USER GUIDE PIEZOMETRE
33-30-077-
Piezomètre_UTI UK
Rev : 3 Page 4/41
nke Tel +33 (0)2-97-36-10-12 Fax +33 (0)2-97-36-55-17 http://www.nke-nstrumentation.com PAGE 4/41
1. INTRODUCTION
The piezometer is an instrument that consists of an expendable instrumented lance driven into
the sediment by gravity, based on the principle of a Kullenberg corer, and a retrievable module
that includes data storage and power supply. The sensors in the lance (torque, differential
pressure and temperature) are spaced at predetermined intervals in the lance.
The differential pressure sensors measure the difference between the hydrostatic pressure at the
water/sediment interface and the pressure in the sediment at the sensor via a porous stone filter.
The temperature sensor located as close to the porous stone as possible measures the
temperature of the sediment.
The measurements provided by the pressure/temperature sensors are sampled at regular
intervals.
The data is stored in digital format in a container that also houses the power supply.
After triggering an acoustic release, this container rises to the surface using buoyancy. Surface
tracking is provided by a system that comprises a flag, a beacon and a VHF radio.
The piezometer can be used in "yo-yo" mode, whereby it remains connected to the coring cable,
with a measurement time of a few hours, while the ship remains directly above the station. Once
the measurement is made, the piezometer and its tube are retrieved by heaving the coring cable.
In "yo-yo" mode, the acoustic release system, surface tracking system and trip gear are not
used.
In both modes, a query sent to an acoustic release may provide the tilting angle of the system
after it has sunk into the sediment.
The optional "MDS module" can manage up to two measuring systems at the same pressure
and provides data storage. It also includes an interface for configuration and calibration of the
instrument, as well as an interface to connect the instrument to a potential ocean bottom
observatory, which will provide real time data transmission to the user.
The instrumented lance has "connections" spaced at predetermined intervals, which
accommodate two types of sensors:
- A temperature sensor (CTN) with a measurement range of 0°C to +50°C
- A differential pressure sensor +/- 2 bar
Inclinometers integrated to the module indicate if the system is poorly sunk (e.g. buckling)..
