. Electrical instruments and telephones of the Signal corps . ke the placeof the galvanometer, balance being indicated by the cessation of theclicks and frying sound when the toucher has reached the propergraduation on the l)iidi>e wire. ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. 271 DIRECTIONS FOR USING THE OHMMETER, MODEL 1904. (See figs. 185, 189, and 190.) Connect a battery, preferably a couple of dry cells external to thetesting- set. to posts marked B A and the unknown resistance to postsAl, Ao. If the resistance is small, insert the plug at 10, and if largeat 100. Depress the ke
. Electrical instruments and telephones of the Signal corps . ke the placeof the galvanometer, balance being indicated by the cessation of theclicks and frying sound when the toucher has reached the propergraduation on the l)iidi>e wire. ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. 271 DIRECTIONS FOR USING THE OHMMETER, MODEL 1904. (See figs. 185, 189, and 190.) Connect a battery, preferably a couple of dry cells external to thetesting- set. to posts marked B A and the unknown resistance to postsAl, Ao. If the resistance is small, insert the plug at 10, and if largeat 100. Depress the key and operate catch; then draw the styluslightly across the horizontal scale, touching the convolutions of wireuntil the galvanometer reverses its deflection. ]Multiples of 50 are read on the horizontal scale, and fractions ofa turn on the drum at the right. The tabular number correspondingto this number, as found in the table on the lid of the ohmmeter, whenmultiplied by 10 or 100, depending on whether the plug is at 10 or100. Avill oive the correct ISO.—Circuit of olimmeter. model 1904. For example, if the balance is found between convolutions Nos. 150and 200 on the horizontal scale and the drum scale reads 46, the exactreading is 196. Referring to the table, the number corresponding tothis is and the resistance, if the plug is inserted in 10, Avill ohms; or, if the plug is inserted in 100, will be ohms. A telephone receiver may be in place of the galvanometer inthe ohmmeter by disconnecting one of the cords from the post marked Tel.^ and connecting the receiver to those posts. The portable galvanometer may be used in the place of the galva-nometer in the ohunueter by proceeding as for the receiver. In thiscase it would be advisable, however, to make use of the galvanometerwith shunt. 272 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. The method of measuring conductor resistance of a cable is shownin figure 1S»0. The copper resistance i
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