Commit 5cd2bcba authored by remi.clement's avatar remi.clement

change website

parent 47f219a5
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OhmPi V 1.01
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*****************************************
OhmPi V 1.01 (limited to 32 electrodes)
*****************************************
The philosophy of Ohmpi
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......@@ -51,4 +51,46 @@ The measurement board must be printed using the PCB file (Source file repository
Measurement board installation with Raspberry Pi
Current injection
******************
\ No newline at end of file
******************
To carry out the electrical resistivity measurement, the first step consists of injecting current into the ground.
In our case, a simple 12-V lead-acid battery is used to create an electrical potential difference that results
in current circulating into the ground. The current is injected through electrodes A and B (see Fig. 2). This
injection is controlled via a 4-channel relay module board connected to the Raspberry Pi. The mechanical relay
module board is shown in Figure 4. Relays 1 and 2 serve to switch on the current source. The common contacts
of relays 1 and 2 are connected to the positive and negative battery poles, respectively. The normally open
contacts of both relays are connected to the common contacts of relays 3 and 4. Relays 1 and 2 are connected
to the GPIO 7 on the Raspberry Pi and therefore activate simultaneously. The role of relays 3 and 4 is to reverse
the polarity at electrodes A and B. Thus, when relays 3 and 4 are energized by the GPIO 8 in the open position,
the positive battery pole is connected to electrode A and the negative pole to electrode B. When not energized,
they remain in the normally closed position. This set-up offers a simple and robust solution to inject current.
.. figure:: current_board.jpg
:width: 800px
:align: center
:height: 400px
:alt: alternate text
:figclass: align-center
Wiring of the 4-channel relay module board for current injection management
Electrical resistivity measurements
************************************
To measure electrical resistivity with Raspberry Pi, an ADS1115 was introduced, as proposed by Florsch [7]. The ADS1115 is a 16-bit ADC (Analog-to-Digital Converter), with an adaptable gain. Its value has been set at 1 in this study. The input signal value could lie between - to + 6.114 V. The ADS1115 is mounted on a board adapted from an in-house design. Figure 5 shows the general diagram for the electronic measurement board developed. This figure also displays the test circuit used to test the board in the laboratory, which mimics the behavior of a soil subjected to current injection. In this test circuit, resistance R11 represents the soil resistance.
Soil resistance R11 is connected to electrodes A and B for the current injection. Resistors R10 and R12 constitute the contact resistances between soil and electrodes; they are typically made of stainless steel. The battery, which allows for direct current injection, is connected in series with resistors R10, R11 and R12. In this part of the board, resistance R9 has been added to measure the current flowing between electrodes A and B. This resistance value has been set at 50 ohms in order to ensure:
• a precise resistance,
• a resistance less than the sum of resistors R10, R11 and R12; indeed, R10 and R12 generally lie between 100 and 5,000 ohms.
To measure the current intensity between A and B, the electrical potential difference at the pole of the reference resistor (R9) is measured. The intensity (in mA) is calculated by inserting the resulting value into the following: ?
To measure the potential difference needed to measure current intensity, the ADS 1115 is connected to the ground of the circuit. In our case, the ground reference is electrode B. The analog inputs A1 and A0 of the ADS1115 are connected to each pole of the reference resistor (R9). In order to increase input impedance and adapt the signal gain, tracking amplifiers have been included and completed by a divider bridge (R5, R8, R6 and R7) located between the two amplifiers. The resistance of the divider bridge ensures that the signal remains between 0 and 5 V, in accordance with the ADS1115 signal gain. To measure the potential difference, the M and N electrodes are connected to analog inputs A2 and A3 of the ADS 1115. Between the ADC and the electrodes, two tracking amplifiers and a divider bridge have been positioned so as to obtain a potential lying within the 0-5 V range at the analog input of the ADS 1115.
Let's note that the potential difference value would equal the potential measured with ADS1115 multiplied by the voltage reduction value of the divider bridge (see Section 5.2). Despite the use of high-resolution resistance (i.e. accurate to within 1%), it is still necessary to calibrate the divider bridge using a precision voltmeter. For this purpose, the input and output potentials of the divider bridge must be measured using an equivalent circuit for various electrical potential values. These values serve to calculate the gain. With this electronic board, it is possible to measure the potential and intensity without disturbing the electric field in the ground, with the total input impedance value being estimated at 36 mega-ohms.
A shortcut between Electrodes A and B will generate excessive currents, whose intensities depend on the type of battery used. A lithium ion battery or automobile-type lead-acid battery can deliver a strong enough current to damage the board and, as such, constitutes a potential hazard. We therefore recommend adding a 1.5-A fuse between the battery and resistor R9.
