Project Orig c

BOILER AUTOMATION PROJECT REPORT,2014

1 EIE DEPARTMENT KMEA ENGINEERING COLLEGE

CHAPTER 1

INTRODUCTION

Boilers are pressure vessels designed to heat water or produce steam, which

can then be used to provide space heating and/or service water heating to a building.

In most commercial building heating applications, the heating source in the boiler is a

natural gas fired burner. Oil fired burners and electric resistance heaters can be used

as well. Steam is preferred over hot water in some applications, including absorption

cooling, kitchens, laundries, sterilizers, and steam driven equipment.

Boilers have several strengths that have made them a common feature of

buildings. They have a long life, can achieve efficiencies up to 95% or greater,

provide an effective method of heating a building, and in the case of steam systems,

require little or no pumping energy. However, fuel costs can be considerable, regular

maintenance is required, and if maintenance is delayed, repair can be costly.

Boilers are often one of the largest energy users in a building. For every year

a boiler system goes unattended, boiler costs can increase approximately 10% (1).

Boiler operation and maintenance is therefore a good place to start when looking for

ways to reduce energy use and save money.

1.1 OBJECTIVE

The Objective of this project is to develop a boiler control system in order to

prevent the boiler accident due high pressure and temperature. A boiler system is an

integral component of a plant and control of liquid level ,pressure and temperature

in the drum of the boiler is a critical operational consideration. Nowadays, instead of

conventional control techniques, modern control techniques have been implemented

for a lot of industrial models practically or theoretically. In this project, we describe

the effectiveness of LabVIEW in order to provide better drum level control of

various products evolved in an industry.



1.2 SCOPE

When a boiler is switched ON we must be always check the Temperature,

Pressure, and level of the water. Their values must be kept in track in order to avoid

major accidents such as explosion of boiler, deviation from the values set etc., Hence

the set value of pressure, temperature and the liquid level has to be maintained.

1.3 METHODOLOGY

Temperature sensors are often sensing devices embedded within some sort of

insulation. The insulation may often be for electrical purposes - to isolate the sensor

electrically. However, good electrical insulation is often also good thermal

insulation, and the presence of that insulation causes the sensor to respond tardily

when the sensor heats up. The Temperature sensor senses the temperature in the

boiler. Similarly the Pressure sensor senses the pressure level in the boiler and the

level sensor also senses the level of the liquid in the Boiler and the signal is given to

the ADC port of the micro controller.

The Analog to Digital port converts the analog to corresponding digital

values. A microcontroller (or MCU) is a computer on a chip used to control any

electronic device. The micro controller is programmed already according to our

objective .

If the water level in the boiler is lower then set value, the microcontroller turn

on the pump motor through relay driver circuit. Similarly the pressure and

temperature is lower then set value , the pressure pump(by closing soft walve) and

heater is turned on respectively. If the water level in the boiler is greater than the set

value, the microcontroller turn off the pump motor through relay driver circuit.

Similarly the pressure and temperature is higher than set value, pressure pump(by

opening solenoid valve) . Set values are given through program.



Keeping this in mind the boiler tool kits like Control, design and Simulation

were used in order to study the dependencies of the input variables to the output

variables. LabVIEW platform provides ease of analysis at your desktop.



CHAPTER 2

LITERATURE SURVEY

In excess of the years the require for high quality, better effectiveness and

automatic machinery have improved in the industrial region of power plants. Power

plants have need of continuous monitoring and check at frequent intervals. There are

possibilities of errors at measuring and various stages involved with human workers

and also the lack of few features of microcontrollers.

Power plant section is one of most important department in the industry.

There it is having number of boiling section. This boiling section produces the high

temperature water of the steam level temperature. This steam level temperature is

used for power generation and the steam waters are applied to the turbine section.

After the power is generated, steam waters are supplied to various plants for reuses. If

the supply of the high temperature is reduced to low temperature, it will be used for

all other plants which needs the low temperature.

In this project the microcontroller based automation of boilers are done.

Conventional equipment systems are prone to errors due to the involvement of

humans in the data collection and processing using complicated mathematical

expressions. A microcontroller is used which is a small computer on a single

integrated circuit containing a processor core, memory, and programmable

input/output peripherals.



Labview is used for monitoring purpose. LabVIEW is the industry standard

for instrument connectivity.it provides Versatility with a robust, high quality

instrument driver that includes a complete set of functions, Multiple platform support

and Complete flexibility for the user.By using LCD for monitoring we will not be

able to get the correct variation in the temperature.



CHAPTER 3

WORKING OF BOILERS

Both gas and oil fired boilers use controlled combustion of the fuel to heat

water. The key boiler components involved in this process are the burner, combustion

chamber, heat exchanger, and controls.

Fig 3.1 Firetube Boiler



The burner mixes the fuel and oxygen together and, with the assistance of an

ignition device, provides a platform for combustion. This combustion takes place in

the combustion chamber, and the heat that it generates is transferred to the water

through the heat exchanger. Controls regulate the ignition, burner firing rate, fuel

supply, air supply, exhaust draft, water temperature, steam pressure, and boiler

pressure. Hot water produced by a boiler is pumped through pipes and delivered to

equipment throughout the building, which can include hot water coils in air handling

units, service hot water heating equipment, and terminal units. Steam boilers produce

steam that flows through pipes from areas of high pressure to areas of low pressure,

unaided by an external energy source such as a pump. Steam utilized for heating can

be directly utilized by steam using equipment or can provide heat through a heat

exchanger that supplies hot water to the equipment. The discussion of different types

of boilers, below, provides more detail on the designs of specific boiler systems.

