# Monitoring and Data Analysis in Small-Scale Landslide Physical Model
## 3 Review of Landslide Monitoring Equipment
### Geotechnical Monitoring System
#### 3.2.2 MEMS Accelerometers  
Sensors used for observations of acceleration in the model are micro-electro-mechanical systems (MEMS) that are made using the techniques of microfabrication and have miniaturized mechanical and electromechanical elements. Two different types of MEMS accelerometers were used in the tests--ADXL345 by ANALOG DEVICES (Analog Devices Inc., Wilmington, MA, USA) and MXR9150M by MEMSIC (MEMSIC Inc., Tianjin, China), which are shown in Figure 6 and their specifications compared below in Table 7. Production and development of MEMS sensors is very broad with different base designs; therefore, comparisons between similar sensors are hard to make, but [PERSON] et al. [19; 47], [PERSON] et al. [48], and [PERSON] and [PERSON] [49] used similar types of ADXL sensor by ANALOG DEVICES. Results from the MEMS sensors also depend on the operators' method of calibration, sensor bias (offset), and sensitivity of each sensor type. The ADXL345 MEMS is a 3-axis digital accelerometer with high-resolution (13-bit) and measurement ability up to \(\pm\)16 g. It is supplied in a small, thin LGA package with dimensions of 3 \(\times\) 5 \(\times\) 1 mm. Sensor has low power dissipation due to intelligent motion-based power management where power is 0.1 uA in standby mode and 23 uA in measurement mode at typical power supply of 2.5 V. It can measure both dynamic accelerations resulting \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Accelerometer** & **Manufacturer** & **Type** & \begin{tabular}{c} **Measurement** \\ **Range** \\ \end{tabular} & **Sensitivity** & **Bandwidth** & **Voltage Range** \\ \hline ADXL345 & \begin{tabular}{c} ANALOG \\ DEVICES \\ \end{tabular} & \begin{tabular}{c} Digital accelerometer, \\ 3-axis \\ \end{tabular} & \(\pm\)16 g & 256 LSB/g & \
\begin{tabular}{c} min. 0.05–max. \\ 1600 Hz \\ \end{tabular} & 2.0–3.6 V \\ \hline MXR9150M & MEMSIC &
\begin{tabular}{c} Analog accelerometer, \\ 3-axis \\ \end{tabular} & \(\pm\)5 g & 150 mV/g & typ. 17 Hz & 2.7–3.6 V \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Specifications of accelerometer types—ADXL345 MEMS by ANALOG DEVICES and MXR9150M MEMS by MEMSIC. Figure 6: MEMS accelerometers: **(a)** ADXL345 by ANALOG DEVICES; **(b)** MXR9150M by MEMSIC. from motion or shock and static acceleration, such as gravity, which allows it to be used as a tilt sensor. ADXL345 has free-fall detection, \(10,000\) g shock survival, wide operating temperature from \(-40^{\circ}\) to \(+85^{\circ}\), and a very small device weight of 30 mg. Because of its high resolution, it can measure inclination changes smaller than \(1.0^{\circ}\)[64]. The sensor consists of polysilicon surface-micromachined structure that is built on top of a silicon wafer. Springs suspend the structure over the wafer and provide a resistance to forces from the acceleration. The shift in the structure is measured using differential capacitors that consist of fixed plates and plates attached to the moving mass. Acceleration causes a shift of the proof mass and unbalances the differential capacitor which results in a sensor output amplitude proportional to acceleration [64]. The MXR9150M MEMS is a low-cost 3-axis analog accelerometer with measurement ability up to \(\pm 5\) g. It is supplied in a hermetically sealed, surface mount LCC package with dimensions of \(7\times 7\times 1.8\) mm. It can measure both dynamic acceleration and static acceleration such as gravity. Operating temperature is in a wide range from \(-40^{\circ}\) to \(+85^{\circ}\) and has a shock survival rating \(>50,000\) g.  
Unlike the ADXL345, the MXR9150M MEMS is a thermal accelerometer designed based on heat convection and does not require proof mass to function, which gives it such a big shock survival rating. This MEMSIC sensor operates like other accelerometers with proof mass except it is a gas in the sensor. In the center of the silicon chip is a heat source, suspended across a cavity with four equally distanced aluminum/polysilicon thermopiles on all four sides of the heat source.