wk116 smoke fire detector water sprinkler

8/2/2019 WK116 Smoke Fire Detector Water Sprinkler

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www.WineYardTechnologies.com WK116

Smoke/Fire Detector With Automatic Water

Sprinkler System to Avoid Fire Accidents

Wine Yard Technologies, A2, II Floor, Eureka Court, Beside Image Hospitals, Himayathnagar, Hyderabad - 73R&D Center: 3-5-587, Near Narayana College, Vittalwadi, Himayathnagar, Hyderabad - 29


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INDEX

1. ABSTRACT

2. BLOCK DIAGRAM

3. POWER SUPPLY

4. SMOKE SENSOR

5. DECADE COUNTER

6. SWITCHING CIRCUIT

7. RELAY

8. SCR FIRING CIRCUIT

9. LED

10. AC MOTOR

11. APPLICATIONS

12. ADVANTAGES

13. CONCLUSION

14. REFERENCES



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security against fire. The detector will sense smoke caused by fire

accident and switch on the water sprinkler to prevent major damage.

The circuit works off a 5V battery or 5V regulated power supply

and uses smoke detector as its principal component. Initially, when the

power is switched on, decade counter is reset by power-on-reset

components. As a result, output of Decade counter goes high and the entire

circuit is in idle state. LED indicates the power status. In the event of

smoke, decade counter is clocked by the pulses from the piezo ceramic

element connected to its clock pin. All the outputs of decade counter are

fed to relay- driver switching transistor through diodes connected in OR

mode. Immediately after clocking, any of the outputs of decade counter

would go high and NPN transistor would conduct. As a result, SCR is fired

through its gate. This, in turn, energizes relay. The relay contacts can be

used to switch any water sprinkler device to prevent major damage

caused by fire. The circuit can be reset by momentarily pressing switch.

Two Zener diodes at the clock input of IC1 are used for protection

against high voltage input. In the case of repeated false triggering of

decade counter, add a 100nF capacitor in parallel to the piezoceramicelement.



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Block Diagram


Smoke / fire

detector

Decade

Counter

SCR Firing

Circuit

5 V

Supply

Relay

Power supply to all sections

Step

down

T/F

Bridge

Rectifier

Filter

CircuitRegulator

Switching

Circuit

LED

Display

AC Input AIR

Blower


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POWER SUPPLY



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POWER SUPPLY DESIGN



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POWER SUPPLY:

The input to the circuit is applied from the regulated power supply. The a.c. input i.e.,

230V from the mains supply is step down by the transformer to 12V and is fed to a

rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order to get

a pure d.c voltage, the output voltage from the rectifier is fed to a filter to remove any a.c

components present even after rectification. Now, this voltage is given to a voltage

regulator to obtain a pure constant dc voltage.

Fig 4: Power supply

Transformer:

Usually, DC voltages are required to operate various electronic equipment and

these voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the

a.c input available at the mains supply i.e., 230V is to be brought down to the required


Regulator

FILTER

HF

Bridge

Rectifier

Step down

transformer

230V AC

50Hz

D.C

Output


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voltage level. This is done by a transformer. Thus, a step down transformer is employed to

decrease the voltage to a required level.

Fig 5: Transformer

Rectifier:

The output from the transformer is fed to the rectifier. It converts A.C. into

pulsating D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a

bridge rectifier is used because of its merits like good stability and full wave rectification.

Fig 6: Rectifier



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The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both

half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit

has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally

opposite ends of the bridge. The load resistance is connected between the other two ends of the

bridge.

For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas

diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load

resistance RL and hence the load current flows through RL.

For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas,

D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load

resistance RL and hence the current flows through RL in the same direction as in the previous

half cycle. Thus a bi-directional wave is converted into a unidirectional wave.



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Fig 7: Bridge rectifier



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Filter:

Capacitive filter is used in this project. It removes the ripples from the output of rectifier

and smoothens the D.C. Output received from this filter is constant until the mains voltage

and load is maintained constant. However, if either of the two is varied, D.C. voltage

received at this point changes. Therefore a regulator is applied at the output stage.

Voltage regulator:

As the name itself implies, it regulates the input

applied to it. A voltage regulator is an electrical

regulator designed to automatically maintain a constantvoltage level. In this project, power supply of 5V and

12V are required. In order to obtain these voltage

levels, 7805 and 7812 voltage regulators are to be used.

The first number 78 represents positive supply and the numbers 05, 12 represent the

required output voltage levels. The L78xx series of three-terminal positive regulators is

available in TO-220, TO-220FP, TO-3, D2PAK and DPAK packages and several fixed

output voltages, making it useful in a wide range of applications. These regulators can

provide local on-card regulation, eliminating the distribution problems associated with

single point regulation. Each type employs internal current limiting, thermal shut-down and

safe area protection, making it essentially indestructible. If adequate heat

sinking is provided, they can deliver over 1 A output current. Although

designed primarily as fixed voltage regulators, these devices can be used

with external components to obtain adjustable voltage and currents.