3.1 TYPES OF BOILERS

Boilers are classified into different types based on their working pressure and

temperature, fuel type, draft method, size and capacity, and whether they condense

the water vapor in the combustion gases. Boilers are also sometimes described by

their key components, such as heat exchanger materials or tube design. These other

characteristics are discussed in the following section on Key Components of Boilers.

Two primary types of boilers include Firetube and Watertube boilers. In a Firetube

boiler, hot gases of combustion flow through a series of tubes surrounded by water.

Alternatively, in a Watertube boiler, water flows in the inside of the tubes and the hot

gases from combustion flow around the outside of the tubes. A drawing of a

watertube boiler is shown in Figure 3.2



Fig 3.2 Watertube Boiler

Firetube boilers are more commonly available for low pressure steam or hot

water applications, and are available in sizes ranging from 500,000 to 75,000,000

BTU input (5). Watertube boilers are primarily used in higher pressure steam

applications and are used extensively for comfort heating applications. They typically

range in size from 500,000 to more than 20,000,000 BTU input (5).

Cast iron sectional boilers are another type of boiler commonly used in

commercial space heating applications. These types of boilers dont use tubes.

Instead, theyre built up from cast iron sections that have water and combustion gas

passages. The iron castings are bolted together, similar to an old steam radiator.



The sections are sealed together by gaskets. Theyre available for producing

steam or hot water, and are available in sizes ranging from 35,000 to 14,000,000 BTU

input (2). Cast iron sectional boilers are advantageous because they can be assembled

on site, allowing them to be transported through doors and smaller openings. Their

main disadvantage is that because the sections are sealed together with gaskets, they

are prone to leakage as the gaskets age and are attacked by boiler treatment

chemicals.



CHAPTER 4

BLOCK DIAGRAM

Fig 4.1 block diagram

Power supply Max232

Pic microcontroller

Uln2003 Relay to drive



4.1 BLOCK DIAGRAM COMPONENT DESCRIPTION

4.1.1 power supply

The system requires a regulated +5v supply for the semiconductors and a

+12V unregulated supply for the relay. These can be delivered from the 230V

domestic supply. Before applying this to the system we must step down this high

voltage to an appropriate value. After that it should be rectified. To achieve +5 V DC

we should regulate this.All this are run in the power supply circuitry.

Power supply is used to give sufficient power to the microcontroller. A step

down transformer and a bridge rectifier is used here to convert AC to DC. A regulator

IC is also used here to give constant supply.7805 IC is used for power supply and it is

connected to the bridge rectifier.

A 12-0-12V step down transformer is connected to provide the necessary low

voltage. The transformer also works as an Isolator between the hot and cold end. The

hot end refers to the 230v supply, which is hazardous one, and the cold one refers to

the low ,safe voltage .Now the hot portion appears only at the primary of the

transformer. The secondary of the transformer deliver 12v ac pulses along with a

ground.

This ac supply goes to a center tap rectifier, which converts the ac into a

unidirectional voltage. The ripples in the resulting supply is filtered and smoothed by

a 2200micro FD/25V capacitor. The 0.1 microfarad capacitor bypasses any high

frequency noises. The resulting supply has magnitude above 17V.This voltage is

given to the regulated IC 7805.This IC provides a regulated 5V positive supply at its

3rd

pin. This required input for this is more than 7.5V.



Fig 4.2 power supply

This circuit can give +5V output at about 150

mA current, but it can be increased to 1 A when good cooling is added to 7805

regulator chip. The circuit has over overload and terminal protection.

Circuit diagram of the power supply.

Fig 4.3 circuit diagram for power supply

The capacitors must have enough high voltage

rating to safely handle the input voltage feed to circuit. The circuit is very easy to

build for example into a piece of Vero board.

O/P

.

.

.1 5

4 8

AC I/P

.

RECTIFIER

REGULATOR IC



Pin out of the 7805 regulator IC.

Fig 4.4 ic 7805

1. Unregulated voltage in

2. Regulated voltage out

3. Ground

If we need other voltages than +5V, we can modify the circuit by

replacing the 7805 chips with another regulator with different output voltage from

regulator 78xx chip family. The last numbers in the the chip code tells the output

voltage. Remember that the input voltage must be at least 3V greater than regulator

output voltage ot otherwise the regulator does not work well.



4.1.2 Max232

It is a voltage level converter. It converts RS232 voltage levels to

TTL .The serial port of PC uses RS232 voltage levels ,and microcontroller uses TTL

levels. To match these voltage levels MAX232 IC is used . This IC includes a pair of

transmitter and receiver. One advantage of using MAX232 is that, no negative

voltage is required for its working. So need of dual supply is eliminated.

The MAX232 is an integrated circuit that converts signals from an RS-232

serial port to signals suitable for use in TTL compatible digital logic circuits. The

MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS

signals.The drivers provide RS-232 voltage level outputs (approx. 7.5 V) from a

single + 5 V supply via on-chip charge pumps and external capacitors. This makes it

useful for implementing RS-232 in devices that otherwise do not need any voltages

outside the 0 V to + 5 V range, as power supply design does not need to be made

more complicated just for driving the RS-232 in this case.

The receivers reduce RS-232 inputs (which may be as high as 25 V), to

standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a

typical hysteresis of 0.5 V.The later MAX232A is backwards compatible with the

original MAX232 but may operate at higher baud rates and can use smaller external

capacitors 0.1 F in place of the 1.0 F capacitors used with the original device.

