PASI - Model POLARES - Resistivity Meter with Multi Electrode
From Electrical Imaging
Applications: Shallow detailed investigations of pollutant plums in the ground. Archaeological surveys. Waste site deposit monitoring. Mapping and monitoring of salty water contamination of groundwater reservoirs along coastal areas.
Till this moment the use of Electrical Resistivity Tomography (ERT) for geology has always been basically the same since its debut, based on the original vertical Electrical Soundings (VES) principles: applying a continuous current to two stakes inserted into the ground and measuring the corresponding voltage between other two. The applied current and thus the relative tension have always been continuous, with an inversion in polarity for each measure. The new tool POLARES uses an alternate current, instead, sinusoidal type, with an adjustable frequency.
- Advantages of the new POLARES system
Considering the higher complexity of the device, the alternating current stimulation has shown particular advantages with regard to the faster implementation of the measures with the same quality of results. This higher speed can reduce the time required to perform a set of field measurements by a factor of at least 10 (or 20 in most cases!) in respect to traditional system. Moreover, the measure of the relationship between the detected voltage and the injected current, in sinusoidal state, both as form and as a phase (delay of a signal over the other), these two pieces of information, with only one measure, allow the simultaneous detection of the resistivity and the induced polarization of the ground.
- POLARES Benefits: The proposed new instrument brings together into a single small and lightweight case the management and control system and the power section, the only external part is the signal switching system, so to offer the a great flexibility.
Available configurations: from 16 to 256 electrodes.
Compared to the previous generations, the new electrical imaging system POLARES is lighter, smaller, faster and more reliable. The user interface is built with a high brightness LCD monitor with touch screen, all operations are made without using either the mouse or keyboard. The use of an embedded ultra low power PC combined with the lack of fans and traditional HD, correlate with the using of an open source operating system (Linux), provides a far superior battery life and overall reliability improved. The only interface to the outside is a USB port to which you can connect a number of different devices such as pen drives for data storage, network interfaces, WiFi, Bluetooth, GPS antennas, keypads, and more. Another advantage of not using a traditional PC is the wider range of working temperature and humidity that makes POLARES the best solution even in marsh environmental conditions.
- CPU: Arm 9 32 bit
- Operating system: Linux
- Display: QVGA 5.7” with LED background lighting
- Touch Screen: 4 wire resistive
- Data storage: Solid state flash memory
- External data ports: USB host 1.1
- Connectivity: USB key
- Optional connectivity: Ethernet, Wi-Fi, Bluetooth, RS232, RS485, USB cli-ent, GPS, etc.
- GPS: Integrated receiver for georeference of measures
- DSP: Freescale (Motorola) 120 MIPS
- Converters: A/D 16 bit SAR and D/A to 16 bit
- Voltage measurement range: 300V, 30V, 3V
- Current measurement range: 3A, 300mA, 30mA
- Frequencies that can be generated: 114Hz, 28.6Hz, 7.15Hz, 1.79Hz, 0.45Hz, 0.11Hz
- Measurement soundness check: DC component, distortion, background noise, phase excess, module sigma, phase sigma
- Maximum number of spikes: Unlimited
- Maximum number of scans per measurement: > 40,000
- Results that can be stored to memory (scan): > 200,000
- Peak voltage that can be generated: 700 Vpp
- Peak current that can be generated: 2 A
- Peak power output that can be generated: 200 W
- Thermal protections: Heatsink and inside case alarms and system shut-down
- Power supply: 8.5V= / 15V= lead or lithium batteries, 30 A internal fuse, protection against polarity inversions
- Operating temperature: -20°C / 50 °C outside
- Dimensions and weight: 410x300x170mm; 6kg
- Shallow detailed investigations of pollutant plums in the ground
- Archeological surveys
- Waste site doposit monitoring
- Mapping and monitoring of salty water contamination of groundwater reservoirs
Electrical imaging applied to geophysical exploration has been using the same traditional method for acquiring data of the traditional VES soundings with 4 electrodes: an electric current was applied between two electrodes and the correspondent voltage was measured between other two electrodes inserted in the ground. Applied current and the related voltage were always continuous, with an inversion of polarity for each measurement. POLARES 2.0 uses a sinusoidal alternate current of variable frequency. Even if the instrument designing could be more complicated, the use of alternate current had shown great vantages, in particular considering the absolutely greater velocity of acquisitions, that may increase of at least 10 times in respect of standard DC measuring time. Moreover, the measurement of the ratio between Voltage and Current can be done in a sinusoidal condition for both module and phase (delay of a signal in respect of the other); these two information obtainable with a single measurement, allow the system to acquire both resistivity and IP data.
The survey purpose was to identify the lithology of the ground in a building area, in addition and support of Static Penetrometer Tests and Vs30 seismic profiles made on the same line. The high resolution survey with 48 electrodes with 2m spacing (total length 94 m), made using Wenner- Schluberger method, reached a medium exploration depth of approx.15 m from the surface.
3D Resistivity profiles, test site CNR (National Research Center) Torino. Sandpit surrounded by a coarse-grained silty-sandy soil type.
The site shows a net anomaly of resistivity, since the high permeability of the sand with which is filled the tank causes the latter is in a condition of minimum saturation (especially during the dry season, in which was made the survey) compared to the surrounding soil.
Compact, easy-to-use, the POLARES IMAGING SYSTEM can measures and display: ground resistance, current, voltage, self potential and standard deviations and IP. Computation of the apparent resistivity for the most used configurations of electrodes arrays: Schlumberger, Wenner, Dipole-Dipole (User defined configurations are also available trough Utility Software delivered with the instruments) With its automatic “multiplexer” to commute signals on the different electrodes, the istrument can measure both Current and Voltage with microprocessor controlled sequence of measurements.
In the same instrument you have both the control&measuring system and the power system ; only the battery and the commutation system are external
POLARES 2.0 is lighter, smaller, faster and more reliable in respect to the former generation of electrical imaging systems. Thanks to an intuitive user interface - realised through a high quality LCD touch screen - all operations can be controlled without a mouse or a keyboard. With its very low consuming embedded system (that doesn’t require cooling fans or traditional HD) and the “open source” operating system the User can appreciate a greater autonomy and a greater reliability of this instrument.
Several external devices can be connected through the USB port: USB dongles, network interfaces, WiFi, Bluetooth, GPS antennas, keyboards, etc... Moreover, the use of a nonconventional PC extends working conditions to wide environmental humidity and temperature ranges.