Electrical Products

OhmMapper Capacitively Coupled Resistivity System

Fast resistivity measurements without probes

Resources:

The new Geometrics OhmMapper is a  capacitively coupled resistivity meter that measures  the electrical properties of rocks and soil without cumbersome ground stakes used in  traditional resistivity surveys. A simple coaxial-cable array with transmitter and  receiver sections is pulled along the ground either by a single person or attached to an  all-terrain vehicle. Data collection is many times faster than systems using conventional  DC resistivity.

Features:
Ohmphoto.jpg (21830 bytes)
  • Full dipole-dipole resistivity profile can be done in a  fraction of the time taken for traditional resistivity measurement.
  • Operates over frozen ground, ice, concrete, and other areas  where grounded dipole measurements are difficult to make.
  • Data is logged to Geometrics DataMapper logging console for  easy tracking and positioning of resistivity data.
  • Post acquisition processing is facilitated with Geometrics  DataMap software for editing of data, positioning of data, and creating output compatible  with third-party mapping and processing software.

Configurations:

This diagram shows the physical configuration of the OhmMapper TR1.  At the far end of the sensor array is the transmitter. This consists of the transmitter  electronics and batteries along with two transmitting dipole cables. The transmitter is  towed via the nonconductive tow link connecting it to the receiver. The receiver consists  of the transmitter electronics, batteries, and dipole cables. The received voltage level  is converted to a digital signal in the receiver and transmitter to the data logger worn  by the operator. The operator carries the data-logging console (DataMapper) at his waist.

Specifications:

Operating principle:

 Constant-current capacitively-coupled,  dipole-dipole resistivity

Operating range:

 Less than 1 Ohm-meters to greater than  100,000 Ohm-meters

Cycle Rate:

 Signal sample and data logging rate at  2 times per second

Data Storage:

2 Mbytes of nonvolatile RAM

Audio Output:

Metronome, signal amplitude, disconnect

Visual Output:

 320 by 200 graphic LCD display,  daylight visible with selectable outputs for:

Data Display: 5 line profiles of resistivity

  1. All system setup functions
  2. All survey functions: survey profile number and  direction, station number, test line number
  3. Survey monitor functions
  4. Survey diagnostics

Internal Clock:

Resolution of 0.1 drift <1  second/day.

Weight:
  1. Console: 1.6 kg
  2. Transmitter: 2 kg
  3. Receiver: 2 kg
  4. Battery pack/Harness: 1.6 kg
  5. Array Depressor Weight: 3 kg (estimate)

Transmitter specifications:
  1. Frequency under 18 kHz
  2. Output current: variable from 16 mA to 0.25 mA

Receiver Specifications:
  1. Dipole lengths: 5 m, 10 m, 15 m, 20 m, longer lengths  optional
  2. Input Specifications: 5 Mhos
  3. Measured Voltage Accuracy: 1%
  4. Input Voltage Range 0-2 V RMS
  5. Power Line Rejections: >100 dB

Spacing:

    Variable Spacing.

Dimensions:
  1. Console: 15 x 8 x 28 cm
  2. Battery: 8 x 14 x 20 cm

Battery:
  1. Transmitter receiver: 12 V DC
  2. Console: 28 V DC
  3. Internal battery backup for clock and nonvolatile RAM

Survey Types:

    Continuous, constant-offset  dipole-dipole resistivity. (Multi-line with constant transmitter-receiver spacing for  plan-view mapping.)

    Variable-offset,  dipole-dipole resistivity. (Variable transmitter-receiver spacing for multiple passes on a  single profile line to create a pseudosection.)
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