Hartmann & Braun, Bockenheim- Frankfort o. M. 



175 



79. Voltmeter and Amperemeter for continuous and alter- 

 nating currents. Circular case. Two different sizes. Reciprocal action 

 within a solenoid (attraction or repulsion) of two or more extremely 

 light segments of a cylinder shell of soft iron. Index on aluminium 

 center with jewelled steel points. 



In spite of the presence of iron these instruments are available 

 both for continuous and alternating currents, with the same calibration, 

 irrespective of the rapidity of pole reversion. Range from 1 to 10-fold. 



Made as a voltmeter in 15 differently calibrated forms, from 0.5 

 to 3000 volts. 



Made as an amperemeter, in, 16 differently calibrated, forms, from 

 0.5 to 3000 amp. 



91. 



80. Double Solenoid Voltmeter and Amperemeter for conti- 

 nuous and alternating currents. 



An annular iron core of extremely small polar distance is excentri- 

 cally pivoted between two conaxial solenoids; the current tends to place 

 the core conaxial with respect to the solenoids. 



81. Hot wire Voltmeter and Amperemeter, for continuous 

 and alternating currents; with small consumption of energy. In the case of 

 the voltmeters the bend of a short, very thin wire, through which the 

 current passes, is heated and the amount of the expansion is transmitted 

 by a peculiar device to the axle of the pointer. These voltmeters are 

 by means of suitable introduction of resistances calibrated to indicate 

 from 3 to 3000 volts. 



In the case of amperemeters a shunt is added to the heating wire 

 or a heating wire of suitable thickness is made to heat a metal tube 

 fixed at one end and the expansion of the latter is transmitted by means 

 of a contact lever to the center of the index. 



