PASI Polares 32 User manual
POLARES 32
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Contents
Contents.............................................................................................................................4
Important notice ................................................................................................................2
Warranty information and safety notes .............................................................................3
1. Introduction ...............................................................................................................4
Content of the manual ...................................................................................................4
2. Electrical imaging system for tomography Polares 32..............................................5
A brief introduction.......................................................................................................5
What is the difference with conventional DC electrical tomography? .........................5
Why is POLARES32 an innovative instrument? ..........................................................6
What are the main strengths of POLARES 32? ............................................................6
POLARES32 main features ..........................................................................................8
Automatic adjustment of current and voltage output values.....................................8
3. Mode of use.............................................................................................................10
Caution ....................................................................................................................10
Test plug to check operation of MPX and MPX extension cable ...............................11
Hardware and logic electrodes ....................................................................................13
4. Getting started .........................................................................................................19
Opening of a measurement template...........................................................................19
Moving on to the measurement session ......................................................................20
Execution of measurement sessions............................................................................20
Displaying and continuing a measurement session.....................................................21
5. Description of the Polares 32 programme...............................................................22
Main screen .................................................................................................................22
Templates ....................................................................................................................24
Templates selection and opening ................................................................................24
Templates display........................................................................................................25
Session parameters ......................................................................................................26
POLARES 32
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Electrodes................................................................................................................ 27
Measurements ......................................................................................................... 27
Electrodes configuration ............................................................................................. 28
Measurements configuration....................................................................................... 29
Electrical parameters................................................................................................... 31
Moving on to measurement sessions .......................................................................... 32
Saving a template........................................................................................................ 32
Entering custom measurements from file ................................................................... 32
Format of the measurement input file..................................................................... 33
Measurement sessions................................................................................................. 34
Selecting a measurement session................................................................................ 34
Session display............................................................................................................ 34
Editing the parameters ................................................................................................ 35
Testing the electrodes ................................................................................................. 35
Performing and deleting the measurements................................................................ 36
Pseudo-section ............................................................................................................ 39
Save session ................................................................................................................ 39
Template management ................................................................................................ 40
Delete template ........................................................................................................... 41
Export template........................................................................................................... 41
Import template........................................................................................................... 41
Multiplexer test ........................................................................................................... 42
System......................................................................................................................... 42
Software upgrades....................................................................................................... 44
Insights........................................................................................................................ 45
Meaning of Sigma value ......................................................................................... 45
Format of the files used .............................................................................................. 45
Output GPD format................................................................................................. 46
Input and output BPD format.................................................................................. 46
Output TXT format ................................................................................................. 46
6. Appendixes ............................................................................................................. 48
Technical specifications.............................................................................................. 48
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GPD file format...........................................................................................................49
General structure .....................................................................................................49
File header ...............................................................................................................50
Electrodes table .......................................................................................................54
Measurements table.................................................................................................55
Important notice
All rights to this manual are owned solely by P.A.S.I. srl. All rights reserved. Copying
this manual (without the written permission of the owner) for printing, copying, recording
or by any other means, translating all or part of the manual into any other language,
including all programming languages, using any electrical, mechanical, magnetic, optical,
manual or other methods is prohibited.
P.A.S.I. reserves the right to change the technical specifications or functions of its
products, or to discontinue production of one of its products, or to discontinue support for
one of its products, without prior written notice and urges its customers to ensure that the
information available to them is valid.
P.A.S.I. software and programmes are supplied "as is". The manufacturer does not grant
any kind of guarantee including that of the suitability and applicability of a certain
application. Under no circumstances shall the manufacturer or developer of a programme
be liable for any damage caused by the use of a programme.
P.A.S.I. products are not designed to be used in any way or applied in any way other than
mentioned.
Torino, ITALY 2021
Copyright: 2021 P.A.S.I. srl
POLARES 32
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Warranty information and safety notes
Read the instructions carefully before using the product:
- This instrument was designed and built to measure electrical resistivity in the soil for
geophysical/geological purposes. Please read this manual carefully before use.
- The warranty will be void if the product is not used according to the instructions in
this manual.
- The warranty will be void if the appliance is tampered with.
- The device must only be used in accordance with the instructions described in this
manual. Correct and safe operation can only be guaranteed if the instrument is properly
transported, stored and treated.
- To avoid damage, use only original accessories or those approved by PASI srl.
- The case containing the instrument is only waterproof when closed. Once the
instrument has been placed on the measurement site, it should always be adequately
protected to prevent it from being exposed to the elements (rain, snow, direct sunlight,
etc.). It is not advisable to install the instrument on a vibrating surface.
