. The street railway review . be adjusted to closer measure-ments. Since zero instruments may be set to read zeroat normal current or voltage, and may be so sensitve that a small variation will give a large deflection whichmay be seen across the room, they are of special value inthe entwine room or dynamo room, where the machinesmust be regulated to give constant current or constantpotential. What is commonly called an electric current is materi-ally diiferent from a current of water in that it cannot beobserved by the senses directly. It can only be detectedand measured indirectly by its effe
. The street railway review . be adjusted to closer measure-ments. Since zero instruments may be set to read zeroat normal current or voltage, and may be so sensitve that a small variation will give a large deflection whichmay be seen across the room, they are of special value inthe entwine room or dynamo room, where the machinesmust be regulated to give constant current or constantpotential. What is commonly called an electric current is materi-ally diiferent from a current of water in that it cannot beobserved by the senses directly. It can only be detectedand measured indirectly by its effects. An electric cur-. WESTON A. C. AND D. C. VOLTMETER. rent heats the conductor, produces a magnetic field in thesurrounding space, gives the conductor an electric chargewhich attracts or repels other charged conductors, andchemically acts upon any portion of the conductor thatmay be aliquid (unless the liquid be an elementary sub-stance). All these effects are proportional to the quantityof current, hence any one of them may be used as ameasure of the current. Instruments based upon these effects may be arrangedfor use either as ammeters or voltmeters. For use asammeters either the conductors in the instruments aremade large enough to carry the entire current withoutintroducing undue resistance and without being over-heated; or only a known fractional amount of the totalcurrent passes through the instrument, the remainderpassing through a shunt. When used as voltmeters theyare really only modified ammeters, the conductor being afine wire of high resistance (an external resistance beingsometimes added), s
Size: 2273px × 1099px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1800, bookdecade1890, booksubjectstreetrailroads
