Rheostat vs Potentiometer: What Sets Them Apart?

Rheostats and potentiometers are two types of variable resistors that are commonly used in electronic circuits. While they may appear similar in function, there are some key differences between the two that are important to understand when selecting the appropriate component for a particular application. Understanding the differences between these two components can help ensure that the correct component is selected for the specific application.

Differences Between Rheostat and Potentiometer

The differences between a rheostat and a potentiometer are the following:

1. Definition

The potentiometer is a three-terminal device used for voltage control while the rheostat is a two-terminal device used for current control. The potentiometer name comes from the concept of varying potential differences. The rheostat is nothing but a variable resistor. The rheostat is derived from the Greek words ‘rheos’ and ‘statis’ means the current controlling device.

2. Operating principle and construction

The rheostat has mainly two parts one is resistive material or you can say resistor and another is a movable wiper. The rheostat has two terminals. One terminal is connected to one end of the resistor and another is connected to the wiper. By moving the wiper, we can vary the resistance across the two terminals.

The construction of a potentiometer is shown in simplified form in the figure. A resistive strip is bent into a nearly complete circle and terminals are connected to either end. This forms a fixed resistance. To obtain the variable resistance, a sliding contact is attached to a rotatable shaft and bearing and is connected to a third terminal. The resistance between this middle terminal and either of the end terminals can vary from zero up to the resistance of the whole strip.

3. Number of terminals

A potentiometer is a resistor with three terminals and sliding contact with an adjustable voltage divider while a rheostat is a variable resistor with two terminals.

4. Connection type

A potentiometer is connected in parallel with the source meaning it is used to adjust the voltage across the load. A rheostat, on the other hand, is connected in series with the load and source meaning it is used to adjust the current flowing through the load.

5. Main function

The basic function of a potentiometer is voltage dividing. While the usual function of a rheostat is to determine the flow of current.

6. Application areas

A potentiometer has low power and is used for audio devices, television control, and as a transducer while a rheostat is used for control of appliances like fans, mixers, and the motors of large industrial machines.

Potentiometers are used for low-power applications (less than about one watt), but rheostats are used for high-power applications (more than about one watt).

7. Usage

A rheostat cannot be used as a potentiometer. A potentiometer can be used as a rheostat. A potentiometer may be used as a rheostat by simply using the wiper terminal and one of the other terminals, the third terminal is left unconnected and unused. Another method is to wire the unused terminal to the center terminal.

8. Types

The potentiometer has linear, rotary and digital types. Rheostat has linear, rotary and preset types.

9. Materials

A potentiometer is made with resistive elements such as graphite, resistance wire, carbon particles and cermet while a rheostat is made of several different materials such as metal ribbons, fluids and carbon disks.

10. Adjustment

A rheostat is not continuously adjustable as a potentiometer is. This is because the movable contact slides along from turn to turn of the wire coil. The smallest possible increment is the resistance in one turn of the coil. The rheostat resistance, therefore, adjusts in a series of little jumps.

11. Cost

The price of a rheostat is higher than a potentiometer. Potentiometers provide a cost-effective solution in trimming applications and the ever-present necessity of control for the man-machine interface.

12. Size

Generally, the physical size of a rheostat is bigger than a potentiometer. Rheostats are designed for higher power applications and may have a larger physical size to accommodate the larger components needed for handling higher power levels. Potentiometers, on the other hand, are typically used for lower-power applications and may have a smaller physical size. However, this is not always the case as there are also small-size rheostats and large-size potentiometers available in the market.