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Smoke Detector

DESCRIPTION



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This sensor is used to detect any fire accidents. Whenever a fire accident occurs some

smoke is generated. This sensor detest that smoke and gives the response to the

microcontroller. The arrangement of this sensor in our sensor board is as shown below.



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CD 4017 Decade Counter/Divider



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General Description

The CD4017BM/CD4017BC is a 5-stage divide-by-10 Johnson counter

with 10 decoded outputs and a carry out bit. The CD4022BM/CD4022BC

is a 4-stage divide-by-8 Johnson counter with 8 decoded outputs and a

carry-out bit. These counters are cleared to their zero count by a logical

``1'' on their reset line. These counters are advanced on the positive

edge of the clock signal when the clock enable signal is in the logical

``0'' state. The configuration of the CD4017BM/CD4017BC and

CD4022BM/CD4022BC permits medium speed operation and assures a

hazard free counting sequence. The 10/8 decoded outputs are normally

in the logical ``0'' state and go to the logical ``1'' state only at their

respective time slot. Each decoded output remains high for 1 full clock

cycle. The carry-out signal completes a full cycle for every 10/8 clock

input cycles and is used as a ripple carry signal to any succeeding

stages.

Features

Wide supply voltage range 3.0V to 15V

High noise immunity 0.45 VDD (typ.)

Low power Fan out of 2 driving 74L

TTL compatibility or 1 driving 74LS

Medium speed operation 5.0 MHz (typ.) with 10V VDD

Low power 1 0 mW (typ.)

Fully static operation

Applications

Automotive

Instrumentation

Medical electronics

Alarm systems

Industrial electronics



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Remote metering



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Timing Diagrams



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TRANSISTOR :

A Transistor consists of two p-n junctions formed by sandwiching either p-type or

n-type semiconductor between a pair of opposite types . Accordingly ; there are two types

of transistors , namely ;

(i) n-p-n transistor

(ii) p-n-p transistor

An n-p-n transistor is composed of two n-type semiconductors

Seperated by a thin section of p-type as shown in fig . How ever a p-n-p transistor is

formed by two p-sections seperated by a thin n-type as shown in fig.

In each type of transistor , the following points may be noted :

(i) There are two p-n junctions . Therefore , a transistor may be regarded as a

combination of two diodes connected back to back .



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(ii) There are three terminals , taken from each type of semiconductor .

(iii) The middle section is a very thin layer. This is most important factor in the

function of a transistor.

5.7 COMMONLY USED TRANSISTOR CONNECTION:

Out of the three transistor connections, the common emitter circuit is the most

efficient. It is used in about 90 to 95 per cent of all transistor applications. The main

reasons for the widespread use of this circuit arrangement are :

HIGH CURRENT GAIN :

In a common emitter connection, IC

is the output current and IB input current. In this circuit arrangement, collector current is

given by ;

IC = B IB + ICEO

As the value of B is very large, therefore, the output current IC is much more than the input

current IB. Hence, the current gain in CE arrangement is very high. It may range from 20

to 500.

HIGH VOLTAGE AND POWER GAIN :

Due to high current gain, the common emitter circuit has the highest voltage and

power gain of three transistor connections. This is the major reason for using the transistor

in this circuit arrangement.

MODERATE OUTPUT TO INPUT IMPEDANCE RATIO :



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In a common emitter circuit, the ratio of output impedance to input impedance is

small (about 50). This makes this circuit arrangement an ideal one for coupling between

various transistor stages. However, in other connections, the ratio of output impedance to

input impedance is very large and hence coupling becomes highly inefficient due to gross

mismatching.

5.8 TRANSISTOR AS AN AMPLIFIER IN CE ARRANGEMENT :

Below figure shows the common emitternpn amplifier circuit. Note that a battery

VBB is connected in the input circuit in addition to the signal voltage. This d.c. voltage is

known as bias voltage and its magnitude is such that it always keeps the emitter-base

junction forward biased regardless of the polarity of the signal source.

OPERATION :

During the positive half-cycle of the signal, the forward bias across the emitter-base

junction is increased. Therefore, more electrons flow from the emitter to the collector via



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the base. This causes an increase in collector current. The increased collector current

produces a greater voltage drop across the collector load resistance RC. However, during

the negative half-cycle of the signal, the forward bias across emitter-base junction is

decreased. Therefore, collector current decreases. This results in the decreased output

voltage ( in the opposite direction ). Hence, an amplified output is obtained across the

load.

5.10 PERFORMANCE OF TRANSISTOR AMPLIFIER :

The performance of a transistor amplifier depends upon input resistance , output

resistance , effective collector load , current gain , voltage gain and power gain. As

common emitter connection is universally adopted , therefore the following mode of

connections are taken into consideration

INPUT RESISTANCE :

It is the ratio of small change in base -emitter voltage to the resulting change in the

base current at constant collector emitter voltage i.e.

