Three phase welding rectifier circuit working

Three phase welding rectifier circuit working 

Introduction:- A three phase welding rectifier is used in places where very smooth and perfect welding work is required. It consist of three phase step down transformer, rectifier and current controlling saturable reactor.

Circuit description:- A three phase  transformer is used for step down three phase 400 volt to 3 phase 100 v ac for welding rectifier. In a three phase transformer there are three winding in primary connected in star/delta connection and three secondary winding also connected in star / delta connection. A three phase bridge configuration is used, as shown in diagram for ac to dc conversion.

for output current contolling saturable reactor is used.saturable reactor has two winding one is used in series with output dc line and other winding is connected dc power source with variable resistance to control output current.

A  MCB, Contactor and Over Load relay is used  in control circuit to switch on power to welding transformer and protection from over load. one cooling fan is also used for cooling of transformer not shown in diagram. Start and stop button is provided for on/off contactor.

Controlling Current:- When controlling current is less saturable reactor reactance is more causing low output current. As control current trough reactor is increases the reactor reactance decreases causing more output current.


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A simple Arduino program, blinking a LED for beginners

A Simple Arduino program, blinking a LED for beginners

Introduction:- Arduino UNO  board is a complete board for learning use of micro controller.It uses micro controller IC ATMega328 16 Mega Hertz. It is 8 bit micro controller with 32 kb of program memory. It has inbuilt programmer to upload program through USB port. Input dc supply jack is provided for giving input dc supply 8-12 volt. Inbuilt voltage regulator are used to provide 5 volt and 3.3 volt regulated power supply for internal use. 13 numbers digital input / output pins are provided for external devices connection. one LED is internally connected to pin number 13. Analog I/O pins, PWM pin and serial transfer Rx Tx pins are also provided.

Micro controller is a very small computer on a single chip. It consist of inbuilt CPU, storage memory, input output ports. Arduino board has every thing required for use of micro controller. It needs to upload a program and run. In this post I am writing a very small program to explain program structure and syntax use for Arduino programming. It used open source integrated environment development software for arduino. Screen shot of arduino IDE for windows is as shown below. Software can be downloaded from net.

When you open this arduino IDE in PC you will see this screen. Open blink example from menu bar
file  examples//basic/ blink . you will see screen open with above code. now please see the code it is similar to c++ programming language. this is very first and small program for beginners. first part of program is void setup() in this function we write the code which has to executed  only once. To use any digital input/output pin we have to configure the pin as input or output with a line of code like pinMode(pin number, OUTPUT/INPUT). Here we are using function pinMode to declare LED_BUILTIN (pin 13) as a output pin.

void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

Second part of program is loop function it runs continuously till the program is not stopped.
In loop function   digitalWrite(LED_BUILTIN, HIGH);  is use to write (give) a high value to  LED_BUILTIN (pin  13). when high value is given to pin 13 led connected to this pin gets on. Function   delay(1000);   Provides a delay of 1000 mili  seconds. This keeps pin 13 high for 1000 ms. Then the function digitalWrite(LED_BUILTIN, LOW);  is use to write low on  LED_BUILTIN (pin  13). When low value is given to pin 13 led connected to this pin gets off. Again function delay(1000); is used to give 1000 ms off time for pin 13 led. this complete code is repeated continuously as it is in loop function. Code for loop function is as given below.

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}

After writing the program code in editor window it need to compile. in editor. Below menu bar there is a tool bar. In tool bar there are tab buttons for compile and upload the program.there is tool tip on each button. so by clicking on compile button program will compile and a message of successfully compiled or some error will display in output window.if your program is written correctly it will compile successfully.after compile we have to upload the program in Arduino board. For this we have to connect our board to computer with the help of USB cable which comes with board. The USB cable serves two purpose first it gives the power supply to the board and second it upload the hex code to the board. As soon as code upload is completed a message is displayed on IDE that upload is completed. Now micro controller runs this program and you will see that led connected to pin 13 starts blinking at the rate  of 1 second off and 1 second on. To blink a led can be done by any electronic circuit. but to change on/ ff duration will required to change components. With micro controller we have to change delay time in our program and upload. you can experiment by changing time period. any other output pin can also be use to control other led. We can also use 5 volt miniature relay in place of led and control any device from relay. Maximum output current of any output pin is max 50 ma. so we should be care full to connect load to pin that current should be in safe limit. Arduino is very vast can not be cover in such a small post. so for any doubt please ask in comment or take some help from net.
This program as well as many programs are given in  examples of arduino IDE that can be used for further learning. I hope this post will help full to you. your valuable suggestion and comments are welcome for improvement.



