DYNAMIC MEASUREMENTS ON ELECTROMAGNETIC DEVICES 1435 



For the other nine configurations, one or the other of the wires will 

 carry nearly the full battery voltage. The leads to the time selector 

 switches are indicated by the arrows marked from to 4, oil and 5L, 

 inclusive. 



When the (5) tube reverts after the tenth impulse, its step plate voltage 

 rise is differentiated by a small capacitor. This drives another pseudo 

 cathode follower to shift the tens counter exactly as has been described 

 for the units counter. For this tens ring, the take off leads to the time 

 selector are identified as 00 to 50. 



In a similar manner the hundreds counter leads are identified as 000 

 to 500. 



Thus by exactly six wires, two for each decade, any cycle in 1000 can 

 be selected. Note that for and 500, needed for the A relay the (500) 

 tube itself provides complete information. This eliminates the need for 

 a coincidence and memory circuit for the A relay drive tube. Also by 

 choosing 480 and 980 for the C relay, an abbreviated coincidence circuit 

 can be used, as access to the units counter is not needed. 



Neon lamps are provided as indicators for each ring to aid in circuit 

 checking, trouble shooting, and as the counter indicator when used with 

 the gate circuit. 



The separation between successive time intervals which can be selected 

 is one/one thousandths of one complete closure and open cycle, being 

 25 microseconds for a cycle time of 25 milliseconds, 100 microseconds for 

 a cycle time of 100 milliseconds, etc. This is controlled by the discrete 

 states of the counting rings used to generate the switching signals. This 

 relation between the cycle time and the successive a^'ailable time inter- 

 vals is not a handicap because if the device is slow and a long cycle time 

 has to be employed, it is slow because the flux buildup or decay is slow 

 and hence closely spaced measurements are superfluous. 



The maximum speed is 40 on-off cycles a second obtained with a 40-kc 

 oscillator. The lowest speed is limited only by the ability of the vacuum 

 tube filter to suppress instrument pointer vibration. 



The counting ring system with its discrete steps precludes an auto- 

 matically recording de\'ice as would be possible with a motor driven 

 commutator and a gear driven take-off brush. However, the elimination 

 of brush troubles is considered to be worth this sacrifice. 



Time Selector. The time selection is controlled by two two-gang decade 

 switches for the units and tens selections and one five position switch 

 for the hundreds selection. The schematic is shown in Fig. 14. The dial 

 positions are marked directly in time for a lO-kc oscillator, that is the 

 units selector indicates one-tenth milliseconds, ihc tens milliseconds, and 