The newer MAX3232 is also backwards compatible, but operates at a broader voltage

range, from 3 to 5.5V.

When a MAX232 IC receives a TTL level to convert, it changes a TTL Logic

0 to between +3 and +15V, and changes TTL Logic 1 to between -3 to -15V, and vice

versa for converting from RS232 to TTL. This can be confusing when you realize that

the RS232 Data Transmission voltages at a certain logic state are opposite from the

RS232 Control Line voltages at the same logic state.



4.1.3 Pic microcontroller

PIC micro controllers are low-cost computers-in-a-chip; they allow

electronics designers and hobbyists add intelligence and functions that mimic big

computers for almost any electronic product or project.

The programming of the system is done using a PIC micro controller

16F877. This powerful (200 nanosecond instruction execution) yet easy-to-program

(only 35 single word instructions) CMOS FLASH-based 8-bit micro controller packs

Microchip's powerful PIC architecture into a 40-pin package and is upwards

compatible with the PIC16C5X, PIC12CXXX and PIC16C7X devices. It is has five

ports. I.e. port A, port B, port C, port D, port E. The PIC 16F877 has flash memory of

8K and Data memory of 368 bytes Data EEPROM of 256 bytes.

4.1.4 Uln2003

The ULN2001A, ULN2002A, ULN2003 and ULN2004A are high voltage,

high current darlington arrays each containing seven open collector darlington pairs

with common emitters. Each channel rated at 500mA and can withstand peak currents

of 600mA. Suppression diodes are included for inductive load driving and the inputs

are pinned opposite the outputs to simplify board layout. The four versions interface

to all common logic families.



Table 4.1 uln

These versatile devices are useful for driving a wide range of loads including

solenoids, relays DC motors, LED displays filament lamps, thermal print heads and

high power buffers. The ULN2001A/2002A/2003A and 2004A are supplied in 16 pin

plastic DIP packages with a copper lead frame to reduce thermal resistance. They are

available also in small outline package (SO-16) as ULN2001D/2002D/2003D/2004D

Design of ULN-2003

Fig 4.5 ULN-2003

This relay driver needs a 12V power supply at the pin 9 and the pin 8 is

grounded . Pins 1 and 2 are inputs. It connected to the pin 27 and 28 respectively.

Pins 16 and 15 are connected to the relay system.



Relay

All relays operate using the same basic principle. example will use a

commonly used 4 -pin relay. Relays have two circuits: A control circuit (shown in

GREEN) and a load circuit(shown in RED). The control circuit has a small control

coil while the load circuit has a switch. The coil controls the operation of the switch.

Fig 4.6 relay

relay energized (on)

Current flowing through the control circuit coil (pins 1 and 3) creates a small

magnetic field which causes the switch to close, pins 2 and 4. the switch, which is

part of the load circuit, is used to control an electrical circuit that may connect to it.

current now flows through pins 2 and 4 shown in red, when the relay in energized.



Fig 4.7 energised relay

relay de-energized (off)

when current stops flowing through the control circuit, pins 1 and 3, the relay

becomes deenergized. without the magnetic field, the switch opens and current is

prevented from flowing through pins 2 and 4. the relay is now off.

fig 4.8 relay de-energised

relay operation

when no voltage is applied to pin 1, there is no current flow through the coil.

no current means no magnetic field is developed, and the switch is open. when

voltage is supplied topin 1, current flow though the coil creates the magnetic field

needed to close the switch allowing continuity between pins 2 and 4.



CHAPTER 5

CIRCUIT DIAGRAM

Fig 5.1 circuit diagram



CHAPTER 6

CRITICAL CONTROL PARAMETERS IN BOILER

The control parameters in a boiler are:

6.1 LEVEL CONTROL

Level control is to ensure that the right amount of water is added to the boiler

at the right time.

Low water alarm - For safe boiler operation, the low water alarm ensures that

the combustion of fuel does not continue if the water level in the boiler has

dropped to, or below a predetermined level. For automatically controlled

steam boilers, national standards usually call for two independent low level

alarms, to ensure safety. In the UK, the lower of the two alarms will 'lockout'

the burner, and manual resetting is required to bring the boiler back on line.

High water alarm - The alarm operates if the water level rises too high,

informing the boiler operator to shut off the feedwater supply. Although not

usually mandatory, the use of high level alarms is sensible as they reduce the

chance of water carryover and water hammer in the steam distribution system.



Fig 6.1 Operating levels for water controls

6.2 PRESSURE CONTROL

Pressure reduction is essential in boilers. Steam boilers are usually designed to

work at high pressures. Working them at lower pressures can result in carry over of

water. Steam at high pressure has a lower specific volume which means that a greater

weight can be carried by a pipe of a given size.

Spirax recommends distribution of steam at high pressure and reduction at the

point of usage. This reduces capital loss for piping and insulation and also reduces

distribution losses.



6.3 FLOW CONTROL

The flow of water to the boiler is to be controlled. A control valve is used to

control the flow.if the boiler reaches the required level of water the flow is stopped .

The volumetric flow rate, (also known as volume flow rate, rate of fluid flow or

volume velocity) is the volume of fluid which passes through a given surface per unit

time. The SI unit is m3s1 (cubic meters per second).

6.4 TEMPERATURE CONTROL

Steam temperature is one of the most challenging control loops in a power

plant boiler because it is highly nonlinear and has a long dead time and time lag.

