LSI LASTEM Greta Geo Resistivimeter Instruction Manual

LSI LASTEM Greta Geo Resistivimeter

Notes on this manual
The information included in this manual is subject to changes without notice. No part of this manual may be reproduced in any form or by any electronic or mechanical means, for any use, without LSI LASTEM written permission.
LSI LASTEM reserves the right to intervene on the product, without the obligation to update this document promptly.
Copyright 2019-2022 LSI LASTEM. All rights reserved.

General requirements

Only qualified service staff shall be authorized to carry out installation and maintenance procedures.
Install the tool in a clean, dry and safe place. Humidity, dust and extreme temperatures tend to deteriorate or damage the instrument. In such environments it’s recommended to install inside suitable containers.
Power the instrument appropriately. Respect the supply voltages indicated for the instrument model owned.
Make the connections appropriately. Carefully follow the connection schemes provided with the instrumen-tation.
Do not use the product if you suspect the presence of malfunctions. If a malfunction is suspected, do not power the instrument and ask for the intervention of qualified service staff.

Before any operation on electrical connections, power, sensors and communication equipment:

• Turn off the power.
• Discharge the accumulated electrostatic charges by touching a conductor or a grounded system.

Do not operate the product in presence of water or moisture.
Do not operate the product in an explosive atmosphere.
Lithium-ion battery inside. Replacing the battery with an incorrect type can cause risk of explosion.

Specific requirements

The large heatsink protruding from the front of the SDU module is used to remove the high temperatures produced by the power circuits performing current injection. The temperature of this heatsink is normally less than 60 °C, but this depends on the conditions in which the instrument operates and the injection set-tings, as well as the conditions of the soil and could exceed even 80 °C, therefore be careful not to touch it during the functioning of the system.
The very same SDU unit is responsible for the ignition of high voltage circuits (200 Vcc) through the PWR unit; the ignition of this section of power occurs only during measurement operations; in this case the presence of high voltage is reported at several points:

• HV alert on the top of the SDU module.
• Green lights for each of the 4 power sections, at the bottom right corner of the box.

If the system is powered by power grid, there is a presence of potentially dangerous voltage inside the box; the mains voltage is connected to the circuit breaker; this can be deactivated to remove the presence of mains voltage in places other than the switch itself; however, consider that the high voltage is generated during the measurements even if only the battery voltage is available. If you want to shut down the system completely use the switch located on the top of the PWR unit.

The electrical cables that bring the connections back to the measuring electrodes also carry currents with potentially dangerous voltages. LSI LASTEM has carefully considered the safety conditions for those working with GReTA- ONE, in particular the situation in which a subject could come into contact with the measuring electrodes. In this regard, the following should be considered:

• Each individual electrode is powered by the system only for short instants and quite rarely (alto-gather a few seconds in each measurement session; typically, there is only one scheduled measurement session each day).

The electrocution can occur by holding in the hands two electrodes that at a given moment are activated by the system to perform the measurement in the ground right at the position of the subject. It should be considered that the typical duration of the injection is about 300 ms x 2 (twice because for each measurement the injection is considered in the opposite direction and then in the direct direction for the depolarization of the soil) and 1000 ms x 2 at the most, therefore still insufficient to cause death. Considering a condition highly unlikely to occur, but not theoretically impossible, in which the operator is in contact with two electrodes, the instrument is performing a measurement precisely on those elements and, fatally, just at that moment a block to the automatic signal switching system occurs, in this case there would be a permanent presence of the voltage to the electrodes in contact with the subject; in this situation there is a circuit specifically provided
in the instrument that can detect the system’s block condition and therefore authoritative in the deactivation
command of the entire high voltage supply system.
This circuit, in order to ensure maximum operating conditions and reliability, works with dedicated hardware and is completely independent from the other parts of the injection and measurement system managed by the logical units of the instrument.

Pre-installation requirements

Power connection
Whenever available at the installation site, the G.Re.T.A. system should preferably be connected directly to the electrical grid. For this purpose, a 230 Vac power line should be laid in order to reach the plinth and have
sufficient spare cable to reach the G.Re.T.A. box located approximately at 1 m height from the soil’s surface.
If the electric grid is not available at the installation site, the system may be powered by a solar panel placed on top of the pole.

Internet connection
The G.Re.T.A. system communicates via Internet connection. The system comes with a 3G/4G modem/router however without a SIM card, which must be provided locally by the user. Make sure to make available a 3G/4G SIM card at the day of installation and to have tested the coverage of the related telephone operator at the installation site beforehand.
If a local Ethernet network is available at installation site, the system can be connected through a LAN cable. In this case an Ethernet line should be laid in order to reach the plinth and have sufficient spare cable to
reach the G.Re.T.A. box located approximately at 1 m height from the soil’s surface.

Installation

Plinth installation

The G.Re.T.A. system comes in a IP66 box mounted on a pole. The pole is supported by a galvanized iron tripod which has to be placed and fixed on a concrete plinth (preferred) or buried in the soil.
The plinth has to be placed in correspondence of the centre of the trench. If the plinth is made in situ, con-crete drying period must be considered before installation. Precast concrete plinths can be used too.

Excavation of the trench

If the installation foresees buried cables and electrodes, a trench must be excavated before the installation.

The trench must have these characteristics:

• 30…40 cm wide
• 30…40 cm deep
• long as the profile length, depending on the spacing between electrodes:
  • 1 m spacing = 47 m long
  • 2 m spacing = 94 m long
  • 3 m spacing = 141 m long

Unwind of the cable

The two cables come rolled up on reels, start unwinding the cables starting from the end of the trench and coming towards the center of the profile, where the plinth is installed. The first electrode must be positioned in correspondence of the m. 0 of the trench.

Screw the electrodes

The electrodes are provided separately from the cables. Both plate and rod electrodes must be screwed to the outlets of the cable.
Bolts and washers are provided with the electrodes. Breaker bar 7 mm is required.
This operation can be performed while the excavator is proceeding.

Mount the pole and the G.Re.T.A. box

Meanwhile preparing the cables, mount the pole, the box and possible additional sensors on pole.

Insert the cables in the trench and bury the electrodes

When the trench is buried, insert the cables inside the trench, taking care of the distance of the central electrodes (last electrode of first cable and first electrode of second cable) from the pole, the must be cor-rectly spaced (e.g. if the electrode distance is 3 m they must be spaced 3 m).
Connect the cables to the box: the first cable (el. 0…23) to SSU1 module and the second cable (el. 24…47) to SSU2 module.
Then cover only the electrodes with soil and press them to obtain a good contact, water and bentonite can be added the enhance the contact.

Switch on the device and do the contact resistance test

Switch on the system and start the contact resistance test as described in Chapter 5 “Installation, first start-up and system configuration” of Manual INSTUM_04378.
If the contact resistance test is ok (Contact resistances < 1000 ohm, preferably < 500 ohm) proceed, if not pour water or salty water on the electrodes, press them and cover them with more soil or use bentonite to enhance the contact. Re-do the contact resistance test.

Cover the trench
Mark the position of the electrodes before covering the trench, with pickets or signs. GPS coordinate of the electrodes can be measured.
First and last electrode’s coordinates are mandatory to configure the system on the cloud software, these coordinates can be measured before installation to configure the system before going on site.
Use the excavator to cover the trench, taking care of not moving the cables and electrodes.
Press gently of the electrodes with the excavator while putting the soil inside the trench to enhance the contact.

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