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Antique Army Mine Blasting Galvanometer 1800’s

$382

Posted 28 days ago in Queen Creek, AZ

Condition: Used (normal wear)

Listed in categories: Collectibles & Art - Antiques - Other - Antiques

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Antique Army Mine Blasting Galvanometer 1800’s

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Type

Mining

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Description

Still works old antique mine blasting galvanometer Bethlehem Instrument Co., Inc. Blasting Galvanometer The battery is a specialized Silver Chloride cell, NSN: 6135-00-128-1632, Open Circuit Voltage: 1.0261. The top scale is resistance in Ohms. Zero Ohms at full scale and 112 Ohms at half scale. 112 Ohms is the nominal internal resistance of the meter. If the battery leads are shorted the resistance between the test terminals is 117.5 Ohms. Minus the two resistors (112 Ohms) leaves 5.5 Ohms as the meter internal resistance. 1.0261 Volts / 117.5 = 8.73 mA full scale. This is a safe current for a No. 6 blasting cap, so a guess would be that it takes more than 90 mA (10 X safe current) to set it off. The bottom scale goes from 0 at the left (zero current) to 25 at the right (8.73 mA).

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