178 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



division starts and ends exactly in the ratio of the effective series re- 

 sistances by virtue of the method used in determining them. For times 

 after circuit closure, a transient voltage error does develop, but it will 

 not approach in magnitude the initial transient error of the linear net- 

 work. The operate time error will be still smaller. The operate time 

 varies as the two-thirds power of the voltage (power varies as the volt- 

 age squared). 



These considerations lead to the conclusion that ignoring the eddy 

 currents in setting up the equivalent relays, results at the most in errors 

 of operate time estimates for series connected relays of the order of a 

 few per cent. 



RELEASE TIME 



The relase time of a relay is not as directly affected by the winding. 

 as is the operate time. For instance, if it is opened by the controlling 

 contact without an RC network, the winding current, ignoring arcing 

 at the contacts, abruptly drops to zero. The winding subsequently plaj^s 

 no part in the flux decay. If the winding has a shunting resistor or RC 

 circuit, then winding current does flow and some effect is present. A 

 resistor always increases the release time. A favorable RC choice can 

 cause a slight decrease in release time. Because of this minor effect, the 

 winding almost always is designed from operate time or sensitivity 

 considerations. 



Differing slightly from operate time, the release time is divided into 

 two parts, (1) waiting time plus motion time vnitil actuation of the 

 nearest contact and (2) stagger time. For simplicity the combination (1) 

 above is merely called release waiting time. 



The release time of a relay is a more complicated function than is the 

 operate time. The primary cause of this is the closed gap situation, with 

 little stabilizing effect from an air gap. For the earlier operate time 

 studies the air gap largely contributed to the simple exponential relation- 

 ships. A second effect in release is that the magnetic material is almost 

 always in the non-linear saturated portion of its characteristic. Hence 

 an approximately linear relationship between steady state flux and 

 current cannot be assumed. Finally, for release without an RC network, 

 the only current flows in the core, so it completely controls the flux 

 decay. Even with an RC network, only a minor decrease in release time 

 is possible. For these reasons, except for rough preliminary estimates 

 of release times during preliminary design, all release data are based 

 on measurements. 



