Thursday, April 4, 2013

Buck–boost converter

 

The buck–boost converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude.
Two different topologies are called buck–boost converter. Both of them can produce a range of output voltages, from an output voltage much larger (in absolute magnitude) than the input voltage, down to almost zero.

Conceptual overview

Like the buck and boost converters, the operation of the buck-boost is best understood in terms of the inductor's "reluctance" to allow rapid change in current. From the initial state in which nothing is charged and the switch is open, the current through the inductor is zero. When the switch is first closed, the blocking diode prevents current from flowing into the right hand side of the circuit, so it must all flow through the inductor. However, since the inductor doesn't like rapid current change, it will initially keep the current low by dropping most of the voltage provided by the source. Over time, the inductor will allow the current to slowly increase by decreasing its voltage drop. Also during this time, the inductor will store energy in the form of a magnetic field.
When the switch is then opened, the inductor will be cut off from the input voltage supply, so the current will tend to drop to zero. Again, the inductor will fight such an abrupt change in current. To do so, it must now act like a voltage source to the rest of the circuit, which it can do using the energy it stored while charging. Since current was previously flowing "down" the inductor, it will want to maintain this direction, and so the voltage that it provides will be inverted relative to input supply. During this time, the inductor will discharge through the load and the rest of the circuit, which will cause its voltage to decrease over time. Also during this time, the capacitor in parallel with the load will charge up to the voltage presented by the inductor.
When the switch is once again closed, the diode is forward biased by the input supply, cutting the load off from the left hand side of the circuit. During this time, the capacitor will discharge into the load, providing energy and voltage to it. By cycling the switch fast enough, the inductor can be allowed to charge and discharge only slightly in each cycle, maintaining a relatively steady voltage to the load. Similarly, the capacitor will only need to discharge slightly while the switch is open before it has a chance to recharge again while the switch is closed.
The voltage presented by the inductor to the load depends on how long the switch is opened and closed. When the switch is closed and the inductor is charging, the current through the inductor is ramping up linearly. The longer the switch is closed, the higher the current will get. When the switch is then opened, it is the end current that the inductor will try to maintain by acting like a voltage source. The higher this current is, the more voltage the inductor will need to provide in order to produce it. Thus, the longer the switch is closed during the on stage, the higher the output voltage will be.


Choosing an Inverter and Battery for Home



Choosing an Inverter and Battery for Home
By: mr_suresh |
Knowledge must be shared. So I thought of sharing my knowledge gained during research on inverters. I hope it will be useful for others to decide the right inverter quickly.
DIFFERENCE BETWEEN UPS AND INVERTER
Inverter is an electronic circuit for converting Direct Current to Alternating Current. They are used in a wide range of applications from small switched power supplies to large electric utility applications to transport bulk power (like Air Conditioners, Fridge, Mixie etc.)

A UPS typically includes the battery and battery charger in one stand alone unit, especially used for computer backups. UPS will effectively switch from utility power to its own power source almost instantaneously.
WAVES - SQUARE WAVE, SINE WAVE AND QUASI SINE WAVE
Square Wave Inverters
Simplest and least expensive in the market. Computers, televisions, induction motors, transformer loads and even light bulbs are not recommended to run on this waveform, because square wave has a high harmonic content.
Sine Wave Inverters
This is the correct waveform on which all electronic equipment, televisions, and computers are designed to run. They filter the output voltage well and recommended.
Quasi-Sine Wave Inverters
Indeed correct selection for running some types of motors and incandescent lighting and not fit for all types of equipments, hence it is not recommended.
CALCULATE YOUR POWER CONSUMPTION
This can be done by adding up the watts on the equipment specifications normally printed below or behind the equipments.

I selected 800 VA which delivers approximately 640 watts. Don’t select very high inverter than the requirement as it will consume more electricity and loss of power is also higher.
CHOOSING THE INVERTER
After calculating the consumption the next step is to select the Inverter VA.

The formula is
Watts / Power Factor = VA
For me it was
542 Watts / 0.8 Power Factor = 677 VA
(Power Factor: 0.8 for most of the UPS, incase of APC Inverters the power factor is 0.6, you can refer product manual or ask dealer for this info)

So the available VA’s in market are 500 VA, 800 VA, 1000 VA, 1400 VA and above. I selected 800 VA.

