Potentiometers & Rheostats

Commonly used for laboratory and industrial means, potentiometers and rheostats are two different types of variable resistors that are used in various electronics. To ensure networks are operating at peak efficiency, both devices are designed to control current and voltage flowing through a circuit by the means of actuating one or more knobs. However, while they may perform similar functions, they should not be interchanged with one another unless specified because of their individual and particular construction. To better understand how potentiometer and rheostat components function separately, we will go into detail on when each should be applied, alongside what to look for when choosing the appropriate part.

As a type of resistor, potentiometers are essentially used as a type of variable voltage divider, and to allow this process to happen, they are made with three terminals. Consisting of an input terminal and two output terminals, the potentiometer’s extra output terminal enables it to achieve a grounded state, which also allows it the capability to function as a rheostat.

When applied to a system, potentiometers are utilized to control electrical equipment in devices pertaining to audio control, television, motion control, transduction, and computation. Depending on the industry in which a potentiometer is being applied, common types to be considered include: slide pot or slider pot, thumb pot or thumbwheel pot, and trimpot or trimmer pot varieties. In lieu of analog potentiometers, digital potentiometers (or digipots) also exist to control volatile and non-volatile operations for factory adjustment and calibration equipment. In addition, they are renowned for their immunity towards long-term mechanical vibrations and environmental contamination.

Relatively inexpensive, potentiometers are constructed with their two output terminals affixed to a resistive element and necessitate the need for a sliding contact or wiper, mechanisms to move the contact/wiper, and an apparatus which encases the entire unit. Typically used for small and controlled loads, potentiometers should not be applied to control power larger than a watt.

Unlike potentiometers, rheostats are built with two terminals: an input terminal and an output terminal. However, as rheostats are missing an additional terminal, they cannot function as potentiometers as they are incapable of achieving a grounded output.

Considered the predecessor of potentiometers, while rheostats are the optimal choice to continuously vary resistance in a circuit, they are slowly being phased out by the latter and their mechanical diversity. Moreover, they must be rated to operate at power levels exceeding a watt and can be easily applied to loads carrying several thousands of watts.

Simple in design, you can find that rheostats are often made with a resistive wire wrapped around a semicircular insulator and a mechanical wiper which motions back and forth to switch between two wire inputs. On the other hand, their life-expectancy and tolerance to high temperatures can be increased by implementing a heat-resisting cylinder as the insulator.

When it comes down to selecting whether a potentiometer or rheostat is right for your operations, you must first consider the maximum amount of resistance your device can handle. This will ultimately determine a preferred current and/or voltage load your equipment can handle. From here, contact/wiper resistance and taper style should be scrutinized to ensure adequate fluctuation is achieved between the current to the load when instigated. Lastly, as both potentiometers and rheostats cater to different power ratings, their tolerances vary, and they demand implementation amongst devices that cater towards their particular construction and hysteresis.

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