Adding to the challenge, steam temperature is affected by boiler load, rate of change

of boiler load, air flow rate, the combination of burners in service, and the amount of

soot on the boiler tubes.



CHAPTER 7

EXPERIMENTAL DESCRIPTION

PIC microcontroller 16F877A of operating volt of 5V and frequency of 10MHz is

used for this project.

7.1 TEMPERATURE MEASUREMENT DESCRIPTIONS

1) Principle of Temperature: Temperature is the degree of hotness or coolness of a

body. When the temperature changes the internal resistance also changes to the

corresponding material.

2) Sensing Device: A sensor is call transducer. The output of the transducer is in the

form of voltage current, resistance, or capacitance.

Fig 7.1 sensing device



Fig 7.2 block diagram

Temperature Sensor

Level Sensor(high)

Driver Circuit Relay

Heater is

ON

Driver Circuit Relay Solenoid

valve

open

Driver Circuit Relay Outflow

is ON

PC

(LAB View)

Level Sensor(low)

PIC

16F877A



7.2 OPERATION

Firstly level is 7.2 sensed,if it is low, the solenoid valve is open .water from

the container flows to the boiler.At this time the flow sensor shows the corresponding

flow.water gets rised in the boiler.When a maximum level is reached solenoid valve

is shut off, this max level is sensed by the coressponding level sensor. At this max

level, the boiler is ready,so the heater gets ON.Temperature gets increased when

boiling is continued. When the limit of the temperature is reahed, the outflow

solenoid valve Is ON and steam gets out.when the water level becomes below the low

level the boiler gets OFF automatically.



CHAPTER 8

COMPONENT DESCRIPTION

8.1 TEMPERATURE SENSOR

In industry, there are different types of high temperature measurement,

according to the variety of temperature. For example, LM35 is used to measure the

temperature in the range of -55C to +150C. . The LM35 series are precision

integrate-circuit temperature sensors whose output voltage is linearly proportional to

the Celsius high temperature. The LM35 hence has an improvement more than linear

temperature sensors calibrated in Kelvin, as the user is not required to subtract a

large constant voltage from its output to obtain convenient Centigrade scaling. If we

want to measure temperature greater than 1000C we have to use Thermocouples.

features

2 Calibrated Directly in Celsius (Centigrade)

Linear + 10 mV/C Scale Factor

0.5C Ensured Accuracy (at +25C)

Rated for Full 55C to +150C Range

Suitable for Remote Applications

Low Cost Due to Wafer-Level Trimming

Operates from 4 to 30 V

Less than 60-A Current Drain

Low Self-Heating, 0.08C in Still Air

Nonlinearity Only C Typical

Low Impedance Output, 0.1 for 1 mA Load



Specification:

Supply Voltage +35V to -0.2V

Output Voltage +6V to -1.0V

Output Current 10 mA

Storage Temp TO-46 Package, +60 0c to-180

0 C

TO-92 Package +60 0 C to -150

0 C

SO-8 Package +65 0 C to -150

0 C

TO-202 Package +65 0 C to -150

0 C

Lead Temp

TO-46 Package, (Soldering, 10 seconds) 300 0 C



Fig 8.1 Temperature sensor

8.2 WATER FLOW SENSOR

Water flow sensor consists of a plastic valve body, a water rotor, and a hall-

effect sensor. When water flows through the rotor, rotor rolls. Its speed changes with

different rate of flow. The hall-effect sensor outputs the corresponding pulse Signal.



Fig 8.2 flow sensor

Specification:

Working voltage :5V-24V

Maximum current :15 mADC 5V)

Weight :43 g

External diameters :20mm

Flow rate range :130 L/min

Operating

temperature

:080

Liquid

temperature

:



CHAPTER 9

PCB DESCRIPTION

The first step of assembling is to procure a printing circuit board .The

fabrication of the program counter plays a crucial role in the electronic field. The

success of a circuit is also depends on the PCB. As far as the cost is concerned the

more than 25% of the total cost is gone for the PCB design and fabrication.

We are using a micro controller-based system that handles high frequencies.

In the high frequency circuit the data may easily be violated in the PCB due to the

physical parameters .That is the track capacitance and inductance can cause the cross

talk in the buses. Also unwanted noise can be induced to supply rails and from there it

can affect the total response . Hence the PCB design has a major role in system

performance.

Design of a PCB is consider as the last step in electronics circuit design as

well as the first step in production of the PCBs . It forms a distant factor in electronics

circuits performance and reliability. The productivity of the PCB and its assembly

and service ability also depends on the design .The designing of the PCB consist of

the designing of the layout followed by the generation of the artwork . Orcad is low

cost feature rich software package for designing electronics circuit diagrams. The

various tools in orcad and their implementation and designing the PCB is discussed

below.

Electronics Design Automation (EDA) tools:With the Advent of powerful

computing system and interactive software , several stages in the design and

development of an electronic circuit has undergone automation .The software and

this hardware tool, which enables this automation ,is called EDA tools.



This tool helps us in such a way that we can draw that circuit ; list the

functioning of the circuit in response to the best input in assimilation software after

successful simulating the circuit.

The placing and routing software does the PCB artwork in the project the design

automation tool used in orcad, which includes.

Or cad Capture:

For circuiting the diagram ,create schematic and net list.

Or cad Layout: For creating the PCB artwork the design process is of the following

steps.

