Getting source characterization first-time right, can be a challenging task. To achieve good quality, it is essential to detect overloads, detached sensors, broken cables, and noise issues.
The operational consistency evaluates the consistency of the response data through the Virtual Point Transformation.
At low frequencies, all sensors linked to a Virtual Point should move consistently as a rigid body. When this is the case, the operational consistency is close to 100% and your data is good. If this value drops, it means that your structure has some flexibility or that the operational dataset has some problems that you can understand and fix immediately before moving on.
The operational consistency provides information at Virtual Point level. If the operational consistency of a VP is low, you need to use other means (ODS, graphs, etc.) to spot which sensor or channel is causing the issue.
It is essential that you check the operational consistency of each recorded operational condition. You must check it right after each measurement to ensure that problems (such as detached sensors or sensor overloads) do not propagate while you measure different operational conditions.
The white areas correspond to channels with the lowest consistency. If the whole plot turns white at the same time while zooming in on the consistency axis, you have very similar data quality. If you’re satisfied with the minimum consistency, you can move on to the next quality checks.
Here are some general guidelines when checking operational consistency.
A good model has an overall operational consistency at low frequencies of 90% or more. However, this threshold varies according to the component, the chosen setup and the checked frequency range.
The more sensors are in a VP group, the lower the overall consistency will be.
You want to make sure that all sensors stay glued in place during your measurements. Due to the vibrations, sensors can detach and fall. This has to be spotted immediately after the measurement. The operational consistency of the whole VP group will be reduced mainly in the higher frequency range as the cable acts like a low-pass filter on the sensor. In this case, you should check if all sensors in this VP group are still well attached.
You could also check the ODS, to see which sensor does not move consistently.
When a sensor measures a voltage that is higher than its measurement range, it gets overloaded. When a sensor is overloaded, the operational consistency drops at the time block when the overload happened.
If the operational consistency drops when comparing different time blocks, there is a signal problem, e.g., an overload. Overloads are also visible in time and waterfall plots. If you have overloads, you need to repeat the operational measurement. If you keep getting overloads, you might want to use less sensitive sensors. If you replace sensors, remember to repeat artificial excitation measurements and change the sensor in DIRAC.
To perform the calculations needed for a source characterization, you must correctly map the FRF and the operational channels. If something goes wrong with the mapping, the operational consistency of the sensors of that Virtual Point will decrease in the whole frequency range.
If you see low operational consistency of one Virtual Point over the entire frequency range, you might have wrongly mapped the channels. Open the channels card, check and correct the mapping. ODS can also help to spot inconsistent sensor movement.
If one sensor is rotated on the test setup compared to how it is oriented in the DIRAC file, the operational consistency of that Virtual Point is low.
If you see low operational consistency of one Virtual Point over the entire frequency range and at different time blocks, you might have a wrongly oriented sensor in your test setup. You can check the sensors movement by playing the ODS.
To fix it, you must open the DIRAC file, compare the design of experiment with the physical test setup, and rotate the sensor in DIRAC correctly. Then, you must correct the orientation in SOURCE. You can either manually type the new sensor orientation in the channels card or remove the master channels, import the corrected DIRAC file, create new master channels and redo the mapping.
Contact us for more VIBES
Contact our support team or call us on +31 85 822 50 49
Subscribe to our newsletter
Privacy statement. By submitting this form you agree to having your details registered in our database. At your request, we'll remove your details from our database immediately *