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A number of dataloggers are capable of withstanding harsh environments, including hot and
cold temperatures and high relative humidity. Such data collecting platforms should be considered
as an alternative to transmitting small analog signals through long cables back to a central
facility. Once the data is collected it can be transferred much more reliably as a digital signal.
(3) All cables that run along the ground should be buried to a depth where they will not normally
be disturbed by routine maintenance operations. Cables not specifically capable of withstanding
burial should be placed in conduits. This increases the overall neatness of the site and reduces
the danger of personnel being injured or the cable being accidentally pulled from the instrument
when overly strained. When effort is being expended to place cables underground, extra capacity
for future expansion should be considered.
(4) Signal cables should be run through separate conduits from electrical power cables whenever
possible. Cables should cross at right angles to reduce electrical interference. When such
arrangements are impractical, specially shielded cables should be used.
(5) At remote locations, secondary signal processing and serial or satellite communications should
be considered to transfer data to a permanent storage device. In the design of such a system,
the potential for communication failures must be considered in the overall plan.
Cabling between the instrument and the data acquisition system should be carefully grounded and
protected against lightning. Figure 3.4 gives a general illustration on how the grounding and lightning
protection should be placed within the instrument/cable/acquisition system configuration.
Whenever a system is wired, care must be taken to accurately map both the physical location of the
cables (especially if underground) and the connections running from the instruments through the junction
boxes to the data acquisition system.
3.5.3.2 Electrical Cable
Electricity should be available at the location of the sensors, both for the operation of the instruments
and for use in the maintenance of the observation platform. Separate circuits for each set of instruments
is desirable, but not always practical. Whenever redundant instrumentation is used, it should be operated
on separate electrical circuits. All electrical wiring should meet or exceed local electrical codes. The
local electrical utility, an electrical engineer or qualified electrician should be able to provide information
on local electrical regulations and provide an estimate of the electrical consumption of the site.
Just as in the case of the signal cables, all electrical cables should be buried or securely fastened to
the instrument mounting platforms. Furthermore, for safety, switches or circuit breakers should be installed
close to the equipment for easy servicing.
The quality of power supplied to the instruments should be the same as described in Section 3.4.2.
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