CHOOSING INVERTER BRAND
This was quite difficult. I selected few known brands in market like Luminous (widely advertised in 2004), Genus (OEM supplier for LG and Samsung), Su-Kam (From few years they are in the market, but most advertised), Hyundai (New, manufactured by Luminous under license from Hyundai Korea), Microtek (Addidas group) and APC (New to Home Inverter).

CHOOSING BATTERY SIZE
Batteries are available in various Amperes. You need to decide how much backup you require and decide on the amperes.
Here is the formula to calculate the backup
Load/Voltage x Backup hours = Amperes
In my case it was
542 Watts / 12 V x 3 hrs = 135 Ah
I selected 130 Ah Standard Furokawa battery for my home.

CHOOSING BATTERY
Battery is a backbone for any inverter. There are different types of battery available in the market.

Maintenance battery
These batteries requires maintenance every month. The distilled water needs to be filled every month.

Maintenance free battery
This comes with flat plate collectors and maintenance free. These batteries will have a life of 4 years.

Tubular batteries
Here the active material (lead oxide) is encapsulated in polyester tubes to prevent ‘Shedding’. The electrode geometry facilitates ‘cyclic’ deep discharges. They are recommended for back up power for UPS and Inverters where environmental conditions are tough and high ambient temperatures are common. These are capable of long hours of backup.



Wednesday, April 3, 2013

List of Holidays 2013


DateDayHolidayState
JANUARY


1 JanuaryTuesdayNew Year's DayAR ML MN MZ NL PY SK TN
13 JanuarySundayBhogiAP
13 JanuarySundayMakara SamkrantiAN AP AR AS GJ KA PY TN
14 JanuaryMondayPongalAN AP AR AS GJ KA PY TN
15 JanuaryTuesdayThiruvalluvar DayPY TN
16 JanuaryWednesdayUzhavar ThirunalTN
18 JanuaryFridayGuru Govind Singh JayantiCH HR PB
23 JanuaryWednesdayNetaji Subhas Chandra Bose JayantiTR WB
25 JanuaryFridayMilad-un-NabiAN AP CH DL KA KL MH MP MZ PY TN UK UP
26 JanuarySaturdayRepublic DayNational
FEBRUARY


15 FebruaryFridayVasanta Panchami / Shree PanchamiHR OR TR WB
19 FebruaryTuesdayChatrapati Shivaji Maharaj Jayanti MH
25 FebruaryMondayGuru Ravidas JayantiCH HR PB
MARCH


10 MarchSundayMaha ShivaratriAP CG CH GJ HP HR JK KA KL MH MP OR UK UP
15 MarchFridayKashiramji JayantiUP
26 MarchTuesdayDoljatra / Holika DahanAS ML MN PB UP WB
27 MarchWednesdayHoliall states except AP AS HR KA KL MN NL PB PY TN TR WB
29 MarchFridayGood Fridayall states except CG GJ HP HR JK OR PB RJ TR
APRIL


5 AprilFridayBabu Jagjivan Ram's Birthday (tentative)AP
11 AprilThursdayGudi Padva / Ugadi / Chetti Chand / Telegu New YearAP GA KA MH PY UP TN
13 AprilSaturdayVishuKL
14 AprilSundayTamil New Year / Varsha Purappu / PuthanduTN
14 AprilSundayDr Ambedkar JayantiAP BR CH GJ DL HR JK KA KL MH OR PY TN UK UP
14 AprilSundayBengali New Year / Vaisakh / MasadiTR WB
18 AprilThursdayRam Navami (Smarta)AP GJ HR
19 AprilFridayRam Navami (Vaishnava)BR CH DL MH MP OR PB RJ SK UK UP
24 AprilWednesdayMahavir JayantiAN CG DL HP KA MH MP RJ TN UK UP
MAY


1 MayWednesdayMay DayAP AS BR GA KA KL MN PY TN TR WB
1 MayWednesdayMaharashtra DayMH
11 MaySaturdayShiv JayanthiKA
12 MaySundayMaharshi Parasuram JayantiUP
13 MayMondayBasava JayantiKA
24 MayFridayHazrat Alis BirthdayUP
25 MaySaturdayBuddha PurnimaAN AR CG DL HP JK MH MP MZ UK UP
JUNE


