Berufsgenossenschaftliches Institut für Arbeitsschutz (BGIA)
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 Mobile Data-logger for Stress Analysis
of the Musculo-skeletal System
CUELA (computer-supported recording and long-term analysis of
musculo-skeletal load) was developed at BIA in order to measure loads
on the musculo-skeletal system, as occur in a number of occupational
activities, directly at the workplace and under actual occupational
conditions. It is a person-related measurement system, which consists
of modern sensor systems and can be worn on the cloths. The associated
software, WIDAAN, makes possible automated evaluation of the
measurement data according to occupational and biomechanical evaluation
criteria. On this basis, it is possible to make statements on the steps
necessary for preventing occupational health hazards.
The data storage unit is the central component of the CUELA measurement
system. Here the analog measurement signals from the sensors are read
in, digitized and saved on a compact flash card. The sampling frequency
is adjustable and is normally 50Hz. The data logger is capable of
acquiring up to 96 channels with a 10-bit resolution. The pressure
values of the measurement soles are acquired – likewise up to 96 cells.
In a standard sensor configuration consisting of movement acquisition
and a pair of measurement soles, memory of approximately 22MB/h is
required; in other words, more than eight hours of measurement data can
be recorded on a conventional 192MB compact flash memory card. The
minimal energy consumption allows four hours of operation using a
compact Li-Ion battery. The signal connection of the sensor boxes to
the data logger is done using a specially developed bus-system.
Operation of the data logger is incredibly simple. A combined
start/stop button is all that is needed to operate the CUELA
measurement system. Four status LEDs display the current operating
status such as Boot Procedure, Ready to Measure, Measuring or Storing
Data.
SYS TEC 's development part consisted of the hardware and software for
the data logger. The device is compact, lightweight and portable. Power
consumption was minimized despite the frequent memory access. Because
of the high data volume, standard solutions were inadequate. A special
flash driver compresses the data and saves it in a log file on the
flash card. The technical challenge was to sample 168 sensors without
loss of data and to do so at a maximum sampling rate of 50 Hz and at
the same time to store the data on the compact flash card. In this
project, too, SYS TEC assumed the entire development activity up to
manufacturing. Creation of the specs, circuit diagram development,
circuit board layout, prototype startup, software development, device
testing and integration as well as manufacture of the production-ready
item were part of the performances. The project work at SYS TEC was
done in accordance with the quality guidelines of DIN EN ISO 9001: 2000.
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