First of all what is resistor? Answer is: A resistor is a passive two-terminal electrical component that implements electrical resistance(opposition) as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages and terminate transmission lines, among all other uses.
What is Variable Resistor?
A variable resistor is a resistor of which the electric resistance value can be adjusted. A variable resistor is in essence an electromechanical transducer and normally works by sliding a contact (wiper) over a resistive element. OR A resistor of which the ohmic resistance value can be adjusted. Either mechanically (potentiometer, rheostat) or electronically (digital potentiometer).
What is Potentiometer?
- Potentiometer is the most common variable resistor.
- It is 3 terminal type variable resistor.
- Potentiometer which is also known as “Pot” on circuit diagrams, a resistor with three terminals and a sliding contact with an adjustable voltage divider.
- It is used to generate a voltage signal depending on the position of the potentiometer.
- This signal couldused for a very wide variety of applications including: Amplifier gain control(audio volume), measurement of distance or angles, tuning of circuits and much more.
- Potentiometers, are made with a resistive element, usually graphite, which is formed into an arc and a sliding contact or wiper that travels over the arc. The wiper is connected to another sliding contact to another terminal.
- Position of the wiper depends on the type of POT used. For a panel POT, the wiper is kept in the middle.
What is Rheostat?
- Rheostats are very similar in construction to potentiometers, but are not used as a potential divider, but as a variable resistance.
- Rheostat which is a variable resistor with two terminals.
- There are two types of rheostats; the rotary which have a curved wire coiled to save space, and the slider or linear which have a straight coiled wire.
- Rheostats are made of several different materials, such as, metal ribbons, fluids, and carbon disks. It uses the principles of Ohm’s law which states that the current will decrease as resistance to it increases, and it will increase as resistance to it is decreased. They are not polarized so they can operate in reverse.
- In the past rheostats were used as power control devices in series with the load, such as a light bulb. Nowadays rheostats are not used as power control anymore as this is an inefficient method.
- Preset variable resistors, wired as rheostats are used in circuits to perform tuning or calibration.
What is Digital Resistor?
- A digital variable resistor is a type of variable resistor where the change of resistance is not performed by mechanical movement but by electronic signals.
- They can change resistance in discrete steps and are often controlled by digital protocols such as I2C or by simple up/down signals.
Symbols of Variable Resistors:
Credits: Wikipedia, ResistorGuide.com