The resistors are mainly divided into two types, first Fixed Resistors and second, variable resistors. In Fixed resistors, the electrical resistance of the resistor the remains same while in variable resistor it does change with some physical variable. These widely used resistors are a having fixed resistance value defined at the time of manufacturing.
Their resistance value is either printed over the resistor or color-coded over them. Following are the types of fixed resistors. These resistors were used commonly in past but are rarely used nowadays. Because of the use of a large negative temperature coefficient and some erotic irreversible changes.
They are formed from carbon grains with the help of binding aid, which generates noise during current flow. Carbon film resistors are formed by the deposition of carbon material into an insulating substrate.
Because of the absence of binding aid, as compared to carbon composition these resistors produce less noise. Instead of carbon, the metal oxide resistor uses metal oxide deposition on to a ceramic rod. The thickness of the metal oxide film can adjust the resistance value. In some variations, some metals such as nickel alloys can be used instead of metal oxide as an upper layer.
By winding a metal wire i. 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 Ohms. The available power rating of these resistors is 3 to 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.
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.
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.
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 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. 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 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. The material which is used to make these kinds of resistors is called photo conductors, e. 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.
It means photo resistors have a negative temperature coefficient. You can read mor details about special resistors i. SMD Resistor with color coding methods which we have already discussed before. These types of resistors are used in burglar alarm, Door Openers, Flame detectors, Smock detectors, light meters, light activated relay control circuits, industrial, and commercial automatic street light control and photographic devices and equipment.
Practically, both types of resistors Fixed and Variable are generally used for the following purposes. Resistors are used :. Related Posts:. Yes Sure… Just put your email address in the top lift corner email subscription box… and you will get each of post like this in your email. Dear Sirs, Thank you very much for your resistor presentation. I would like to download for this chapter for my own study and to teach my marine students. Could you please send me this basic concept chapters.
I will appreciate for it. There are many different types of resistor. Some are for special applications like being used as variable resistors, and others are used for surge limitation whilst others provide a variable resistance with temperature.
All of these characteristics can be used. However for fixed resistors there are different characteristics that need to be taken into account. Even though the actual resistance of the component is of paramount importance, other characteristics also need to be taken into consideration. Power dissipation, noise, inductance, thermal stability and a number of other characteristics may all have a bearing on the operation of the circuit in which the resistor is used.
Different materials and different structures within the resistor can have a major impact. Accordingly when selecting a resistor to be used, these characteristics must also be taken into consideration. The first major categories into which the different types of resistor can be fitted is into whether they are fixed or variable.
These different resistor types are used for different applications:. Whilst the majority of resistors are standard fixed resistors or variable resistors, there is a number of other resistor types that are used in some more niche or specialised applications.
Although resistors may be thought of as simple electronics components to use, there are a number of parameters that need to be considered when choosing the correct resistor type.
Parameters apart from just the resistance are important. Voltage withstand, power dissipation and the actual type of resistor itself all have an impact on the performance.
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