416 ELECTRICAL MACHINERY 



135. Meters. A complete description of the various 

 types of meters used in electrical circuits would be out of 

 place here and would take up too much space. We shall 

 describe, in an elementary fashion, a few of the more 

 important instruments and point out those qualities which 

 a manufacturer tries to incorporate in his meters. 



Meters may be divided into three general classes: indi- 

 cating, recording and watt-hour meters. The latter are 

 sometimes called integrating meters. 



Indicating Meters. An indicating meter is one, the 

 pointer of which deflects over a graduated scale, and so 

 indicates at any instant the current or voltage in the cir- 

 cuit to which it is connected. It has no rotating parts and 

 makes no record of the motion of its finger. These instru- 

 ments show the operator how much current a feeder is 

 carrying at any instant, or what voltage a machine is genera- 

 ting. From their indications the operator may properly 

 adjust the voltage, re-distribute the load from one machine 

 to another, etc. 



They are subdivided into switchboard instruments and 

 portable instruments. The first are fastened permanently 

 on a switchboard and can generally be used only for indica- 

 tion on the machine or feeder to which they are attached. 

 The portable meters are smaller and more compact than the 

 switchboard instruments and are made for laboratory 

 work, or for carrying out to different parts of a distributing 

 system to read the current or voltage. 



Switchboard Meters. A switchboard meter should be 

 compact, have a large, well marked scale of uniform grad- 

 uations (except in some special cases), have a large, black 

 pointer on the end of the indicating finger, and should be 

 well damped. Of course there are numerous other points 

 to consider, such as permanency of calibration, freedom 

 from temperature errors, etc., but we shall take up only 

 those mentioned above. 



On large switchboards, having many generators connected 



