Rheostat

Reostat (Rheostat)

Cara paling umum untuk mengubah-ubah resistansi dalam sebuah sirkuit adalah dengan menggunakan resistor variabel atau rheostat. Sebuah rheostat adalah resistor variabel dua terminal dan sering kali direka untuk menangani arus dan tegangan yang tinggi. Biasanya rheostat dibuat dari kawat resistif yang dililitkan untuk membentuk koil toroid dengan penyapu yang bergerak pada bahagian atas toroid, menyentuh koil dari satu lilitan ke lilitan seterusnya. Potensiometer tiga terminal dapat digunakan sebagai resistor variabel dua terminal dengan tidak menggunakan terminal ketiga. Seringkali terminal ketiga yang tidak digunakan disambungkan dengan terminal penyapu untuk mengurangi fluktuasi resistansi yang disebabkan oleh kotoran. 

The most common way to vary the resistance in a circuit continuously is to use rheostat.[6] It is basically used to adjust magnitude of current in a circuit by changing length. The word rheostat was coined about 1845 by Sir Charles Wheatstone, from the Greek ῥέος rheos meaning "stream", and -στάτης -states (from ἱστάναι histanai, " to set, to cause to stand") meaning "setter, regulating device",[7][8][9] which is a two-terminal variable resistor. For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper. Where the rheostat must be rated for higher power (more than about 1 watt), it may be built with a resistance wire wound around a semicircular insulator, with the wiper sliding from one turn of the wire to the next. Sometimes a rheostat is made from resistance wire wound on a heat-resisting cylinder, with the slider made from a number of metal fingers that grip lightly onto a small portion of the turns of resistance wire. The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point. Wire-wound rheostats made with ratings up to several thousand watts are used in applications such as DC motor drives, electric welding controls, or in the controls for generators. The rating of the rheostat is given with the full resistance value and the allowable power dissipation is proportional to the fraction of the total device resistance in circuit. Carbon-pile rheostats are used as load banks for testing automobile batteries and power supplies. 

Reference: Wikipedia

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