Electrical Engineering ⇒ Topic : Crompton D.C. Potentiometer
|
Sachin
| |
Crompton D.C. Potentiometer Fig. (a) shows the general arrangement of Crompton d.c. potentiometer. A graduated slide wire AC is connected in series with 14 (or more) resistance coils, each of which has a resistance exactly equal to the resistance of the whole slide wire. There are two moving contacts P1 and P2.The contact P1 can slide over the slide wire and contact P2 can slide over the studs connected to the resistance coils. B is the supply battery (2 volts) and R1 and R2 are two variable resistors. The resistor R1 consists of a number of coils in series and is meant for coarse adjustment of potentiometer current.The resistor R2 is in the form of a slide wire and is meant for fine adjustment of potentiometer current. The connections C1, C2 are taken to selector switch S (double-pole, three position switch) for connecting either the standard cell (S.C.) or cell of unknown e.m.f. The terminals for cell connections are marked Positive (+) and negative (-) for correct polarity connection. figure (a) Working. The potentiometer is first "standardised" (i.e., made direct reading) by adjustment of the current from the supply battery B. For this purpose, we connect Weston type standard cell whose e.m.f. is 1.0183 volts to the terminals marked S.C. (Be sure to connect correct polarity). The moving contacts P1 and P2 are set to a reading equal to the e.m.f. of the standard cell i.e., contact P2 is placed on stud 1.0 and contact P1 on 0.0183 on the slide wire. The regulating resistances R1 and R2 are varied until the galvanometer reads zero. Now the potentiometer is standardised i.e., reading of the potentiometer (= 1.0 + 0.0183 = 1.0183) is directly read as the voltage being measured. Therefore,the potentiometer becomes direct reading. Note that after standardisation of the potentiometer, the setting of R1 and R2 is not to be changed. The source of e.m.f. whose e.m.f. is to be measured is connected between the terminals + 1 and -1 (or + 2 and -2) and the selector switch is switched over to the position + 1 and -1. The moving contacts P1 and P2 are adjusted until the galvanometer reads zero. The reading of the potentiometer will give the e.m.f. or potential difference to be measured directly | |
| |
!! OOPS Login [Click here] is required for more results / answer