This potentiometer is provided with a double throw switch which allows the connection of either the standard cell or the unknown emf to be applied to the working circuit. Construction and Working of basic(slide wire) dc Potentiometers.This textbook “ Electrical and Electronics Measurements by S.
It is quite comfortable to interpolate readings upto 1/5 of a scale division and therefore with this potentiometer it is possible to estimate the readings upto 0.0001 V. The slide wire is provided with 200 scale divisions and since the total resistance of slide wire corresponds to a voltage drop of 0.1 V, each division of slide wire corresponds to 0.1/200 = 0.0005 V. The working current of the potentiometer is 10 mA and therefore each step of dial switch corresponds to 0.1 V. Thus the dial has a total resistance of 150 Ω and in addition, the slide wire has a resistance of 10 Ω. There is also a single turn circular slide wire.įor the case shown, the resistance of slide wire is 10 Ω and the dial resistors have a value of 10 Ω each. There is one dial switch with fifteen steps, each having a precision resistor. The circuit of a simple DC Crompton’s potentiometer theory is shown in the below figure. Modern laboratory type potentiometers use calibrated dial resistors and a small circular wire of one or more turns, thereby reducing the size of the instrument. The long slide wire is awkward, and even for the length shown cannot be read to a very great degree of precision. The slide-wire type of potentiometer described in the previous article is not a practical form of construction. Laboratory-type or DC Crompton’s Potentiometer:
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