VW2100 Vibrating Wire Piezometer
RST Instruments Ltd.
Page 24
3
Avoid traversing transition zones in the fill where large differential settlements
could occur and create excessive strain in the cable. If cables must traverse
these zones, install them with additional length for cable snaking which will allow
slack for settlement to occur, rather than creating excessive cable strain.
4
Avoid cable splices. Only use an RST ELSPLICE4 Electrical Cable Splice Kit for
Vibrating Wire Cables if splicing is required. The kit will ensure a strong and
waterproof splice.
5
Spend time on the design of the cable layout in the trench. Avoid overlaying or
crossing the cable runs on top of each other. If overlaying and crossing cannot
be avoided, the cables must be separated by a 50 mm blanket of compacted
fine-grained soil.
6
Use horizontal or vertical snaking of the cable within trenches to provide a certain
amount of potential slack to avoid overstressing the cables during backfilling and
the subsequent fill placement.
◼
For most materials, a pitch of 1.8 m with an amplitude of 0.4 m will be
suitable.
◼
In very wet clays, which could be subject to settlement, increase the
amplitude from 0.4 m to between 0.6 m and 1.0 m.
7
During cable routing, read the instruments at regular intervals to ensure their
continued function. This is especially important prior to backfilling any trenches.
5.9
L
IGHTNING
P
ROTECTION
All RST Model 2100 Vibrating Wire Piezometers have highly reliable surge/lightning
protection incorporated into the sensor circuitry. This surge protection is adequate for
most applications. The entire instrumentation system needs to be considered to be
effectively isolated in all situations, especially when multiple instruments are
connected by wires into a large area network. The network could be subject to
transient and/or induced currents which could damage sensors and/or data
acquisition equipment.
In cases where there may be additional risks of surge damage to the network and/or
data loss, the following suggestions for additional surge protection are provided:
•
If a vibrating wire piezometer is connected to a terminal box or multiplexer on
surface, components such as plasma surge arrestors (spark gaps) could be
installed in the terminal box/multiplexer to provide an increased measure of
transient protection. Terminal boxes and multiplexers available from RST provide
built-in locations for the installation of these surge protection devices.
•
Lightning arrestor boards and enclosures are available from RST that install at
the exit point of an instrument cable from a drill hole or structure. The enclosure
can be easily accessed and opened so that in the event that the protection board
(Surge 4C) is damaged by a surge event, the user may easily service the
components or replace the board. A connection is made between this enclosure