1.Drawing the circuit schematic:

This is done in orcad schematic capture.It includes many libraries with

thousands of component symbol.We can select the required symbol from library and

place it on the schematic page.After placing the component symbol , the inter

connection is completing using bus tool.After drawing the schematic, the following

operations are performed.

2.Routing :

Routing is the interconnection of component using upper tracks of

required width .Before starting routing the following thinks are done.

1.Enabling/disabling required layers:

The number of layers used and enabling the artwork depends upon the

complexity of the circuit , and fabrication technology available . If the board is single

sided , enable only bottom or solder side layer, so that track will come only on one

side of the PCB If the circuit is much more complex the enable the required number

of inner layer consider the fabrication technique and cost.

Manual routing :

In this , the PCB design has to manually connect each track. This is time

consuming process , but is required some cases. On this also the software checks for

errors and reports.



CHAPTER 10

PCB FABRICATION

Fig:10.1:PCB fabrication

A printed circuit board, or PCB, is used to mechanically support and

electrically connect electronic components using conductive pathways, tracks or

signal traces etched from copper sheets laminated onto a non-conductive substrate. It

is also referred to as printed wiring board (PWB) or etched wiring board.



A PCB populated with electronic components is a printed circuit

assembly (PCA), also known as a printed circuit board assembly (PCBA). Printed

circuit boards are used in virtually all but the simplest commercially-produced

electronic devices.

PCBs are inexpensive, and can be highly reliable. They require much more

layout effort and higher initial cost than either wire wrap or point-to-point

construction, but are much cheaper and faster for high-volume production; the

production and soldering of PCBs can be done by totally automated equipment. Much

of the electronics industry's PCB design, assembly, and quality control needs are set

by standards that are published by the IPC organization.

10.1 MATERIALS

Conducting layers are typically made of thin copper foil. Insulating

layers dielectric are typically laminated together with epoxy resin prepreg. The board

is typically coated with a solder mask that is green in color. Other colors that are

normally available are blue, black, white and red. There are quite a few different

dielectrics that can be chosen to provide different insulating values depending on the

requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene

(Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known prepreg materials used in the

PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4

(Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and

polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2

(Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass

and epoxy), CEM-5 (Woven glass and polyester). Thermal expansion is an important

consideration especially with BGA and naked die technologies, and glass fiber offers

the best dimensional stability.FR-4 is by far the most common material used today.

The board with copper on it is called "copper-clad laminate.



Copper foil thickness can be specified in ounces per square foot or

micrometers. One ounce per square foot is 1.344 miles or 34 micrometers.

10.2 PATTERNING (ETCHING)

The vast majority of printed circuit boards are made by bonding a layer of copper

over the entire substrate, sometimes on both sides, (creating a "blank PCB") then

removing unwanted copper after applying a temporary mask (e.g. by etching), leaving

only the desired copper traces.

A few PCBs are made by adding traces to the bare substrate (or a substrate

with a very thin layer of copper) usually by a complex process of multiple

electroplating steps. The PCB manufacturing method primarily depends on whether it

is for production volume or sample/prototype quantities.

Commercial (Production Quantities, Usually PTH)

Silk screen printing -the main commercial method.

Photographic methods. Used when fine line widths are required.

Hobbyist/prototype (small quantities, usually not PTH)

Laser-printed resist: Laser-print onto paper (or wax paper), heat-transfer with

an iron or modified laminator onto bare laminate, then etch.

Print onto transparent film and use as photo mask along with photo-sensitized

boards. (i.e. pre-sensitized boards), Then etch. (Alternatively, use a film photo

plotter).

Laser resist ablation: Spray black paint onto copper clad laminate, place into

CNC laser plotter. The laser raster-scans the PCB and ablates (vaporizes) the

paint where no resist is wanted. Etch. (Note: laser copper ablation is rarely

used and is considered experimental.)



Use a CNC-mill with a spade-shaped (i.e. 45-degree) cutter or miniature end-

mill to route away the undesired copper, leaving only the traces.

There are three common "subtractive" methods (methods that remove copper) used

for the production of printed circuit boards:

Silk screen printing uses etch-resistant inks to protect the copper foil.

Subsequent etching removes the unwanted copper. Alternatively, the

ink may be conductive, printed on a blank (non-conductive) board.

The latter technique is also used in the manufacture of hybrid circuits.

Photoengraving uses a photo mask and developer to selectively

remove a photo resist coating. The remaining photo resist protects the

copper foil. Subsequent etching removes the unwanted copper. The

photo mask is usually prepared with a photo plotter from data

produced by a technician using CAM, or computer-aided

manufacturing software. Laser-printed transparencies are typically

employed for photo tools; however, direct laser imaging techniques are

being employed to replace photo tools for high-resolution

requirements.

PCB milling uses a two or three-axis mechanical milling system to

mill away the copper foil from the substrate. A PCB milling machine

(referred to as a 'PCB Prototype') operates in a similar way to a plotter,

receiving commands from the host software that control the position of

the milling head in the x, y, and (if relevant) z axis. Data to drive the

Prototype is extracted from files generated in PCB design software and

stored in HPGL or Gerber file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In

this version, the unpatterned board has a thin layer of copper already on it. A reverse

mask is then applied. (Unlike a subtractive process mask, this mask exposes those

parts of the substrate that will eventually become the traces.)



Additional copper is then plated onto the board in the unmasked areas; copper

may be plated to any desired weight. Tin-lead or other surface platings are then

applied. The mask is stripped away and a brief etching step removes the now-exposed

original copper laminate from the board, isolating the individual traces. Some boards

with plated through holes but still single sided were made with a process like this.