Input resistance , Ri = VBEIB

The value of input resistance is quite small because the input circuit is always forward

biased. It ranges from about 500 ohms for small forward transistors to as low as 5 ohms for

high powered transistors. In fact . input resistance is the opposition offered by the base

emitter junction to the flow of signal. Thus , if the input resistance is 500 ohms and the

signal voltage at any instant is 1V , then

Base current ib = 1V/500 ohms

= 2mA

OUTPUT RESISTANCE :



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It is the ratio of change in collector emitter voltage (VCE ) to the resulting

change in collector current (IC) at constant base current i.e.

Output resistance , Ro = VCE

IC

The output characteristics reveal that collector current changes very slightly with change in

collector emitter voltage. Therefore , output resistance is very high. This value is of the

order of several hundred kilo-ohms.

EFFECTIVE COLLECTOR LOAD :

It is the total load as seen by the a.c.collector current.

In case of single stage amplifiers , the effective collector load is a parallel combination of

Rc and Ro as shown in fig below.

Effective collector load, RAC = Rc||Ro=Rc x RO

RC+RO

= * RC

It follows, therefore, that for a single stage amplifier, effective load is equal to collector

load Rc.

However, in multistage amplifier ( i.e. having more than one amplification stage ), the

input resistance Ri of the next stage also comes into picture as shown in below figure.

Therefore, effective collector load becomes parallel combination of Rc, Ro, Ri

i.e.

Effective collector load, RAC = Rc || Ro || Ri

= Rc || Ri= Rc x Ri

Rc + Ri

As input resistance Ri is quite small (25 ohm to 500 ohm ), therefore, effective load is

reduced.

CURRENT GAIN :



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5.11 Crystal oscillators :

If a piezoelectric crystal, usually quartz, has electrodes Plated on opposite faces

and if a potential is applied between these electrodes, forces will be exerted on the bound

charges with in the crystal. If this device is properly mounted, deformation takes place with

in the crystal, and an electromechanical system is formed which will vibrate when properly

excited. The resonance frequency and Q depend upon the crystal dimensions, how the

surfaces are oriented with respect to its axes, and how the device is mounted. Frequencies

ranging from a few kilohertz to a few megahertz, and Qs in the range from several

thousand to several hundred thousand , are commercially available. These extraordinarily

high values of Q and the fact that the characteristics of quartz are extremely stable with

respect to time and temperature account for the exceptional frequency stability of

oscillators incorporating crystals .

The electrical equivalent circuit of a crystal is indicated in below figure. The inductor L,

capacitor C, and resistor R are the analogs of the mass, the compliance ( thee reciprocal of

the spring constant ) , and the viscous-damping factor of the mechanical system



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Typical values for a 90-Khz crystal are L = 137 H , C = 0.0235 pF , and R = 15 K ,

corresponding to Q = 5500.The dimensions of such a crystal are 30 by 4 by 1.5 mm. Since

C represents the electrostatic capacitance between electrodes with the crystal as a

dielectric, its magnitude (~ 3.5 pF) is very much larger than C. If we neglect the resistance

R, the impedance of the crystal is a reactance jX whose dependence upon frequency is

given by

jX = - j - SC - p

where , S = 1/LC is the series resonant frequency ( the zero impedance frequency ),

and p = (1/L) (1/C + 1/C) is the parallel resonant frequency ( the infinite impedance

frequency ). Since C C, then p S. for the crystal whose parameters are specified

above, the parallel frequency is only three tenths of 1 percent higher than the series

frequency. For S< < p, the reactance is inductive, and outside this range it is

capacitive, as indicated in above fig.Hence the circuit will oscillate at a frequency which

lies between S and p but close to the parallel-resonance value. Since p S, the

oscillator frequency is essentially determined by the crystal, and not by the rest of the

circuit.

PNP GENERAL PURPOSE TRANSISTORS BC547,557,567

FEATURES

Low current (max. 100 mA)

Low voltage (max. 65 V).



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APPLICATIONS

General purpose switching and amplification.

DESCRIPTION

PNP transistor in a TO-92; SOT54 plastic package.

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT

VCBO collector-base voltage open emitter

BC556 - -80 V

BC557 - -50 V



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VCEO collector-emitter voltage open base

BC556 - -65 V

BC557 - -45 V

VEBO emitter-base voltage open collector - -5 V

IC collector current (DC) - -100 mA

ICM peak collector current - -200 mA

IBM peak base current - -200 mA

Ptot total power dissipation Tamb 25 C - 500 mW

Tstg storage temperature -65 +150 C

Tj junction temperature - 150 C

Tamb operating ambient temperature -65 +150 C

NPN GENERAL PURPOSE TRANSISTORS BC546; BC547

FEATURES

Low current (max. 100 mA)

Low voltage (max. 65 V).

