How Does cement fixed resistors Work?

Jun. 24, 2024

Resistors

Units, values and symbols

The symbols for resistors in circuits diagram are shown below. Notice that American symbols are different.

Resistor, European and American
In formulas the letter R is used for the resistor and the unit is &#; (Ohm). To keep large numbers small and handy the units are used in conjunction with the SI prefixes.

1 000 &#; is 1 k&#;
and
1 000 k&#; is 1 M&#;

In circuit diagrams very often the dot is replaced by the R or &#;.

47K    = 47 K&#;
1K5    = 1.5 K&#;
1M0    = 1.0 M&#;
2R2    = 2.2 &#;
0&#;22    = 0.22 &#;

The resistors R9 and R14 have the value of 4k7 or 4.7 K&#;.
All resistor without any wattage information are common ¼ W resistors. Otherwise it is mentioned. Like the two 5W-types R12 and R13.

Exercises

For more cement fixed resistorsinformation, please contact us. We will provide professional answers.

:

To see the answer just the space behind the values.

Transfer in K&#;: 1 M&#;

K&#;

2K2

2.2K&#;

560 &#;

0.56K&#;

3,300 &#;

3.3K&#;

Transfer in &#;: 2.7 K&#;

&#;

56 K&#;

56,000&#;

120 K&#;

120,000&#;

2&#;7

2.7&#;

Preferred values

Resistors are not available in all possible values and gradations but only in selected values. The industry provides a specific range of standard values, known as preferred values. The most common group of preferred values is the E12 series with 12 different numbers and their multiples. The gradations are:

10 12 15 18 22 27 33 39 47 56 68 82

Example

: Available resistor are: 33 k&#;, 150 &#; , 2.2 M&#;, 82 &#;
But the following resistors do not exist: 74 k&#;, 14 M&#;, 460 k&#;, 21 &#;

All resistors of the E12 series are common types with 5%.

Beside the E12 series a E24 with 24 values and even a E48 with 48 values exist. Because the gradation is smaller the series consist of only precise resistors with smaller tolerances. The resistors are metal film resistors with 2% or 1%.

E-12 Series (5%)

1 &#;

1.2 &#;

1.5 &#;

1.8 &#;

2.2 &#;

2.7 &#;

3.3 &#;

3.9 &#;

4.7 &#;

5.6 &#;

6.8 &#;

8.2 &#;

10 &#;

12 &#;

15 &#;

18 &#;

22 &#;

27 &#;

33 &#;

39 &#;

47 &#;

56 &#;

68 &#;

82 &#;

100 &#;

120 &#;

150 &#;

180 &#;

220 &#;

270 &#;

330 &#;

390 &#;

470 &#;

560 &#;

680 &#;

820 &#;

1 k&#;

1.2 k&#;

1.5 k&#;

1.8 k&#;

2.2 k&#;

2.7 k&#;

3.3 k&#;

3.9 k&#;

4.7 k&#;

5.6 k&#;

6.8 k&#;

8.2 k&#;

10 k&#;

12 k&#;

15 k&#;

18 k&#;

22 k&#;

27 k&#;

33 k&#;

39 k&#;

47 k&#;

56 k&#;

68 k&#;

82 k&#;

100 k&#;

120 k&#;

150 k&#;

180 k&#;

220 k&#;

270 k&#;

330 k&#;

390 k&#;

470 k&#;

560 k&#;

680 k&#;

820 k&#;

1 M&#;

1.2 M&#;

1.5 M&#;

1.8 M&#;

2.2 M&#;

2.7 M&#;

3.3 M&#;

3.9 M&#;

4.7 M&#;

5.6 M&#;

6.8 M&#;

8.2 M&#;

Exercises

:

The result of resistance calculations are the following. Which resistors can be used?
To see the answer just the space behind the values.

235 &#;

220&#;

1.4 k&#;

1.5k&#;

620 &#;

680_or_560k&#;

13 k&#;

12k&#;

1.35 M&#;

1.2_or_1.5M&#;

995 &#;

1k&#;

13.5 k&#;

12k&#;_or_15k&#;

Resistor Combinations

There are two different ways to connect resistors: Serial and parallel connection. In addition to that a combination of this two principles is possible, the serial-parallel connection.

Resistor in Series

Two or more resistors can put together like a chain. The values of the single resistors simply have to be added to get the value of the whole combination.

In

series connection

the total resistance is always

higher

than the

highest

value of a single resistor.

Example

: The total value of this resistor combination is: 10 &#; + 22 &#; + 33 &#; = 65 &#;

Respect the prefixes &#;, k&#;, M&#;. Do not mix them.

Resistors in Parallel

The calculation of a resistor combination in parallel is slightly more difficult.
But in general one can say:

In

parallel connection

the total resistance is always

lower

than the

lowest

value of a single resistor.

Example

:    The total value of this resistor combination is:

If only two resistors are put in parallel a more simple formula can be used (Fig.11).
Then, the total resistance is the product of the two resistors, divided by the sum of the two resistors.

Example

:

Much easier is the calculation when resistors with the same resistance are taken.
For two resistors the result is half the of resistor value.

For three resistors the result is one third of resistor value.

For four resistors the result is one fourth of the value. And so on...

Example: 2 resistors of 10 k&#;
3 resistors of 330 k&#;
4 resistors of 100 &#; R = 5 k&#;
R = 110 k&#;
R = 25 &#;

Colour code

The resistance and the tolerance of the resistor are printed on the body of the resistor with a colour code. The power rating is determined by the physical size of the resistor.
Common carbon resistors have four colour bands (three for the value, one for the tolerance) and metal film resistors have five colour bands.
In the common four band system the first two bands represents the number of the value and the third band the multiplier or easier number of zeros. The last band shows the tolerance (mostly gold) and also indicates the direction of reading (always right).

For reading the colour code the band of the tolerance lays always right (here gold).

Colour

1st colour band

2nd colour band

3rd colour band

black

brown

red

orange

000

yellow

0 000

green

00 000

blue

000 000

violet

0 000 000

grey

00 000 000

white

000 000 000

The resistor above (brown-black-red) has the following value:

brown   = 1
black   = 0
red    = 2 x 0 = 00

=

&#;

1 k&#;

The 4th colour band indicates the tolerance of the resistor value or the precision of the resistor value. The smaller the value the more precise the value. The following tolerances exist:

silver    = 10%    (no more common, in old equipment)
gold    = 5%    (most common)
red    = 2%    (for measurement purposes)
brown  = 1%    (for precise measurement purposes)

Example

: A 100 K&#; with a golden band has a tolerance of +/- 5%. The value will be
between 95 K&#; (100 K&#; &#; 5 K&#;) and 105 K&#; (100 k&#; + 5 K&#;)

With this system all resistor values can be outlined, as long as they are not under 10 &#;. Brown&#;black&#;black is the smallest value which can be expressed with the system.
If a resistance of less than 10 &#; has to be outlined, then the 3rd band is gold. The golden band in this case stands for a dot between the 1st and 2nd band.
The colour code of red&#;red&#;gold stands for 2.2 &#;.

But those resistors are uncommon and in practice resistors with small resistance values are bigger wire-wound resistors where the value is printed in numbers on the body.

Problems reading the colours

Very often the colour is not easy to define. Green could be blue and orange maybe red. A short look at the E-12 preferred value list helps.

Example

: Is the first band green the second must be blue
Is the first band red the second can only be red or violett

Exercise

:
Which value have the following resistors?
To see the answer just the space behind the resistors.

560 &#;

330 &#;

2.2 K&#;

470 &#;

100 K&#;

270 &#;

10 K&#;

100 &#;

4.7 K&#;

1 &#;

Wattage

The wattage of a resistor is identify by its size.
Smaller resistance values are needed where higher current flows. The wattage which is produced by the resistor gets higher and the produced heat has to be delivered to the surrounded air. The resistors gets bigger.
The high power resistors are wire-wound resistors with a body of cement or ceramic. Wattages of 5 W, 7 W, 11 W and 17 W are common.

The common resistor has a power rating of ¼ W.

5 W wire resistor

7 W wire resistor, both with cement body.

More seldom and expensive 50 W resistor in metal housing

The resistor R 77 is a bigger 2 W-type.
The wattage of the other resistors is not mentioned. In this case they are common carbon resistors with ¼ W.

Metal film resistors

In measurement or reference circuits (e.g. digital multimeter, ECG and other measurement equipment) high quality resistors with low tolerance are needed. Metal film resistors with 2% (red) or 1% (brown) from the E24 or E48 series are used.
Because the values get more precise and the numbers get bigger an additional colour band is needed. With a 5th colour band a value of 432 k&#; (E48) can be expressed.

