ELECTRONIC RELAY TESTER 935 



armature position, the clifferentiatod voltage is proportional to the 

 armature velocity. After amplification the voltage from the gauge is 

 applied to a tube with a transformer in the plate circuit. The voltage 

 across the secondary coil of the transformer is the differentiated voltage, 

 proportional to the armature velocity. It is applied to a germanium diode 

 bridge, which may be connected as a half-wave or full-wave rectifier by 

 the selector switch. The rectified voltage is amplified and clipped and 

 then applied to the Z axis terminals of the scope. The scope trace is 

 brightened during operate, during release, or during both in accordance 

 with the setting of the bridge selector switch. 



GAUGING A RELAY 



The rela}' is plugged into a holding fixture with a jack for the coil and 

 contact terminals. The jack connects the relay coil to the circuit which 

 provides power for operating the relay. It also connects the relay contact 

 terminals to the scanning circuit. 



The electrostatic transducer electrode is mounted on a bracket which 

 is attached to the front end of the fixture by means of a hinged bracket. 



After the relay is plugged into the jack, it is clamped and the gauge 

 electrode is rotated into position near the armature. Then the "zero set" 

 potentiometer on the dc amplifier is used to align the operated armature 

 position with the zero marking on the calibrated horizontal scale of the 

 scope. 



The contact selector switch is used to select the combination of con- 

 tacts to be scanned such as: all contacts, all breaks, or all makes. For 

 convenience in checking relays with 8 contacts or less a switch on the 

 scanning circuit is used to connect 8 of the multivibrators in a ring 

 instead of 16 so that onh^ 8 lines appear on the scope. These 8 lines 

 may be shifted to obtain greater spacing for easier reading. A typical 

 gauging pattern on an oscilloscope screen is shown on Fig. 7. 



This also improves the gauging accuracy which depends upon the 

 amount of armature motion between successive scanning dots. For 16 

 horizontal lines on the screen the time interval between successive dots 

 is 32 microseconds. For an armature velocity of 30 inches per second the 

 corresponding distance between successive dots on one line is about 1 

 mil-inch. If 8 lines are used this distance is about 0.5 mil-inches. The 

 gauging error resulting from this dot definition is actually less than 

 indicated because successive operations of the armature give a small 

 random variation in the dot locations. 