16 JuneSundayMartyrdom Day of Sri Guru Arjun Dev JiPB
23 JuneSundaySant Kabir JayantiHR
AUGUST


2 AugustFridayJumat-ul-WidaJK UK UP
9 AugustFridayRamazan / Idu'l Fitrall states except GA JH KL LD UP
10 AugustSaturdayTeejHR
15 AugustThursdayIndependence DayNational
18 AugustSundayParsi New Year (Shahenshahi)MH
19 AugustMondayFirst OnamKL
20 AugustTuesdayOnam / ThiruonamKL PY
21 AugustWednesdayRaksha BandhanGJ RJ UK UP
28 AugustWednesdayJanmashtami (Smarta)BR OR
28 AugustWednesdayJanmashtami (Vaishnava)CH DL GJ HR JK PB RJ UK UP
28 AugustWednesdaySri Krishna JayantiTN
SEPTEMBER


9 SeptemberMondayGanesh Chaturthi / Vinayaka ChaturthiAP GA GJ MH OR PY TN
21 SeptemberSaturdaySree Narayana Guru Samadhi DayKL
23 SeptemberSundayHaryana Veer and Shahidi DivasHR
OCTOBER


2 OctoberWednesdayMahatma Gandhi's BirthdayNational
5 OctoberSaturdayMahalayaKA WB
6 OctoberSundayMaharaja Agrasen JayantiHR
11 OctoberFridayDussehra (Maha Saptami)SK TR WB
12 OctoberSaturdayDussehra (Maha Ashtami)AP AR AS ML MN OR TR WB
13 OctoberMondayDussehra (Maha Navami)BR KA KL ML NL PY SK TN UK UP WB
14 OctoberMondayDussehra (Vijaya Dashami)all states except AR JH KA MN PB PY SK
16 OctoberWednesdayBakri Id / Idu'l Zuha (Feast of Sacrifice)all states except CH GA HP MZ PB SK
18 OctoberFridayLakshmi PujaTR WB
18 OctoberFridayBirthday of Maharishi Valmiki JiHR KA PB
NOVEMBER


1 NovemberFridayKannada RajyothsavaKA
1 NovemberFridayHaryana DayHR
2 NovemberSaturdayNaraka ChaturdashiKA
2 NovemberSaturdayDeepavali (Festival of Lights)AP CH DL GJ HR KL MH PY TN WB
3 NovemberSundayDiwali (Festival of Lights)all states except AP CH DL GJ JH HR KA KL MH MN PY TN WB
3 NovemberSundayBalipadyami Diwali (Gobardhan Puja/Vishavakarma DayGJ HR KA MH UK UP
5 NovemberTuesdayBhai Duj / Chitragupth JayantiMH UK UP
14 NovemberThursdayMuharramAN AP BR CG CH DL HP JK KA MH MP OR RJ TN UK UP WB
17 NovemberSundayGuru Nanak JayantiAN CG CH DL HP HR JK MH MP NL PB RJ UK UP WB
21 NovemberThursdayKanaka JayantiKA
DECEMBER


25 DecemberWednesdayChristmas Dayall states except HR JH

Tuesday, April 2, 2013

Methods of computing square roots

square root

(algorithm)
Definition: This describes a "long hand" or manual method of calculating or extracting square roots. Calculation of a square root by hand is a little like long-hand division.
Suppose you need to find the square root of 66564. Set up a "division" with the number under the radical. Mark off pairs of digits, starting from the decimal point and working left. (Here the decimal point is a period (.) and commas (,) mark pairs of digits.)
               ___________ 
             \/  6,65,64. 
 
Look at the leftmost digit(s) (6 in this case). What is the largest number whose square is less than or equal to it? It is 2, whose square is 4. Write 2 above, write the square below and subtract.
               __2________ 
             \/  6,65,64. 
                -4  
               ----  
                 2  
 
Now bring down the next two digits (65). The next "divisor" is double the number on top (2x2=4) and some other digit in the units position (4_).
               __2________ 
             \/  6,65,64. 
                -4  
                -----  
             4_ ) 265  
 
What is the largest number that we can put in the units and multiply times the divisor and still be less than or equal to what we have? (Algebraically, what is d such that d × 40+d ≤ 265?) It looks like 6 might work (since 6 × 40 = 240), but 6 is too big, since 6 × 46 = 276:
               __2__6_____ 
             \/  6,65,64. 
                -4  
                -----  
             46 ) 265  
                 -276   TOO BIG 
 