Metal film resistor with 2% or 1% have five colour bands.
The last colour band indicates the tolerance: red = 2 %, brown = 1 %
The gradation of the E24 series are the following:

10 11 12 13 15 16 18 20 22 24 27 30 33 36 39 43 47 51 56 62 68 75 82 91

The metal resistor above has the following value:

yellow    = 4
violet    = 7
black    = 0
orange   = 3 x 0 = 000
= 470 000 &#;
=

470 k&#;

The 5th colour band is brown. The resistor has a tolerance of 1 %.

E-24 Series (2%)

1 &#;

1.1 &#;

1.2 &#;

1.3 &#;

1.5 &#;

1.6 &#;

1.8 &#;

2.0 &#;

2.2 &#;

2.4 &#;

2.7 &#;

3.0 &#;

3.3 &#;

3.6 &#;

3.9 &#;

4.3 &#;

4.7 &#;

5.1 &#;

5.6 &#;

6.2 &#;

6.8 &#;

7.5 &#;

8.2 &#;

9.1 &#;

10 &#;

11 &#;

12 &#;

13 &#;

15 &#;

16 &#;

18 &#;

20 &#;

22 &#;

24 &#;

27 &#;

30 &#;

33 &#;

36 &#;

39 &#;

43 &#;

47 &#;

51 &#;

56 &#;

62 &#;

68 &#;

75 &#;

82 &#;

91 &#;

100 &#;

110 &#;

120 &#;

130 &#;

150 &#;

160 &#;

180 &#;

200 &#;

220 &#;

240 &#;

270 &#;

300 &#;

330 &#;

360 &#;

390 &#;

430 &#;

470 &#;

510 &#;

560 &#;

620 &#;

680 &#;

750 &#;

820 &#;

910 &#;

1 k&#;

1.1 k&#;

1.2 k&#;

1.3 k&#;

1.5 k&#;

1.6 k&#;

1.8 k&#;

2.0 k&#;

2.2 k&#;

2.4 k&#;

2.7 k&#;

3.0 k&#;

3.3 k&#;

3.6 k&#;

3.9 k&#;

4.3 k&#;

4.7 k&#;

5.1 k&#;

5.6 k&#;

6.2 k&#;

6.8 k&#;

7.5 k&#;

8.2 k&#;

9.1 k &#;

10 k&#;

11 k&#;

12 k&#;

13 k&#;

15 k&#;

16 k&#;

18 k&#;

20 k&#;

22 k&#;

24 k&#;

27 k&#;

30 k&#;

33 k&#;

36 k&#;

39 k&#;

43 k&#;

47 k&#;

51 k&#;

56 k&#;

62 k&#;

68 k&#;

75 k&#;

82 k&#;

91 k &#;

100 k&#;

110 k&#;

120 k&#;

130 k&#;

150 k&#;

160 k&#;

180 k&#;

200 k&#;

220 k&#;

240 k&#;

270 k&#;

300 k&#;

330 k&#;

360 k&#;

390 k&#;

430 k&#;

470 k&#;

510 k&#;

560 k&#;

620 k&#;

680 k&#;

750 k&#;

820 k&#;

910 k &#;

1 M&#;

1.1 M&#;

1.2 M&#;

1.3 M&#;

1.5 M&#;

1.6 M&#;

1.8 M&#;

2.0 M&#;

2.2 M&#;

2.4 M&#;

2.7 M&#;

3.0 M&#;

3.3 M&#;

3.6 M&#;

3.9 M&#;

4.3 M&#;

4.7 M&#;

5.1 M&#;

5.6 M&#;

6.2 M&#;

6.8 M&#;

7.5 M&#;

8.2 M&#;

9.1 M &#;

Other fixed resistors

Fixed resistors sometimes appear in other versions. Modern electronic boards are often equipped with SMD devices. SMD stands for Surface Mounted Devices. SMD are very small and have not connection wires. They are mounted directly on the board.

SMD resistors and capacitors (below) in comparison with common resistors (above).
SMD resistors are not marked with a colour code. But the numbers which are printed on the body follows the same rules as the colour code. The first two are numbers and the third numbers indicates the number of zeros.

Example

:    564 = 5 6 = 560 k&#;
        222 = 2 2 00 = 2.2 k&#;
        105 = 1 0 = 1 M&#;

When a lot of resistors of the same value are needed electronic manufactures sometime use resistor network. Several resistors of the same value are conflated in one package.

Two resistor networks in an electronic board of a UPS device.
Sometimes resistors with only one black band can be found. These resistors do not have a resistance. Their value is 0 &#;. They are used when robots assemble the boards because robots can not handle wire bridges.

The lower resistor really is a 0 &#; resistor!

Variable resistors

Beside the fixed resistor there are also variable resistors.
All variable resistors have three pins. Two ends with the resistor in between and one wiper. The wiper can take a resistor value between zero and the maximum according to the position.

Variable resistors which are set with a little screwdriver are called trimmer. They are mounted on the electronic board and made for the technician to calibrate the circuit. Where fine calibration is needed multi-turn trimmers are used. From one end to the other the adjustment screw then has to be turned 10 turns or more.

Resistors which can be set from outside by the user are called potentiometer or just pots.
For audio purpose (e.g. volume control) a stereo potentiometer is used.

Potentiometer (pot) in stereo version for audio purpose and trimmer.
The last trimmer is a 10-turn trimmer for fine calibration.
The symbols for variable resistors in circuits diagram are shown below. American symbols again are different.

Trimmer
European new and old, American

Potentiometer
European new and old, American Potentiometers are available in two different versions: Linear or logarithmic (lin or log)
The final value is the same but the change of resistance compare to the position of the control shaft is different. In general all pots which set voltages and DC applications are linear and pots for audio use, especially for volume control, are logarithmic ones.

The change of the resistor compare to the rotation angel. The blue line shows a lin pot, the yellow line a log pot.

Applications

Trimmer or pots have 3 connecting pins (1) and can be connected in different ways for different purposes.
The most common method is shown in (2). The resistor is variable and has 2 pins.
For audio applications the variable resistor is always connected as a voltage divider (3). Input and output are related to ground and the input resistor is always stable.
For stereo usage 2 pots have to be used. Both are working against ground (4)

Function check

Resistors can checked directly with an ohmmeter or multimeter. Therefore the equipment has to be switched off and one connector of the resistor has to be disconnected from the board. Otherwise other devices on the board can distort the measurement result.

When R5 would be measured while connected with the board, the resistances of R2, R5, T1, T2 will deliver a wrong result. Also checking a removed resistor by holding the probes with the fingers will lead to a wrong result. The body resistance distort the measurement.

It is allowed to touch one terminal of the resistor during the measurement, but the second must not be touched. With some experience it is sometimes easier and faster to check the function of a resistor by switching on the equipment and measuring the voltage over the resistor. A voltage drop indicates that the resistor works.

In general a measurement is really not necessary. Because a defective resistor is usually burned the defect is visible. Bigger power resistors always get warm during operation. Just touch the resistor. If heat is produced the resistor is OK.

Common problems

When resistors get broken they always become high-resistance or interrupted. Compare to capacitors the resistance never get smaller. Interrupted in practice means burned and burned resistors are easy to spot. It is always a good idea to do a thoroughly optical inspection of the board first.

Keep in mind that a burned resistor always has a reason. The reason is an unusual high current which can not produced by the resistor itself. Check the following device (specially transistors) for shorts. After replacing and switching on the equipment be prepared to switch off immediately when the resistor gets hot again. Sometimes it is a good idea to disconnect the following stage or device first to surround the fault.

Bigger power resistors get hot and can produce cold solder joints. Very often the solder joints of power resistors are the source for faults. It is good practice to resolder all poor solder joints.

Defective resistors are easy to spot. This resistor is burned. It of course has to be replaced but the resistor is NOT the cause of the problem. A burned resistors always means: There is a problem somewhere else. For changing a resistor not only the value is important but also the wattage and the tolerance. That means also the size and the last colour band must be respected.

Sometimes for a repair the needed value is not available. Then two or more resistors can put together according to Ohm's law. And because also the wattage increases it is also possible to put several small resistors together to get a resistor with a higher wattage.

Pots very often are 'jumping' or in audio amplifiers 'cracking' and 'scratching' when turning. Just dirt inside the pot housing is the cause. Contact spray helps or just some fast turns from one end to the other.

Broken SMD resistors or network resistor can replaced by common carbon resistors.

