TELKOMNIKA: Indonesian Journal of Electrical Engineering
ISSN: 1693-6930, e-ISSN: 2087-278X
accredited by Directorate General of Higher Education of Indonesia, SK No: 51/Dikti/Kep/2010
A Simple Instrumentation System for Large Structure Vibration Monitoring (Didik R.Santoso)
A Simple Instrumentation System for Large Structure
Didik R. Santoso
Division of Instrumentation, Physics Department, Brawijaya University
Jl. Veteran 2 Malang 65145; Telp. +62-341-575833, Fax. +62-341-575834
Traditional instrumentation systems used for monitoring vibration of large-scale
infrastructure building such as bridges, railway, and others structural building, generally have a
complex design. Makes it simple would be very useful both in terms of low-cost and easy
maintenance. This paper describes how to develop the instrumentation system. The system is
built based on distributed network, with field bus topology, using single-master multi-slave
architecture. Master is a control unit, built based on a PC equipped with RS-485 interface. Slave
is a sensing unit; each slave was built by integrating a 3-axis vibration sensor with a
microcontroller based data acquisition system. Vibration sensor is designed using the main
components of a MEMS accelerometer. While the software is developed for two functions: as a
control system hardware and data processing. To verify performance of the developed
instrumentation system, several laboratory tests have been performed. The result shows that
the system has good performance.
Keywords: Instrumentation system, MEMS accelerometer, Microcontroller, Distributed system.
The aim of structural health monitoring (SHM) is to provide periodic or continuous
inspections of structural members to get current data for verification if the structure is under a
load, behaves unusually, or damaged . The SHM covers a broad field that encompasses a
number of synergistic technologies that together can provide a system. Viewed from the aspect
of instrumentation system, SHM at least has three main parts; sensor technology, data
acquisition topologies, and network architecture .
Vibration is one of physical parameter that’s often used on the SHM activity , , .
Vibration can be measured by using some kinds of sensors, such as strain gauge, fiber optic,
piezoelectric, and accelerometer. Of course each of them has own merits and limitations.
Currently, the use of MEMS accelerometer as a vibration sensor began to demand. The
advantage is its small size, compact, sensitive, lightweight, and relatively cheap , . MEMS
accelerometer is also available in commercial markets in various types, including those that had
3-axis sensing. And then measurement of vibration in three directions (XYZ) can be performed
only by using a single MEMS sensor.
The other hand, the application of the microcontroller-based instrumentation system
recently has been growing , . In the development of modern instrumentation systems, the
use of microcontrollers as the brains of the data acquisition system is commonly done. It has
small size, programmable, simple, reliable and low-cost. The use of microcontroller in hardware
design can improve performance, simplify design and implementation.
Furthermore, a commercial SHM Instrumentation system usually has complex design and
then very expensive. Therefore, development of the system in the simple way and low-cost in
budget is desirable and challenge for researchers. This is useful not only for in truth simple and
low-cost application, but also to conduct research activities in the structural safety system. In
this research, a simple and inexpensive instrumentation system, which may be useful for on-line
distributed 3-axis structural vibration monitoring has been developed.
TELKOMNIKA Vol. 8, No. 3, December 2010 : 265 – 274
2. Description of the System
Usually SHM instrumentation using a distributed system architecture, it is an open and
standardized system to bring varieties of sensors under one umbrella. The system is powerful
for large area of measurement, due to distributed burden, easy system growth, lower possibility
of data losses, and easiness of measurement of simultaneous events . Figure 1 shows the
architecture of the developed system. The system builds on a multi-drop network topology with
single-master multi-slave architecture. It has consists of single master unit (called as master
terminal unit, MTU), and several slave units (called as remote terminal unit, RTU). MTU is
control unit and RTU is sensing unit. Communication between MTU and RTU is conducted
through RS-485 bus system, which meets the requirements for a truly multi-point
communications network, and the standard specifies up to 127 nodes even more on bus.
Maximum cable length can be as much as 1200 m and can be either half-duplex or full-duplex.
This architecture has the advantages such as high noise immunity and fast signaling rate, up to
115.200 kbps even more .
RS-485 Fieldbus network (data & power)
RS232 to RS485
MASTER UNIT (MTU)
Figure 1: System architecture
In the RS-485 MTU-RTU communication procedure, RTU device takes over the control
while RTU devices get the address, which upon they can be called. Every RTU has its unique
address and responds only to packets addressed to this unit. A protocol is required to ensure
that no more than one RTU transmits at any one time on the network. In this design, the MTU
contacts a particular RTU by transmitting its address number, followed by a command, for
example sampling time, number of data sampling, etc. All RTU hear the address number and
ignore any command not addressed to them. RTU device with matching address sends its
address to the MTU device as a confirmation of successful transfer and receives data, so lets
the MTU know that it is alive and well. In case that RTU device does not send its address in
some specified (time out) period, MTU will declare the RTU. After RTU get its correct address
from MTU, then internal process for data acquisition is beginning soon. Figure 2 shows flow
chart of communication procedure between MTU and RTU.
TELKOMNIKA Vol. 8, No. 3, December 2010 : 265 – 274
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