AUTOMATIC TESTING IN TELEPHONE MANUFACTURE 



1139 



to a sensitrol relay, which is mechanically biased in amount and sense to 

 correspond to the limit. If the sensitrol operates it prevents rejection. 



In the three capacitance test positions 12, 13, and 14, capacitors in 

 the networks are connected into a 60 c.p.s. comparison bridge. The out- 

 put signal from the bridge is amplified and rectified, and impressed on a 

 balanced dc amplifier which drives a sensitrol relay. If the bridge is out 

 of balance (that is if the capacitance is greater or less than nominal) cur- 

 rent flows in the relay, but always in the same sense. If the current in the 

 relay exceeds an amount corresponding to either capacitance limit, re- 

 jection occurs. Determination of which capacitance limit was violated is 

 done manually in a separate analysis of defects. It may be observed also 

 that any rejection at the capacitance positions could have been caused 

 by a loss unbalance of the bridge. If the conductance of the test capacitor 

 were such as to cause this it would so appear in the separate analysis, 

 mentioned above. The effect of any ordinary conductance deviation at 

 60 c.p.s. is neghgible. Quality is protected by the fact that a conductance 

 deviation could not cause an out-of -limit capacitor to be accepted. 



Considerable pains are taken at each capacitance test position to pre- 

 vent damage to the equipment from various kinds of mishaps. The sen- 

 sitive winding of the sensitrol is short circuited at all times except for 

 about 0.2 second when the actual test is performed. This prevents dam- 

 age and erroneous rejections that would otherwise be caused by switching 



Table II — Sequence of Events in Network Test Machine 



CAM ROTATION — 



(TWELFTHS OF A POSITION) 