Prices

Resistors are cheap and a selection of standard values of the E-12 series belongs in every workshop. Here are the average prices for resistors in Europe:

Standard carbon resistor ¼ W 0.05 &#; SMD resistor 0.05 &#; Carbon resistor 2 W 0.30 &#; Metal film resistor 1 % 0.10 &#; Wire resistor 5W 0.40 &#; Wire resistor 17W 0.80 &#; Trimmer 0.20 &#; Multi turn trimmer 0.50 &#; Pot 0.70 &#; Pot stereo 1.40 &#;

Sources and additional information

Resistor:
Resistor, practical:
Potentiometer:
Potentiometers:
Colour code calculator:

A resistor is an electronic device which has a specified amount of electrical resistance. The resistor has two terminals and works in both directions. It has no polarization.The primary characteristic of a resistor is its resistance (&#;) and the power rating (W).Resistors are usually made out of carbon. Resistors for higher wattages are made out of resistance wire and a body of cement. High precision resistors are metal film resistors.The symbols for resistors in circuits diagram are shown below. Notice that American symbols are different.In formulas the letter R is used for the resistor and the unit is &#; (Ohm). To keep large numbers small and handy the units are used in conjunction with the SI prefixes.1 000 &#; is 1 k&#;and1 000 k&#; is 1 M&#;In circuit diagrams very often the dot is replaced by the R or &#;.47K = 47 K&#;1K5 = 1.5 K&#;1M0 = 1.0 M&#;2R2 = 2.2 &#;0&#;22 = 0.22 &#;To see the answer justthe space behind the values.Transfer in K&#;: 1 M&#;2K &#;3,300 &#;Transfer in &#;: 2.7 K&#;56 K&#;120 K&#;2&#;7Resistors are not available in all possible values and gradations but only in selected values. The industry provides a specific range of standard values, known as preferred values. The most common group of preferred values is the E12 series with 12 different numbers and their multiples. The gradations are:10 12 15 18 22 27 33 39 47 56 68 82: Available resistor are: 33 k&#;, 150 &#; , 2.2 M&#;, 82 &#;But the following resistors do not exist: 74 k&#;, 14 M&#;, 460 k&#;, 21 &#;All resistors of the E12 series are common types with 5%.Beside the E12 series a E24 with 24 values and even a E48 with 48 values exist. Because the gradation is smaller the series consist of only precise resistors with smaller tolerances. The resistors are metal film resistors with 2% or 1%.The result of resistance calculations are the following. Which resistors can be used?To see the answer justthe space behind the values.235 &#;1.4 k&#;620 &#;13 k&#;1.35 M&#;995 &#;13.5 k&#;There are two different ways to connect resistors: Serial and parallel connection. In addition to that a combination of this two principles is possible, the serial-parallel connection.Two or more resistors can put together like a chain. The values of the single resistors simply have to be added to get the value of the whole combination.Inthe total resistance is alwaysthan thevalue of a single resistor.: The total value of this resistor combination is: 10 &#; + 22 &#; + 33 &#; = 65 &#;The calculation of a resistor combination in parallel is slightly more difficult.But in general one can say:Inthe total resistance is alwaysthan thevalue of a single resistor.: The total value of this resistor combination is:If only two resistors are put in parallel a more simple formula can be used (Fig.11).Then, the total resistance is the product of the two resistors, divided by the sum of the two resistors.Much easier is the calculation when resistors with the same resistance are taken.And so on...The resistance and the tolerance of the resistor are printed on the body of the resistor with a colour code. The power rating is determined by the physical size of the resistor.Common carbon resistors have four colour bands (three for the value, one for the tolerance) and metal film resistors have five colour bands.In the common four band system the first two bands represents the number of the value and the third band the multiplier or easier number of zeros. The last band shows the tolerance (mostly gold) and also indicates the direction of reading (always right).The resistor above (brown-black-red) has the following value:brown = 1black = 0red = 2 x 0 = 00orThe 4th colour band indicates the tolerance of the resistor value or the precision of the resistor value. The smaller the value the more precise the value. The following tolerances exist:silver = 10% (no more common, in old equipment)gold = 5% (most common)red = 2% (for measurement purposes)brown = 1% (for precise measurement purposes): A 100 K&#; with a golden band has a tolerance of +/- 5%. The value will bebetween 95 K&#; (100 K&#; &#; 5 K&#;) and 105 K&#; (100 k&#; + 5 K&#;)With this system all resistor values can be outlined, as long as they are not under 10 &#;. Brown&#;black&#;black is the smallest value which can be expressed with the system.If a resistance of less than 10 &#; has to be outlined, then the 3rd band is gold. The golden band in this case stands for a dot between the 1st and 2nd band.The colour code of red&#;red&#;gold stands for 2.2 &#;.But those resistors are uncommon and in practice resistors with small resistance values are bigger wire-wound resistors where the value is printed in numbers on the body.Very often the colour is not easy to define. Green could be blue and orange maybe red. A short look at the E-12 preferred value list helps.: Is the first band green the second must be blueIs the first band red the second can only be red or violettWhich value have the following resistors?To see the answer justthe space behind the resistors.The wattage of a resistor is identify by its size.Smaller resistance values are needed where higher current flows. The wattage which is produced by the resistor gets higher and the produced heat has to be delivered to the surrounded air. The resistors gets bigger.The high power resistors are wire-wound resistors with a body of cement or ceramic. Wattages of 5 W, 7 W, 11 W and 17 W are common.The common resistor has a power rating of ¼ W.In measurement or reference circuits (e.g. digital multimeter, ECG and other measurement equipment) high quality resistors with low tolerance are needed. Metal film resistors with 2% (red) or 1% (brown) from the E24 or E48 series are used.Because the values get more precise and the numbers get bigger an additional colour band is needed. With a 5th colour band a value of 432 k&#; (E48) can be expressed.The gradation of the E24 series are the following:10 11 12 13 15 16 18 20 22 24 27 30 33 36 39 43 47 51 56 62 68 75 82 91The metal resistor above has the following value:yellow = 4violet = 7black = 0orange = 3 x 0 = 000= 470 000 &#;The 5th colour band is brown. The resistor has a tolerance of 1 %.Fixed resistors sometimes appear in other versions. Modern electronic boards are often equipped with SMD devices. SMD stands for Surface Mounted Devices. SMD are very small and have not connection wires. They are mounted directly on the board.SMD resistors are not marked with a colour code. But the numbers which are printed on the body follows the same rules as the colour code. The first two are numbers and the third numbers indicates the number of zeros.: 564 = 5 6 = 560 k&#;222 = 2 2 00 = 2.2 k&#;105 = 1 0 = 1 M&#;When a lot of resistors of the same value are needed electronic manufactures sometime use resistor network. Several resistors of the same value are conflated in one package.Sometimes resistors with only one black band can be found. These resistors do not have a resistance. Their value is 0 &#;. They are used when robots assemble the boards because robots can not handle wire bridges.Beside the fixed resistor there are also variable resistors.All variable resistors have three pins. Two ends with the resistor in between and one wiper. The wiper can take a resistor value between zero and the maximum according to the position.Variable resistors which are set with a little screwdriver are called trimmer. They are mounted on the electronic board and made for the technician to calibrate the circuit. Where fine calibration is needed multi-turn trimmers are used. From one end to the other the adjustment screw then has to be turned 10 turns or more.Resistors which can be set from outside by the user are called potentiometer or just pots.For audio purpose (e.g. volume control) a stereo potentiometer is used.The symbols for variable resistors in circuits diagram are shown below. American symbols again are different.Potentiometers are available in two different versions: Linear or logarithmic (lin or log)The final value is the same but the change of resistance compare to the position of the control shaft is different. In general all pots which set voltages and DC applications are linear and pots for audio use, especially for volume control, are logarithmic ones.Trimmer or pots have 3 connecting pins (1) and can be connected in different ways for different purposes.The most common method is shown in (2). The resistor is variable and has 2 pins.For audio applications the variable resistor is always connected as a voltage divider (3). Input and output are related to ground and the input resistor is always stable.For stereo usage 2 pots have to be used. Both are working against ground (4)Resistors can checked directly with an ohmmeter or multimeter. Therefore the equipment has to be switched off and one connector of the resistor has to be disconnected from the board. Otherwise other devices on the board can distort the measurement result.Also checking a removed resistor by holding the probes with the fingers will lead to a wrong result. The body resistance distort the measurement.With some experience it is sometimes easier and faster to check the function of a resistor by switching on the equipment and measuring the voltage over the resistor. A voltage drop indicates that the resistor works.In general a measurement is really not necessary. Because a defective resistor is usually burned the defect is visible. Bigger power resistors always get warm during operation. Just touch the resistor. If heat is produced the resistor is OK.When resistors get broken they always become high-resistance or interrupted. Compare to capacitors the resistance never get smaller. Interrupted in practice means burned and burned resistors are easy to spot. It is always a good idea to do a thoroughly optical inspection of the board first.Keep in mind that a burned resistor always has a reason. The reason is an unusual high current which can not produced by the resistor itself. Check the following device (specially transistors) for shorts. After replacing and switching on the equipment be prepared to switch off immediately when the resistor gets hot again. Sometimes it is a good idea to disconnect the following stage or device first to surround the fault.Bigger power resistors get hot and can produce cold solder joints. Very often the solder joints of power resistors are the source for faults. It is good practice to resolder all poor solder joints.For changing a resistor not only the value is important but also the wattage and the tolerance. That means also the size and the last colour band must be respected.Sometimes for a repair the needed value is not available. Then two or more resistors can put together according to Ohm's law. And because also the wattage increases it is also possible to put several small resistors together to get a resistor with a higher wattage.Pots very often are 'jumping' or in audio amplifiers 'cracking' and 'scratching' when turning. Just dirt inside the pot housing is the cause. Contact spray helps or just some fast turns from one end to the other.Broken SMD resistors or network resistor can replaced by common carbon resistors.Resistors are cheap and a selection of standard values of the E-12 series belongs in every workshop. Here are the average prices for resistors in Europe:Resistor: http://en.wikipedia.org/wiki/Resistor Resistor, practical: http://www.kpsec.freeuk.com/components/resist.htm Potentiometer: http://en.wikipedia.org/wiki/Potentiometer
Thermistor: http://en.wikipedia.org/wiki/Thermistor Potentiometers: http://sound.westhost.com/pots.htm Colour code calculator: http://www.ese.upenn.edu/rca/calcjs.html

