954 



Popular Science Monthly 



Operating Furnace Checks and Drafts 

 by Electricity 



THE device described comprises an 

 actuating lever to operate the 

 draft and checic; a relay — a skeleton bell 



ro Check 



BocMof Oock 



Defai,' of 

 Check Release 



Electrical connections and wiring for an alarm 

 clock to work the furnace check and draft 



or buzzer — to release the lever, and a 

 clock to close the electrical circuit at 

 the proper hour. A thermostat may also 

 be used and connected in the circuit. In 

 addition, there is a trigger intervening 

 between the relay and the lever, and a 

 circuit-breaker which effectively pre- 

 \ents loss of power by short-circuiting 

 the battery after the mechanism has 

 been tripped. 



Reference to the sketch will show that 

 the circuit-closer consists simply of an 

 ordinary alarm clock, back of which 

 extends upward a metal strip which 

 makes contact with the winding key in 

 re\olution as the alarm goes off and 

 forms a circuit through the clock and a 

 turn or two of bare wire on which the 

 clock rests and which leads to the 

 other terminal. The relay is short- 

 circuited so that the armature does not 

 buzz but is simply drawn sharply up to 

 the magnets, thus pulling the trigger 

 li\-er forward by the wire connection 

 and releasing the lever by raising the 

 bent wire stop. 



As the le\er falls it not only opens the 

 draft and closes the check, but pulls a 

 third cord which opens a small battery- 

 switch connected between relay and clock, 

 thus preventing current waste should 



the winding key chance to remain in 

 contact with the metal strip when the 

 alarm has ceased ringing. 



It was found that the check- valve on 

 the furnace in question must be lowered, 

 not raised, to make it draw. The detail 

 sketch shows how this difficulty was 

 overcome by providing a stout wire 

 support for the check-valve which is 

 jerked loose as the lever falls, thus 

 allowing the check to drop to its closed 

 position by its own weight. On a single 

 cell of battery the device will be found to 

 work perfectly. — De.^xe S. Kint.ner. 



Transformer Trouble in Radio Trans- 

 mitting Apparatus 



AMONG the many sources of trouble 

 r\. by which a radio set's efficiency is 

 reduced, a short-circuit of a few turns 

 in the primary of the transformer is to 

 an inexperienced man one of the most 

 difficult to locate, as well as to find a rem- 

 edy for. With the primary of the trans- 

 former short-circuited, two fundamental 

 principles will explain the cause for the 

 lack of efficiency: 



1. In order for the greatest etificiency 

 to be obtained, there must be resonance 

 between the primary circuit and the 

 secondary circuit. It is evident that, if 

 some of the turns are cut out of the 

 primary of the transformer, the two will 

 be thrown out of resonance, since the 

 electrical inductance of the primary will 

 be reduced. This, of course, results in 

 poor working. 



2. The other fundamental principle is 

 explained by the potential drojj in a cir- 

 cuit. Suppose a circuit, as shown, 

 to be partially short-circuited so as to 

 cut out three turns of the nine turns 



3. S OHMS 

 ■ 200 V 



ilNTERNAL RES. Of 

 GEN. I5 0HM5 



CUT OUT 3 TURNS 



RES, 5 OHMS "" 



2.5 OHMS 



Locating the short circuit in the turns 

 of a primary of the transformer 



which constitute the primary of the 

 transformer, as from A to B. The total 

 elect roTUotive force and the internal 

 resistance will remain constant, biic the 

 external resistance and current are 