.. figure:: schema_measurement_board.jpg
:width: 800px
:align: center
:height: 400px
:alt: alternate text
:figclass: align-center
Measurement board
\ No newline at end of file
......@@ -82,7 +82,7 @@
<ul>
<li class="toctree-l1"><a class="reference internal" href="page0.html"><strong>Introduction to OhmPi</strong></a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01</a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01 (limited to 32 electrodes)</a></li>
</ul>
......
......@@ -83,7 +83,7 @@
<ul>
<li class="toctree-l1"><a class="reference internal" href="page0.html"><strong>Introduction to OhmPi</strong></a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01</a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01 (limited to 32 electrodes)</a></li>
</ul>
......@@ -156,11 +156,12 @@
<div class="toctree-wrapper compound">
<ul>
<li class="toctree-l1"><a class="reference internal" href="page0.html"><strong>Introduction to OhmPi</strong></a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01</a><ul>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01 (limited to 32 electrodes)</a><ul>
<li class="toctree-l2"><a class="reference internal" href="page1.html#the-philosophy-of-ohmpi">The philosophy of Ohmpi</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#os-installation-on-a-raspberry-pi">OS installation on a Raspberry Pi</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#construction-of-the-measurement-board-and-connection-to-the-raspberry">Construction of the measurement board and connection to the Raspberry</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#current-injection">Current injection</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#electrical-resistivity-measurements">Electrical resistivity measurements</a></li>
</ul>
</li>
</ul>
......
No preview for this file type
......@@ -7,7 +7,7 @@
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>OhmPi V 1.01 &mdash; Ohmpi: open hardware resistivity-meter documentation</title>
<title>OhmPi V 1.01 (limited to 32 electrodes) &mdash; Ohmpi: open hardware resistivity-meter documentation</title>
......@@ -83,11 +83,12 @@
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="page0.html"><strong>Introduction to OhmPi</strong></a></li>
<li class="toctree-l1 current"><a class="current reference internal" href="#">OhmPi V 1.01</a><ul>
<li class="toctree-l1 current"><a class="current reference internal" href="#">OhmPi V 1.01 (limited to 32 electrodes)</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#the-philosophy-of-ohmpi">The philosophy of Ohmpi</a></li>
<li class="toctree-l2"><a class="reference internal" href="#os-installation-on-a-raspberry-pi">OS installation on a Raspberry Pi</a></li>
<li class="toctree-l2"><a class="reference internal" href="#construction-of-the-measurement-board-and-connection-to-the-raspberry">Construction of the measurement board and connection to the Raspberry</a></li>
<li class="toctree-l2"><a class="reference internal" href="#current-injection">Current injection</a></li>
<li class="toctree-l2"><a class="reference internal" href="#electrical-resistivity-measurements">Electrical resistivity measurements</a></li>
</ul>
</li>
</ul>
......@@ -136,7 +137,7 @@
<li><a href="index.html" class="icon icon-home"></a> &raquo;</li>
<li>OhmPi V 1.01</li>
<li>OhmPi V 1.01 (limited to 32 electrodes)</li>
<li class="wy-breadcrumbs-aside">
......@@ -155,8 +156,8 @@
<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
<div itemprop="articleBody">
<div class="section" id="ohmpi-v-1-01">
<h1>OhmPi V 1.01<a class="headerlink" href="#ohmpi-v-1-01" title="Permalink to this headline"></a></h1>
<div class="section" id="ohmpi-v-1-01-limited-to-32-electrodes">
<h1>OhmPi V 1.01 (limited to 32 electrodes)<a class="headerlink" href="#ohmpi-v-1-01-limited-to-32-electrodes" title="Permalink to this headline"></a></h1>
<div class="section" id="the-philosophy-of-ohmpi">
<h2>The philosophy of Ohmpi<a class="headerlink" href="#the-philosophy-of-ohmpi" title="Permalink to this headline"></a></h2>
<p>The philosophy of Ohmpi V1.01 is to offer a multi electrode resistivity meter, from a set of commercially available electronic cards it is a resistivity meter limited to 32 electrodes only. It is limited to low-current injection, but suitable for small laboratory experiments and small field time monitoring</p>
......@@ -192,6 +193,36 @@ Raspbian GUI settings menu. Failure to carry out this task may cause damage to t
</div>
<div class="section" id="current-injection">
<h2>Current injection<a class="headerlink" href="#current-injection" title="Permalink to this headline"></a></h2>
<p>To carry out the electrical resistivity measurement, the first step consists of injecting current into the ground.