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1.Introduction
The Polares 32 instrument is a device made and assembled by P.A.S.I. srl, a leading
Italian company in the production of instruments for geology and geophysics.
This guide lists the technical specifications and explains how to use the device.
Adhere to these guidelines.
Content of the manual
•Chapter 2, Electrical imaging system for tomography Polares 32, contains a brief
presentation of the instrument
•Chapter 3, Mode of use, describes how to use the system from a hardware point
of view.
•Chapter 4, Getting started, describes how to perform some basic operations using
the Polares 32 system and its PC control programme, referring to the subsequent
chapters of the manual and allowing the operator to start learning about and using
the system.
•Chapter 5, Description of the Polares 32 program, describes the mode of operation
of the PC control programme and the use of the system controlled in this way,
illustrating in detail all the functions offered by the programme and their
interaction with the system.
•Chapter 5, Annexes, reports the technical characteristics of the system and the
definition of the proprietary GPD (Geophysics Pasi Data) format used for storing
the results of a measurement session on file.
POLARES 32
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2.Electrical imaging system for tomography
Polares 32
A brief introduction
POLARES 32 is a lightweight, easy-to-carry and fast AC electrical imaging system for
tomography.
It is designed to accurately measure AC currents and voltages in order to provide the user
with apparent resistivity and phase values in the frequency domain.
It operates with an adjustable transmission frequency in the range of 7 to 125 Hz.
POLARES32 can be used in many applications: laboratory measurements, electrical
surveys, surface electrical resistivity tomography, 3D surveys, mobile surveys of canals,
lakes, sea, etc.
Access to POLARES32 functions is intuitive through the use of an external PC
(Windows™) connected via USB cable.
The use of an external Windows™ PC offers much longer battery life and improved
overall system reliability. Computer faults can be easily solved by replacing the PC,
software updates do not require delicate interventions on the instrument's firmware, and
the user can benefit from remote assistance from our company for fault diagnosis.
The communication interface is a USB port on the PC, through which the user can upload
measurement configurations, install new software versions, download measured data and,
in addition, connect a number of different devices (network interfaces, WiFi routers,
Bluetooth or GPS antennas, keyboards, etc.).
What is the difference with conventional DC electrical
tomography?
The use of Electrical Resistivity Tomography (ERT) for geology has been essentially the
same since its début, based on the original principles of Vertical Electrical Soundings
(VES): apply a direct current to two stakes inserted into the ground (current electrodes A
B or C1 C2) and measure the corresponding voltage between two others (voltage
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electrodes M N or P1 P2). As far as “traditional” instruments are concerned, the applied
current and thus the corresponding voltage have always been continuous, with reversed
polarity for each measurement. POLARES32 uses a sinusoidal alternating current with
adjustable frequency.
Why is POLARES32 an innovative instrument?
The use of alternating current has shown particular advantages in terms of speed of
execution of measurements with the same quality of results. Compared to conventional
DC systems, this increased speed can reduce the time to perform the same set of
measurements in the field by at least a factor of 10 (or even 20, in most cases).
Furthermore, the measurement of the relationship between the detected voltage and the
injected current, in a sinusoidal state, both in terms of amplitude and phase (delay of one
signal on the other), allows the simultaneous detection of resistivity and induced
polarisation of the ground.
What are the main strengths of POLARES 32?
- COMPLEX RESISTIVITY ACQUISITION: being designed as an AC system,
POLARES32 involves both the conduction and polarisation properties of the material
under investigation. Since the complex resistivity modulus deals with the electrolytic
properties of the pore-filling fluids, the phase shift between the voltage and current signals
is directly influenced by the polarisation of the material. Thus, each individual data set
can be used to analyse both resistivity and induced polarisation.
Resistivity (as the reciprocal of conductivity) is a complex, frequency-dependent property
of a material and is described by the following equation:
where σ * and ρ * define complex conductivity and resistivity respectively, | σ | is the
modulus of conductivity, φ is the phase shift between voltage signal and current, σ’ and
σ” are the real and imaginary part of the complex resistivity.
POLARES 32
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The real (in-phase) and imaginary (or quadrature) components of the complex resistivity
can be obtained from the following relationships:
Real resistivity is mainly related to electrolytic conduction phenomena (resistivity of rock
or soil, and even more so to the resistivity of pore-filling fluids), and to various aspects
of induced polarisation (surface polarisation, presence of metallic minerals, contaminants
and so on).
Many studies and works have shown a growing interest in AC geoelectric surveys, which
have demonstrated their effectiveness for mineral exploration, structural characterisation
of geological features and monitoring of contaminated sites.
