ODiSI 6
ODiSI 6
User’s Guide
Page 93
System Operation Guidelines
The ODiSI 6 system provides precise strain or temperature change measurements at a high
spatial resolution along the length of an optical fiber sensor. It is best suited for static or low
loading rate tests.
Vibration Tolerance
Test Setup
Like most highly sensitive testing instruments, the ODiSI 6 system is susceptible to
environmental disturbances, most often vibration or motion of the sensor. Since the ODiSI 6
operates on signals reflected from the sensor, environmental disturbances, usually vibration,
can corrupt the measured data. It is very important to design tests that ensure that
environmental disturbances do not affect the measurements. In designing the testing, several
vibration related items to keep in mind include:
•
Check for vibration from other machinery on the test floor
•
Monitor vibration coupling to the sensor from the load frame
•
Check for shaking of unbonded sensor fiber
Strain Test Setup
The key to obtaining quality strain measurements is to ensure that the fiber sensor is properly
attached to the test piece. The surface needs to be prepared (scuffed and cleaned with
ethanol) and the fiber needs to be uniformly bonded down. Epoxy selection is also very
important as it determines cure temperature, optimal temperature range for use, and the
surface roughness of the test piece.
For tests at elevated temperature that require thermal compensation of strain measurements,
ensure that the compensation measurement device (unbonded fiber, thermocouple, or
dummy gage) is in the same thermal environment as the strain sensor.
See the
Applying Strain Sensors
document for more detailed instructions on mounting and
positioning sensors, which can be accessed from the Help menu on the ODiSI 6.
Troubleshooting Dropouts
The ODiSI 6 relies on a correlation of reference and measurement gage data to calculate the
strain along the sensing fiber. Environmental disturbances such as mechanical vibration can
lead to a degradation of the measurement data. Enough disturbance weakens the correlation
sufficiently to make a strain or temperature calculations unreliable. In these situations, the
software drops the unreliable strain measurement and replaces it with a NaN (not a number).
If a high number of dropouts are observed along the sensing fiber, the distribution of dropouts
over the sensing fiber’s length can help diagnose the source of the problem.
