WEEK 4 : DAY 1 BASIC KNOWLEDGE

4.1 BASIC KNOWLEDGE

        The first question he asked was " What electronics is all about ?" A difficult as well as brainstorming question. His simple answer to this question was " Electronics is all about controlling different physical processes according to our desire. " This really left me dumbstruck for the fact that I never really thought about it. Nevertheless according to him basics is what matters the most so he started out with basic knowledge of electronics

1) RESISTANCE

        Resistance as we all know is hindrance to flow of electrons and a very important component of every electronic devices. Let's start with the basic color coding of resistors.

COLOR	1st ROW	2nd ROW	3rd ROW	TOLERANCE (+/-)
BLACK	0	0	0	-
BROWN	1	1	1	1%
RED	2	2	2	2%
ORANGE	3	3	3	-
YELLOW	4	4	4	-
GREEN	5	5	5	-
BLUE	6	6	6	-
VIOLET	7	7	7	-
GREY	8	8	8	-
WHITE	9	9	9	-
GOLD	-	-	-1	5%
NO COLOR	-	-	-2	20%

        It follows like this (1st row)*10 + (2nd row) X (10^3rd row). Fourth row will be tolerance which is the maximum value from which the resistance of resistor can be sway form its value. Sometimes there are also resistances with 5 or 6 color bands. They basically give higher precision value to low tolerance resistances

TYPES OF RESISTANCES

        There are basically two types of resistance used in railway circuits 

1) Fixed resistances

        As the name suggests these resistances have fixed values.They are of further three types :- 

1) Carbon resistances

        They are made by compressing carbon . These resistances have low power rating but can have high resistance values. They are usually used in circuits having low current values ( in range of ma ). They have colour coding on it to determine their value since they are small in size. They have high tolerance but are comparatively cheaper.

2) Metal film resistances

        They contain basically have coating of film of metal  or its oxide. They have low tolerance of the level of around 0.1%. 

3) Wire wound resistances

        They are wire bounded on china plate. China plate acts as conductors for heat produced in the wire. These resistance have higher power rating (0.25 W to 2 W) but have low resistance values. They also have larger size than above two. They are used in power circuits where the current gets to the range of 10 A. There power as well as resistance value are written on it. But in place of Ω symbol E is used since Ω is difficult to print.

2) Variable Resistance

        These resistances can be varied according to our needs to a certain extents as allowed by it. They are also of two types.

1) Rheostat

        They are basically wire wound resistances having a slider on top to vary the resistance. They are bulky and seldom used in small circuits but have high power rating.

2) Carbon resistances

        They are basically made from carbon only hence have low power rating but high resistance range. They are of two types :-

a) Potentiometer

        It is used in places where you have to change the value of resistance frequently. e.g A knob for radio etc. It has one round handle which is turned to increase or decrease resistance values

b) Preset

          It is used in circuits where the value of resistance is varied rarely that is it is a one time affair as it is difficult to change its resistance. Presets are also of two types :-

1) Open type presets :- They have no covering on the components of the preset so they are prone to getting affected due to environmental factors. 

2) Closed type presets :- They are enclosed within plastic covering so they are less prone to getting affected due to environmental factors.

         Apart from it there is one more type of classification i.e

1) Single turn preset :- These preset simply have a metal conductor touching a carbon resistance whose position can be changed in a single turn. It is less precise.

2) Multi-turn preset :- These preset are connected to the metal conductor by a screw which gives more precise variation of resistance. It can be turned in same direction multiple times and produces a click sound at the end of range of preset.

1) Capacitor

        There are three types of capacitors used in railways:-

1. Electrolytic capacitor :- An electrolytic capacitor is a capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals and storing large amounts of energy.
2. Ceramic capacitor :- A ceramic capacitor is a fixed value capacitor in which ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes
3. Film capacitor :- A Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called “film caps” as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometimes combined with paper as carrier of the electrodes.

2) Batteries

         Types of batteries used in railways:-

  

      1) Primary batteries :- 

• Use and throw
• not chargeable

      2) Secondary batteries :-

• Chargeable
• Multi-use

        Examples are Alkaline, dry cell, Lithium cell batteries.

Lead Acid batteries

        They are the most commonly used secondary batteries due to their higher power output, cheap price and more durability .

Electro-chemistry

Discharge

        Negative plate reaction: 
 Pb(s) + HSO− 4(aq) → PbSO 4(s) + H+ (aq) + 2e− 

        Positive plate reaction: 
 PbO 2(s) + HSO− 4(aq) + 3H+ (aq) + 2e− → PbSO 4(s) + 2H 2O(l) 

The total reaction can be written as 
 Pb(s) + PbO 2(s) + 2H 2SO 4(aq) → 2PbSO 4(s) + 2H 2O(l)

Recharge

        Negative plate reaction:
 PbSO 4(s) + H+ (aq) + 2e− → Pb(s) + HSO− 4(aq) 
       
        Positive plate reaction: 
PbSO 4(s) + 2H 2O(l) → PbO 2(s) + HSO− 4(aq) + 3H+ (aq) + 2e−

Features

• Provides voltage of 2.2 per volt.
• Ph level of electrolyte is maintained at 1.2 pH due to distilles water has to be added to it often.
• Specific gravity has to be maintained at 1.2 kg/L
• for charging 20% more voltage is given above the capacity of battery.

Valve regulated lead acid batteries

• Maintenance free batteries.
• can be used in any orientation.
• They need to be refilled with distilled water.
• It uses gel absorbed on paper as electrolyte

       That ends my lecture here. Have a nice day. Gud luck!!!!!!

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