APPLICATIONS

General purpose switching and amplification.

DESCRIPTION

NPN transistor in a TO-92; SOT54 plastic package.



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LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

1. Transistor mounted on an FR4 printed-circuit board.

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT

VCBO collector-base voltage open emitter

BC546 - 80 V

BC547 - 50 V

VCEO collector-emitter voltage open base

BC546 - 65 V

BC547 - 45 V

VEBO emitter-base voltage open collector

BC546 - 6 V



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BC547 - 6 V

IC collector current (DC) - 100 mA

ICM peak collector current - 200 mA

IBM peak base current - 200 mA

Ptot total power dissipation Tamb 25 C; note 1 - 500 mW

Tstg storage temperature -65 +150 C

Tj junction temperature - 150 C

Tamb operating ambient temperature -65 +150 C



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RELAY



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A relay is an electrical switch that opens and closes under control of another

electrical circuit. In the original form, the switch is operated by an electromagnet to open or

close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a

relay is able to control an output circuit of higher power than the input circuit, it can be

considered, in a broad sense, to be a form of electrical amplifier.

Operation:

When a current flows through the coil, the resulting magnetic field attracts an

armature that is mechanically linked to a moving contact. The movement either makes or

breaks a connection with a fixed contact. When the current to the coil is switched off, the

armature is returned by a force approximately half as strong as the magnetic force to its

relaxed position. Usually this is a spring, but gravity is also used commonly in industrial

motor starters. Most relays are manufactured to operate quickly. In a low voltage

application, this is to reduce noise. In a high voltage or high current application, this is to

reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to

dissipate the energy from the collapsing magnetic field at deactivation, which would

otherwise generate a spike of voltage and might cause damage to circuit components. If thecoil is designed to be energized with AC, a small copper ring can be crimped to the end of

the solenoid. This "shading ring" creates a small out-of-phase current, which increases the

minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state

relay is made with a thyristor or other solid-state switching device. To achieve electrical

isolation, a light-emitting diode (LED) is used with a photo transistor.

The contacts can be either Normally Open (NO), Normally Closed (NC), or change-

over (CO) contacts.

Normally-open contacts connect the circuit when the relay is activated; the circuit is

disconnected when the relay is inactive. It is also called Form A contact or "make"



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contact. Form A contact is ideal for applications that require to switch a high-

current power source from a remote device.

Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is

connected when the relay is inactive. It is also called Form B contact or "break" contact.

Form B contact is ideal for applications that require the circuit to remain closed until the

relay is activated.

Selection of an appropriate relay for a particular application requires evaluation of many

different factors:

Number and type of contacts - normally open, normally closed, changeover

(double-throw)

In the case of changeover, there are two types. This style of relay can be

manufactured two different ways. "Make before Break" and "Break before Make".

The old style telephone switch required Make-before-break so that the connection

didn't get dropped while dialing the number. The railroad still uses them to control

railroad crossings.

Rating of contacts - small relays switch a few amperes, large contactors are rated

for up to 3000 amperes, alternating or direct current Voltage rating of contacts - typical control relays rated 300 VAC or 600 VAC,

automotive types to 50 VDC, special high-voltage relays to about 15,000 V

Coil voltage - machine-tool relays usually 24 VAC or 120 VAC, relays for

switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few

milliamperes

Package/enclosure - open, touch-safe, double-voltage for isolation between circuits,

explosion proof, outdoor, oil-splashresistant

Mounting - sockets, plug board, rail mount, panel mount, through-panel mount,

enclosure for mounting on walls or equipment

Switching time - where high speed is required

"Dry" contacts - when switching very low level signals, special contact materials

may be needed such as gold-plated contacts



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Contact protection - suppress arcing in very inductive circuits

Coil protection - suppress the surge voltage produced when switching the coil

current

Isolation between coil circuit and contacts

Aerospace or radiation-resistant testing, special quality assurance

Accessories such as timers, auxiliary contacts, pilot lamps, test buttons

Regulatory approvals



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Silicon-Controlled Rectifier (SCR)



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Shockley diodes are curious devices, but rather limited in application. Their usefulness may

be expanded, however, by equipping them with another means of latching. In doing so,

each becomes true amplifying devices (if only in an on/off mode), and we refer to these as

silicon-controlled rectifiers, orSCRs.

