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PIEZOMETER

Interstitial pressure measurement down to 6000m. Device developed by the IFREMER, manufactured and marketed by nke Instrumentation.

This new piezometer allows two types of measurements to be carried out:

  • Short-term measurement:

To determine the hydraulic parameters of the sediments based on the dissipation of the interstitial pressure generated by the sinking of the piezometer;

To identify and quantify the hydraulic gradients in the sedimentary layers.

  • Long-term measurement:

To detect the processes responsible for interstitial overpressures (thermal gradient, dissociation of gas hydrates, seismic shock, fluid migration...)

To quantify the effect of these unpredictable processes on the generation and dissipation of interstitial overpressures.

Data logging card (MDS module)

The MDS module allows the measurement acquisition rate to be set, and the values to be recorded on a memory card (e.g. SD Card). This module is located in a waterproof Titanium container in the retrievable part.

  • Maximum sampling rate: 1s
  • Max. number of MPTs: 12
  • Autonomy with 5 MPTs: 200 days at 1s rate, 800 days at 60s rate
  • Storage memory size: 1 to 8 Gb SD card
  • Time setting: via PC or GPS clock

Sensors

The sensors are located in the tip of the piezometer. The differential pressure sensor is subjected to hydrostation pressure and sediment pressure.

  • differential pressure: Keller PD-10LH
    • accuracy: +/- 0.5KPa
    • measurement range: +/-200kPa (1kPa = 10mb)
    • Maximum pressure: -300kPa / + 400kPa
  • temperature:
    • accuracy: +/- 0.05°C (0.1% over the measurement range)
    • measurement range: 0°C to +50°C (accuracy: +/- 0.05°C)

The tip of the piezometer is made up of tubes and connecting elements (sleeve). An electronic board is integrated in the sleeve, which digitizes the data from the differential pressure sensor and temperature probe (MPT card) The sleeve provides the mechanical link between the tubes, and the assembly forms the tip.

A digital link bus interconnects the digitizing boards; this link is controlled by a data storage module (MDS) located in the retrievable assembly.

Digitizing board (MPT module)

The MPT module digitizes two sensors and sends the result to an RS482 digital bus. This module and all the sensors operate under balanced pressure.

Tip

The tip is made up of an assembly of tubes joined together by a connecting sleeve. The tubes that make up the tip are available in various lengths:

  • Tube diameter: .ext 60mm / int 47mm
  • First tube length: 75cm
  • Standard tube length: 75, 150 and 300cm
  • Tip length: 45cm

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