. The Street railway journal . heir shunts can be adjusted to correspond to thecurrent flowing in the rails. For instance, the normal currentin the local circuit in each rail—that is, from one wheelinto the rail and back through the other wheel on thesame side, and which is provided by the motor-dynamoon the test car—is 200 amps. This current is, of course,increased by the return currents of all the other cars onthe system, so that the voltmeter readings depend uponthe total amount of current in the rail. For this reasonthe voltmeters are shunted so that the full scale can beused for measuring
. The Street railway journal . heir shunts can be adjusted to correspond to thecurrent flowing in the rails. For instance, the normal currentin the local circuit in each rail—that is, from one wheelinto the rail and back through the other wheel on thesame side, and which is provided by the motor-dynamoon the test car—is 200 amps. This current is, of course,increased by the return currents of all the other cars onthe system, so that the voltmeter readings depend uponthe total amount of current in the rail. For this reasonthe voltmeters are shunted so that the full scale can beused for measuring the variations in the voltage aroundeach joint. As a rule, each joint is measured on therecord by the proportion which its resistance bears to 4 ft. ofstraight track. The record sheet moves 1 in. while the carprogresses 100 ft., giving the bond record the scale of 1 in. to100 ft. of track. As the voltmeters might be injured by an excess of voltagecaused by a defective bond, an automatic cut-out (see Fig. 2) induction Coil. * See Street Railway Journal, Feb. 3, 1900, page 126; also Herricks Elec-tric Railway Hand Book, page 40. Street By .Journal FIG. 2.—DIAGRAM OF CONNECTIONS FOR BOND TEST is inserted in the circuit of each so that it cuts out the instru-ment before it can swing to full scale. This automatic cut-outis also electrically connected to a pen which makes a continuousstraight line on the record when the track is in good condition,but a side dash, as shown, in the typical record sheet, Fig. 4,when the car passes any joint that has over 150 millivolts drop,or is practically open. When this automatic cut-out opens itcloses another circuit which operates the valve of an air pump,by which a jet of whitewash is squirted on to the roadbed ad-jacent to the defective joint. In this way an open joint canbe located the following day by the trackmen without referenceto the autographic record, which is kept in the roadmastersoffice. The autographic record gives more inform
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