For users who prefer to work with chargeability as an IP parameter, POLARES32
automatically stores the chargeability (in ms) associated with each measurement, thanks
to the relationships between phase shift (IP in the frequency domain) and chargeability
(IP in the time domain).
- SPEED: POLARES32 can be used to measure single high-frequency data sets (7 to
125Hz). In many common applications, ensuring good electrode-to-ground contact is
sufficient to acquire accurate datasets of apparent resistivity values, ready for subsequent
inversion using special external software.
The higher the frequency, the higher the speed: field data from moderately noisy sites can
be acquired at a rate of up to 3 measurements/second, in any measurement matrix. In
many cases, the time necessary to complete the series of measurements can be reduced
by a factor of 10 to 20 compared to traditional DC systems.
- ACCURACY: the high resolution of the acquisition system (0.4 μA for current signal
and 1.5 μV for voltage signal) allows accurate interpolation of sinusoidal current and
voltage signals. This becomes even more important when POLARES32 is used for
spectrally-induced polarisation surveys, where phase shift values must be measured with
the highest level of accuracy.
For users requiring noise-free phase data, POLARES32 can be used with non-polarisable
electrodes to avoid any inductive EM coupling along the wires between the transmission
and measurement circuits.
- MODULARITY: POLARES32 contains, integrated in a robust Peli case, the
transmission and measuring system, all the necessary guards and also 2xMPX
(Multiplexer) with 16 electrodes each (for the first 32 electrodes). Additional external
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MPXs (16 el. each) can be connected externally to POLARES32 to increase the number
of electrodes following the first 32 (thus implementing the number of electrodes to 48,
64, 80, 96, etc.).
POLARES32 main features
• Transmitter and receiver in one unit; power supply via external battery of any type (lead,
lithium, etc.) from 8.5 to 15V
• Very fast measurements: up to 3 scans/sec.
• Fully automatic microprocessor-controlled measurement: automatic correction of
spontaneous potential, automatic measurement, digital stacking, error display in case of
procedural problems
• Quality check of electrode-soil connections before measurement.
• Measurement and recording of ground resistance (with contact resistance measurement),
current, voltage, chargeability (IP), spontaneous potential and standard deviation
(SIGMA).
• Calculation of apparent resistivity for various electrode arrays: Schlumberger, Wenner,
Wenner-Schlumberger, Dipole-Dipole, Pole-Dipole, Pole-Pole, etc.
• Ability to support any user-designed 2D and 3D electrode array
• Measurement and display of chargeability (phase shift in current and voltage sine
waves) simultaneously with resistivity measurement: IP and resistivity are measured and
acquired in the same measurement session
• Multi-electrode mode for use with the automatic switching system (unlimited number
of electrodes)
• 4 auxiliary electrodes (A, B, M, N) for unlimited poles, special measurements and VES
measurements
Automatic adjustment of current and voltage output values
• Output power: max. 200 W.
• Maximum output voltage: Max 700 Vpp
• Maximum output current: Max 4App
Output current specifications
• Resolution: 0,4uA
POLARES 32
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• Accuracy: standard 0.15% max 1% from -20 °C to 60 °C
Waveform: sinusoidal from 7 to 150 Hz
Input impedance: 10 MOhm
Input overvoltage protection: 1000 V.
Input voltage ranges: +/- 300 V and +/- 6 V.
Automatic power line rejection 50 / 60Hz
Voltage measurement specifications:
Actual resolution: 1.5uV
Accuracy: standard 0.15% max 1% from -20 °C to 70 °C
Chargeability accuracy (measurement): 0.1%
Power supply: external (8.5V = to 15V =) lead-acid or lithium battery, internal 30 A fuse,
reverse polarity protection, power cable supplied, battery to be sourced locally by
customer.
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3.Mode of use
Caution
The electrical imaging system for tomography POLARES 32 is a very sophisticated
instrument, but at the same time quite simple to use.
It should be remembered that the instrument uses potentially lethal electrical voltages and
currents; this means that the POLARES 32 instrument must be used by specially trained
personnel who have the necessary knowledge of the theoretical principles and methods
of measuring electrical resistivity in the soil, whether by quadripole or multi-electrode
tomographic methods.
In order not to leave room for improvisation, before using the instrument in the field it is
strongly recommended to read this manual carefully and to be familiar with the theory
(electrical engineering and geophysics) relating to the principles underlying the
methodology.
Before proceeding with field measurements, please do not hesitate to contact PASI
technical support to clarify any doubts.
Always bear in mind that there are physical limits to the application of the method, once
these limits are exceeded (resistivity too high or too low) the measurement is not possible,
even if the instrument is fully operational.
