Geology Reference
In-Depth Information
more difficult. The foldable proton magnetometer staff, discussed below, is
a case in point.
If different instruments can, in principle, do the same job to the same
standards, practical considerations become paramount. Some of these are
listed below:
Serviceability:
Is the manual comprehensive and comprehensible? Is a
breakdown likely to be repairable in the field? Are there facilities for
repairing major failures in the country of use or would the instrument
have to be sent overseas, risking long delays
en route
and in customs?
Reliability is vital, but some manufacturers seem to use their customers
to evaluate prototypes.
Power supplies:
If dry batteries are used, are they of types that are easy
to replace or will they be impossible to find outside major cities? If
rechargeable batteries are used, how heavy are they, and will they be ac-
ceptable for airline transportation? In either case, how long will they keep
the instruments working at the temperatures expected in the field? Battery
life is reduced in cold climates, and the reduction can be dramatic if the
battery is used to keep the instrument at a constant temperature, since not
only is the available power reduced but the demands made are increased.
Data displays:
Are these clearly legible under all circumstances? A torch
is needed to read some displays in poor light, and others are almost
invisible in bright sunlight. Large displays are needed if continuous traces
or profiles are to be shown, but can exhaust batteries very quickly.
Hard copy:
If hard-copy records can be produced directly from the field
instrument, are they of adequate quality? Are they truly permanent, or
will they become illegible if they get wet or are abraded?
Comfort:
Is prolonged use likely to cripple the operator? Some instruments
are designed to be suspended on a strap passing across the back of the
neck. This is tiring under any circumstances and can cause actual medical
problems if the instrument has to be levelled by bracing it against the
strap. Passing the strap over one shoulder and under the other arm may
reduce the strain, but not all instruments are easy to operate when carried
in this way.
Convenience:
If the instrument is placed on the ground, will it stand upright?
Is the cable then long enough to reach the sensor in its normal operating
position? If the sensor is mounted on a tripod or pole, is this strong
enough? The traditional magnetometer pole, made up of sections that
screwed together and ended in a spike that could be stuck into soft ground,
has now been largely replaced by unspiked hinged rods that are more
awkward to stow away, much more fragile (the hinges can twist and break),
can only be used if fully extended and must be supported at all times.
