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Plate 238:  Wiring the point motors through the distribution center, Part 16: preparing for an electrical continuity test
(This plate added NOV 2003)

As we continue with the wiring, we want to be certain our connections are correct by running electrical continuity tests. For this purpose, we have decided to use an ohmmeter (resistance tester). The tester shown in the accompanying picture uses a d'Arsonval-type meter movement, named in honor of Professor Jacques-Arsene d'Arsonval, the distinguished French inventor, physicist and physiologist who patented this type of meter in the nineteenth century. Professor d'Arsonval also performed early research in OTEC (Ocean Thermal Energy Conversion), a method of obtaining heat from ocean waters.

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Our meter is undergoing a "zero-adjustment" in this picture. The test leads have been connected together in order to provide a temporary "zero-resistance" circuit, and the meter's pointer has been positioned at the zero-point by means of the adjustment wheel. When we test for continuity, we look for a reading of "true zero" resistance; this is why we first adjust the meter to the zero-point.

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