Electric & Hybrid Vehicle Technology - July 2021
See the light (imc DataWorks)
2021-07-21 02:35:25
Fiber-optic CAN measurement modules provide safe and consistent isolation of the HV environment without the need for added equipment
▶▶The capabilities of fiber-optic measurement systems are many and diverse, with the field of e-mobility being one of the major and fastest growing applications.
Thanks to their purely optical measuring principle, fiber-optic CAN measurement modules offer a perfect isolation concept against high-voltage and eliminate the need for special safety equipment and training. As they are completely immune to electromagnetic interference, EMI/ESD related concerns can be dismissed.
The physical principle of FBG sensors is based on a glass fiber in which an optical grating is engraved. While measuring, white light fed into the fiber from a broadband laser source is selectively reflected at this interference grating. The narrow spectrum returned by the sensor represents the measured variable corresponding to the characteristic Bragg wavelength λ_B. It’s proportional to the strain and temperature of the fiber because these determine the optical grating intervals. The challenge in sensor development is to clearly separate these two influencing variables.
For temperature sensors, the fiber may only react to the inherent temperature expansion α(T) and the refraction behavior of quartz glass as function f(T). Therefore, it needs to be embedded stress-free to avoid the influence of external expansion or mechanical tension.
FBG sensor technology from imc DataWorks, a specialist in test and measurement solutions, has been specially developed to encapsulate the fiber in a glass capillary with a diameter of only 0.51mm. The extremely small design and minimal thermal mass ensures a correspondingly fast response speed with time constants of approximately 100ms. Such extreme dynamics are relevant for start-up tests on electric motors.
The FBG module uses an innovative approach to determine the Bragg wavelength. It measures the intensity in conjunction with an edge filter. This color filter, comparable to a frequency high-pass cut-off filter, attenuates the overall signal along the linear or exactly known filter characteristic. The measured intensity corresponds to the integrated narrow-band spectrum of this reflected and filtered signal.
Therefore, the change in intensity allows detection of the exact shifting of the Bragg wavelength along this filter characteristic. Finally, the relative ratio of filtered and bypass raw signal I_0 is examined. As a result, general transmission losses in the fiber or fluctuations of the laser source intensity do not have any effect.
For use within wider applications, the FBG module is electrically and mechanically compatible with the imc CANSASflex series. Users can dock directly to any measurement module within the flex series via the integrated click connector. This means that the entire imc portfolio of electrical measurement technology is available, including the intelligent imc BUSDAQflex CAN data logger, allowing fiber-optic and electrical measurement modules to be combined into a fully integrated measurement system. A wide variety of measurement, testing and control applications can be covered, and a wide range of vehicle and industrial buses can be integrated.
Not limited to cars only, fiber-optic measurements also applies to the electrification of agricultural machines and their previously hydraulically operated work implements. In addition to battery systems, many of their components and subsystems need to be developed and tested, such as charging infrastructure, cable harnesses, power electronics modules, connectors, etc.
The inherent EMC robustness of FBG technology also opens new areas of application, such as the direct measurement of temperatures inside the windings of electric motors. Developers of power inverters or power electronics, like those with new wide-bandgap semiconductors and modern inductive components can also benefit from the miniaturized and highly dynamic sensors in their development tests: Temperature profiles of power electronic components under load can be acquired without drastic electromagnetic interference fields affecting results.
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