The progression from Shockley diode to SCR is achieved with one small addition, actually

nothing more than a third wire connection to the existing PNPN structure: (Figurebelow)

If an SCR's gate is left floating(disconnected), it behaves exactly as a Shockley diode. It

may be latched by breakover voltage or by exceeding the critical rate of voltage rise

between anode and cathode, just as with the Shockley diode. Dropout is accomplished by

reducing current until one or both internal transistors fall into cutoff mode, also like the

Shockley diode. However, because the gate terminal connects directly to the base of the

lower transistor, it may be used as an alternative means to latch the SCR. By applying a

small voltage between gate and cathode, the lower transistor will be forced on by the

resulting base current, which will cause the upper transistor to conduct, which then supplies

the lower transistor's base with current so that it no longer needs to be activated by a gate

voltage. The necessary gate current to initiate latch-up, of course, will be much lower than

the current through the SCR from cathode to anode, so the SCR does achieve a measure of

amplification.

This method of securing SCR conduction is called triggering, and it is by far the most

common way that SCRs are latched in actual practice. In fact, SCRs are usually chosen so

that their breakover voltage is far beyond the greatest voltage expected to be experienced

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from the power source, so that it can be turned on only by an intentional voltage pulse

applied to the gate.

It should be mentioned that SCRs may sometimes be turned off by directly shorting their

gate and cathode terminals together, or by "reverse-triggering" the gate with a negative

voltage (in reference to the cathode), so that the lower transistor is forced into cutoff. I say

this is "sometimes" possible because it involves shunting all of the upper transistor's

collector current past the lower transistor's base. This current may be substantial, making

triggered shut-off of an SCR difficult at best. A variation of the SCR, called a Gate-Turn-

Off thyristor, or GTO, makes this task easier. But even with a GTO, the gate current

required to turn it off may be as much as 20% of the anode (load) current! The schematic

symbol for a GTO is shown in the following illustration: (Figurebelow)

The Gate Turn-Off thyristor (GTO)

SCRs and GTOs share the same equivalent schematics (two transistors connected in a

positive-feedback fashion), the only differences being details of construction designed to

grant the NPN transistor a greater than the PNP. This allows a smaller gate current

(forward or reverse) to exert a greater degree of control over conduction from cathode to

anode, with the PNP transistor's latched state being more dependent upon the NPN's than

vice versa. The Gate-Turn-Off thyristor is also known by the name of Gate-Controlled

Switch, orGCS.

A rudimentary test of SCR function, or at least terminal identification, may be performed

with an ohmmeter. Because the internal connection between gate and cathode is a single

PN junction, a meter should indicate continuity between these terminals with the red test

lead on the gate and the black test lead on the cathode like this: (Figure below)

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Rudimentary test of SCR

All other continuity measurements performed on an SCR will show "open" ("OL" on some

digital multimeter displays). It must be understood that this test is very crude and does not

constitute a comprehensive assessment of the SCR. It is possible for an SCR to give good

ohmmeter indications and still be defective. Ultimately, the only way to test an SCR is to

subject it to a load current.

If you are using a multimeter with a "diode check" function, the gate-to-cathode junction

voltage indication you get may or may not correspond to what's expected of a silicon PN

junction (approximately 0.7 volts). In some cases, you will read a much lower junction

voltage: mere hundredths of a volt. This is due to an internal resistor connected between the

gate and cathode incorporated within some SCRs. This resistor is added to make the SCR

less susceptible to false triggering by spurious voltage spikes, from circuit "noise" or from

static electric discharge. In other words, having a resistor connected across the gate-cathode

junction requires that astrongtriggering signal (substantial current) be applied to latch the

SCR. This feature is often found in larger SCRs, not on small SCRs. Bear in mind that an

SCR with an internal resistor connected between gate and cathode will indicate continuity

in both directions between those two terminals: (Figurebelow)

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Larger SCRs have gate to cathode resistor.

"Normal" SCRs, lacking this internal resistor, are sometimes referred to as sensitive gate

SCRs due to their ability to be triggered by the slightest positive gate signal.

The test circuit for an SCR is both practical as a diagnostic tool for checking suspected

SCRs and also an excellent aid to understanding basic SCR operation. A DC voltage source

is used for powering the circuit, and two pushbutton switches are used to latch and unlatch

the SCR, respectively: (Figurebelow)

SCR testing circuit

Actuating the normally-open "on" pushbutton switch connects the gate to the anode,

allowing current from the negative terminal of the battery, through the cathode-gate PN

junction, through the switch, through the load resistor, and back to the battery. This gate



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current should force the SCR to latch on, allowing current to go directly from cathode to

anode without further triggering through the gate. When the "on" pushbutton is released,

the load should remain energized.

Pushing the normally-closed "off" pushbutton switch breaks the circuit, forcing current

through the SCR to halt, thus forcing it to turn off (low-current dropout).

If the SCR fails to latch, the problem may be with the load and not the SCR. A certain

minimum amount of load current is required to hold the SCR latched in the "on" state. This

minimum current level is called the holding current. A load with too great a resistance

value may not draw enough current to keep an SCR latched when gate current ceases, thus

giving the false impression of a bad (unlatchable) SCR in the test circuit. Holding current

values for different SCRs should be available from the manufacturers. Typical holding

current values range from 1 milliamp to 50 milliamps or more for larger units.

