AUTOMATIC MACHINE FOR TESTING CAPACITORS AND NETWORKS 1193 



tors from 0.02 to 5 microfarads are tested on this machine to an accuracy 

 of ±2 per cent. 



The modified microfarad meters are equipped with two brass seg- 

 ments, covered with an overlay of silver (Fig. 10). These segments are 

 mounted end to end in a predetermined cutout portion of the meter 

 scale, representing maximum and minimum capacitance conditions. The 

 physical distance between the adjacent ends of these two segments is as 

 small as possible without the two segments touching. A small silver con- 

 tact is mounted on an insulated portion of the meter pointer, directly 

 at)Ove but not touching the segments while the meter pointer traverses 

 its arc of rotation. The armature of the relay, mounted on the meter, 

 i actuates a contactor arm which forces the silver contact on the pointer 

 I down against the silver overlay segment, thus closing external circuits 



connected to the segments and contactor. 

 I The testing machine is equipped with three ranges of the special 

 microfarad meters as follows: 



1. Suppressed scale from 1.2 to 1.8 mf, with the dividing point be- 

 tween the two segments at 1.60 mf. 



2. Suppressed scale from 0.25 to 0.75 mf, with the dividing point be- 

 tween the two segments at 0.63 mf. 



3. Suppressed scale from 0.051 to 0.075 mf with the dividing point 

 between the two segments at 0.062 mf. 



Two meters for each of the above ranges are necessary in each testing 

 machine, one for each unit in a dual unit. Likewise, four capacitance 

 boxes are necessary, two for each unit in a dual unit. 



The discussion that follows, which is divided into two headings, A 

 and B, is a detailed description of the capacitance test circuit. The cir- 

 cuit component designations are those shown in Fig. 11. 



A . Capacitance Test on Dual Unit Capacitors or Networks 



The cammed switch S5 is opened momentarily at the beginning of the 

 test to restore the test circuit to normal; following this, the cammed 

 switch S8 closes and operates relay K14, which applies power and closes 

 the power supply circuit through the microfarad meters and the capacitor 

 on test. 



The capacitance decade box "less than maximum" C2 is shown in 

 series with test capacitor No. 1 by the preset series-parallel switch SIO, 

 and in a like manner a capacitance box is connected in series with test 

 capacitor No. 2. 