So try 5 instead.
               __2__5_____ 
             \/  6,65,64. 
                -4  
                -----  
             45 ) 265  
                 -225  
                 -------  
                   40  
 
Repeat: bring down the next two digits, and double the number on top (2 × 25 = 50) to make a "divisor", with another unit.
               __2__5_____ 
             \/  6,65,64. 
                -4  
                -----  
             45 ) 265  
                 -225  
                 -------  
             50_ ) 4064  
 
It looks like 8 would work. Let's see.
               __2__5__8__ 
             \/  6,65,64. 
                -4  
                -----  
             45 ) 265  
                 -225  
                 -------  
             508 ) 4064  
                  -4064  
                  ------  
                      0  
 
So the square root of 66564 is 258. You can continue for as many decimal places as you need: just bring down more pairs of zeros.
Here is an example spanning the decimal point. When a number does not have a rational square root, you can continue calculating (significant) digits as long as you wish.
       __1__6.8_4_0_4_2_7_5_...
     \/  2,83.6  
        -1  
        -----  
     26 ) 183  
         -156  
         ------  
     328 ) 2760  
          -2624  
          ------- 
     3364 ) 13600 
           -13456 
           -------- 
     33680 )  14400 
                 -0 
            --------- 
     336804 ) 1440000 
             -1347216 
             ---------- 
     3368082 )  9278400 
               -6736164 
              ----------- 
     33680847 ) 254223600 
               -235765929 
               ------------ 
     336808545 ) 1845767100 
                -1684042725 
                ----------- 
                  161724375 
 
Why does this work?
Consider (10A + B)² = 100A² + 2 × 10AB + B² and think about finding the area of a square. Remember that 10A + B is just the numeral with B in the units place and A in the higher position. For 42, A=4 and B=2, so 10 × 4 + 2 = 42.
diagram of a square that is 10A + B on a side showing a 100A squared  rectangle, two 10AB rectangles, and a B squared rectangle
The area of the two skinny rectangles is 2 × 10A × B. The tiny square is B². If we know A and the area of the square, S, what B should we choose?
We previously subtracted A² from S. To scale to 100A², we bring down two more digits (a factor of 100) of the size of S. We write down twice A (2A), but shifted one place to leave room for B (10 × 2A or 2 × 10A). Now we add B to get 2 × 10A + B. Multiplying by B gives us 2 × 10AB + B². When we subtract that from the remainder (remember we already subtracted A²), we have subtracted exactly (10A + B)². That is, we have improved our knowledge of the square root by one digit, B.
We take whatever remains, scale again by 100, by bringing down two more digits, and repeat the process.

square root of 3 by division method






















Source :-http://xlinux.nist.gov 

Monday, March 25, 2013

Domestic violence act of india is Against Men !!

 Domestic violence act of india is Against Men !!



This website attemps to explain the future disastrous results of badly formulated and gender biased law Domestic violence against women law - 2005 which grossly violates the liberty and dignity of an average man and his family members. Anyone who is educated and reads the guidelines of the law can see how vicious this law is and what it's social implications will be. 

On the face of it, the law appears to be a blessing for people in abusive or violent relationships. However, a careful analysis reveals that, under the ploy of “women and children welfare”, this law is yet another misguided attempt to enact legislation to grant women legal supremacy over men and to create a society where men are deprived of their rights.

There are three fundamental problems with this law – a) it is overwhelmingly gender biased in favor of women, b) the potential for misuse is astounding and c) the definition of domestic violence is too expansive.

The DV act singles out men as perpetrators of domestic violence and assumes that only women are victims. As per this law, only a woman can file a complaint against her male partner. A man, who is a victim of domestic violence, has no rights under this law. The fact is that it has been comprehensively proven in numerous studies [please see references] that women are no less abusive as men in intimate relationships. Giving such sweeping legal powers to women while withholding protection to male victims is tantamount to systematic legal victimization of men. In the western world, the domestic violence laws are gender neutral and provide protection to the victims, both men and women. The fact that the Indian version explicitly prohibits any male victim to seek relief under this law defies all logic and is beyond comprehension.