The instrument is protected - to the maximum of current technical possibilities - against
all foreseeable incorrect operations (indicated as such by the instrument itself); however,
the execution of incorrect operations may lead to damage to the instrument or danger to
the operator.
In these cases, only PASI's authorised technical support will decide whether or not the
fault falls within the scope of the warranty provided with the instrument. Any sending of
damaged or malfunctioning instruments to our laboratories must always be authorised in
advance by PASI technical support and must be performed according to the instructions
that will be communicated by PASI when necessary.
POLARES 32
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Test plug to check operation of MPX and MPX extension cable
We would like to remind you here of the importance of the test plug which you found in
the holder inside the lid of the POLARES 32 case.
Although it can also be performed on field it is advisable to perform this procedure before
going to the building site. This is a very simple and quick test, which is essential for the
subsequent correct execution of measurements in the field (especially to avoid arriving
on site with a faulty MPX or extension cable).
FIGURE 1: TEST PLUG
The test is described in detail on page XX of this manual. Here we would just like to
remind you that if you have more than 32 electrodes, it is advisable to connect all external
MPXs and their extensions (note: multi-electrode cables should not be connected). This
will test not only the MPX, but also its extension cable or short connection cable (2.5m,
optional) such as the one shown in the photo of the external MPX test (this cable is
normally used for 3D measurements when MPXs are connected close together).
This will be done by testing the MPXs one at a time, putting the plug on each one and
leaving the others only connected to all the extensions.
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FIGURE 2: INTERNAL MPXS TEST,1/A AND 1/B
FIGURE 3: EXTERNAL MPXS TEST 2, 3, ...N
POLARES 32
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Hardware and logic electrodes
Please assimilate this concept because, although it is simple, it is very important to
understand the logic behind the operation of the stringings.
Hardware electrodes are the positions that the designer has physically foreseen for each
electrode as they exit the connector (the electrode with the lowest number is always the
one next to the connector).
Logic electrodes are the positions that the operator can decide to assign to each electrode
and which are independent of the physical position.
Suppose a 32-electrode linear measurement is to be carried out: electrodes 1 to 16 come
out of the first MPX and electrodes 17 to 32 come out of the second MPX. If we wanted
to connect all electrodes linearly, having said that the electrode with the lowest number
is the one closest to the connector on the ground, the sequence of hardware electrodes on
the left of POLARES 32 would be:
16–15–14–13–12–11–10–9–8-7–6–5–4-3-2-1
while on the right would be:
17-18-19-20-21-22-23-24-25-26-27-28-29-30-31-32
However, in order to measure along our linear profile, we need the sequence of electrodes
to start at 1 on the left and go up to 16 near the instrument and then continue with
electrodes 17 to 32 on the right. In order for this to be possible we will have to “rename”
1 of the first 16 electrodes and consequently the hardware electrode 16 will have to
become the logic electrode 1, the hardware electrode 15 will have to become the logic
electrode 2 and so on.
In conclusion, it follows that the position of the hardware electrodes is immutable while
the position of the logic electrodes is decided by us according to our needs. With reference
to FIG. 4, the positions of the logic electrodes are shown in black and those of the
hardware electrodes in red.
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FIGURE 4: CONFIGURATION WITH 32 ELECTRODES
Acquiring this concept, thanks to the software functions described later in the manual, it
will be possible to define an arbitrary position for each electrode (logic electrode)
independently of their hardware position.
After planning the stringing procedure (purpose of the measurement, type of stringing,
logistics, etc.), the field is prepared for the measurement by first clearing a strip (in the
case of linear measurements) or an area (in the case of 3D measurements) so that the
electrodes (stakes) and the measuring cable are clearly visible.
If the planned spacing is the same as the cable spacing, you can proceed by directly laying
the multi-electrode cable along the established profile, then driving the electrodes into the
ground beside each takeout to which they will be connected.
If the required spacing is smaller, it will of course be necessary to use a tape measure to
position the electrodes at the correct distance from each other before connecting them to
the respective takeouts on the cable.
The electrodes should be driven into the ground to a depth of about 1/3 of their length
and then connected to the takeouts on the cable by means of the appropriate connecting
cables, fitted with clips.
POLARES 32
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FIGURE 5: ELECTRODE CONNECTION
Next, connect the cables to the MPXs (remember that the first 2 MPXs are internal to the
Polares 32) using the cable outputs on each MPX (“TO ELECTRODES” connector).
FIGURE 6: POLARES32 PANEL
The first 16 stakes will be connected to the POLARES connector identified as “1-16
ELECTRODES” (Hardware); stakes 17 to 32 (Hardware) will be connected to the
connector identified as “17-32 ELECTRODES” (Figures 6 and 7).
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