General Electric made consumer radio sets in the late 1960s using boards like these.

10.3 ETCHING

Chemical etching is done with ferric chloride, ammonium persulfate, or

sometimes hydrochloric acid. For PTH (plated-through holes), additional steps of

electrolysis deposition are done after the holes are drilled, then copper is electroplated

to build up the thickness, the boards are screened, and plated with tin/lead. The

tin/lead becomes the resist leaving the bare copper to be etched away.

10.4 LAMINATION

Some PCBs have trace layers inside the PCB and are called multi-layer PCBs.

These are formed by bonding together separately etched thin boards.

10.5 DRILLING

Holes through a PCB are typically drilled with tiny drill bits made of solid

tungsten carbide. The drilling is performed by automated drilling machines with

placement controlled by a drill tape or drill file. These computer-generated files are

also called numerically controlled drill (NCD) files or "Excellon files". The drill file

describes the location and size of each drilled hole. These holes are often filled with

annular rings (hollow rivets) to create vias. Vias allow the electrical and thermal

connection of conductors on opposite sides of the PCB.



Most common laminate is epoxy filled fiberglass. Drill bit wear is partly due

to embedded glass, which is harder than steel. High drill speed necessary for cost

effective drilling of hundreds of holes per board causes very high temperatures at the

drill bit tip, and high temperatures (400-700 degrees) soften steel and decompose

(oxidize) laminate filler. Copper is softer than epoxy and interior conductors may

suffer damage during drilling.

When very small vias are required, drilling with mechanical bits is costly

because of high rates of wear and breakage. In this case, the vias may be evaporated

by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole.

These holes are called micro vias.

It is also possible with controlled-depth drilling, laser drilling, or by pre-

drilling the individual sheets of the PCB before lamination, to produce holes that

connect only some of the copper layers, rather than passing through the entire board.

These holes are called blind vias when they connect an internal copper layer to an

outer layer, or buried vias when they connect two or more internal copper layers and

no outer layers.

The walls of the holes, for boards with 2 or more layers, are made conductive

then plated with copper to form plated-through holes that electrically connect the

conducting layers of the PCB. For multilayer boards, those with 4 layers or more,

drilling typically produces a smear of the high temperature decomposition products of

bonding agent in the laminate system. Before the holes can be plated through, this

smear must be removed by a chemical de-smear process, or by plasma-etch.

Removing (etching back) the smear also reveals the interior conductors as well



Exposed Conductor Plating and Coating

PCBs are plated with solder, tin, or gold over nickel as a resist for etching

away the unneeded underlying copper. After PCBs are etched and then rinsed with

water, the solder mask is applied, and then any exposed copper is coated with solder,

nickel/gold, or some other anti-corrosion coating.

Matte solder is usually fused to provide a better bonding surface or stripped to

bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of

bare copper. The places to which components will be mounted are typically plated,

because untreated bare copper oxidizes quickly, and therefore is not readily

solderable. Traditionally, any exposed copper was coated with solder by hot air solder

leveling (HASL). The HASL finish prevents oxidation from the underlying copper,

thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however

new solder compounds are now used to achieve compliance with the RoHS directive

in the EU and US, which restricts the use of lead. One of these lead-free compounds

is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of

60ppm germanium.

It is important to use solder compatible with both the PCB and the parts used.

An example is Ball Grid Array (BGA) using tin-lead solder balls for connections

losing their balls on bare copper traces or using lead-free solder paste.

Other plantings used are OSP (organic surface protectant), immersion silver

(IAg), immersion tin, electrolysis nickel with immersion gold coating (ENIG), and

direct gold plating (over nickel). Edge connectors, placed along one edge of some

boards, are often nickel plated then gold plated. Another coating consideration is

rapid diffusion of coating metal into Tin solder. Tin forms intermetallics such as

Cu5Sn6 and Ag3Cu that dissolve into the Tin liquids or solidus (at 50C), stripping

surface coating and/or leaving voids.



Electrochemical migration (ECM) is the growth of conductive metal filaments

on or in a printed circuit board (PCB) under the influence of a DC voltage bias silver,

zinc, and aluminum is known to grow whiskers under the influence of an electric

field. Silver also grows conducting surface paths in the presence of halide and other

ions, making it a poor choice for electronics use. Tin will grow "whiskers" due to

tension in the plated surface. Tin-Lead or Solder plating also grows whiskers, only

reduced by the percentage Tin replaced. Reflow to melt solder or tin plate to relieve

surface stress lowers whisker incidence. Another coating issue is tin pest, the

transformation of tin to a powdery allotrope at low temperature.

Solder Resist

Areas that should not be soldered may be covered with a polymer solder resist

(solder mask) coating. The solder resist prevents solder from bridging between

conductors and creating short circuits. Solder resist also provides some protection

from the environment. Solder resist is typically 20-30 micrometers thick.

Screen Printing

Line art and text may be printed onto the outer surfaces of a PCB by screen

printing. When space permits, the screen print text can indicate component

designators, switch setting requirements, test points, and other features helpful in

assembling, testing, and servicing the circuit board.

Screen print is also known as the silk screen, or, in one sided PCBs, the red

print. Lately some digital printing solutions have been developed to substitute the

traditional screen printing process. This technology allows printing variable data onto

the PCB, including serialization and barcode information for traceability purposes.