In our case, a simple 12-V lead-acid battery is used to create an electrical potential difference that results
in current circulating into the ground. The current is injected through electrodes A and B (see Fig. 2). This
injection is controlled via a 4-channel relay module board connected to the Raspberry Pi. The mechanical relay
module board is shown in Figure 4. Relays 1 and 2 serve to switch on the current source. The common contacts
of relays 1 and 2 are connected to the positive and negative battery poles, respectively. The normally open
contacts of both relays are connected to the common contacts of relays 3 and 4. Relays 1 and 2 are connected
to the GPIO 7 on the Raspberry Pi and therefore activate simultaneously. The role of relays 3 and 4 is to reverse
the polarity at electrodes A and B. Thus, when relays 3 and 4 are energized by the GPIO 8 in the open position,
the positive battery pole is connected to electrode A and the negative pole to electrode B. When not energized,
they remain in the normally closed position. This set-up offers a simple and robust solution to inject current.</p>
<div class="align-center figure" id="id3">
<a class="reference internal image-reference" href="_images/current_board.jpg"><img alt="alternate text" src="_images/current_board.jpg" style="width: 800px; height: 400px;" /></a>
<p class="caption"><span class="caption-text">Wiring of the 4-channel relay module board for current injection management</span><a class="headerlink" href="#id3" title="Permalink to this image"></a></p>
</div>
</div>
<div class="section" id="electrical-resistivity-measurements">
<h2>Electrical resistivity measurements<a class="headerlink" href="#electrical-resistivity-measurements" title="Permalink to this headline"></a></h2>
<p>To measure electrical resistivity with Raspberry Pi, an ADS1115 was introduced, as proposed by Florsch [7]. The ADS1115 is a 16-bit ADC (Analog-to-Digital Converter), with an adaptable gain. Its value has been set at 1 in this study. The input signal value could lie between - to + 6.114 V. The ADS1115 is mounted on a board adapted from an in-house design. Figure 5 shows the general diagram for the electronic measurement board developed. This figure also displays the test circuit used to test the board in the laboratory, which mimics the behavior of a soil subjected to current injection. In this test circuit, resistance R11 represents the soil resistance.
Soil resistance R11 is connected to electrodes A and B for the current injection. Resistors R10 and R12 constitute the contact resistances between soil and electrodes; they are typically made of stainless steel. The battery, which allows for direct current injection, is connected in series with resistors R10, R11 and R12. In this part of the board, resistance R9 has been added to measure the current flowing between electrodes A and B. This resistance value has been set at 50 ohms in order to ensure:
• a precise resistance,
• a resistance less than the sum of resistors R10, R11 and R12; indeed, R10 and R12 generally lie between 100 and 5,000 ohms.
To measure the current intensity between A and B, the electrical potential difference at the pole of the reference resistor (R9) is measured. The intensity (in mA) is calculated by inserting the resulting value into the following: ?
To measure the potential difference needed to measure current intensity, the ADS 1115 is connected to the ground of the circuit. In our case, the ground reference is electrode B. The analog inputs A1 and A0 of the ADS1115 are connected to each pole of the reference resistor (R9). In order to increase input impedance and adapt the signal gain, tracking amplifiers have been included and completed by a divider bridge (R5, R8, R6 and R7) located between the two amplifiers. The resistance of the divider bridge ensures that the signal remains between 0 and 5 V, in accordance with the ADS1115 signal gain. To measure the potential difference, the M and N electrodes are connected to analog inputs A2 and A3 of the ADS 1115. Between the ADC and the electrodes, two tracking amplifiers and a divider bridge have been positioned so as to obtain a potential lying within the 0-5 V range at the analog input of the ADS 1115.
Let’s note that the potential difference value would equal the potential measured with ADS1115 multiplied by the voltage reduction value of the divider bridge (see Section 5.2). Despite the use of high-resolution resistance (i.e. accurate to within 1%), it is still necessary to calibrate the divider bridge using a precision voltmeter. For this purpose, the input and output potentials of the divider bridge must be measured using an equivalent circuit for various electrical potential values. These values serve to calculate the gain. With this electronic board, it is possible to measure the potential and intensity without disturbing the electric field in the ground, with the total input impedance value being estimated at 36 mega-ohms.
A shortcut between Electrodes A and B will generate excessive currents, whose intensities depend on the type of battery used. A lithium ion battery or automobile-type lead-acid battery can deliver a strong enough current to damage the board and, as such, constitutes a potential hazard. We therefore recommend adding a 1.5-A fuse between the battery and resistor R9.</p>
<div class="align-center figure" id="id4">
<a class="reference internal image-reference" href="_images/schema_measurement_board.jpg"><img alt="alternate text" src="_images/schema_measurement_board.jpg" style="width: 800px; height: 400px;" /></a>
<p class="caption"><span class="caption-text">Measurement board</span><a class="headerlink" href="#id4" title="Permalink to this image"></a></p>
</div>
</div>
</div>
......
