Vehicular electronics and interiors have their own testing standards that can differ dramatically from those of other industries.
James Bryans,
Manager, Environmental and Performance
Intertek Group plc
One might assume that many of the tests run at third-party testing facilities would already have been completed by product developers. Surprisingly, that is frequently not the case. Often there are significant and severe issues to be addressed.
Take, for example, tests of security measures on infotainment equipment. We have been known to receive release candidates with beta code still enabled: encryption is turned off. A basic security sweep will reveal this fact before the equipment hits the market. It’s a good idea for third parties to perform basic security tests in almost all circumstances. The costs are relatively low and the risk is high if equipment fails one of those tests.
Generally, many organizations that are focused on producing and developing new products approach testing from the point of view that, now that it works, let’s find new things that don’t work. A third-party organization assumes everything will fail, and we consistently find problems and issues that our customers miss.
That’s unfortunate because a car or truck’s interior electronics can play an important role in overall performance and customer satisfaction. So the testing of these components should be a high priority for manufacturers and suppliers. A variety of tests apply to automobile interiors, many relating to the electronic components.
Environmental testing considers how climate impacts a car’s interior. Materials see various simulated environmental conditions in chambers that replicate accelerated aging and environmental elements. Typical test conditions include exposure to infrared (IR) light, soaking in extreme temperatures, temperature shocks, humidity, and exposure to chemicals and solvents.
An often-referenced specification for testing is one developed by General Motors Corp. called GMW (for GM Worldwide standard) 3172, which encompasses environmental testing and provides information on the various material, components, assemblies and end-products that should get tested, as well as qualifying results.
Similar to environmental testing, durability testing can apply to a variety of materials including plastics, metals, composites and more. Durability testing is typically some form of life cycle testing; simulating the “life” of a product to see whether the design is of a robust nature and will perform as intended for the life of the vehicle. It incorporates environment as part of the “stressor.” The Device Under Test (DUT) will see a set number of durability cycles at temperature extremes of 85°C, -20°C, and 45°C along with 85% relative humidity.
Most manufacturers in the automotive industry examine the ten-year lifespan of various interior products, including electronics, through durability testing, based on 7,000-10,000 cycles. In all, durability testing can take two to three weeks, depending on the product, how robust the process is, and manufacturer requirements. A few specifications that are often applied to durability testing include GMW 3172, GMW 8287 covering highly accelerated life tests, stress screening, and auditing; and the Ford environmental cycles/exposure specification DVO-0001-IP. These address which components should be tested, how testing should take place, cycle requirements, and required results.
The chemical and physical properties of materials must also be assessed. These evaluations provide information on how materials can be used together, how they will stand up to usage/wear and how they may interact with fire or environmental factors.
Materials testing can cover a range of items: discoloration, scratching, scuffing, abrasion and material break down; functionality; resistance to ozone, mildew and chemicals; spot tests and more. Laboratory accreditation to ISO 17025 is important for material testing. This is the main ISO standard used by testing and calibration laboratories. In most major countries, labs must be accredited to ISO/IEC 17025 to be deemed technically competent. In many cases, suppliers and regulatory authorities won’t accept test or calibration results from a lab lacking this accreditation. ISO/IEC 17025 has many commonalities with the ISO 9000 standard but contains more specific requirements for competence.
Similarly, sound, or lack thereof, can play an important role in the experience of driving or riding in a vehicle, and unexpected or unwanted sounds can be distracting, and possibly dangerous. Buzz, squeak and rattle (BSR) testing examines components that may make unwanted or unwarranted noises, such as instrument panels, radios, speakers, audio equipment and more.
Industry specifications such as GMW 7293, GMW 14011, Ford CETP 01.01-L-407 and Ford CETP 15.01-L-402 help set parameters for acceptable loudness levels. BSR testing uses low-noise vibration/shaker systems to simulate movement to identify components that aren’t properly installed. This takes place in a quiet, soundproofed room with sensitive microphones and recording systems, or by having a technician stand in the quiet testing area to physically evaluate what can be heard.
Failure Analysis/Accelerated Stress Testing
Failure analysis and accelerated stress testing (AST) can be applied to virtually any element, material, component or assembly in a vehicle’s interior, including electronics. Failure analysis testing examines why and how issues arise and what can be done to prevent them. AST simulates more comprehensive real-life conditions to help assess product life and reliability. Failure analysis testing can often last two to six weeks, although that time range can vary greatly.
AST can relate to environmental, electrical and mechanical durability tests methods for many automotive interior products, including instrument panels, center consoles, seats and mechanisms and infotainment systems. A variety of accelerated stress test methods can help check out automotive interior components and assemblies.
Failure-mode verification testing (FMVT) can help identify product weaknesses from failures coming out of the simultaneous interaction of multiple combined real-world stresses, including thermal vibration with humidity, mechanical shock, electrical stress, mechanical cycling, contaminants, and solar radiation.
FMVT can be used to validate failures predicted by the Failure Mode and Effects Analysis (FMEA) process. Multiple failure modes (and their sequence and distribution) are produced by exposing a design to a combined set of amplified environments/stresses.
The value of FMVT is the context it can provide to failure modes. FMVT examines what will fail, what will cause the failure, and how the failure ranks against other failures. This differs from conventional methods that apply a single test (say, a high-temperature soak) to a group of samples and note which ones fail. A single-point test like this can yield statistical failure data but doesn’t necessarily identify weaknesses in designs.