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Bi stable Multi vibrator or Set Reset Flip Flop

Bi Stable Multi Vibrator or Set Reset Flip Flop

Introduction:- Bi stable multi vibrator has two stable states that is its output can be set to 1 with set pulse or can be set to 0 with reset pulse. It is also known as set reset flip flop or SR flip flop. It is the basic unit of electronic solid state memory. It stores one bit of data that is 0 or 1.To store 8 bits data set of 8 flip flop are used. Register also uses the flip flops for storing data. Additional logic circuitry is also used to write read data.

Basically in all digital circuit supply voltage used is 5 volt dc. So in this set reset flip flop working voltage 5 volt is given to Vcc and - ve to ground. There are two input points set and reset. When a positive pulse is given to set input the output of flip flop changes to state 1. This state remains constant until a reset pulse is given to reset input. Again when we want to reset a reset pulse is given to reset input, the output reset to 0 state and remain in 0 state until set pulse is given to set input.
this property of SR flip flop make it suitable for digital bit storage. According to data bits all flip flop of eight bit storage locations are set to their corresponding bit. In simple electronics this flip flop can be used to make latching relay circuit.

Circuit Working:- When set switch is pressed positive voltage goes to the base of transistor T1 make it conducting. So the collector voltage of transistor T1 becomes 0 so biasing of transistor T2 base through R3 resistance reduce to 0 volt and T2 gets cutoff. Due to cutoff of  transistor T2 collector voltage of transistor T2 becomes 5 volt which start providing biasing to base of  transistor T1  through resistance R4 this makes T1 to remain in saturation level even after set button is depressed.
Same process is repeated when reset button is pressed. Transistor T2 start conducting so the collector voltage of T2 becomes 0 volt so biasing of T1 base trough resistance R4 reduced to 0 volt and T1 gets cutoff. Due to cutoff of transistor T1 the collector voltage of T1 becomes 5 volt which start providing biasing to base of transistor T2 trough resistance R3 this makes transistor T2 to remain in saturation level even after reset button is depressed.


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Astable multivibrator clock pulse generator

Astable multivibrator clock pulse generator

Astable multivibrator:- It consist of two transistor two base biasing resistance and two feed back capacitor connected as shown in fig.The frequency of square wave generated depends on the values of resistance and capacitance. The product of R and C is known as time constant of RC circuit. Time period of one cycle is equal to 2x0.693xRC. So frquency of square wave is equal to 1/2x0.693xRC hertz. For example resistace of 10k and capacitance of 0.1MFD. The clock frequency will be 1/2x0.693x10k×0.1×10^-6 =1/2x,0.693x0.1×10^-6=10×10^3 = 7.2 khertz. 

Working
When the circuit is switched on one transistor will driven to saturation  and other will driven to cutoff.  Consider T1 is ON and T2 is OFF. During this time Capacitor C2 is charging to Vcc through resistor R1. T2 is OFF due to the - ve voltage from the discharging capacitor C1 which is charged during the previous cycle.As C2 charged fully base current of T1 decay so T1 gets cut off and T2 gets switched on.base current of T2 is maintained by charging current of  C1. As C1 gets fully charged its charging current decay and T2 gets cut off.at this time T1 is swiched on which causes  C1 discharge which gives negative voltage to base of T2 for instant cut off of T2.this cycles repeat continously hence square wave output voltage is generated at the collector of both transistors. This type of oscillater are also designed with integrated circuits. For highly stable frequency clock pulses Cristal is used. crystal comes with various frequencies.In all digital devices which uses micro processer must have clock generator circuit. It controls all activities.

Load Control with Transistor

Load Control with Transistor

Introduction:- To control any load on/off we can use Transistor as a control element. As per rating of transistor we can directly control dc load. for higher load we can use suitable relay and Contactor.

Relay:- A relay is electro mechanical device. It consist of a electromagnet, moving armature with moving contacts and fixed contacts. When supply is given to coil electromagnet attract the armature and  moving contact of armature touches to fixed contact on relay body. This make no contact changes to closed contact. Simply saying a relay has a coil and set of change over contacts. Coil is rated for some voltage like 12 v dc 24 v dc and coil resistance like 50 ohm 100 ohms etc. For example a coil is 24 volt 100 ohms resistance. Again the contact are also rated for current and voltage for example 250 v dc 10 amp. It means contacts are suitable for 250 v dc voltage up to 10 amp load.
now if we want to control a load of 230 volt 20 amp we need to select relay whose contact rating is more than 250 v 20 amp. For safety reason we should choose slightly higher rating. Now comes to coil voltage we can make circuit of our choice either 12 volt, 24 volt or 5 volt. For  small current we can get relay with 5 v dc coil voltage or 12 v dc coil voltage. But for larger load we may get coil voltage 48 v or 230 ac/dc.in such case we use an intermediate relay to control main / Contactor.

