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4.
Apply a coat of paint over the primed areas.
In severe environments and for long term protection, the space between the coil
housing and the Model 4100 gauge, and the space between the cover plate and
the Model 4150 gauge, can be filled with a stiff grease (e.g., axle grease). For
further protection, the entire assembly can be covered by a layer of insulating
mastic (e.g. Plymouth 10 Plyseal), which is available from
3.5 PROTECTION FROM ELECTRICAL NOISE
Be sure to install instrument cables as far away as possible from sources of
electrical interference such as power lines, generators, motors, transformers, arc
welders, etc. Cables should never be buried or run with AC power lines. Doing
so will cause the instrument cables to pick up the frequency noise from the
power cable, and this will likely make obtaining a stable reading difficult.
3.6 PROTECTION FROM SUNLIGHT AND TEMPERATURE CHANGES
If attached to a steel structure, the thermal coefficient of expansion of the steel
vibrating wire inside the instrument is the same as that for the structure. This
means that no temperature correction for the measured strain is required when
calculating load-induced strains. However, this is only true if the wire and the
underlying steel structure are at the same temperature. If sunlight is allowed to
impinge directly onto the gauge, it could elevate the temperature of the wire
above the surrounding steel and cause large changes in apparent strain.
Therefore, always shield strain gauges from direct sunlight. Protection from
thermal effects is best provided by covering the gauges with a layer of insulating
material such as Polystyrene foam or fiberglass.
3.7 LIGHTNING PROTECTION
Unlike numerous other types of instrumentation available from
vibrating wire strain instruments do not have any integral lightning protection
components, such as transorbs or plasma surge arrestors.
SUGGESTED LIGHTNING PROTECTION OPTIONS:
■
Lighting arrestor boards and enclosures are available from
units install where the instrument cable exits the structure being monitored.
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.
MODEL 4100/4150 SERIES VIBRATING WIRE STRAIN GAUGES | INSTRUMENT PROTECTION | 7
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GEOKON
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GEOKON
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GEOKON
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