Test

Unpopulated boards may be subjected to a bare-board test where each circuit

connection (as defined in a netlist) is verified as correct on the finished board. For

high-volume production, a Bed of nails tester, a fixture or a Rigid needle adapter is

used to make contact with copper lands or holes on one or both sides of the board to

facilitate testing. A computer will instruct the electrical test unit to apply a small

voltage to each contact point on the bed-of-nails as required, and verify that such

voltage appears at other appropriate contact points. A "short" on a board would be a

connection where there should not be one; an "open" is between two points that

should be connected but are not. For small- or medium-volume boards, flying probe

and flying-grid testers use moving test heads to make contact with the

copper/silver/gold/solder lands or holes to verify the electrical connectivity of the

board under test.

Printed Circuit Assembly

After the printed circuit board (PCB) is completed, electronic components

must be attached to form a functional printed circuit assembly or PCA (sometimes

called a "printed circuit board assembly" PCBA). In through-hole construction,

component leads are inserted in holes. In surface-mount construction, the components

are placed on pads or lands on the outer surfaces of the PCB. In both kinds of

construction, component leads are electrically and mechanically fixed to the board

with a molten metal solder.

There are a variety of soldering techniques used to attach components to a

PCB. High volume production is usually done with machine placement and bulk

wave soldering or reflow ovens, but skilled technicians are able to solder very tiny

parts (for instance 0201 packages which are 0.02 in. by 0.01 in.) by hand under a

microscope, using tweezers and a fine tip soldering iron for small volume prototypes.

Some parts are impossible to solder by hand, such as ball grid array (BGA) packages.



Often, through-hole and surface-mount construction must be combined in a

single assembly because some required components are available only in surface-

mount packages, while others are available only in through-hole packages. Another

reason to use both methods is that through-hole mounting can provide needed

strength for components likely to endure physical stress, while components that are

expected to go untouched will take up less space using surface-mount techniques.

After the board has been populated it may be tested in a variety of ways:

While the power is off, visual inspection, automated optical inspection.

JEDEC guidelines for PCB component placement, soldering, and

inspection are commonly used to maintain quality control in this stage of

PCB manufacturing.

While the power is off, analog signature analysis, power-off testing.

While the power is on, in-circuit test, where physical measurements (i.e.

voltage, frequency) can be done.

While the power is on, functional test, just checking if the PCB does what

it had been designed for.

To facilitate these tests, PCBs may be designed with extra pads to make

temporary connections. Sometimes these pads must be isolated with resistors. The in-

circuit test may also exercise boundary scan test features of some components. In-

circuit test systems may also be used to program nonvolatile memory components on

the board.

In boundary scan testing, test circuits integrated into various ICs on the board

form temporary connections between the PCB traces to test that the ICs are mounted

correctly. Boundary scan testing requires that all the ICs to be tested use a standard

test configuration procedure, the most common one being the Joint Test Action

Group (JTAG) standard. The JTAG test architecture provides a means to test

interconnects between integrated circuits on a board without using physical test

probes. JTAG tool vendors provide various types of stimulus and sophisticated



algorithms, not only to detect the failing nets, but also to isolate the faults to specific

nets, devices, and pins. When boards fail the test, technicians may desolder and

replace failed components, a task known as rework.

Protection and Packaging

PCBs intended for extreme environments often have a conformal coating,

which is applied by dipping or spraying after the components have been soldered. The

coat prevents corrosion and leakage currents or shorting due to condensation. The

earliest conformal coats were wax modern conformal coats are usually dips of dilute

solutions of silicone rubber, polyurethane, acrylic, or epoxy. Another technique for

applying a conformal coating is for plastic to be sputtered onto the PCB in a vacuum

chamber. The chief disadvantage of conformal coatings is that servicing of the board

is rendered extremely difficult.

Many assembled PCBs are static sensitive, and therefore must be placed in

antistatic bags during transport. When handling these boards, the user must be

grounded (earthed). Improper handling techniques might transmit an accumulated

static charge through the board, damaging or destroying components. Even bare

boards are sometimes static sensitive. Traces have become so fine that it's quite

possible to blow an etch off the board (or change its characteristics) with a static

charge. This is especially true on non-traditional PCBs such as MCMs and

microwave PCBs.

Design

Schematic capture or schematic entry is done through an EDA tool.

Card dimensions and template are decided based on required circuitry and

case of the PCB. Determine the fixed components and heat sinks if required.

Deciding stack layers of the PCB. 4 to 12 layers or more depending on design

complexity. Ground plane and Power plane are decided. Signal planes where

signals are routed are in top layer as well as internal layers.



Line impedance determination using dielectric layer thickness, routing copper

thickness and trace-width. Trace separation also taken into account in case of

differential signals. Microstrip, stripline or dual stripline can be used to route

signals.

Placement of the components. Thermal considerations and geometry are taken

into account. Vias and lands are marked.

Routing the signal trace. For optimal EMI performance high frequency signals

are routed in internal layers between power or ground planes as power plane

behaves as ground for AC.

Gerber file generation for manufacturing.

Safety Certification (US)

Safety Standard UL 796 covers component safety requirements for printed

wiring boards for use as components in devices or appliances. Testing analyzes

characteristics such as flammability, maximum operating temperature, electrical

tracking, heat deflection, and direct support of live electrical parts.

