What is a Rheostat?

[VelMurugan]

What is a Rheostat?

A rheostat is an electrical component that has an adjustable resistance. It is a type of potentiometer that has two terminals instead of three. The two main types of rheostat are the rotary and slider. The symbol for a rheostat is a resistor symbol with an arrow diagonally across it. They are used in many different applications, from light dimmers to the motor controllers in large industrial machines.

Rheostat Construction

Most rheostats are the wire-wound type that have a long length of conductive wire coiled into a tight spiral. The linear type have a straight coil while the rotary type have the coil curved into a torus to save space. The coil and contacts are sealed inside the case to protect them from dirt which can cause an open circuit, and from moisture which can cause a short circuit. Rheostats can be made from other materials such as carbon disks, metal ribbons, and even certain fluids. As long as a material has a significant resistance change over a short length, it can probably be used to make a rheostat.

How They Work

The basic principle used by rheostats is Ohm's law, which states that current is inversely proportional to resistance for a given voltage. This means the current decreases as the resistance increases, or it increases as the resistance decreases. Current enters the rheostat through one of its terminals, flows through the wire coil and contact, and exits through the other terminal. Rheostats do not have polarity and operate the same when the terminals are reversed. Three-terminal potentiometers can be used as rheostats by connecting the unused third terminal to the contact terminal.

Applications

Some light dimmers use rheostats to limit the current passing through the light bulbs in order to change their brightness. The greater the resistance of the rheostat, the lower the brightness of the light bulbs. Some lights cannot use dimmers, such as fluorescents and gas-discharge lamps. These lights have large resistance loads, called ballasts, that maintain a constant current through them. Rheostats have no effect on their brightness and can even damage them.

Motor controller also use rheostats to control the speed of a motor by limiting the flow of current through them. They are used in many small appliances such as blenders, mixers, fans, and power tools. Rheostats are also used as test instruments to provide an accurate resistance value. While rheostats can be used to control electric ovens and cooktops, thermostats are preferred because they have additional parts which automatically adjust the current flow to maintain a constant temperature.

The rheostat is still a common and fundamental electronic component used to control the flow of current in a circuit. However, it has largely been replaced by the triac, a solid-state device also known as a silicon controlled rectifier (SCR). A triac do not waste as much power as a rheostat and has better reliability due to the absence of mechanical parts. Rheostats commonly fail because their contacts become dirty or the coil wire corrodes and breaks.

Source : TechFaqs

[Gflorante]

              What mainly or usually acclimated this accessory or what we alarm rheostat. In what a lot of acreage do you think?

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Refrigerator filter

[johndoown]

Rheostat is a device that is used to change the resistance of the circuit without interrupting the circuit. Most of the rheostat is the winding type, has a long length of conductive wire rolled into a tight spiral. Linear with straight, while the rotating coil, the coil bent into a loop, to save space. It may be the most familiar form of rheostat or dimmer slider for different intensity of light.

[aggiearthur]

Rheostat is that it is used to change the circuit without interrupting the circuit resistance device. It may be the most consistent in the dimming light, or the slider to change the light intensity for the formation of a rheostat familiar. Rheostat is used to set or mood lighting comfort level so that people change, without changing the lamp light levels. Rheostat also used the number of applications in electronics and a variety of industries. Many companies and people who manufacture these devices can do it themselves, because sometimes in science class to introduce students to the topic of resistance.

[Ross Townsend]

This a old name of variable resistance.The most two types of rheostat used are a rotary-type rheostat and a sliding rheostst, these are  used in applications that require adjustment of current or the varying of resistance in an electric circuit.

[alenfort]

Rheostat is a device that is used to change the resistance of the circuit without interrupting the circuit. It may be the most familiar form of rheostat or dimmer slider for different intensity of light. Rheostat to set the lighting level of comfort or emotional, to get people to change light intensity lamp, without change. Rheostat is also used in digital electronic applications and a variety of industries.

[changdellen]

A rheostat is a accessory which is acclimated to alter the attrition in an electrical ambit after arresting the circuit. Rheostats are also used in a number of electrical applications and a variety of industries. Many companies manufacture these devices and people can also make their own, as is sometimes done in science classes to introduce students to the topic of electrical resistance.