Page:Popular Science Monthly Volume 88.djvu/808

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An Automatic Pressure-Gage Alarm

AN ordinary pressure-gage may be easily equipped with a simple home-made contact device, which will serve as an automatic alarm, giving the attendant an audible signal, when the pressure has exceeded or dropped be-

��Popular Science Monthly

���Diagram of connections for making an audible pressure-gage alarm

low a previously determined value. This device may be arranged as follows: Carefully remove the glass front of the gage and also the needle from its spindle. Then, on the under side and at the outer end of the pointed end of the needle, fasten a very light piece of spring brass, which is to brush over the contact to be mounted on the face of the dial. This contact is fastened on the face (of dial) in such a position that the spring on the end of the needle is in perfect contact with it, when the needle indicates a pressure correspond- ing to the value at which the alarm ^ is to be given. It is, of course, to be in- sulated from the dial, and in turn, con- nected to a binding post, mounted on the outside of the frame, or containing case,

��of the pressure-gage and properly in- sulated from it. A second binding post is mounted on the case itself, and elec- trically connected with it. These two posts form the contact device, and are connected in series with the bell battery and a small single-pole switch. In re- mounting the needle on its shaft, great care must be exercised to see that it oc- cupies the same position on the face of the dial that it did before. A little error may prove of great damage, in case it should indicate a pound or so less than is really the actual pressure. The spring of brass, on the outer end of the needle, should be very light and flexible, and so adjusted that it will move over the con- tact on the face of the dial with the minimum friction. It would, no doubt, be best to fasten a small piece of plat- inum on the points that touch or coincide with each other, to prevent trouble due to corrosion and arcing.

A diagrammatic sketch of the entire device, including the electrical connec- tions, is presented herewith. One or more additional contacts may be mount- ed on the dial, at various spaces show- ing different pressures, etc. These con- tacts may also be put in circuit with bells, buzzers, and the like with different tones. — Wm. Warnecke, Jr.

Fools Automobile Thieves

PROBABLY the simplest way to dis- appoint the automobile thief is by means of an inconspicuous lock which short-circuits the ignition system. Two springs should be installed in the walls of a rubber tube. When a rubber plug

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��A'short-circuit of the ignition system is the safest guard against automobile thieves

is inserted, the springs are forced apart and the current will go to the spark- plugs as usual. Withdrawing the plug allows the springs to come within sparking distance of each other, and the circuit is temporarily put out of order. One spring should be connected to the terminal of the magneto and the other to the automobile frame.

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