DYNAMIC MEASUREMENTS ON ELECTROMAGNETIC DEVICES 1439 



actuation compared to the state of the memory tube. By making these 

 small and equal, through selection of the relay design, the constant time 

 lags do not alter the relative preset switching instants. 



The relays are special mercury contact, single t ransfer, Western Elec- 

 tric 291-type. They have 38 gauge 1500 ohms, 14,()00 turns windings and 

 are adjusted to operate with 3.5 milliamperes and release with 2.0 

 milliamperes. The 5687 tubes switch from current to 10 milliamixres 

 through the relays. The release and operate times of the relays are about 

 1.3 milliseconds but as described earlier, are selectively adjusted to 1.5 

 milliseconds where necessary, by shunts such as those shown in Fig. 10. 



The bi-stable memory circuits are switched at the grids through the 

 tw^in diodes coupling the coincidence and memory circuits. While waiting 

 for a shift pulse, the grid potential of the memory tube is lower than the 

 cathode potential of the coincidence circuit, and the diode circuit there- 

 fore does not conduct. This is necessary because small voltage variations 

 occur in the coincidence circuit cathode potential as the several tubes 

 folloAV the decade counters. These small variations w^ould shift the 

 memory circuit falsely if directly connected. When the shift coincidence 

 occurs, the cathode voltage drop is to a potential lower than t hai of t lie 

 memory circuit grid and the conduction of the diode connects the two 

 circuits. This negative impulse shifts the memory circuit. This drives 

 the start grid to a new potential low^er than that of the coincidence tubes 

 cathodes, again cutting off the connection through the diode. When the 

 coincidence cathode rises at the end of the shift pulse, the diode is even 

 further cut off. The stop diode behaves in an exactly similar manner due 

 to the symmetry of the circuits. The diodes thus afford a means of only 

 momentarily making connections at the required instants, at all other 

 times isolating the memory circuit from the remainder of the counting 

 system. 



Summary of Dynamic Flvxmeter Description 



Up to this point, the circuit description has been concerned only \\ ith 

 the dynamic fluxmeter. This circuit was designed and built first, aiul put 

 into operation for dynamic current and flux studies of which one will be 

 described later. About fifty standard type tubes in all are used, with good 

 segregation of the circuit functions. This aids in localizing circuit troubles. 

 Particularly useful is the neon indicator lamp di.splay, also employed 

 when the decade system, with the gate circuit, is adapted as a counter or 

 time interval circuit. 



