RESISTANCE DEVICES 



143 



neighbors. Dimensions which have been found satisfactory 

 under exceptionally severe service are shown in Fig. 67. Each 

 block is held in place by four screws; the taper of the plugs is 

 3^o m - per 1 in. of length. 



Dial and Decade Arrangements. A common dial arrangement 

 of coils employs nine 1-ohm coils, nine 10-ohm coils, nine 100-ohm 

 coils and so on. The connections are such that any number of 

 coils in any set may be put in series with any other set or sets. 

 One method of accomplishing this is shown in Fig. 68A. A single 

 plug is used in each dial. 



FIG. 68. Dial and decade connections for resistance coils. 



A great disadvantage of this particular arrangement, when 

 plugs are used, is that it is kept clean with difficulty; dust and 

 dirt collect on the hard rubber between the central block and the 

 coil terminals and may partially short-circuit the coils, especially 

 those of high resistance. 



Obviously this arrangement lends itself readily to the employ- 

 ment of a rotative switch in place of the plug for connecting the 

 central terminal to the coil terminals. It is now very commonly 

 used and when the switch is well made is satisfactory (see Fig. 

 93). 



Fig. 68# shows a decade set, which is the equivalent of a dial 