Fixed Resistor : Construction, Working, Types & Its Applications

Resistors are one of the most crucial components in any electronic circuit. From providing power to preventing short circuits, resistors are an integral part of every power supply and build with the electronics you use on a daily basis. The Fixed Resistor also known as &#;linear&#; or &#;ohmic&#; resistors invented by George Westinghouse and William Stanley, Jr. is a resistor that has a solid, fixed value for all their characteristics, like their resistance and power ranking, at all times.

This article will discuss what these fixed resistors do as well as their function in circuits today to help you understand how they work, their types, and how to properly apply them along with their advantages and limitations.

What is Fixed Resistor?/Definition

A fixed resistor is an electrical resistor with a fixed value. Resistors receive a voltage and restrict the amount of current that flows through it, to create a different voltage and reduce power by turning it into heat.

Fixed resistors are the most common type of resistor in electronic circuits. These are mainly for restricting the flow of current, dividing voltages & signal level adjustment. They are also used as current-sensing components for protection circuits and for making corrections for other circuit parameters.
To learn more about the basic properties and applications of standard resistors, check out our article &#;What is a resistor.&#;

How Does a Fixed Resistor Work?

A fixed resistor is a two-terminal passive component that is used to implement electrical resistance like a circuit element. The flow of current throughout this resistor is directly proportional to the voltage supply across the two terminals of this resistor. So, this relationship can be simply signified by using Ohm&#;s law:

V = I × R

Where &#;V&#; is the voltage across the resistor, &#;I&#; is the current through the resistor and &#;R&#; is the resistance value. For example, if a 100-ohm resistor is connected across a 10-volt potential difference, then a current of 0.1 amperes flows through that resistor.

Fixed Resistor Construction

A fixed resistor has two main parts: the resistive element, which is usually wire wound into a coil, and the outer casing, which may be made of plastic, ceramic, or metal depending on the application. The resistive element is usually coil-shaped in order to increase its surface area without taking up too much space.

The resistance of the fixed resistor depends on its length, diameter, and material properties. The length and diameter can be adjusted during production or after manufacturing by adding more wire or removing it. The material properties can&#;t be changed once the resistor is manufactured, although they can be measured and recorded to improve efficiency when designing new products.

Fixed Resistor Symbol

Resistors with a fixed value are often depicted using one of the following symbols. The most commonly used symbol is the international IEC resistor (Left), but the American resistor symbol (right) is also still in use today.

Fixed Resistor Values

Fixed resistors can have values ranging from 0 to 100 Gigaohms.

Fixed resistors come in many varieties and have different values. The value of a resistor is indicated by its color bands, which are arranged in order from the most to the least significant values. The first two bands indicate the first and second digits, while the third band indicates the number of zeros to add after those two digits. For example, a resistor with red, green, yellow bands would be ohms.

Resistors

Units, values and symbols

Exercises

:

To see the answer just the space behind the values.

Transfer in K&#;: 1 M&#;

K&#;

2K2

2.2K&#;

560 &#;

0.56K&#;

3,300 &#;

3.3K&#;

Transfer in &#;: 2.7 K&#;

&#;

56 K&#;

56,000&#;

120 K&#;

120,000&#;

2&#;7

2.7&#;

Preferred values

Example

E-12 Series (5%)

1 &#;

1.2 &#;

1.5 &#;

1.8 &#;

2.2 &#;

2.7 &#;

3.3 &#;

3.9 &#;

4.7 &#;

5.6 &#;

6.8 &#;

8.2 &#;

10 &#;

12 &#;

15 &#;

18 &#;

22 &#;

27 &#;

33 &#;

39 &#;

47 &#;

56 &#;

68 &#;

82 &#;

100 &#;

120 &#;

150 &#;

180 &#;

220 &#;

270 &#;

330 &#;

390 &#;

470 &#;

560 &#;

680 &#;

820 &#;

1 k&#;

1.2 k&#;

1.5 k&#;

1.8 k&#;

2.2 k&#;

2.7 k&#;

3.3 k&#;

3.9 k&#;

4.7 k&#;

5.6 k&#;

6.8 k&#;

8.2 k&#;

10 k&#;

12 k&#;

15 k&#;

18 k&#;

22 k&#;

27 k&#;

33 k&#;

39 k&#;

47 k&#;

56 k&#;

68 k&#;

82 k&#;

100 k&#;

120 k&#;

150 k&#;

180 k&#;

220 k&#;

270 k&#;

330 k&#;

390 k&#;

470 k&#;

560 k&#;

680 k&#;

820 k&#;

1 M&#;

1.2 M&#;

1.5 M&#;

1.8 M&#;

2.2 M&#;

2.7 M&#;

3.3 M&#;

3.9 M&#;

4.7 M&#;

5.6 M&#;

6.8 M&#;

8.2 M&#;

Exercises

:

The result of resistance calculations are the following. Which resistors can be used?
To see the answer just the space behind the values.

235 &#;

220&#;

1.4 k&#;

1.5k&#;

620 &#;

680_or_560k&#;

13 k&#;

12k&#;

1.35 M&#;

1.2_or_1.5M&#;

995 &#;

1k&#;

13.5 k&#;

12k&#;_or_15k&#;

Resistor Combinations

There are two different ways to connect resistors: Serial and parallel connection. In addition to that a combination of this two principles is possible, the serial-parallel connection.

Resistor in Series

Two or more resistors can put together like a chain. The values of the single resistors simply have to be added to get the value of the whole combination.

In

series connection

the total resistance is always

higher

than the

highest

value of a single resistor.

Example

: The total value of this resistor combination is: 10 &#; + 22 &#; + 33 &#; = 65 &#;

Respect the prefixes &#;, k&#;, M&#;. Do not mix them.

Resistors in Parallel

The calculation of a resistor combination in parallel is slightly more difficult.
But in general one can say:

In

parallel connection

the total resistance is always

lower

than the

lowest

value of a single resistor.

Example

Colour code

Colour

1st colour band

2nd colour band

3rd colour band

black

brown

red

orange

000

yellow

0 000

green

00 000

blue

000 000

violet

0 000 000

grey

00 000 000

white

000 000 000

The resistor above (brown-black-red) has the following value:

brown   = 1
black   = 0
red    = 2 x 0 = 00

=

&#;

1 k&#;

Example

Problems reading the colours

Very often the colour is not easy to define. Green could be blue and orange maybe red. A short look at the E-12 preferred value list helps.

Example

: Is the first band green the second must be blue
Is the first band red the second can only be red or violett

Exercise

:
Which value have the following resistors?
To see the answer just the space behind the resistors.

560 &#;

330 &#;

2.2 K&#;

470 &#;

100 K&#;

270 &#;

10 K&#;

100 &#;

4.7 K&#;

1 &#;

Wattage

Metal film resistors

470 k&#;

The 5th colour band is brown. The resistor has a tolerance of 1 %.

