MULTICELLULAR VOLTMETER 



In the switchboard type of instrument the end of the pointer, 

 bent down as shown in Fig. 43, is arranged to move over a cylindrical 

 scale whose axis coincides with 

 that of the moving system. 



Multicellular voltmeters of 

 this type are constructed to 

 read up to 600 volts. For 

 higher voltages a modified form 

 of the instrument, known as 

 the "dial pattern," and illus- 

 trated in Fig. 45, is used. In 

 this, there are only two movable 

 plates, the axis of rotation is 

 horizontal, and knife-edge sup- 

 ports take the place of the 



suspension used in the former or "vertical scale" pattern. The 

 controlling couple is furnished by gravity, and oil damping is used. 

 Instruments of this kind are made to read up to 8500 volts.* 



FIG. 44. Multicellular Voltmeter. 



POINTER-* 

 MOVABLE PlATlSv 



r 



t 



iHft VAKE 



fLATES-" ^ FIXED PLATES- 



PIG. 45. Dial Pattern of Multiccllulur Voltmeter. 



A somewhat different type of instrument is the Ayrton and 

 Mather electrostatic voltmeter, the working parts of which are shown 

 in Fig. 46. The plates, both fixed and movable, are cylindrical, and 



In instruments of the mnlticellular type, the moving vanos are, in their zero 

 position, displaced from the position of symmetry; otherwise they would be in a 

 position of instability, and the direction of displacement would be indefinite, being 

 determined by the accidental displacement, at the instant when the p.d. is applied, of 

 the movable vanes from the exact position of symmetry. 



