A rheostat is a variable resistor which is used to control current within an electrical circuit. They are able to vary the resistance in a circuit without interruption. Rheostats are very similar in construction to potentiometers.
How Rheostats Operate
Rheostats use two connections, even when 3 terminals are present, the first connection is made to one end of the resistive element and the other connection to the wiper (sliding contact). Resistive wire is wound around an insulating ceramic core, as the wiper slides over the windings the resistance, and therefore current, produced is altered.
Several types of rheostats exist, with varying functions and applications.
Rotary type – Mostly used in power control applications. Rotary rheostats feature a turnable shaft that adjusts the resistance. They are used to control multiple applications in parallel or to increase the power rating or adjusting range.
Slide type – Slide rheostats are often used for education and in laboratory environments. Linear or slide types are constructed of resistive wire wound on an insulating cylinder, a sliding contact moves along the winding to increase or decrease the resistance.