Now we are starting to calculation.

Suppose we have a relay with coil voltage 12 vdc and coil resistance 120 ohms. This is the starting point of calculation and circuit design.
coil current is equal to coil voltage/coil resistznce
coil current = 12/120 = 0.1 amp or 0.1×1000 =100 ma.
here coil volage is 12 volt coil current is 100 ma. so coil power = coil current ×coil voltage = 12×0.1 =1.2 watts.
Now see for the transistor selection:- As coil current is 100 ma there fore transistor collector current must be more than 100 ma and collector voltage must be more than 20 volt. By seeing transistor data we should select a transistor with collector current 150 ma and collector voltage 30 volt. higher value may serve. With transistor selection we will get the transistor current gain alfa.
With that we can calculate base current. base current is equal to collector current/current gain. here we assume current gain is 80 then base current = collector current/current gain= 100/80 =1.25 ma. Now if we want to control this transistor with 5 volt output of a micro controller then we have to give a resistance from micro controller to base of transistor.  The value of this resistance is equal to voltage 5 volt divide by base current 1.25 ma. (5/1.25)×1000 = 4 k ohms. In this way we can set the components. Main thing is to find out collector current, current gain of transistor, base current and base biasing resistance. While selecting transistor we should see for collector current collector voltage and current gain to optimize the design. these  calculation are based on practical experience basis. 

Circuit diagram

Small loads can be put in collector circuit directly.

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also visit links given below

use-of-transistor-as-amplifier.html

Radio-receiver-block-diagram

And-gate-or-gate-and-not-gate

Half-adder-and-full-adder-working

Half Adder and Full Adder Working

Half Adder and Full Adder  Working

Introduction:- Any electrical or electronic system can represent two states very reliably that is either on or off state. for example a light is on is one state and light is off is second state.There is no confusion about state. These can be state in binary number that is 1 or 0. Similarly in digital electronics  5 volt supply is used. If at any point voltage is 5 volt we say state is 1. If voltage is 0 volt we say state is 0.  To represent numbers in binary system we use set of 4 bit known as nibble. if we use 8 bits then it is known as byte.

if we want to use 4 bit we have to keep four place to store these bits. These places are called as registers. These registers are 4, 8 or 16 bit size. To shift value of one register to another register we need four (8 or 16) lines  known as data bus. To process the number we use airthematic logic unit in any digital computer system.

Basic of binary number addition:- For example if we want to add 6 and 7 in decimal system answer is 13. But in binary system number 6 is written as 0110 and number 7 is written as 0101.
we can add just like decimal system as given below

      11  carry
      0110         number 1    6
 ÷   0111         number 2    7
=    1101
=    13

In this binary addition we first add unit digit bit that is 0 and 1 sum = 1. Then second digit bit 1 ÷ 1 =10  there fore second digit ans is 0 and 1 as  carry for third digit. Now for third digit 1 ÷ 1= 10, again  add carry 1 from second digit so 10 ÷ 1 = 11. So ans for third digit is 1 and carry for forth digit is 1. In forth digit 0 ÷ 0= 0 now adding carry 0 ÷ 1= 1. So ans for forth digit is 1. So four digit ans is 1101 equal to 13 in decimal. Now see in digital system how these 0 and 1 are added in the same way shown above. We will consider only one bit addiyion with ExOo gate. The two bits to be added are connected to input of gate and output is taken as sum.

 Truth table of  ExOr gate
      b1      b2    sum
      0    +   0      0
      0    ÷   1      1
      1    ÷   0      1
      1.   ÷   1      0

So with this we get sum of first digit at  out put of ExOr  gate. To find carry bit we use one and gate with ExOr gate when both bits are 1 the output a of  AND gate become 1 which is used as carry bit for next bit addition.

The diagram of half adder is shown below.

Full Adder diagram

Here we can add two bit and carry bit from previous bit addition. The result is also sum bit and a carry bit for next stage.

Four bit adder diagram

                                                                                                                                                                                           

The addition of four bit make is used  for addition of binary numbers.The Full  adder is the basis of all digital computer ALU.

