# Preventing Overturning of Mobile Cranes Using an Electrical Resistivity Measurement System
## 3 Methodology
### Foldable Electrode with Water Supply Device  
In typical electrical resistivity tomography, current is applied, and potential is measured through pin electrodes buried in the ground. As the spacing between electrodes increases, the exploration depth increases, enabling the measurement of a wider area. High-resolution data acquisition requires densely spaced electrode installation in limited  
Figure 4: Layout of the developed data acquisition device.  
Figure 3: Overview of the Electrical Resistivity Measurement System.  
exploration areas. However, this setup requires significant manual labor for electrode burial, which reduces the mobility and convenience of exploration. This study proposes methods to enhance the convenience of electrode installation. First, cylindrical mass electrodes are proposed as a replacement for typical pin electrodes that require burial. This approach is based on the flat electrode method used in electrical resistivity tomography [51; 52; 53; 54; 55], in which a cylindrical mass lightly contacts the ground surface to apply current and measure potential (Figure 5). Second, a water supply device is used to reduce the contact resistance caused by the gap between the soil and the cylindrical mass electrode. The water supply device includes a small pump, solenoid valve, spray nozzle, and switching terminal. The device functions by placing a cylindrical mass electrode and spraying water between the electrode and soil to reduce contact resistance. Third, a foldable electrode device was developed by combining a cylindrical mass electrode, a water supply device, and a measurement cable (Figure 6). This device is designed to reduce weight by using carbon pipes. The carbon pipe and links are connected to allow folding, and a magnetic clip secures the folded state for easy storage. Connectors are installed at the start, connection link, and end of the foldable electrode device to connect the cables and electrodes; additionally, a hose and spray nozzle for water supply are integrated. The foldable electrode device maintains a 1 m interval, facilitating electrode placement in the Wenner method, and can be manufactured to accommodate the desired number of electrodes. The measurement cable is embedded within the pipe, simplifying the connection to the measuring device.  
Each set of the foldable electrode device consists of 8 electrodes connected by a carbon pipe, and 6 sets (3 on each side) were used. The device can be adjusted to fit the size of a mobile crane. As shown in Figure 5c, the cylindrical mass electrode was fabricated from SUS304 (stainless steel) with a screw tap on the top for connecting the wire and bolt. The cylindrical mass has dimensions of 20 mm diameter and 30 mm length and weighs 50 g. Using a Wenner array with 24 electrodes enabled measurements up to pseudo-depth level 7 (Figure 2). The developed foldable electrode device replaces the typical electrode burial method, enhancing worker convenience and allowing easy movement and installation of electrodes, thereby improving the efficiency of ground exploration work.  
Figure 5: Pin and cylindrical mass electrodes: (**a**) pin electrode; (**b**) cylindrical mass; (**c**) cylindrical mass electrode.