72 ELECTRICAL MEASUREMENTS 



vanes a, b, and the pointer. When no current is passing, the 

 plane of the vanes makes a slight angle with that of the coil; on 

 the passage of the current the vanes tend to place themselves 

 along the lines of force, that is, perpendicular to the plane of the 



coil. 



By adopting the inclined coil 

 arrangement, a long scale is ob- 

 tained, for in order to turn the 

 plane of the soft iron from a 

 position coincident with the 

 plane of the coil, to one perpen- 

 dicular to it, it is necessary to 

 turn the pivot, and therefore 

 the pointer, through 180; the 

 actual working range of deflec- 

 tion is about 100. These in- 



FIG. 36. Inclined-coil ammeter. (General Electric Co.) 



struments are now made with laminated magnetic shields and 

 magnetic damping. 



THE ELECTRODYNAMOMETER AND THE CURRENT BALANCE 



The electrodynamometer is distinguished from the moving coil 

 galvanometer by having the movable member suspended, not in 

 the field of a permanent magnet, but in that due to a system of 

 fixed coils which are traversed by the current. 



Electrodynamometers may be either absolute or secondary 

 instruments. The coils may be arranged in various ways but in 



