Rheostat Working, Types and Applications

The rheostat is an adjustable resistor and mainly used in the applications where the adjustment of current is required otherwise the changing of resistance in an electric circuit. This kind of resistor can modify the characteristics of the generator, motor speed controlling, dim lights. The resistance element of this can be changed based on its application like a ribbon or metal wire, a conducting liquid or carbon. The metallic type is used only when the average current is required, the carbon type is used only when minute current is required and the electrolytic type is used when large currents are required.

What is a Rheostat?

A rheostat definition is, it is one kind of variable resistor which is mainly used for controlling current as well as to change the resistance within a circuit without disruption. The name of this component was taken from two Greek words namely ““rheos— & ““statis— by an English scientist- Sir Charles.

This type of resistor includes two terminals like fixed terminal and moving terminal. Some types of rheostats like potentiometer includes three terminals but only two terminals are used because twp terminals are fixed and one terminal is movable. Not like potentiometers, these resistors carry a significant quantity of current. Therefore, wire wound resistors are regularly used while designing these resistors.

rheostat-symbols
rheostat-symbols

The rheostat symbols are available in two standards like American standard & the international standard which are shown in the following figures. In the above figures, the American standard symbol represented with three terminals with zigzag lines whereas the international standard symbol represented with a rectangular box by 3-terminals.

Construction

The construction of rheostat is extremely related to potentiometer construction. It has only two connections, even when three terminals are there like in potentiometer. Compare to potentiometers, these resistors have to hold a significant current. Therefore they are frequently designed like a wire wound resistors.

The construction of rheostat is shown below. It has three terminals which are denoted with A, B and C. But, we utilize simply two terminals either A &B terminals otherwise B & C terminals. In this construction, the two terminals like A & C are fixed which are connected toward the track which is known as a resistive element. And terminal B is the uneven terminal and it is connected to the slider otherwise sliding wiper.

rheostat-construction
rheostat-construction

When the sliding wiper moves with resistive element over the resistive lane then it changes the rheostat’s resistance. The rheostat’s resistive element can be made with a loop of wire otherwise a lean carbon film.

These are frequently made with wire-wound. Therefore, sometimes these are also called as variable wire wound resistors. In general, these are designed by winding the wire-like Nichrome in the region of an insulating ceramic core. So this performs like the insulating material toward the heat. Therefore, the ceramic core will not let heat through it.

Types of Rheostat

The rheostats are classified into three type’s namely linear type, rotary type, and preset type rheostats.

1). Linear Type

These types of rheostats include a linear resistive lane, where the sliding terminal can moves smoothly over this lane. It has two permanent terminals but used only one of them whereas the other terminal can be connected to the slider. These are frequently used in laboratory applications.

2). Rotary Type

As the name suggests, it has a rotating resistive lane, which is frequently employed in power applications. These types can be designed with a shaft where the wiper is placed. Here the wiper is a sliding contact, which can move ¾th of a circle over  terminal.

3). Preset Type

Whenever rheostats are used in a PCB (printed circuit board), then they are used as preset rheostats otherwise trimmers. These are small in size and frequently used within calibration circuits. There are two and three terminal trimmers are available but in some cases, three-terminal devices are used like a two-terminal device.

Difference between Potentiometer and Rheostat

  • Both Potentiometer, as well as Rheostat, are connected by the variable resistors. But, technically these represent the two diverse configurations and that is offered by similar components.
  • The construction of both components is the same.
  • A rheostat is a 2-terminal device, whereas a potentiometer is a 3-terminal device.
  • In rheostats, we utilize two terminals for the operation, whereas, in potentiometer, we use three terminals for the operation.
  • A rheostat cannot be utilized like a potentiometer whereas a potentiometer can be utilized like a rheostat.
  • Rheostats are used to change the current, whereas potentiometers are frequently used to change voltage.

Applications of Rheostat

  • Generally, these are used where high current otherwise high voltage is necessary.
  • Rheostats are mainly utilized in dim lights for changing the light intensity. If we amplify the rheostat’s resistance, the electric current flow through the light bulb will reduce. Thus, the intensity of the bulb decreases. Similarly, if we reduce the rheostat’s resistance, then the electric current flow throughout the bulb will enhance. Finally, the light intensity will be increased.
  • Rheostats are used for increasing otherwise decreasing a radio volume as well as to amplify or reduce the electric motor’s speed of an electric motor.
  • These are frequently used like power control devices like light intensity control, motor speed control, heaters, and ovens.
  • At present, these are not used in power control applications due to their low efficiency. So these are substituted by switching electronics
  • In power control applications they are replaced with switching electronics.
  • These are frequently used in circuits which require tuning as well as calibration due to an uneven resistance. In these cases, rheostats are changed while fabrication otherwise tuning the circuit.

Thus, this is all about an overview of the rheostat. The selection of this resistor can be done based on the application. Usually, the current is the main aspect than the rating of wattage. When a rheostat is used for controlling the motor, it is important to know that all kinds of DC motors are speed controlled or not. But, a few types of AC motors are convenient so, it is necessary to get the accurate type of AC motor once speed-control is necessary. Here is a question for you, what kind of resistor is rheostat?

 

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