138 



KLKCTMCAL MEASUREMENTS 



effect, as well as good cooling, the strip is made very thin. The 

 potential leads are brought out so that they do not include any 

 flux and the current leads are strips of copper with very thin 

 insulation between them so that they set up no appreciable stray 

 field. 



When the shunts are immersed in oil, 1 watt per square centi- 

 meter of cooling surface is allowed. Of course only one side of 



FIG. 62. Low-resistance shunts for alternating-current measurements. 

 Designed at the Reichsanstalt. 



the sheet is effective in the cooling. The thickness of the mica 

 insulation between the leaves is from 0.1 to 0.3 mm.; the distance 

 between the resistance strips is from 0.2 to 0.5 mm. In the 

 0.001-ohm shunts the resistance strip is 69 cm. long, 14.5 cm. 

 wide and 0.02 cm. thick; the self-inductance is 5.1 cm. As this 

 resistance is intended for currents up to 1,000 amp. the loss at 

 full load is 1 kw. 



If the resistance is above 0.003 ohms, the construction is that 

 shown at B in Fig. 62; ze and zf are the copper current leads. 