E-24 Series (2%)

1 &#;

1.1 &#;

1.2 &#;

1.3 &#;

1.5 &#;

1.6 &#;

1.8 &#;

2.0 &#;

2.2 &#;

2.4 &#;

2.7 &#;

3.0 &#;

3.3 &#;

3.6 &#;

3.9 &#;

4.3 &#;

4.7 &#;

5.1 &#;

5.6 &#;

6.2 &#;

6.8 &#;

7.5 &#;

8.2 &#;

9.1 &#;

10 &#;

11 &#;

12 &#;

13 &#;

15 &#;

16 &#;

18 &#;

20 &#;

22 &#;

24 &#;

27 &#;

30 &#;

33 &#;

36 &#;

39 &#;

43 &#;

47 &#;

51 &#;

56 &#;

62 &#;

68 &#;

75 &#;

82 &#;

91 &#;

100 &#;

110 &#;

120 &#;

130 &#;

150 &#;

160 &#;

180 &#;

200 &#;

220 &#;

240 &#;

270 &#;

300 &#;

330 &#;

360 &#;

390 &#;

430 &#;

470 &#;

510 &#;

560 &#;

620 &#;

680 &#;

750 &#;

820 &#;

910 &#;

1 k&#;

1.1 k&#;

1.2 k&#;

1.3 k&#;

1.5 k&#;

1.6 k&#;

1.8 k&#;

2.0 k&#;

2.2 k&#;

2.4 k&#;

2.7 k&#;

3.0 k&#;

3.3 k&#;

3.6 k&#;

3.9 k&#;

4.3 k&#;

4.7 k&#;

5.1 k&#;

5.6 k&#;

6.2 k&#;

6.8 k&#;

7.5 k&#;

8.2 k&#;

9.1 k &#;

10 k&#;

11 k&#;

12 k&#;

13 k&#;

15 k&#;

16 k&#;

18 k&#;

20 k&#;

22 k&#;

24 k&#;

27 k&#;

30 k&#;

33 k&#;

36 k&#;

39 k&#;

43 k&#;

47 k&#;

51 k&#;

56 k&#;

62 k&#;

68 k&#;

75 k&#;

82 k&#;

91 k &#;

100 k&#;

110 k&#;

120 k&#;

130 k&#;

150 k&#;

160 k&#;

180 k&#;

200 k&#;

220 k&#;

240 k&#;

270 k&#;

300 k&#;

330 k&#;

360 k&#;

390 k&#;

430 k&#;

470 k&#;

510 k&#;

560 k&#;

620 k&#;

680 k&#;

750 k&#;

820 k&#;

910 k &#;

1 M&#;

1.1 M&#;

1.2 M&#;

1.3 M&#;

1.5 M&#;

1.6 M&#;

1.8 M&#;

2.0 M&#;

2.2 M&#;

2.4 M&#;

2.7 M&#;

3.0 M&#;

3.3 M&#;

3.6 M&#;

3.9 M&#;

4.3 M&#;

4.7 M&#;

5.1 M&#;

5.6 M&#;

6.2 M&#;

6.8 M&#;

7.5 M&#;

8.2 M&#;

9.1 M &#;

Other fixed resistors

Example

Variable resistors

Applications

Function check

Common problems

Prices

Sources and additional information

Resistor:
Resistor, practical:
Potentiometer:
Potentiometers:
Colour code calculator:

Fixed Resistor : Construction, Working, Types & Its Applications

What is Fixed Resistor?/Definition

How Does a Fixed Resistor Work?

V = I × R

Fixed Resistor Construction

Fixed Resistor Symbol

Fixed Resistor Values

Fixed resistors can have values ranging from 0 to 100 Gigaohms.

Fixed Resistor Colour Code

The fixed resistor color code is used to indicate the value or magnitude of resistance of a resistor. The fixed resistor is a resistor whose value cannot be adjusted after installation. It is possible to determine the value of resistance by identifying the band colors and then looking up the corresponding values in a table.

Fixed resistors have four bands that are marked with different colors, and each band represents an important piece of information: the first two bands represent the resistance value, while the third band denotes its tolerance. The fourth band is sometimes included on metal-film resistors&#;however, they can also just be blank or have a gold stripe. So let&#;s take a closer look at each band and what it means:

The first and second bands both represent numbers in ohms. For example, if the first band is brown and the second band is black, you know that the resistance value is 100Ω.

The third band indicates how much variance there is from this nominal resistance value; for example, if the third band is red, then this means that there can be a percent tolerance of 2%.

The fourth band is either gold or silver; these metals indicate 5% tolerance.

Sometimes a fifth band can indicate failure rate.

Types of Fixed Resistor

There are several different types of fixed resistors. The most common are:

1). Carbon-composition Resistor.

2). Wirewound Resistor.

3). Thin-film resistor

Carbon-film Resistor

Metal Film Resistor

4). Thick film resistor

Metal Oxide Film Resistor.

Cermet oxide resistor.

Fusible resistor.

5). Sand-cast Resistor.

6). Metal glaze resistor.

7). Foil resistor.

8). Precision Wire resistor.

9). Power Wire resistor.

10). Metal Glaze resistor.

Carbon-composition Resistor

They consist of a mixture of graphite and clay that&#;s molded into a cylindrical shape with two lead wires attached to each end. They come in a variety of resistance values, tolerances, and power ratings.

Carbon-composition resistors work well when they&#;re used at low frequencies and low power levels, but they aren&#;t ideal for high frequencies or high power levels because they tend to absorb moisture from the air. They also tend to be noisier than other types of resistors (i.e., produce more voltage noise).

Wirewound Resistor

A wire-wound resistor consists of a rectangular length of a ceramic-coated glass rod with a wound metal wire running through its center. The wire is connected at both ends to copper terminals that extend from the top and bottom of the ceramic case.

The two primary types of wire wound fixed resistors are precision wire wound resistors and power wire wound resistors.

Thin Film Resistor

The thin-film resistor is generally made with a resistive material and also a high grid ceramic rod. These resistors have a thin resistive layer that is located on top of a ceramic base.

The main difference between thin and thick film resistors is the width of the resistive layer. These resistors have around 0.1 microns thickness. These resistors are available in two types carbon film and metal film.

Carbon-film Resistor

A carbon-film resistor is one type of fixed resistor that uses a carbon film as its resistive element. This is made by coating the surface of a ceramic core with carbon powder and then baking it at a high temperature. The resistive value is controlled by varying the length and thickness of the film, and also by laser trimming it during post-production.

Carbon-film resistors are inexpensive and widely available. They are typically used for applications that require a resistance between 100 ohms and 1 megaohm (1,000,000 ohms).

Metal Film Resistor

Metal film resistors are made using a process similar to that used for carbon film resistors, but instead of applying the resistor element as a carbon film, it is applied as a metal film. Metal film resistors are used in applications where stability is important, such as in audio equipment.

They also have a low level of noise and temperature coefficients. Because they&#;re made from metals instead of carbon, they tend to be more durable than carbon film resistors. Metal film resistors are the most common type of resistor on the market.

Thick Film Resistor

The design of Thick film resistors is similar to thin-film except for the resistive material layer like thick film. These resistors are available in three types metal oxide, fusible and cermet film resistor.

Metal Oxide Film Resistor

This is a type of fixed resistor that uses a resistive element like thin metal oxide film. It is similar in construction to the carbon film resistor, but the metal oxide material provides higher temperature stability and lowers noise characteristics. They&#;re more stable than carbon and metal film resistors and provide excellent temperature performance.

Metal oxide resistors are often used in low-power applications, such as audio electronics and small power supplies, where their performance qualities make them preferable to cheaper carbon film resistors.

Cermet Oxide Resistor

These resistors are also known as network resistors. In these types of resistors, the inside region mainly includes ceramic insulation materials, and a metal alloy or carbon film layer is wrapped around the cermet resistor. These resistors are designed in a rectangular or square shape & the terminals are used for connecting in PCBs (printed circuit boards) easily. These resistors offer a stable operation within maximum temperature as their resistance values do not vary when the temperature changes.

Fusible Resistor

This is a special kind of resistor that is used to protect any circuit. The material used to make this resistor has fusing characteristics without surplus heat generation or flames once the current load moves suddenly more than necessary. These resistors are used in highly sensitive circuits where the surge handling, as well as overload requirement, is not very severe. Please refer to this link to know more about the fusible resistor.

Precision Wire Wound Resistor

Precision wire wound resistors feature a low resistance value ranging from less than 1 ohm to approximately 100 Kilo ohms with a low tolerance rating, typically no greater than 1%. The power rating for this type of fixed resistor is relatively low with typical ratings ranging from less than 1 watt to approximately 20 watts.

Power Wire Wound Resistor

Power wire wound resistors also feature limited resistance values; however, their resistance values range from less than 1 ohm to several megaohms. The power rating for this type of fixed resistor is much higher than those offered by precision wire wound resistors with typical ratings ranging from 10 watts to hundreds of watts or more.

Metal Glaze Resistor

This is one kind of passive component where the mixture of metal particles & glass powder is mainly used to limit the electric current flow to a fixed level. These resistors have less temperature coefficient of resistance or TCR. Here TCR is when the temperature increases then the resistance of the material changes.