For the test to be fully comprehensive, more than the triggering action needs to be tested.

The forward breakover voltage limit of the SCR could be tested by increasing the DC

voltage supply (with no pushbuttons actuated) until the SCR latches all on its own. Beware

that a breakover test may require very high voltage: many power SCRs have breakover

voltage ratings of 600 volts or more! Also, if a pulse voltage generator is available, thecritical rate of voltage rise for the SCR could be tested in the same way: subject it to

pulsing supply voltages of different V/time rates with no pushbutton switches actuated and

see when it latches.

In this simple form, the SCR test circuit could suffice as a start/stop control circuit for a DC

motor, lamp, or other practical load: (Figurebelow)



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DC motor start/stop control circuit

Another practical use for the SCR in a DC circuit is as a crowbardevice for overvoltage

protection. A "crowbar" circuit consists of an SCR placed in parallel with the output of a

DC power supply, for placing a direct short-circuit on the output of that supply to prevent

excessive voltage from reaching the load. Damage to the SCR and power supply is

prevented by the judicious placement of a fuse or substantial series resistance ahead of the

SCR to limit short-circuit current: (Figurebelow)

Crowbar circuit used in DC power supply

Some device or circuit sensing the output voltage will be connected to the gate of the SCR,

so that when an overvoltage condition occurs, voltage will be applied between the gate and

cathode, triggering the SCR and forcing the fuse to blow. The effect will be approximately

the same as dropping a solid steel crowbar directly across the output terminals of the power

supply, hence the name of the circuit.



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Most applications of the SCR are for AC power control, despite the fact that SCRs are

inherently DC (unidirectional) devices. If bidirectional circuit current is required, multiple

SCRs may be used, with one or more facing each direction to handle current through both

half-cycles of the AC wave. The primary reason SCRs are used at all for AC power control

applications is the unique response of a thyristor to an alternating current. As we saw, the

thyratron tube (the electron tube version of the SCR) and the DIAC, a hysteretic device

triggered on during a portion of an AC half-cycle will latch and remain on throughout the

remainder of the half-cycle until the AC current decreases to zero, as it must to begin the

next half-cycle. Just prior to the zero-crossover point of the current waveform, the thyristor

will turn off due to insufficient current (this behavior is also known as natural

commutation) and must be fired again during the next cycle. The result is a circuit current

equivalent to a "chopped up" sine wave. For review, here is the graph of a DIAC's response

to an AC voltage whose peak exceeds the breakover voltage of the DIAC: (Figurebelow)

DIAC bidirectional response

With the DIAC, that breakover voltage limit was a fixed quantity. With the SCR, we have

control over exactly when the device becomes latched by triggering the gate at any point in

time along the waveform. By connecting a suitable control circuit to the gate of an SCR,

we can "chop" the sine wave at any point to allow for time-proportioned power control to a

load.

Take the circuit in Figurebelow as an example. Here, an SCR is positioned in a circuit to

control power to a load from an AC source.

http://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03205a.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03205a.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03211.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03205a.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03211.png


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SCR control of AC power

Being a unidirectional (one-way) device, at most we can only deliver half-wave power to

the load, in the half-cycle of AC where the supply voltage polarity is positive on the top

and negative on the bottom. However, for demonstrating the basic concept of time-

proportional control, this simple circuit is better than one controlling full-wave power

(which would require two SCRs).

With no triggering to the gate, and the AC source voltage well below the SCR's breakover

voltage rating, the SCR will never turn on. Connecting the SCR gate to the anode through a

standard rectifying diode (to prevent reverse current through the gate in the event of the

SCR containing a built-in gate-cathode resistor), will allow the SCR to be triggered almost

immediately at the beginning of every positive half-cycle: (Figurebelow)

Gate connected directly to anode through a diode; nearly complete half-wave current

through load.



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We can delay the triggering of the SCR, however, by inserting some resistance into the

gate circuit, thus increasing the amount of voltage drop required before enough gate current

triggers the SCR. In other words, if we make it harder for electrons to flow through the gate

by adding a resistance, the AC voltage will have to reach a higher point in its cycle before

there will be enough gate current to turn the SCR on. The result is in Figurebelow.

Resistance inserted in gate circuit; less than half-wave current through load.

With the half-sine wave chopped up to a greater degree by delayed triggering of the SCR,

the load receives less average power (power is delivered for less time throughout a cycle).

By making the series gate resistor variable, we can make adjustments to the time-

proportioned power: (Figurebelow)

http://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03213.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03214.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03213.pnghttp://www.allaboutcircuits.com/vol_3/chpt_7/5.html#03214.png


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Increasing the resistance raises the threshold level, causing less power to be delivered to

the load. Decreasing the resistance lowers the threshold level, causing more power to be

delivered to the load.

