In this article, we are going to learn about electrical resistors, types, and their applications, both at an industrial and commercial level. Resistors, also technically called resistors, are devices that offer certain opposition to the passage of current and voltage. They are used to regulate the current and voltage in a certain circuit.
Resistors are the most common electronic component. They are a critical piece in almost every circuit and play a very important role in our favorite equation, Ohm’s Law.
The symbol for resistance is the ohm, which is represented by the Greek letter omega (Ω).
The resistance uses sub-multiples such as:
- kilo-ohmio(1K Ω)=1000Ω.
- Mega-ohmio(1MΩ)=1 000 000Ω.
Note: They are only manufactured up to mega-ohm, there are no resistors with values higher than this.
If we want to regulate the current we must place it in series and if, on the other hand, we want to regulate the voltage we would have to place it in parallel with the device we want to protect.
The main function of resistors is to protect devices that cannot withstand certain voltages or currents produced by the power supply.
Types of resistors
A) Resistors of fixed values.
- Carbon or film resistance.
- Fuse alloy resistance.
- Wound or wire resistors.
B) Resistors of variable values.
- Thermistor or thermistors.
- Potentiometer or rheostat.
Carbon or film resistance
This resistance uses a color code to be able to be interpreted, internally they are composed of a very thin film wrapped in a reel or a carbonaceous or graphite material, which depending on its purities to that same extent will carry out the opposition.
Resistance Alloy Fuse
This type of resistance is made of a fluxing material, which turns into ashes under sudden changes in temperature. Unlike the previous resistance, it has its value printed on its body. Fusible alloy resistors are always installed at the input of a signal, to protect a circuit.
Wound or wire resistors
It is the resistor that has the greatest power capacity in electrical and electronic circuits. It usually works against alternating current, since its power is from 0.5 to 27 volts, depending on the capacity of the circuit.Its body is made of ceramic and like the fuse alloy, it also has its values printed on its body.
It is a two-terminal resistor with infinite ohmic value, which under sudden changes in voltage and current, at a given moment can conduct in both directions. This occurs when the winding voltage (maximum) exceeds the infinite level of the varistor capacity.
It works combined with the alternating protection fuse. The fuse protects from sudden changes in current and the varistor from voltage changes.
Note: The varistor returns the excess voltage back and a node is formed, increasing the voltage and blowing the fuse.
If the equipment supports 120 volts and the voltage rises to 180 volts, the varistor returns 60 volts, this voltage is added to the 180 volts, resulting in 240 volts.
When a node is formed, the varistor remains in a short circuit, therefore for the equipment to turn on, one terminal of the varistor must be lifted, just to test, then it must be replaced.
Thermistor or thermistors
This device has a physical structure similar to the varistor, it differs from it in that it produces variations with respect to the current, because it is installed in series with respect to the load. There are two categories regarding this resistance:
A) The negative temperature coefficient (NTC): Works for cold areas or cooling currents.
B) Positive temperature coefficient, works for hot or positive areas (NTC).
Potentiometer or rheostat
It is a three-terminal mechanical resistor that varies both voltage and current.
It makes voltage variations when it works as a potentiometer and current variations when it works as a rheostat.