Metal glaze resistors are used in IR image converters, nuclear devices, navigational radars, communication devices, voltage dividers, particle accelerators, etc.

Foil Resistor

The most stable and precise components are Foil resistors which are used to limit the current flow to a certain range. As compared to other types of resistors, these resistors generate less low noise. An alternate name of this resistor is a high precision resistor and these resistors have less TCR. The applications of foil resistors mainly include aviation, oil rings, audio components, electronic scales, etc.

Differences between Fixed Resistor and Variable Resistor

The main difference between a fixed resistor and a variable resistor is discussed below.

Fixed Resistor

Variable Resistor

The fixed resistor has a fixed value of resistance. The variable resistor has a varying value of resistance. Fixed resistors have their values printed on them so they cannot be changed Variable resistors can have their values changed as they are not printed on them. These resistors are available in different types like thin film, thick film, surface mount, wire wound, metal film chip & metal oxide resistors. These resistors are available in three types trimmer, potentiometer, and rheostat. This resistor includes two terminals that are used to connect different components in a circuit. Variable resistor includes three terminals where two terminals are fixed and another terminal is movable which is called the wiper. The materials used in this resistor are a manganin wire or nichrome wire for winding the core because they provide high resistance and glass, ceramic, or plastic are used for the core. A variable resistor includes a resistance track that is made with carbon, cermet, or a wire coil. These resistors restrict the current flow in a circuit at a certain level. These resistors are used to regulate the voltage or current values in a circuit. A fixed resistor is used in amplifiers, TV sets & other costly electronic circuits. A variable resistor is used in a dimmer switch for light & the knob for volume control on a radio. The resistance values of these resistors mainly include 10Ω, 100Ω,10kΩ & 100KΩ. The resistance values of the variable resistor range from &#;0&#; to a certain highest value.

Advantages & Disadvantages

The advantages of a fixed resistor are discussed below.

Lower Cost&#;high power and high-performance carbon film resistors are inexpensive.

Low Noise&#;carbon film resistors result in low noise levels compared with other types of resistors.

Small Size&#;carbon film resistors, particularly thick film, and thin-film types have small sizes compared with other types of resistors.

High Stability&#;carbon film resistors are more stable than metal oxide resistors because they are not affected by changes in temperature and humidity levels.

The disadvantages of a fixed resistor are discussed below.

Low Power Rating &#; carbon film resistors have low power ratings. The maximum power rating is usually 1/8 watt or less.

Decreased Accuracy&#;carbon film resistors are not as accurate as metal oxide resistors or wire wound resistors.

Fixed Resistance Value &#; Resistance values can&#;t be adjusted once the resistors have been manufactured.

They are not waterproof and cannot be used underwater.

They can only withstand up to 1 volt per second.

They are prone to noise and interference, especially if there is a lot of electromagnetic radiation around, due to their low resistance.

Applications/Uses

The applications of fixed resistors include the following.

They are used in power supplies to reduce the incoming voltage, they can also be used in circuits to limit the flow of current, and they are used in heaters that need to dissipate heat energy.

Fixed resistors are often used for biasing transistors and diodes, which means that they are used to set the working point (also known as Q-point) of active devices such as diodes and transistors.

The fixed resistor may be placed at various points throughout the circuit, depending on its desired effect on the overall operation of the circuit.

They are commonly used as pull-up resistors in digital circuits because they help prevent floating inputs from changing state due to noise or other interference.

What is the Main Purpose of a Fixed Resistor?

The main purpose of a fixed resistor is to control or limit the flow of electrical current in an electronic circuit. They are usually used with one or more other components such as capacitors, inductors, and transistors to form electronic circuits.

What are the Features of a Fixed Resistor?

Features of fixed resistors include:

High stability and reliability.

A wide range of resistance values, from very small to a gigaohm.

Can be used in various environments and conditions, such as temperature, humidity, pressure, vibration, and radiation.

Low noise generation.

Low power consumption

Why are Fixed Resistors Ohmic?

Fixed resistors are ohmic because they have a fixed resistance or a resistance that&#;s not dependent on the amount of current flowing through the component.

This means that the same amount of voltage (V) will always turn into the same amount of current (I) when passing through a fixed resistor. The formula for this relationship is V = I x R, where R represents the fixed resistance.

Is Potentiometer a Fixed Resistor?

A fixed resistor is a type of resistor that has a fixed value. A potentiometer is also a type of resistor, but it&#;s not a fixed resistor. Instead, it has a variable value: the value changes according to whether you&#;re at the top or bottom of its range.

Both types of resistors help regulate the flow of electricity in a circuit, which can help protect the circuit from damage.

Thus, this is an overview of a fixed resistor which includes its types, differences, advantages, disadvantages, and applications. The two main characteristics of the fixed resistor are; nominal resistance value & maximum dissipation. The nominal resistance value is color-coded otherwise printed on the resistor body. Usually, the maximum dissipation is not marked on the resistor body, but the resistor&#;s specification will have its maximum dissipation by using these values like 0.125 W, 0.25 W, 0.5 W, etc. Here is a question for you, what is the tolerance value of a fixed resistor?

Non-linear resistors

R 5.1 NTC THERMISTORS

In this section we shall describe some non-linear resistor styles, meaning that they don&#;t follow Ohm&#;s law. Simplified, the resistor material consists of doped granule compounds containing various oxides that by means of binders have been pressed to a desired shape and then sintered. The terminals either are inserted into the resistor body or soldered to metallized surfaces. There are a number of encapsulation types.

R 5.1.1 Designs

NTC thermistors exist as rods, discs, beads covered with lacquer, epoxy, glaze or melted glass and as SMDs.

Figure R5-1. Thermistor design examples.

SMD thermistors in low ohmic designs are made with a number of internal electrodes as shown in Figure R5-2. The reduced resistance is achieved by a construction that connect &#;resistor elements&#; in parallel inside the thermistor body.

Figure R5-2. Construction of a low ohmic chip thermistor.

R 5.1.2. Temperature dependence and tolerances

NTC stands for negative TCR (Negative Temperature Coefficient). The temperature dependence is strong and exponential and follows the formula

The material constant A determines the resistance and B its temperature dependence, i.e. the slope of the resistance &#; temperature curve. T means the temperature in Kelvin (°C + 273). If we apply the formula [R5-1] on a reference temperature T0 and a general temperature T and combine the two expressions we obtain the formula

The constant B generally is determined by measurements at 25 and 50 °C. It usually has values between and . The value varies a little with temperature. Hence the &#; symbol in the formulas. The thermistor material shrinks strongly during the sintering process which causes great difficulties keeping the tolerances on both the R25 and the B value within specified limits. The B value is stated with tolerances that usually are 5 %. The reference value R0 relates to 20 or 25 °C and has tolerances of 5, 10 or 20 %. However, by sawing already sintered chips to close dimensions one increases the accuracy considerably. R25 tolerances of 0.2&#;&#;&#;1 % no longer are exclusive, nor are tolerance of 1 % on the B value. The result of these superimposed tolerances looks like the illustrations in Figures R5-3&#;R5-5.

Figure R5-3. Thermistor tolerances at the reference temperature T25.

Figure R5-4. B tolerance effect.

Figure R5-5. The combined effect of the R25 and B tolerances.

For more accurate applications two or more points on the Resistance/Temperature curve &#; abbreviated R/T curve &#; are specified, a so called curve-tracking application. The B tolerances then are of less importance. The tolerances of such a two or three point sensor may be stated either as a resistance deviation &#;R in percent of R or as a temperature deviation &#;T in °C, at the temperatures in question (Figure R5-6). In the latter case we have to calculate &#;R by means of the temperature coefficient α in the Formula R5-3.

Figure R5-6. Example of alternative tolerance specification by means of a so called butterfly curve.

Slope and Temperature coefficient
The slope of the R/T curve for an NTC thermistor is determined by the B value. Sometimes the temperature coefficient a is also specified. If we derive the expression in Equation R5-1 we obtain:

Compared to the Formula R1-4, where TCR = 1/R x &#;R/&#;T, we find the same basic expression as for α. As follows from Equation R5-3 α varies strongly with temperature. Around 25 °C α usually has values between &#;3 and &#;5.5%/°C. Yet another way of specifying the slope of the R/T curve is by using resistance ratios. For example the ratios of R0/R50 or R25/R125 are compared. The ratios are stated with tolerances.

R 5.1.3 Self-heating effects

The self-heating of the NTC thermistor influences the resistance. If we apply a voltage over the thermistor the current at the beginning rises linearly according to Ohm&#;s law. But as soon as the internal power generates palpable heat the resistance starts decreasing. Further voltage rises gradually force resistance reductions that occur faster than the current increases. The V/I curve starts declining (Figures R5-7 and R5-8).