Unfortunately, this control scheme has a significant limitation. In using the AC source

waveform for our SCR triggering signal, we limit control to the first half of the waveform's

half-cycle. In other words, it is not possible for us to wait until after the wave's peak to

trigger the SCR. This means we can turn down the power only to the point where the SCR

turns on at the very peak of the wave: (Figurebelow)

Circuit at minimum power setting



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Raising the trigger threshold any more will cause the circuit to not trigger at all, since not

even the peak of the AC power voltage will be enough to trigger the SCR. The result will

be no power to the load.

An ingenious solution to this control dilemma is found in the addition of a phase-shifting

capacitor to the circuit: (Figurebelow)

Addition of a phase-shifting capacitor to the circuit

The smaller waveform shown on the graph is voltage across the capacitor. For the sake of

illustrating the phase shift, I'm assuming a condition of maximum control resistance where

the SCR is not triggering at all with no load current, save for what little current goes

through the control resistor and capacitor. This capacitor voltage will be phase-shifted

anywhere from 0o to 90o lagging behind the power source AC waveform. When this phase-

shifted voltage reaches a high enough level, the SCR will trigger.

With enough voltage across the capacitor to periodically trigger the SCR, the resulting load

current waveform will look something like Figurebelow)



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Phase-shifted signal triggers SCR into conduction.

Because the capacitor waveform is still rising after the main AC power waveform has

reached its peak, it becomes possible to trigger the SCR at a threshold level beyond that

peak, thus chopping the load current wave further than it was possible with the simpler

circuit. In reality, the capacitor voltage waveform is a bit more complex that what is shown

here, its sinusoidal shape distorted every time the SCR latches on. However, what I'm

trying to illustrate here is the delayed triggering action gained with the phase-shifting RC

network; thus, a simplified, undistorted waveform serves the purpose well.

SCRs may also be triggered, or "fired," by more complex circuits. While the circuit

previously shown is sufficient for a simple application like a lamp control, large industrial

motor controls often rely on more sophisticated triggering methods. Sometimes, pulse

transformers are used to couple a triggering circuit to the gate and cathode of an SCR to

provide electrical isolation between the triggering and power circuits: (Figurebelow)



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Transformer coupling of trigger signal provides isolation.

When multiple SCRs are used to control power, their cathodes are often notelectrically

common, making it difficult to connect a single triggering circuit to all SCRs equally. An

example of this is the controlled bridge rectifiershown in Figurebelow.

Controlled bridge rectifier

In any bridge rectifier circuit, the rectifying diodes (in this example, the rectifying SCRs)

must conduct in opposite pairs. SCR1 and SCR3 must be fired simultaneously, and SCR2

and SCR4 must be fired together as a pair. As you will notice, though, these pairs of SCRs

do not share the same cathode connections, meaning that it would not work to simplyparallel their respective gate connections and connect a single voltage source to trigger

both: (Figurebelow)



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This strategy will not work for triggering SCR2 and SCR4 as a pair.

Although the triggering voltage source shown will trigger SCR4, it will not trigger SCR2

properly because the two thyristors do not share a common cathode connection to reference

that triggering voltage. Pulse transformers connecting the two thyristor gates to a common

triggering voltage source willwork, however: (Figurebelow)

Transformer coupling of the gates allows triggering of SCR2 and SCR4 .

Bear in mind that this circuit only shows the gate connections for two out of the four SCRs.

Pulse transformers and triggering sources for SCR1 and SCR3, as well as the details of the

pulse sources themselves, have been omitted for the sake of simplicity.



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Controlled bridge rectifiers are not limited to single-phase designs. In most industrial

control systems, AC power is available in three-phase form for maximum efficiency, and

solid-state control circuits are built to take advantage of that. A three-phase controlled

rectifier circuit built with SCRs, without pulse transformers or triggering circuitry shown,

would look like Figurebelow.

Three-phase bridge SCR control of load

REVIEW:

A Silicon-Controlled Rectifier, or SCR, is essentially a Shockley diode with an

extra terminal added. This extra terminal is called the gate, and it is used to trigger

the device into conduction (latch it) by the application of a small voltage.

To trigger, orfire, an SCR, voltage must be applied between the gate and cathode,

positive to the gate and negative to the cathode. When testing an SCR, a momentary

connection between the gate and anode is sufficient in polarity, intensity, and

duration to trigger it.

SCRs may be fired by intentional triggering of the gate terminal, excessive voltage

(breakdown) between anode and cathode, or excessive rate of voltage rise between

anode and cathode. SCRs may be turned off by anode current falling below the

holding current value (low-current dropout), or by "reverse-firing" the gate



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(applying a negative voltage to the gate). Reverse-firing is only sometimes

effective, and always involves high gate current.

