Principle of Operation

An iGrav operates similarly to a spring-type gravity meter but differs fundamentally in that it does not use a physical metal spring. Instead, the mechanical spring in a conventional spring gravimeter is replaced by the magnetic levitation of a superconducting niobium sphere within the field of two superconducting, persistently connected coils. By utilizing the perfect stability of superconducting currents, a completely stable, non-mechanical spring is created.

The system operates in liquid helium to achieve the superconducting state.

To maintain this state, the iGrav sensor is operated at 4.2 K inside a 16-liter dewar filled with liquid helium and integrated with a 4 K refrigeration system. In this "closed-cycle" system, the 4 K refrigerator re-liquefies gaseous helium in the so-called neck of the dewar, allowing it to drip back into the storage volume. As a result, no helium is lost during operation.

Operating an iGrav is complex and, due to the 4 K cooling system, relatively energy-intensive. Additionally, a temperature-stable housing is typically required.

• Projects:  

  • HYGRA

   

• Study area:  

  • Geodetic Observatory Wettzell, Germany
  • South African Geodynamic Observatory (SAGOS)
  • TERENO - Terrestrial Environmental Observatories
  • Geothermal Technologies: continuous microgravity monitoring for integrated mass and stress balance analysis in a volcanic geothermal field - contribution for exploitation sustainability in Indonesia and Iceland - MikroGraviMoTiS

   

Manufacturer: GWR Instruments Inc.

The section Hydrology currently operates four systems of this type (iGrav006, iGrav015, iGrav032 & iGrav033).