MoHo s.r.l.

- Digital System for Geoelectrical Surveys

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A new approach to geoelectrical surveying. Electra is the MoHo’s digital system for geoelectrical surveys. A number of unique features make it a very special georesistivimeter. Acquisition times are considerably reduced due to the simultaneous acquisition on all channels and the use of alternate current. Weight, size and consumption are orders of magnitude lower than traditional systems. Data quality is improved due to signal digitization directly at the receivers and to data averaging techniques.

ELECTRA is a multichannel digital resistivimeter, composed of a central unit and a very light cable along which small moduli are connected to the electrodes. Each module has the double function of injecting current in the subsoil and of receiving the signal, which is transmitted to the central unit in a digital form.

The digital transmission prevents any cross-talk and signal degradation and warrants high quality measurements even by injecting very small currents.

ELECTRA can input any current in the subsoil: measurements in alternate current are faster and more precise, since no time is needed for the signal stabilization and induced polarization of the electrodes is minimized.

Search for water, cavities, ores, environmental problems, archaeological research, foundation and wall integrity studies are only a few of the fields where the geoelectrical prospection at small and large scale can be of big help.

ELECTRA permits the investigation of the subsoil and anthropic artifacts with efficiency and ease of use.

With ELECTRA, the classical Wenner, Schlumberger, dipole-dipole, pole-dipole, spontaneous potentials, induced polarization, methods (and more) can be performed in a fully automatic way.

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ELECTRA exists also in the MATRIX version (central units + small cables to the electrodes) for small scale and high resolution applications.

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Two new concepts for geoelectrical surveying: Electra and Electra Matrix

Search for water, cavities, ores, environmental problems, archaeological research, foundation and wall integrity studies are only a few of the fields where the geoelectrical prospection at small and large scale can be of big help.

More than 30 years’ experience of the developers in the medical microelectronic field have been translated to the Geophysical sector to create Electra and Electra Matrix: two new systems for 2D and 3D electrical tomography.

Electra and Electra Matrix allow to investigate the subsoil and anthropic artifacts with an uncommon easiness of use.

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Electra is composed of a central unit (2 kg, rechargeable battery included) to be connected to any PC and of a very light cable along which the small moduli to be connected to the electrodes are attached. Each module has the double function of injecting current in the subsoil and of receiving the signal, by amplifying and digitizing it directly at the source (the electrodes). The signal is then transmitted to the central unit in a digital form through the very simple, light and high performing main cable, which prevents any cross-talk and signal degradation phenomenon.

Electra can inject any current in the subsoil (from continuous to alternate) at different frequencies. Measurements in alternate current are faster and more precise, because no time is needed for the signal stabilization and induced polarization of the electrodes is minimized. The possibility to inject different waveforms also opens the way to new studies on the relations between the energization procedures and the subsoil response.

A unique feature of Electra is the simultaneous acquisition of the signal from all the channels of the deployment, both of electric injection and of measurement. This greatly reduces acquisition time, particularly in some configurations.

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The dedicated acquisition and visualization software allows to set any energization/measurement geometry in an intuitive way. The classical methods of the geoelectric prospection (Wenner, Schlumberger, dipole-dipole, poledipole, spontaneous potentials, induced polarization in the frequency domain, etc.) can be performed in a fully automatic way.

The possibility to record the signal from all channels continuously, with no time limits, opens the way to the study of the time dependency of the monitored parameters (e.g. spontaneous potential).

The fully digital nature of the system, the use of alternate current, the averaging techniques, the simultaneous measurements at all the electrodes increase the signal-tonoise ratio and allow to obtain excellent results by inputting in the subsoil fractions of energy compared to traditional systems.

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The ideas behind Electra:

  1. improve data quality
  2. strongly decrease weight, size, power consumption
  3. offer new measurement procedures by keeping the system easy and intuitive

  • POWER: internal rechargeable 12 V battery,  included in the central unit
  • A/D CONVERSION: synchronous on all energization and measurement modules
  • MAX CHANNEL NO.: 255 (nominal) in groups of 24 or 32

CENTRAL UNIT

  • SIZE: 24 x 20 x 8 cm, weight 2.3 kg
  • WAVEFORM: D/A converter with continuous control of current and voltage (feedback)
  • CURRENT: ±200 mA, typical usage values ±10 mA
  • INPUT FREQUENCY: 1-32 Hz
  • OUTPUT: 4 ports or cable
  • OUTPUT TENSION: automatic, up to 400 V p.p.

MODULES

  • SIZE: 5 x 6 x 2 cm
  • INPUT: automatically commutable among 4 functions (+ and - stimuli, reference, input)
  • INPUT IMPEDANCE: 100 MW on 6 V dynamic range, 100 kW on 12 V dynamic range
  • SAMPLING: synchronous on all modules at 256-512 Hz
  • DATA TRANSMISSION: continuous and in real time to the central unit and the PC

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