A variant of the SCR, called a Gate-Turn-Off thyristor (GTO), is specifically

designed to be turned off by means of reverse triggering. Even then, reverse

triggering requires fairly high current: typically 20% of the anode current.

SCR terminals may be identified by a continuity meter: the only two terminals

showing any continuity between them at all should be the gate and cathode. Gate

and cathode terminals connect to a PN junction inside the SCR, so a continuity

meter should obtain a diode-like reading between these two terminals with the red

(+) lead on the gate and the black (-) lead on the cathode. Beware, though, that

some large SCRs have an internal resistor connected between gate and cathode,

which will affect any continuity readings taken by a meter.

SCRs are true rectifiers: they only allow current through them in one direction. This

means they cannot be used alone for full-wave AC power control.

If the diodes in a rectifier circuit are replaced by SCRs, you have the makings of a

controlledrectifier circuit, whereby DC power to a load may be time-proportioned

by triggering the SCRs at different points along the AC power waveform.

Light Emitting Diodes (LEDs)



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Example: Circuit symbol:

Function

LEDs emit light when an electric current passes through them.

Connecting and soldering

LEDs must be connected the correct way round, the diagram may be

labelled a or+ for anode and kor- for cathode (yes, it really is k, not c,

for cathode!). The cathode is the short lead and there may be a slight

flat on the body of round LEDs. If you can see inside the LED the cathode is the larger

electrode (but this is not an official identification method).

LEDs can be damaged by heat when soldering, but the risk is small unless you are very

slow. No special precautions are needed for soldering most LEDs.

Testing an LED

Never connect an LED directly to a battery or power supply!

It will be destroyed almost instantly because too much current will

pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe

value, for quick testing purposes a 1k resistor is suitable for

most LEDs if your supply voltage is 12V or less. Remember to connect the LED the

correct way round!

Colours of LEDs

LEDs are available in red, orange, amber,

yellow, green, blue and white. Blue and

white LEDs are much more expensive than

the other colours.



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The colour of an LED is determined by the semiconductor material, not by the colouring of

the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages

which may be diffused (milky) or clear (often described as 'water clear'). The coloured

packages are also available as diffused (the standard type) or transparent.

Advantages

Efficiency: LEDs produce more light per watt than incandescent bulbs.

Color: LEDs can emit light of an intended color without the use of color filters that

traditional lighting methods require. This is more efficient and can lower initial

costs.

Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto

printed circuit boards.

Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000

to 50,000 hours of useful life, though time to complete failure may be longer.

AC motorElectric motor

An electric motor uses electrical energy to produce mechanical energy. The reverse

process, that of using mechanical energy to produce electrical energy, is accomplished by a

http://en.wikipedia.org/wiki/Mechanical_energyhttp://en.wikipedia.org/wiki/Mechanical_energy


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generatoror dynamo.Traction motors used on locomotivesand some electric and hybrid

automobiles often perform both tasks if the vehicle is equipped withdynamic brakes.

Electric motors are found in household appliances such as fans,

refrigerators, washing machines, pool pumps, floor vacuums, and fan-forced ovens. They

are also found in many other devices such as computer equipment, in its disk drives,

printers, and fans; and in some sound and video playing and recording equipment as

DVD/CD players and recorders, tape players and recorders, and record players. Electric

motors are also found in several kinds of toys such as some kinds of vehicles and robotic

toys.

http://en.wikipedia.org/wiki/Electrical_generatorhttp://en.wikipedia.org/wiki/Traction_motorhttp://en.wikipedia.org/wiki/Traction_motorhttp://en.wikipedia.org/wiki/Locomotivehttp://en.wikipedia.org/wiki/Locomotivehttp://en.wikipedia.org/wiki/Dynamic_brakehttp://en.wikipedia.org/wiki/Dynamic_brakehttp://en.wikipedia.org/wiki/Electrical_generatorhttp://en.wikipedia.org/wiki/Traction_motorhttp://en.wikipedia.org/wiki/Locomotivehttp://en.wikipedia.org/wiki/Dynamic_brake


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Advantages:

Highly sensitive

Fit and Forget system

Low cost and reliable circuit

Applications:

Home / Office

Banks

Factories

Store Rooms

Conclusion



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In this project, we have used Smoke/Fire Detector With Automatic Water Sprinkler

System to Avoid Fire Accidents. So using Triac have derived the AC motor. This project

can be applied in various areas like spinning industries, offices and in manufacturing of

home appliances etc.

This project used regulated 5V, 500mA power supply. 7805 three terminal voltage

regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the

ac out put of secondary of 230/12V step down transformer.



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REFERENCE

Text Books:

Basics of Secuirty Engineering By David Louis

Sensors Engineering Applications By Morris Hamington

Website:

www.howstuffworks.com

www.answers.com

www.soundtech.com

www.WineYardProjects.com

Magazines:

Electronics for you

Electrikindia

wk116 smoke fire detector water sprinkler

Documents