Dr. IT Solutions Forum: Basics concept of : Resistors

1. The concept of resistance.

What is resistance? I understand a simple way - Resistivity is the resistance of a power line conductor, if a good conductor, the resistor small, poor electrical conductor, the greater the resistance, the insulator resistance is enormous.

Resistance of conductors:
Resistance of conductor sub poked the material, length and cross section of the wire. is calculated by the following formula:

R = ρ.L / S

In which electrical resistivity ρ is dependent on the material

L is the length of the wire

S is the cross section of conductor

R is the Ohm resistor unit

2. Resistors in electronic devices.

a) The shape and symbols: In electronics resistor is an important component, they are made from carbon and metal compounds, depending on the mixing ratio that people create the kind of value resistor different numbers.

The shape of the resistors in electronic devices.

Symbol of resistance on the principle diagram.

b) Units of resistors

The unit is Ω resistor (Ohm), k, MΩ

1KΩ = 1000 Ω

1MΩ = 1000 K Ω Ω = 1000.000

b) The stated value of the resistor

The small size resistor is recorded equal value from the stripe in a general convention of the world. (See picture above)

The resistor has a larger size from 2W or more often recorded values directly on the body. For example, the resistor capacity, ceramic resistors.

Go porcelain large capacity, values are written directly.

3. How to read the resistance value.

International conventions mystery

Colors	Worth	Colors	Worth
Black	0	Green	5
Brown	1	Blue	6
Red	2	Purple	7
Oranges	3	Gray	8
Gold	4	White	9
		Yellow emulsion	-1
		Silver emulsions	-2

Resistors are usually denoted by 4-round color, precision resistors are denoted by 5 round color.

* How to read resistance value 4 ring color:

How to read resistor 4 ring mystery

Round 4 is the last round in always glosses colored gold or silver emulsion, it is within tolerance of the resistor only when one reads the bypass loop.

Facing the last round is round No. 1, next to the ring No. 2, No. 3

Round 1 and Round 2 is tens and units

Round 3 is a multiple of the base 10.

Value = (round 1) (Round 2) x 10 ^{(hat round 3)}

May calculate round numbers 3 is not "0" added

Mystery emulsions only in error loop or loops of 3, if the emulsion is round 3 of the base-10 exponent is negative.

* How to read resistance value 5 colored rings (accurate resistor)

Round 5 is the final round, are within the error record, or 5 rounds, the color color bias are more colors, thereby making it difficult for us to determine what EOF last round, but the last lap is always the distance a little further.

Opposite the final round is round No. 1

Similarly reading of the return value 4 ring mystery but here within the 4 is a multiple of base 10, round No. 1, No. 2 and No. 3 respectively hundreds, tens and units.

Value = (round 1) (Round 2) (3) x 10 ^{(4 caps)}

May calculate round numbers No.4 is not "0" added

4 - Practice reading resistance values.

The various resistor in 3rd round color

When the different resistor in 3rd round color, I see within the mystery multiples often change from color to color emulsions green silver, equivalent resistance <1 Ω to MΩ row.

The resistor color ring number 1 and number 2 changed.

In the image above the resistor values are often encountered in practice, when the mystery within 3 change the resistor values on the rise down 10 times.

Exercise - Make quick guess values before the answer came out, when all the values that you have guessed correctly before results appear as your knowledge in this section were all right there!

Exercise - Quick Guess resistance value results.

5 - The common resistance value.

You can not earn a resistor with any value, the only manufacturer offering 150 kinds of common resistance value, the table below is the color and the resistance value of the common.

The common resistor values.

6 -. Classification resistor.

Ordinary resistor: Resistor usually has a small resistor from 0,125W to 0,5W

Resistor capacity : A resistor with greater capacity from 1W, 2W, 5W, 10W.

Ceramic resistors, thermistors: The other calling capacity of the resistor, this resistor sheathed ceramic heat when operating them.

The resistor: 2W - 1W - 0,5W - 0,25W

Ceramic thermal resistor or return

7 - The capacity of the resistor.
When getting into the circuit resistors, resistor itself an export consumption is calculated according to the formula P

P = U. I = U ² / R = I ² .R

According to the formula above we can see, the output consumed by the resistor depends on the current through a resistor or voltage dependent resistors on both ends.

Output of consumer resistance is completely calculated before mounting resistance in the circuit.

If bringing a resistor with a nominal capacity of smaller capacity it will consume the resistor will burn.

Usually one resistor inserted into the circuit with a nominal capacity of> = 2 times the capacity that it will consume.

Fire resistance due to capacity

In the diagram above shows: Source Vcc is 12V, the resistors are 120Ω values are different but have capacity, while K1 and K2 switches closed, the resistors are consumed capacity is

P = U ² / R = (12 x 12) / 120 = 1,2W

When K1 is closed, due to resistor has a larger capacity consumed, so no fire resistance.

When K2 is closed, the resistor has a smaller output capacity consumed, burned up resistor.

8 - Potentiometer, dimmable:
Potentiometer The resistor can be adjusted to change the value, which we have denoted VR shape as follows:

Shape Symbol variable resistor on the diagram

Potentiometer often assembled in the plant in service during repair, calibration technician, a variable resistor has a structure as shown below.

Composed of variable resistors

Dimmable Philosophy analog voltage variable resistor but also more generally to adjust and arranged in front of the machine for the user to adjust. For example - Philosophy pressure Volume, Bass dimmable, Treec etc. , Dimmable philosophy means a voltage from the input section, depending on the degree of correction.

Dimmable symbol on the principle diagram.

Composed shapes in dimmable dimmable

9 - Resistors in series.

Resistors connected in series.

The resistor in series with the equivalent value of the sum of the resistor elements combined. = R1 + R2 + Rtd R3

Current flows through the resistor in series with equal value and equal I I = (U1 / R1) = (U2 / R2) = (U3 / R3)

From this formula we see that the pressure drop across the resistor in series proportional dient return value.

10 - resistor in parallel.

Parallel resistor

The resistor in parallel with the equivalent value is calculated by a formula Rtd (1 / Rtd) = (1 / R1) + (1 / R2) + (1 / R3)

If the circuit only 2 resistors are parallel
Rtd = R1.R2 / (R1 + R2)

Current flows through the parallel resistor is inversely proportional to the resistance value.
I1 = (U / R1), I2 = (U / R2), I3 = (U / R3)

The voltage across the resistor in parallel are equal

11 - resistor mixed

Mixed resistor.

Warping mixture resistors to create a more optimal resistance.

For example, if we need a resistor 9K we could get two parallel 15K resistor then connected in series with a resistor 1,5K.

12 - Application of the resistor
Resistors are present everywhere in electronics and so resistance is an important component indispensable, in circuits, resistors have the following effects:

To control the current through the load accordingly, for example with a 9V light bulb, but have only 12V, it can be connected in series with a resistor bulb for less 3V voltage drop across resistor.

Lamps connected in series with a resistor.

- As shown above, we can calculate the number and value of export of appropriate resistor as follows: The light bulb and the output voltage of 9V 2W consumption line that is I = P / U = (2/9) = Ampe which is also the current through the resistor.
- Because the source is 12V, 9V bulb should 3V voltage drop across R is the resistance that we infer looking R = U / I = 3 / (2/9) = 27/2 = 13.5 Ω
- Output is consumed resistor: P = UI = 3 (2/9) = 6/9 W so we must use the output resistor P> 6/9 W