The second significant flaw in this law is that it lends itself to such easy misuse that women will find it hard to resist the temptation to “teach a lesson” to their male relatives and will file frivolous and false cases. A similar trend is already being observed in the case of anti-dowry law (498a), which is being misused to such an extent that the Supreme Court has termed it “Legal Terrorism”. To illustrate how easy it is to misuse the DV law, consider the scenarios below. [She means wife/female live-in partner and he means husband/male live-in partner]

a) If she demands any amount of money from him, for any reason whatsoever, he is legally bound to pay that amount in full, failing which he can be imprisoned. Under the pretext of preventing economic abuse of women, this law legalizes the extortion of money by women. Interestingly, if he asks for money from her, he can be jailed for that as well. Furthermore, he is responsible for paying the rent if the couple resides in a shared rented accommodation.

b) As per the law, she retains the right to the residence. This is a very convenient means of getting control of the house regardless of whether she has any legal right on the property. Moreover, if he is booked under DV, he is responsible for paying the rent as well, even though he may not be allowed to live in the house or he might even be in jail.

c) If she decides not to cook and wishes to eat out in a restaurant everyday, he cannot afford not to oblige, lest he invites the DV provision for “not providing food”, for which he could be jailed.

d) If she has an affair and he tries to prevent her from meeting her lover, he could be punished under the DV act, as he is preventing her from meeting someone.

e) He can be booked under the DV act if she feels that she has been insulted. Insult is a relative term, which is totally left to her discretion. Interestingly, if she insults and abuses him verbally or even physically, he does not have any legal recourse in this law

These are just some of the ways in which women can exploit men in a legally permitted manner. The fact that the complaint by a woman will be treated, prima facie, as “true and genuine” opens up a whole new realm of possibilities where innocent men will be accused and implicated in false cases, just because they refuse to give in to her unreasonable demands.

Most people readily agree that the law will be misused. Their counter arguments generally are

a) The number of miuses will be very low OR every law is misused – The objective of any law should be to punish the guilty and protect the innocent. The persecution of innocents cannot be justified in any circumstances. As is the case with 498a, this law will be heavily misused in urban India.

b) If she is happy, then why will she file a complaint – Ah ! So, the man exists at the mercy of the woman. If the wife wants to kick out old parents from home or wants to pursue an affair and should the man dare to object, she can get him incarcerated with alacrity. Any law that forcefully subjects a section of a society to conduct as per the pleasure of another section is deemed oppressive and should be vehemently opposed.

c) There are other provisions to deal with the misuse of this law – The fact is that there are other legal provisions to deal with domestic violence as well. If a strict law is made for a specific purpose, then the provisions for dealing with its misuse should be in the law itself.

The third major flaw in this law is that it provides an all-encompassing definition of domestic violence and some terms (insults, name calling) are extremely subjective. The radical feminists claim that 70% of women in India face domestic violence which comes as no surprise as even an insult is considered domestic violence. Interestingly, they are mum on how many indian men suffer domestic violence using the same criteria. This law strikes at the very foundation of marriage by promoting intolerance and litigation for petty domestic disputes. It is universally recognized that from time to time differences arise in a marriage and sometimes people, both men and women, behave in hurtful ways towards each other. Most people, though, are able to work them out and lead a more or less happy life with their loved one. However, this law makes it very easy to escalate the domestic problems in daily life to such a level that it eventually leads to a breakdown in marriage. Once a man has been accused of domestic violence for a something relatively minor (insult), while he might have been subjected to the same treatment from her, he will perpetually feel threatened by his partner and that is the beginning of the end. This law will lead to more divorces, broken homes and the children will pay the ultimate price by getting deprived of a pleasant childhood.

There are degrees of domestic violence and not all conflicts in a relationship can be termed as domestic violence. This law trivializes the issue of domestic violence by including minor differences in its realm and by explicitly denying protection to half of the population.

The law in its current form is grossly inadequate to tackle the problem of domestic violence. It imposes a lot of responsibility on men, without giving them rights. On the other hand, it gives lots of rights to women without requiring them to be responsible. At the very minimum, it should be made gender neutral, offering protection to both men and women. Also, provisions for stringent punishments need to be incorporated into the law to prevent misuse. Moreover, the law needs to be made more practical by differentiating between various degrees of conflicts and by unambiguously defining what constitutes domestic violence.

The fact is domestic violence is a serious problem and a neutral and unprejudiced law is needed to protect the genuine victims of domestic violence, irrespective of gender. The perpetrators of domestic violence need to be appropriately punished and dealt with. At the same time, protection cannot be withheld from real victims for any reason whatsoever, least of all their gender. One can be certain that there is something sinister about a law, when it intimidates and instills fear in innocent people. When a person who has not committed any crime, begins to fear punishment under the provisions of a law, it is not a law anymore – it is state sponsored terrorism.