......@@ -84,7 +84,7 @@
<ul>
<li class="toctree-l1"><a class="reference internal" href="page0.html"><strong>Introduction to OhmPi</strong></a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01</a></li>
<li class="toctree-l1"><a class="reference internal" href="page1.html">OhmPi V 1.01 (limited to 32 electrodes)</a></li>
</ul>
......
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......@@ -72,4 +72,25 @@ they remain in the normally closed position. This set-up offers a simple and rob
:alt: alternate text
:figclass: align-center
Wiring of the 4-channel relay module board for current injection management
\ No newline at end of file
Wiring of the 4-channel relay module board for current injection management
Electrical resistivity measurements
************************************
To measure electrical resistivity with Raspberry Pi, an ADS1115 was introduced, as proposed by Florsch [7]. The ADS1115 is a 16-bit ADC (Analog-to-Digital Converter), with an adaptable gain. Its value has been set at 1 in this study. The input signal value could lie between - to + 6.114 V. The ADS1115 is mounted on a board adapted from an in-house design. Figure 5 shows the general diagram for the electronic measurement board developed. This figure also displays the test circuit used to test the board in the laboratory, which mimics the behavior of a soil subjected to current injection. In this test circuit, resistance R11 represents the soil resistance.
Soil resistance R11 is connected to electrodes A and B for the current injection. Resistors R10 and R12 constitute the contact resistances between soil and electrodes; they are typically made of stainless steel. The battery, which allows for direct current injection, is connected in series with resistors R10, R11 and R12. In this part of the board, resistance R9 has been added to measure the current flowing between electrodes A and B. This resistance value has been set at 50 ohms in order to ensure:
• a precise resistance,
• a resistance less than the sum of resistors R10, R11 and R12; indeed, R10 and R12 generally lie between 100 and 5,000 ohms.
To measure the current intensity between A and B, the electrical potential difference at the pole of the reference resistor (R9) is measured. The intensity (in mA) is calculated by inserting the resulting value into the following: ?
To measure the potential difference needed to measure current intensity, the ADS 1115 is connected to the ground of the circuit. In our case, the ground reference is electrode B. The analog inputs A1 and A0 of the ADS1115 are connected to each pole of the reference resistor (R9). In order to increase input impedance and adapt the signal gain, tracking amplifiers have been included and completed by a divider bridge (R5, R8, R6 and R7) located between the two amplifiers. The resistance of the divider bridge ensures that the signal remains between 0 and 5 V, in accordance with the ADS1115 signal gain. To measure the potential difference, the M and N electrodes are connected to analog inputs A2 and A3 of the ADS 1115. Between the ADC and the electrodes, two tracking amplifiers and a divider bridge have been positioned so as to obtain a potential lying within the 0-5 V range at the analog input of the ADS 1115.
Let's note that the potential difference value would equal the potential measured with ADS1115 multiplied by the voltage reduction value of the divider bridge (see Section 5.2). Despite the use of high-resolution resistance (i.e. accurate to within 1%), it is still necessary to calibrate the divider bridge using a precision voltmeter. For this purpose, the input and output potentials of the divider bridge must be measured using an equivalent circuit for various electrical potential values. These values serve to calculate the gain. With this electronic board, it is possible to measure the potential and intensity without disturbing the electric field in the ground, with the total input impedance value being estimated at 36 mega-ohms.
A shortcut between Electrodes A and B will generate excessive currents, whose intensities depend on the type of battery used. A lithium ion battery or automobile-type lead-acid battery can deliver a strong enough current to damage the board and, as such, constitutes a potential hazard. We therefore recommend adding a 1.5-A fuse between the battery and resistor R9.
.. figure:: schema_measurement_board.jpg
:width: 800px
:align: center
:height: 400px
:alt: alternate text
:figclass: align-center
Measurement board
\ No newline at end of file
......@@ -161,6 +161,7 @@
<li class="toctree-l2"><a class="reference internal" href="page1.html#os-installation-on-a-raspberry-pi">OS installation on a Raspberry Pi</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#construction-of-the-measurement-board-and-connection-to-the-raspberry">Construction of the measurement board and connection to the Raspberry</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#current-injection">Current injection</a></li>
<li class="toctree-l2"><a class="reference internal" href="page1.html#electrical-resistivity-measurements">Electrical resistivity measurements</a></li>
</ul>
</li>
</ul>
......