Figure R5-7. The self-heating effect on the V/I curve of an NTC thermistor

Figure R5-8. NTC thermistor example of the V/I diagram in log-log scale together with power and resistance grading.

The example in Figure R5-8 helps us realize how the parameters V, I, P and R belong together.

R 5.1.4

&#; Thermal cooling time constant, t

&#; Heat capacity, H

&#; Dissipation factor, D

Another two parameters are associated with Figure R5-8, namely, time and temperature. Size, shape and surrounding medium influence the velocity with which the temperature is changed. A measure of the change velocity is the thermal time constant, t. It is specified for an in-still-air freely mounted thermistor body under zero power conditions and is defined as the time required for the temperature to change by 63.2% &#; exactly (1-1/e) &#; of the difference &#;T between the initial and final body temperature, T0 respectively T&#; (Figure R5-9).

Figure R5-9. Time constant t of an NTC thermistor

With designations from Figure R7-9 the thermistor temperature can be written:

t also can be deduced from two material constants, the heat capacity H (J/°C) and the dissipation factor D (mW/°C).

The heat capacity describes how many Joules (Ws) that have to be conveyed to the thermistor body in order to rise its mean temperature by 1 °C. The dissipation factor D is expressed in mW/°C (or mW/K) and is specified as the power that raises the mean temperature of a thermistor body by 1 °C (or 1 K) when freely mounted in still air. The power dissipation capability, of course, can be increased by means of fans, heat sinks or another cooling medium, for example a suitable liquid. In that case one obtains a practical time constant. If the thermistor is placed in a suitable liquid the time constant is decreased drastically. Among other things this is utilized at production control. The thermistor is immersed into a precise temperature controlled bath and thus in a very short time is conveyed to the stable measurement temperature.

R 5.1.5 Application / Choice of type

We can distinguish three main groups of applications:

1. The temperature dependence of resistance R = f(T) is utilized. The temperature then may be determined

&#; either by the surroundings

&#; or by the internal power of the thermistor.

2. The time dependence R = f(t) is utilized, i.e. we make use of the inherent thermal inertia of the material.

3. The typical NTC characteristics of the material is utilized.

When we choose a thermistor we have to consider the following requirements

&#; Environment and encapsulation requirements. Glass, glaze cover, lacquer/epoxy, no encapsulation.

&#; Temperature range.

&#; Shape and design. Chip/SMD, rod, disc or bead thermistor.

&#; Soldering, spot welding or gluing.

&#; Reference temperature R25 and temperature coefficient α (-B/T2).

&#; Tolerance requirements on R25 and B value. Is it a point-matching or a curve-tracking R/T application?

&#; Power dissipation a) without perceptible heating. b) with maximum change in resistance value.

&#; Thermal time constant τ.

Linearizing the R/T characteristic

If we want a temperature dependence with a particular slope of the R/T characteristic over a broader temperature range, it is usually difficult to find a suitable curve shape. However, by means of fixed resistors combined with the thermistor it is possible to adjust the R/T curve in a desired direction. Figure R5-10 shows some examples of simple circuits to do this.

Figure R5-10. Correction circuits for the R/T characteristic of NTC thermistors.

With alternative c) one may obtain an interesting solution by dimensioning Rp according to Equation R5-6 below. The resulting parallel resistance gives a curve that intersects a straight line in three points, as shown in Figure R5-11.

Figure R5-11. Linearizing the R/T curve of an NTC thermistor.

R 5.1.6 Failure modes

Thermistors often have very small sizes and high resistance values. They are sensitive to every &#;disturbance&#; in the material. An exposed part of the body is the terminal area, especially for small sizes. If the body isn&#;t encapsulated in such a manner that any lead bendings are mechanically unloaded before entrance to the thermistor body, it is easy to create small cracks around the lead entrance. With those cracks, the resistance is changed; there also is left a way for moisture and liquids to penetrate the body.

Glaze covered beads and uncoated discs with terminals soldered direct on top of metallized pads are examples of vulnerable designs. Uncoated disc thermistors are not recommended for use in conductive liquids and aggressive gases. The sintered material sometimes undergoes settlings in the crystalline structure. Such events manifest themselves as sudden resistance changes in the magnitude of 3 to 10 % and may be released by heat, temperature changes and mechanical shocks. The failure rate for non-treated delivery lots varies between 30 to 60 %. The cure is a burn-in process that usually is performed as a heat treatment.

Bead thermistors encapsulated in a melted glass body often have small sizes and corresponding thin leads, consisting of alloys that often are difficult to solder. In such events leads intended for spot welding may be the only solution. Caution. Never try to connect NTC thermistors in parallel in order to increase the power dissipation capability. The thermistor that for the moment has the lowest resistance will get a higher current load, a stronger self-heating, a greater resistance decrease, an even higher current load etc., until the avalanche effect will destroy the component.

R 5.1.7 Reliability

The reliability of NTC thermistors today is regarded as good. It depends not least on serious manufacturers with Statistical Process Control (SPC) based programs for manufacture and verified type qualifications. If we determine that the components are burn-in treated and if we purchase them with hermetic seals, i.e. glass or glass/metal housings, the reliability of such thermistors should be classified in the same group as fixed metallized film resistors.

SMD thermistors eliminate some of the problems connected with sensitive lead terminals. In the beginning there were some solderability problems but today they may be regarded as overcome. We now have got a component that structurally resembles the ceramic chip capacitor, however, with fewer sources of error. The stratified low resistance variant has its electrodes embedded in the material and may from a reliability aspect be comparable to the homogeneous type.

Nuclear radiation

Tests with radioactive radiation in the form of neutron, β and γ radiation show that thermistors are capable of withstanding high intensities without any effects on the characteristics.

Table R5-1. NTC THERMISTORS

ABC of CLR: Chapter R Resistors

Non-linear resistors

EPCI licenced content by:

[1] EPCI European Passive Components Institute experts original articles
[2] CLR Passive Components Handbook by P-O.Fagerholt*

*used under EPCI copyright from CTI Corporation, USA

This page content is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.

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Resistor & Types of Resistors &#; Fixed, Variable, Linear & Non-Linear

Different Types of Resistors &#; Fixed, Variable, Linear and Non-Linear Resistors & Applications

What is Electrical Resistance?

The property of a substance which opposes the flow of electric current (or electricity) through it is called Resistance OR Resistance is the ability of a circuit which opposes current.

Mica, Glass, Rubber, Wood etc. are the examples of resistive materials. The unit of resistance is OHM (&#;) where 1&#; = 1V/1A. which is derived from the basic electrical Ohm&#;s law = V = IR.

Other definitions of Ohm &#;&#;&#; are as follows;

If there is a potential difference of 1 volt between two ends of the conductor and the flowing current through it is 1 Ampere, then the resistance of that conductor would be 1 Ohm (&#;). OR

If 1 ampere of current is flowing through a resistance, and 1 joule per second (1Watt) energy (in the form of heat) is generated, then the measurement of that resistance is 1 &#;.

Ohm is the measurement quantity of resistance, which produces one joule of energy (in the form of heat) in one second, when one ampere of current is flowing through it.

The reciprocal of the resistance is called conductance.

What is an

Eclectic

Resistor?

A resistor is a component or device designed to have a known value of resistance. OR,

Those components and devices which are specially designed to have a certain amount of resistance and used to oppose or limit the electric current flowing through it are called resistors.

Good to know: Resistance of a resistor depends on their length (l), resistivity (ρ) and its cross sectional area (a) which is also known as laws of resistance &#; R = ρ (l/a).

IEEE & IEC symbols of Resistors

Types of Resistors:

Resistors are available in different size, Shapes and materials. We will discuss all possible resistor typesresistor types one by one in detail with pro and cons and application as follow.

There are two basic types of resistors.

Linear Resistors

Non Linear Resistors

Linear Resistors:

Those resistors, which values change with the applied voltage and temperature, are called linear resistors. In other words, a resistor, which current value is directly proportional to the applied voltage is known as linear resistors.

Generally, there are two types of resistors which have linear properties.

Fixed Resistors

Variable Resistors

Fixed Resistors

As the name tells everything, fixed resistor is a resistor which has a specific value and we can&#;t change the value of fixed resistors.

Types of Fixed resistors.

Carbon Composition Resistors

Wire Wound Resistors

Thin Film Resistors

Thick Film Resistors

Carbon Composition Resistors

A typical fixed resistor is made from the mixture of granulated or powdered carbon or graphite, insulation filler, or a resin binder. The ratio of the insulation material determines the actual resistance of the resistor. The insulating powder (binder) made in the shape of rods and there are two metal caps on the both ends of the rod.

