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Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Exploitable results
Functional safety represents that part of overall safety which depends on equipment or a system to operate correctly in its entire operational environment to take into account other environmental effects such as vibration, temperature, and humidity. Performance degradation of components and equipment due to aging and production spread are included in the functional safety concept as well.
While introducing the concept of functional safety, the Safetel project has shown that the immunity problem cannot be characterised by a simple deterministic approach, but shall be viewed within the wider domain of stochastic processes.
In defining the immunity level for equipment the project partners wanted to answer the question: 'How far are we from upsetting that equipment?' More precisely they wanted to know what the probability of obtaining a default (or even a malfunction) is; given that they were exposing the equipment to a certain level of interference.
With an intended purpose of taking into account all the parameters related to functional safety, in both the test and design processes of automotive equipment and systems, engineers shall guarantee a safety margin (which is defined as the difference between the correct performance of an equipment system, and its actual performance in the presence of electromagnetic threats). Therefore it becomes compulsory to put the definition of safety margin within a framework based upon statistical considerations.
The most innovative aspect of the Safetel project has been the introduction of the 'Detection theory', which is part of the 'Statistical signal processing theory', for approaching immunity problems in both the design and testing processes. Detection theory is an engineering term for that which the statistician calls hypothesis testing or decision making. The approach is first to take measurements, and then estimate in which of a finite number of states an underlying system resides.
The subjective assessment of equipment under test (EUT) immunity made by visual and/or aural monitoring of performance degradation is no longer of sufficient quality. The approach proposed by the Safetel project attemtps to fill the gap that exists between the development of new technologies, and immunity test methods that introduce new processing test result techniques. This is done without increasing the cost impact by avoiding the use of sophisticated test equipment.
Instead of increasing the amplitudes of the susceptibility signals the approach proposed in the Safetel framework is to determine in the monitored parameters, trying to find the onset of any failure or default. Obviously, the major problem here is that in most cases the susceptibility signal contribution is hidden in noise generated by the monitoring devices, and also by the susceptibility signal generators, which are not stable in amplitude and frequency.
Once a suitable performance signal is identified, a major effort should be made to filter out all the noise components, and at the same time, to increase the sensitivity of the measuring device. Statistical signal processing algorithms can do both things efficiently, which allows the establishment of a direct link in real time between the susceptibility, and its effect on the monitored EUT performance.
During the Safetel project several detection algorithms have been examined, discussed and tested, in an attempt to match all possible situations of monitored signals:
-Anova,
-abrupt change models based upon generalised likelihood ratio (GLR) usage,
-time series,
-regression with random input data (single input- single output),
-logistic regression.
The last one is very interesting because it is suitable to treat most immunity test cases, which presently are mainly qualitative of 'go - no go' type. In this situation it is difficult to define any susceptibility safety margin. However with the logistic regression algorithm and with the use of a large data base, it becomes possible to overcome the difficulty of a purely qualitative approach.
The 'High intensity susceptibility system' facility is another important topic dealt within the Safetel project. It is not intended to increase the susceptibility signal but, rather, to improve the detection technique by digging in the above signal to find any minimum susceptibility effect, or at least to discover start of any failure mechanism. In the proposed facility the meaning of the word 'high intensity' is introduced in the sense that the facility should allow maintenance of the upward dynamic range (maximum level/specification limit) of the susceptibility signal, equal to the downward dynamic range (guaranteed performance level/minimum detectable level) of the monitored parameter.
Each unit of the vehicle has to be designed to meet the specified limits of electromagnetic compatibility (EMC). The Safetel project considered only the radiated immunity threat characterised by moderately high energy and frequencies that can propagate in unexpected ways to components of circuits, and cause unexpected effects.
The EMC design related to radiated immunity problems should address the following scenarios:
- field to cable coupling,
- field to unit coupling.
In the automotive field cable shields are not common; therefore much attention was paid to the enclosure shielding design. This topic requires special attention. The reason for this is simply that the enclosure is the last line of defence for controlling electromagnetic irradiation (EMI), often the difference between meeting specification requirements and not meeting the requirements. Minor miscalculations in gasket pressure, aperture dimensions and seam design, for example, may result in major EMC problems.
The design rules examined during the Safetel project have been divided into two categories:
- conventional,
- unconventional.
In the former, the design principles are discussed in many EMC textbooks and are mainly related to grounding, bonding, filtering, shielding and cabling. These rules, which represent the basic background of any EMC engineer, represent the reference frame of the design of electrical and electronic equipment and system in any field. For this reason they do not always take into account the important issues of the automotive world related to large production yields, and the great variability of the external electromagnetic environment where vehicles are expected to operate correctly and safely. Additionally, the major EM threats are represented by internal and external wanted sources, which obviously cannot be suppressed. Spurious emissions, which may be detrimental to communication systems, do not actually represent threats to automotive equipment due to their low levels of emissions.
In the latter approach advanced design rules were proposed based upon the extensive use of statistical signal processing techniques. Because we cannot get rid of susceptibility problems, which are becoming more and more important in the EM environments of future years, we have to introduce those hardware and software precautions capable of detecting the start of any failure mechanism to the automotive equipment; and to estimate the parameters of suppression devices which shall be included in the automotive equipment design from the beginning.
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