They are also used as protective relays. By this function all the faults during transmission and reception can be the faults during transmission and reception can be detected and isolated.detected and isolated.