......@@ -88,6 +88,7 @@
<li class="toctree-l2"><a class="reference internal" href="#os-installation-on-a-raspberry-pi">OS installation on a Raspberry Pi</a></li>
<li class="toctree-l2"><a class="reference internal" href="#construction-of-the-measurement-board-and-connection-to-the-raspberry">Construction of the measurement board and connection to the Raspberry</a></li>
<li class="toctree-l2"><a class="reference internal" href="#current-injection">Current injection</a></li>
<li class="toctree-l2"><a class="reference internal" href="#electrical-resistivity-measurements">Electrical resistivity measurements</a></li>
</ul>
</li>
</ul>
......@@ -208,6 +209,21 @@ they remain in the normally closed position. This set-up offers a simple and rob
<p class="caption"><span class="caption-text">Wiring of the 4-channel relay module board for current injection management</span><a class="headerlink" href="#id3" title="Permalink to this image"></a></p>
</div>
</div>
<div class="section" id="electrical-resistivity-measurements">
<h2>Electrical resistivity measurements<a class="headerlink" href="#electrical-resistivity-measurements" title="Permalink to this headline"></a></h2>
<p>To measure electrical resistivity with Raspberry Pi, an ADS1115 was introduced, as proposed by Florsch [7]. The ADS1115 is a 16-bit ADC (Analog-to-Digital Converter), with an adaptable gain. Its value has been set at 1 in this study. The input signal value could lie between - to + 6.114 V. The ADS1115 is mounted on a board adapted from an in-house design. Figure 5 shows the general diagram for the electronic measurement board developed. This figure also displays the test circuit used to test the board in the laboratory, which mimics the behavior of a soil subjected to current injection. In this test circuit, resistance R11 represents the soil resistance.
Soil resistance R11 is connected to electrodes A and B for the current injection. Resistors R10 and R12 constitute the contact resistances between soil and electrodes; they are typically made of stainless steel. The battery, which allows for direct current injection, is connected in series with resistors R10, R11 and R12. In this part of the board, resistance R9 has been added to measure the current flowing between electrodes A and B. This resistance value has been set at 50 ohms in order to ensure:
• a precise resistance,
• a resistance less than the sum of resistors R10, R11 and R12; indeed, R10 and R12 generally lie between 100 and 5,000 ohms.
To measure the current intensity between A and B, the electrical potential difference at the pole of the reference resistor (R9) is measured. The intensity (in mA) is calculated by inserting the resulting value into the following: ?
To measure the potential difference needed to measure current intensity, the ADS 1115 is connected to the ground of the circuit. In our case, the ground reference is electrode B. The analog inputs A1 and A0 of the ADS1115 are connected to each pole of the reference resistor (R9). In order to increase input impedance and adapt the signal gain, tracking amplifiers have been included and completed by a divider bridge (R5, R8, R6 and R7) located between the two amplifiers. The resistance of the divider bridge ensures that the signal remains between 0 and 5 V, in accordance with the ADS1115 signal gain. To measure the potential difference, the M and N electrodes are connected to analog inputs A2 and A3 of the ADS 1115. Between the ADC and the electrodes, two tracking amplifiers and a divider bridge have been positioned so as to obtain a potential lying within the 0-5 V range at the analog input of the ADS 1115.
Let’s note that the potential difference value would equal the potential measured with ADS1115 multiplied by the voltage reduction value of the divider bridge (see Section 5.2). Despite the use of high-resolution resistance (i.e. accurate to within 1%), it is still necessary to calibrate the divider bridge using a precision voltmeter. For this purpose, the input and output potentials of the divider bridge must be measured using an equivalent circuit for various electrical potential values. These values serve to calculate the gain. With this electronic board, it is possible to measure the potential and intensity without disturbing the electric field in the ground, with the total input impedance value being estimated at 36 mega-ohms.
A shortcut between Electrodes A and B will generate excessive currents, whose intensities depend on the type of battery used. A lithium ion battery or automobile-type lead-acid battery can deliver a strong enough current to damage the board and, as such, constitutes a potential hazard. We therefore recommend adding a 1.5-A fuse between the battery and resistor R9.</p>
<div class="align-center figure" id="id4">
<a class="reference internal image-reference" href="_images/schema_measurement_board.jpg"><img alt="alternate text" src="_images/schema_measurement_board.jpg" style="width: 800px; height: 400px;" /></a>
<p class="caption"><span class="caption-text">Measurement board</span><a class="headerlink" href="#id4" title="Permalink to this image"></a></p>
</div>
</div>
</div>
......
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