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AND gate OR gate and NOT gate

AND gate OR gate and NOT gate

Introduction:- Gate mean a door like concept through which some thing can pass or not pass. In digital electronics logical decisions can taken with the help of these gates. An example of logic is like, if person a and person b will come then only person c will perform. This is an example of AND logic. As a and b will present then only c will work. Similarly OR logic and NOT logic work. These logic can be simulate with the help of relay contacts or switches in circuit. in relay logic circuit huge circuit with number of contacts in series and parallel are used to develop complex logic to perform automatic operation of vary big machine/plant automation.With the advancement in electronics now transistors are used to develop different gates. These gates serves as the building blocks of  PLC  system and computer system.

AND Gate;- In AND gate there are 2 or 3 input points and one output point. As per number of input, it is said as 2 input AND gate or 3 input AND gate. The input output relation ship is shown with the help of table known as truth table. As the gate name suggest key word AND the output will only high (1) when all the inputs are high (1). If any of input is low (0) the output will low (0). In discrete components AND gate can be made with diode and transistor known as DTL logic. In ICs gates are made using only transistors is known as TTL logic.

OR gate:- In OR gate output is high if any one of input is high. Output will only low when all inputs are low. It mean if any one input is high output will high. This simulates OR relation ship between all inputs. Either input 1 is high or input 2 is high or input 3 is high output will be high. Example is switching on a light from either switch a or switch b.

NOT gate:- In this gate the output is negation of input means if input is low output is high or if input is high output is low.for example there are two pump in not logic then if pump a will run pump b will not run. or pump b run then pump a will not run. These logic can be programmed in PLC controller.

NOR gate:- If a not gate fixed at output of OR gate it becomes NOR gate.

NAND gate if a not gate is fixed at output of and gate it becomes NAND gate.

ExOR gate:- It is special OR gate it only give output high when exclusively one input is high. output will low if both inputs are high. this is very inportant as it serves to add binary number. first building block of digital computer known as half adder.

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Binary number system

Binary number system 

Introduction:- there are four type of number system.
1. Decimal number system
2. Octal number system
3. Hexa decimal number system
4. Binary number system
1. Decimal number system is what we are using in every day life. Counting from 1 to 2, 2 to 3 till 8 to 9 but when we reach at 9 the number becomes two digit that is 10. We say that one's digit reset to 0 and ten's digit increamented by 1. In this reset takes place after ten digit (0-9) the system is said to be decimal system and its base is 10. The number of digit used before reset to zero is known as base of the number system.
2. Octal system:- In this system base is eight. so after counting from 0 to 7 next count becomes 10. In this system number 8 and 9 are not exists. Again after 17 the next count will 100.
3. Hexa decimal system:- In this system base is 16. to count after 9 the A, B, C, D, E, and F are used to represent numbers 10, 11, 12, 13, 14, 15 respectively. Counting is like 1 to 2 ....... 8 to 9 then 9 to A, A to B, B to C, C to D, D to E, E to F, then F to 10. similarly after complete fill up of two digit that is FF next count will 100.
4. Binary number system:- In this system the base is 2 that's the reason this system is known as binary because binary means 2. There are only two digit 0 and 1.We can count only two thing in this system  for third count the number becomes 2 digit number that is 10. The number of count in any system is equal to the  base number to the power number of digit used. For example in binary system if we use for digit like 0000 then total count can be 2 to power 4 is equal to 16. It mean we can count up to 16 in 4 digit binary number. the number of digit in binary system is also known as number of bits. So we can say 0000 is a 4 bit number. 4 bit number can count from 0 to 15 as 0000 to 1111. Binary system has only two value of bit that 0 or 1 it is similar to electrical system which has only two states that is off or on. This is the reason an electrical system can simulate a binary number system. For 4 bits of  binary number we use four different lines. As the value of binary number the lines or kept off or on. For example to represent binary 0011 the line 1 2 will off and line 3 4 will on.

Decimal number     Binary number       Hexa Decimal number     Octal number ststem
0                                0000                     0                                          0
1                                0001                     1                                          1
2                                0010                     2                                          2
3                                0011                     3                                          3
4                                0100                     4                                          4
5                                0101                     5                                          5
6                                0110                     6                                          6
7                                0111                     7                                          7
8                                1000                     8                                         10
9                                1001                     9                                         11
10                              1010                     A                                         12
11                              1011                     B                                         13
12                              1100                     C                                         14
13                              1101                     D                                         15
14                              1110                     E                                          16
15                              1111                      F                                         17
16                    0001 0000                     10                                         20
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