There are two conductor wires on the both ends of the resistor for easy connectivity in the circuit via soldering. A plastic coat covers the rods with different color codes (printed) which denote the resistance value. They are available in 1 ohm to 25 mega ohms and in power rating from ¼ watt to up to 5 Watts.

Characteristic of Fixed Resistors

Generally, they are very cheap and small in size, hence, occupy less space. They are reliable and available in different ohmic and power ratings. Also, fixed resistor can be easily connected to the circuit and withstand for more voltage.

In other hand, they are less stable means their temperature coefficient is very high. Also, they make a slight noise as compared to other types of resistors.

Wire wound Resistors

Wire wound resistor is made from the insulating core or rod by wrapping around a resistive wire. The resistance wire is generally Tungsten, manganin, Nichrome or nickel or nickel chromium alloy and the insulating core is made of porcelain, Bakelite, press bond paper or ceramic clay material.

The manganin wire wound resistors are very costly and used with the sensitive test equipment e.g. Wheatstone bridge, etc. They are available in the range of 2 watts up to 100 watt power rating or more. The ohmic value of these types of resistors is 1 ohm up to 200k ohms or more and can be operated safely up to 350°C.

in addition, the power rating of a high power wire wound resistor is 500 Watts and the available resistance value of these resistors are is 0.1 ohm &#; 100k Ohms.

Advantages and Disadvantage of Wire wound Resistors

Wire wound resistors make lower noise than carbon composition resistors. Their performance is well in overload conditions. They are reliable and flexible and can be used with DC and Audio frequency range. Disadvantage of wire wound resistor is that they are costly and can&#;t be used in high frequency equipment.

Application of Wire Wound Resistors

Wire wound resistors used where high sensitivity, accurate measurement and balanced current control is required, e.g. as a shunt with ampere meter. Moreover, Wire wound resistors are generally used in high power rating devices and equipment, Testing and measuring devices, industries, and control equipment.

Thin Film Resistors

Basically, all thin film resistors are made of from high grid ceramic rod and a resistive material. A very thin conducting material layer overlaid on insulating rod, plate or tube which is made from high quality ceramic material or glass. There are two further types of thin film resistors.

Carbon Film Resistors

Metal Film Resistors

Carbon Film Resistors

Carbon Film resistors contains on an insulating material rod or core made of high grade ceramic material which is called the substrate. A very thin resistive carbon layer or film overlaid around the rod. These kinds of resistors are widely used in electronic circuits because of negligible noise and wide operating range and the stability as compared to solid carbon resistors.

Metal Film Resistors

Metal film resistors are same in construction like Carbon film resistors, but the main difference is that there is metal (or a mixture of the metal oxides, Nickel Chromium or mixture of metals and glass which is called metal glaze which is used as resistive film) instead of carbon. Metal film resistors are very tiny, cheap and reliable in operation. Their temperature coefficient is very low (±2 ppm/°C) and used where stability and low noise level is important.

Thick Film Resistors

The production method of Thick film resistors is same like thin film resistors, but the difference is that there is a thick film instead of a thin film or layer of resistive material around. That&#;s why it is called Thick film resistors. There are two additional types of thick film resistors.

Metal Oxide Resistors

Cermet Film Resistors

Fusible Resistors

Metal Oxide Resistors

By oxidizing a thick film of Tin Chloride on a heated glass rod (substrate) is the simple method to make a Metal oxide Resistor. These resistors are available in a wide range of resistance with high temperature stability. In addition, the level of operating noise is very low and can be used at high voltages.

Cermet Oxide Resistors (Network Resistors)

In the cermet oxide resistors, the internal area contains on ceramic insulation materials. And then a carbon or metal alloy film or layer wrapped around the resistor and then fix it in a ceramic metal (which is known as Cermet). They are made in the square or rectangular shape and leads and pins are under the resistors for easy installation in printed circuit boards. They provide a stable operation in high temperature because their values do not change with change in temperature.

Fusible Resistors

These kinds of resistors are same like a wire wound resistor. When a circuit power rating increased than the specified value, then this resistor is fused, i.e. it breaks or open the circuit. That&#;s why it is called Fusible resistors. Fusible restores perform double jobs means they limit the current as well as it can be used as a fuse.

They used widely in TV Sets, Amplifiers, and other expensive electronic circuits. Generally, the ohmic value of fusible resistors is less than 10 Ohms.

Variable Resistors

As the name indicates, those resistors which values can be changed through a dial, knob, and screw or manually by a proper method. In these types of resistors, there is a sliding arm, which is connected to the shaft and the value of resistance can be changed by rotating the arm. They are used in the radio receiver for volume control and tone control resistance.

Following are the further types of Variable Resistors

Potentiometers

Rheostats

Trimmers

Potentiometers

Potentiometer is a three terminal device which is used for controlling the level of voltage in the circuit. The resistance between two external terminals is constant while the third terminal is connected with moving contact (Wiper) which is variable. The value of resistance can be changed by rotating the wiper which is connected to the control shaft.

This way, Potentiometers can be used as a voltage divider and these resistors are called variable composition resistors. They are available up to 10 Mega Ohms.

Rheostats

Rheostats are a two or three terminal device which is used for the current limiting purpose by hand or manual operation. Rheostats are also known as tapped resistors or variable wire wound resistors.

To make a rheostats, they wire wind the Nichrome resistance around a ceramic core and then assembled in a protective shell. A metal band is wrapped around the resistor element and it can be used as a Potentiometer or Rheostats (See the below note for difference between Rheostat and Potentiometer).

Variable wire wound resistors are available in the range of 1 ohm up to 150 Ohms. The available power rating of these resistors is 3 to 200 Watts. While the most used Rheostats according to power rating is between 5 to 50 Watts.

Good to Know:

What is the main Difference between Potentiometer and Rheostats?

Basically, there is no difference between Potentiometer and Rheostat. Both are variable resistors. The main difference is the use and circuit operation, i.e. for which purpose we use that variable resistor?

For example, if we connect a circuit between resistor element terminals (where one terminal is a general end of the resistor element while the other one is sliding contact or wiper) as a variable resistor for controlling the circuit current, then it is Rheostats.

On the other hand, if we do the same as mentioned above for controlling the level of voltage, then this variable resistor would be called a potentiometer. That&#;s it.

Trimmers

There is an additional screw with Potentiometer or variable resistors for better efficiency and operation and they are known as Trimmers. The value of resistance can be changed by changing the position of screw to rotate by a small screwdriver.

They are made from carbon composition, carbon film, cermet and wire materials and available in the range of 50 Ohms up to 5 mega ohms. The power rating of Trimmers potentiometers are from 1/3 to ¾ Watts.

Non Linear Resistors

We know that, nonlinear resistors are those resistors, where the current flowing through it does not change according to Ohm&#;s Law but, changes with change in temperature or applied voltage.

In addition, if the flowing current through a resistor changes with change in body temperature, then these kinds of resistors are called Thermistors. If the flowing current through a resistor change with the applied voltages, then it is called a Varistors or VDR (Voltage Dependent Resistors).

Following are the additional types of Non Linear Resistors.

Thermistors

Varisters (VDR)

Photo Resistor or Photo Conductive Cell or LDR

Thermistors

Thermistors is a two terminal device which is very sensitive to temperature. In other words, Thermistors is a type of variable resistor which notices the change in temperature. Thermistors are made from the cobalt, Nickel, Strontium and the metal oxides of Manganese. The Resistance of a Thermistor is inversely proportional to the temperature, i.e. resistance increases when temperature decrease and vice versa.

It means, Thermistors has a negative temperature coefficient (NTC) but there is also a PTC (Positive Temperature Coefficient) which a made from pid Barium Titanate semiconductor materials and their resistance increases when increases in temperature.

Varisters (VDR)

Varisters are voltage dependent Resistors (VDR) which is used to eliminate the high voltage transients. In other words, a special type of variable resistors used to protect circuits from destructive voltage spikes is called varisters.
When voltage increases (due to lighting or line faults) across a connected sensitive device or system, then it reduces the level of voltage to a secure level i.e. it changes the level of voltages.

Photo Resistor or Photo Conductive Cell or LDR (Light Dependent Resistors)

Photo Resistor or LDR (Light Dependent Resistors) is a resistor which terminal value of resistance changes with light intensity. In other words, those resistors, which resistance values changes with the falling light on their surface is called Photo Resistor or Photo Conductive Cell or LDR (Light Dependent Resistor). The material which is used to make these kinds of resistors is called photo conductors, e.g. cadmium sulfide, lead sulfide etc.

When light falls on the photoconductive cells (LDR or Photo resistor), then there is an increase in the free carriers (electron hole pairs) due to light energy, which reduce the resistance of semiconductor material (i.e. the quantity of light energy is inversely proportional to the semiconductor material). It means photo resistors have a negative temperature coefficient.

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