INTRODUCTION TO SONAR 



LOAD CIRCUIT 

 IN SERIES WITH COIL 



i 



POWER SUPPLY 



71.97 

 Figure 10-12. — M;ignetic circuit breaker. 



1. When the switch is closed, current flows 

 from the negative terminal of the battery, 

 through the contact points, the spring, the 

 two coils, and back to the positive terminal 

 of the battery. 



2. The cores are magnetized, and the soft- 

 iron armature (magnetized by induction) is 

 pulled down, thus causing the hammer to 

 strike the bell. 



3. At the instant the armature is pulled down, 

 the contact is broken, and the electromag- 

 net loses its magnetism. The spring pulls 

 the armature up so that contact is reestab- 

 lished, causing the operation to be repeated. 

 The speed with which the hammer is moved 

 up and down depends on the stiffness of the 

 spring and the mass of the moving element. 



The magnetomotive forces of the two coils are 

 in series aiding, therefore the magnetism of the 

 core Is increased over that produced by one coil 

 alone. 



Safety devices also utilizecoilsfor their oper- 

 ation. A circuit breaker, like a fuse, protects a 

 circuit against short circuits and overloading. In 

 the circuit breaker, the winding of an electromag- 

 net is connected in series with the load circuit to 

 be protected and with the switch contact points. 

 The principle of operation is illustrated in figure 

 10-12. Excessive current through the magnet 

 winding causes the switch to be tripped, and the 

 circuit to both breaker and load is opened by a 

 spring. When the circuit fault is cleared, the cir- 

 cuit is closed again by resetting the circuit breaker 

 manually. 



Coils have many more applications and can be 

 studied more thoroughly in Basic Electricity. 



TRANSFORMERS 



Transformers ordinarily are tested by check- 

 ing for shorts, measuring resistance of the indi- 

 vidual windings, and measuring voltage outputs 

 of each winding. 



Descriptions of transformers are contained 

 in the technical manual for the equipment wherein 

 the transformer is used. The manual specifies 

 the terminals to test for each winding and tells 

 what the measurement should read. Small power 

 transformers, of the size used in electronic 

 equipment, usually are color coded as shown in 

 figure 10-13. In an imtapped primary, both leads 

 are black. If the primary is tapped, one lead is 

 common and is colored black, the tap lead is 

 black and yellow, and the other lead is black and 

 red. 



On the transformer secondary, the high-vol- 

 tage winding has two red leads if untapped, or two 

 red leads and a yellow and red tap lead if tapped. 

 On the rectifier filament windings, yellow leads 

 are used across the entire winding, and the tap 

 lead is yellow and blue. If there are other fila- 

 ment windings, they may be green, brown, or 

 slate. The tapped wire is yellow in combination 

 with one of the colors just named; that is green 

 and yellow, brown and yellow, or slate and yellow. 



BLACK (COMMON) 



BLACK-YELLOW 



BLACK-RED 



TAPPED 

 PRIMARY 



RED 



BLACK 



PRIMARY 

 BLACK 



-M^fELLDWyolTAGE 



RED 



YELLOW 



llELUMrLBUiL-^fL^MENT 



YELLOW 



GREEN 



•.GREEN-YELLOW FILAMENT 

 ' NO.l 



GREEN 



BROWN 



. BROWN -YELU3W FI1AMFNT 

 N0.2 

 BROWN 



SLATE 



ISLATMELLOW FILAMENT 

 NO. 3 

 SLATE 



Figure 10-13. — Color coding of 

 transformer leads. 



20.379(71) 

 small power 



164 



