712 



BELL SYSTEM TECHNICAL JOURNAL 



Multi-Test Machine, Automatic Feed 



An automatic gaging machine for applying four tests to a piece of 

 telephone apparatus is shown in Fig. 3. 



The part tested, shown in Fig. 4 {a), is a heat coil used to protect 

 telephone exchange equipment against excessive electrical currents 

 that may accidentally come in over the line wires. It consists of a 

 tiny coil wound around a copper sleeve, into the end of which sleeve is 



SPRINGS 



SHOULDER 



(a) 



soldered with low melting point solder a projecting pin. An excessive 

 current through the coil melts the solder, allowing a contact spring to 

 press the pin into the sleeve, which movement of the contact spring 

 opens the circuit. 



The machine gages the length of the pin X, the external length of 

 sleeve Y, tests the strength of the soldered joint and measures the 

 electrical resistance of the coil for high and low limits. 



Referring to Fig. 3, there is an intermittently rotating disc D fitted 



