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The enclosure has a removable top to allow the customer to service the
components or replace the board in the event that the unit is damaged by a
lightning strike. A connection is made between the enclosure and earth
ground to facilitate the passing of transients away from the instruments.
See the figure below.
■
Plasma surge arrestors can be epoxied into the instrument cable, close to
the instrument. A ground strap then connects the surge arrestor to an earth
ground, such as a grounding stake or the steel structure.
Consult the factory for additional information on available lightning protection.
Terminal Box
or Multiplexer
FIGURE 8: Lightning Protection Scheme
MODEL 4420 VIBRATING WIRE CRACKMETER | INSTRUMENT PROTECTION | 9
Structure
Crackmeter
Lab3
Copper Ground Wire
Enclosure
Instrument Cable
(usually buried)
Ground Connections
8:
Crack
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