"Cordwood" Construction

Cordwood construction can save significant space and was often used with

wire-ended components in applications where space was at a premium (such as

missile guidance and telemetry systems) and in high-speed computers, where short

traces were important. In "cordwood" construction, axial-leaded components were

mounted between two parallel planes. The components were either soldered together

with jumper wire, or they were connected to other components by thin nickel ribbon

welded at right angles onto the component leads. To avoid shorting together different

interconnection layers, thin insulating cards were placed between them. Perforations

or holes in the cards allowed component leads to project through to the next

interconnection layer. One disadvantage of this system was that special nickel leaded

components had to be used to allow the interconnecting welds to be made.



Some versions of cordwood construction used single sided PCBs as the

interconnection method (as pictured). This meant that normal leaded components

could be used. Another disadvantage of this system is that components located in the

interior are difficult to replace.

Before the advent of integrated circuits, this method allowed the highest

possible component packing density; because of this, it was used by a number of

computer vendors including Control Data Corporation. The cordwood method of

construction now appears to have fallen into disuse, probably because high packing

densities can be more easily achieved using surface mount techniques and integrated

circuits.

Multiwire Boards

Multiwire is a patented technique of interconnection which uses machine-

routed insulated wires embedded in a non-conducting matrix (often plastic resin). It

was used during the 1980s and 1990s. (Kollmorgen Technologies Corp., U.S. Patent

4,175,816) Multiwire is still available in 2010 through Hitachi. There are other

competitive discrete wiring technologies that have been developed (Jumatech).

Since it was quite easy to stack interconnections (wires) inside the embedding

matrix, the approach allowed designers to forget completely about the routing of

wires (usually a time-consuming operation of PCB design): Anywhere the designer

needs a connection; the machine will draw a wire in straight line from one

location/pin to another. This led to very short design times (no complex algorithms to

use even for high density designs) as well as reduced crosstalk (which is worse when

wires run parallel to each otherwhich almost never happen in Multi wire), though

the cost is too high to compete with cheaper PCB technologies when large quantities

are needed.



Surface Mount Technology

Surface mounts components, including resistors, transistors and an integrated

circuit. Surface-mount technology emerged in the 1960s, gained momentum in the

early 1980s and became widely used by the mid 1990s. Components were

mechanically redesigned to have small metal tabs or end caps that could be soldered

directly on to the PCB surface. Components became much smaller and component

placement on both sides of the board became more common than with through-hole

mounting, allowing much higher circuit densities. Surface mounting lends itself well

to a high degree of automation, reducing labour costs and greatly increasing

production and quality rates. Carrier Tapes provide a stable and protective

environment for Surface mount devices (SMDs) which can be one-quarter to one-

tenth of the size and weight, and passive components can be one-half to one-quarter

of the cost of corresponding through-hole parts. However, integrated circuits are often

priced the same regardless of the package type, because the chip itself is the most

expensive part. As of 2006, some wire-ended components, such as small-signal

switch diodes, e.g. 1N4148, are actually significantly cheaper than corresponding

SMD versions.

Fabrication Techniques

The fabrication techniques used in this project can be broadly classified into:

MECHANICAL FABRICATION, consisting of mechanical designs i.e.

frame, tower, tank etc.

ELECTRICAL FABRICATION, consisting of electrical design i.e. making

PCB, soldering etc.



Mechanical Fabrication

For the basic frame we are using plywood cut out accordingly so as to adjust

the PCB on the top, the transformer, the main and source tank.

Electrical Fabrication

Soldering

How to Solder?

Mount components at their appropriate place; bend the leads slightly

outwards to prevent them from falling out when the board is turned over

for soldering. No cut the leads so that you may solder them easily. Apply a

small amount of flux at these components leads with the help of a

screwdriver. Now fix the bit or iron with a small amount of solder and

flow freely at the point and the P.C.B copper track at the same time. A

good solder joint will appear smooth & shiny. If all appear well, you may

continue to the next solder connections.

Tips For Good Soldering

Use right type of soldering iron. A small efficient soldering iron (about 10-25

watts with 1/8 or 1/4 inch tip) is ideal for this work.

Keep the hot tip of the soldering iron on a piece of metal so that excess heat is

dissipated.

Make sure that connection to the soldered is clean. Wax frayed insulation and

other substances cause poor soldering connection. Clean the leads, wires, tags

etc. before soldering.



Use just enough solder to cover the lead to be soldered. Excess solder can

cause a short circuit.

Use sufficient heat. This is the essence of good soldering. Apply enough

heat to the component lead. You are not using enough heat, if the

solder barely melts and forms a round ball of rough flaky solder. A good

solder joint will look smooth, shining and spread type. The difference

between good & bad soldering is just a few seconds extra with a hot iron

applied firmly.

Precautions

Mount the components at the appropriate places before soldering.

Follow the circuit description and components details, leads

identification etc. Do not start soldering before making it confirm that

all the components are mounted at the right place.

Do not use a spread solder on the board, it may cause short circuit.

Do not sit under the fan while soldering.

Position the board so that gravity tends to keep the solder where you

want it.

Do not over heat the components at the board. Excess heat may

damage the components or board.

The board should not vibrate while soldering otherwise you have a dry

or a cold joint.



Fig 10.2 Pcb layout



Fig10.3 pcb component layout



CHAPTER 11

CONCLUSION

The most important aspect of any power plant is the boiler control. Several

techniques can be implemented to control the boiler in power plant. The method that

has to be used relies on varied objectives like superior quality, increased efficiency,

high profit and other such points depending upon the purpose of the company that

implies it.With the prime objective of catering to these necessities and the needs of

the industrial sector, significance has been given here to automation.

Documents

Project Orig c