References

1. The US Govt. National family violence surveys of 1975 and 1985 (http://www.ejfi.org/DV/dv-21.htm)

2. Various studies by univ of New Hampshire (http://pubpages.unh.edu/~mas2/ipv-violence-by-women.htm)

3. “When She Was Bad – Violent Women and the Myth of Innocence”, written by Patricia Pearson, a self-described feminist

Source:-www.498a.org

WHAT Is The Role of a CAPACITOR in the operation of a CEILING FAN?

In a ceiling fan there is an single phase induction motor.

Single phase stator produces a non rotating, pulsating magnetic field.The single coil excited by a single phase current produces two counter rotating magnetic field phases, coinciding twice per revolution at 0 degrees and 180 degrees. When the phases rotate to 90 degree and -90 degree they cancel. At 45 deg and -45 deg they are partially additive along the +x axis and cancel along the y axis. The sum of these two phases is a phasor stationary in space, but alternating polarity in time. Thus, no starting torque is developed.

So, in order to generate the starting torque we have to split the phase in two. This configuration comprises two windings main winding W1 and auxiliary winding W2, a centrifugal switch SW1 and a capacitor.

The two windings are wound with a geometric offset, effectively making a second set of poles phase shifted within the stator. The capacitor provides a phase shift to the current flowing in W1 and we therefore have a "two phase" motor while the switch is closed. When the motor is almost up to speed, the switch opens disconnecting W1 and the capacitor. The motor can be reversed by reversing the connections of either W1 or W2 (but not both)

The start winding (W1) and the start capacitor provide for a rotating magnetic field in one direction enabling the motor to start.

Saturday, March 23, 2013

Connecting Voltmeter, Ammeter and Wattmeter in a circuit



Connecting Voltmeter, Ammeter and Wattmeter in a circuit
Written  by Sunil Saharan


Voltmeter, Ammeter, Watt meter and Energy meter are four pillars of electrical energy and are most important devices used in electrical engineering field. You can't imagine any application in electrical engineering without voltage, current, energy and power measurement. Voltmeter, Ammeter, Watt meter and Energy meter connections and basics are discussed here.
If you are an electrical engineer than you must know how to connect various electrical instruments in a circuit, Specially measuring instruments. The most common instruments or measuring apparatus you must know about are Voltmeter, Ammeter, Energy meter and Watt meter.
Voltmeter : -                               

Voltmeter is a device that is used to measure voltage or potential difference across two given points. Essentially a voltmeter is nothing but a galvanometer with infinite resistance connected in series . This makes the resistance of an ideal voltmeter infinite .
Voltmeter is connected in parallel, this is shown below : -


As shown in image a voltmeter is connected in parallel or in shunt configuration, due to voltage division in series.
If we connect it in series high resistance of voltmeter will make the circuit insulating and no current will flow and the system will stop working.
Voltage Division in Series
If two resistances are connected in series the voltage given to the complete system is divided across resistances.
Let us consider two resistances with resistance R1 and R2, then total resistance of series configuration will be given by
R = R1 + R2
and Voltage across each resistance is give by
V1 = R1*V/R,
V2 = R2*V/R,
Here,
V1 is voltage across R1 and
V2 is voltage across R2.
The below Figure shows this more clearly.

Ammeter : - 
It Measure current ( general term ) or rate of flow of charge ( Technical meaning ) between two points on a conductor.
An Ammeter is connected in series because it has low resistance and current remains same in series so the amount of current flowing through load will be same as that of Ammeter and hence Ammeter will give the exact reading. Connection of an ammeter is shown below with circuit diagram : -

Watt Meter : -
 A watt meter Measures power consumed by an apparatus in a given time. Normally watt meter gives reading in watt or kilowatt.
A Watmeter have two coils one is current coil and other is voltage coil. The power is product of Voltage across the load and current flowing through the load i.e. P=V/*I
 Connection of watt meter is shown below : -

The Current coil is connected in series as current remains same in series (concept of Ammeter) and potential coil is connected in parallel as voltage remains same in parallel (concept of Voltmeter)
Try to know the various components in the circuit diagram. In this experiment you can see the 'Transformer', 'Wattmeter', 'Ammeter' and 'Voltmeter'.