In FMVT, parametric functional tests take place at the beginning and the end of a test sequence. The DUT is operated at its maximum operating temperature and voltage, minimum operating temperature and voltage, as well as at the nominal operating temperature and voltage. This process is typically called a three-point or five-point evaluation. Technicians then compare the pre-test parametric measurements to post-test parametric measurements. Any degradation of performance can then be compared and evaluated.
Highly accelerated life testing (HALT) is often used with printed circuit board electronics and other electromechanical products to identify potential issues.
A lot of vehicle design and manufacturing focuses on external lighting of headlights, taillights, brake lights and turn signals. However, interior lighting can be just as critical because it often includes warning lights, internal indicators and cabin illumination. There are specific lighting specifications for all vehicular light sources. And lighting components get subjected to many of the same tests as all other components within the vehicle. Headlamps will see the regular environmental tests with additional tests that evaluate fogging of the lens, for example.
Lighting can be sensitive to temperature, humidity, vibration and other environmental conditions. As such, lighting components (including plastic, metal and glass as well as filaments, coverings, switches, circuitry and other materials) and assemblies must undergo environmental, durability, materials and failure analysis tests.
Audio/information/entertainment (infotainment) systems may include radio and audio, in-dash navigation and information, and even connections to dedicated mobile applications and mobile-synced devices. Testing for in-vehicle infotainment frequently involve using emulators on desktop or laptop computers to test apps and operating systems. Tests typically cover dashboard warnings, navigation systems, phone/Bluetooth connections, radio interfaces and related Internet-connected mobile apps.
Elements of infotainment testing include checks of compatibility, verifying the robustness of signals and connections, ease of use, accuracy of displays and information, battery usage, ability to connect with other apps or in-car programs, quality of the operating systems, timing in usage, how multiple programs interact and work together, load testing based on the number of programs or systems, and more. It’s also important to test devices that might sync or interact with an in-vehicle infotainment system, such as Bluetooth headsets, smart phones, tablets and vehicle-independent navigation systems.
Vehicle elements that connect to the Internet require additional security screening to protect the personal and private information they may contain, and to verify they operate safely. Design engineers often think that security is a matter that should be assured long before vehicle systems get sent out to third-party testing. That’s true, but testing is a complex task. One thing that often happens to internal teams is that they encounter testing fatigue.
Third parties typically don’t run tests much differently than development teams, with the exception perhaps of using a more robust test infrastructure. However, third-party testers do have access to professionals who have seen a wide variety of products and programs, and who can think outside the daily grind of running the same test plan repeatedly.
EMC
Electromagnetic compatibility (EMC) testing often is applied to individual vehicular systems but sometimes takes place at the full vehicle level. Automotive EMC testing is much different than EMC testing for other types of products. Automotive EMC tests are characterized by different limits, test methods, and equipment. There are two ways of running radiated EMC tests for automotive products. The first is radiated emissions testing, where RF signals emanating from the system are measured with an antenna and compared to a limit. The second is radiated immunity testing, where the system is irradiated with an RF signal via an antenna and swept over a determined frequency range while the system-under-test is monitored for performance upsets.
Radiated EMC testing often takes place in an absorber-lined shielded enclosure (ALSE). The ALSE chamber provides a shielded and low-reflective RF environment. It keeps unwanted ambient RF signals from polluting the test environment and keeps the RF generated during immunity testing from possibly interfering with equipment or other tests taking place nearby. Also, the low reflectivity helps keep measured RF fields uniform during testing.
EMC testing covers more than just radiated emissions and immunity testing. There are also conducted- immunity and conducted-emissions tests. These resemble their radiated counterparts, but they focus on lower frequencies and gauge to what degree these lower-frequency RF signals couple to input power lines and other I/O lines. Rather than using an antenna, the conducted emissions measurement is made on-line through a line impedance stabilization network (LISN). A conducted immunity test method often employed on automotive systems is bulk current injection (BCI).
BCI is used to inject RF current into conductors and cables of electrical and electronic equipment undergoing susceptibility testing. This often takes place using an injection probe that applies a controlled RF stress level without a direct connection to the conductor(s) of interest. The probe simply clamps around the test conductor which then becomes a one-turn secondary winding, with the current probe forming the core and primary winding of an RF transformer. RF energy can be injected onto single and multi-conductor cables, grounding and bonding straps, outer conductors of shielding conduits and coaxial cables, etc. A second clamp-on style current probe is used as a monitoring probe to monitor the applied energy during the test.
BCI involves electrical currents in the 1 MHz to 1 GHz range. A BCI test setup gives valuable information about susceptibility to induced high-frequency currents. High-frequency noise can arise from such electrical events as high-voltage electrical ignition modules, relay coil and contact opening or closing, nearby lightning, and other transient electrical events. While BCI can cover the 1MHz to 1GHz range, BCI testing rarely takes place above 400 MHz. Testing above 400 MHz is usually performed by the radiated immunity ALSE method or another technique called the reverb method.
Manufacturers and suppliers may want to seek out testing in reverb chambers instead of in an ALSE for radiated immunity and emissions. It’s possible to perform radiated emissions testing in a reverb chamber, but it is far more common to see reverb chambers used for radiated immunity testing. Electromagnetic reverberation chambers – also known as mode-stirred chambers (MSCs) and mode tuned chambers (MTCs) depending on method used — are shielded rooms designed so they don’t absorb much electromagnetic energy. (As distinguished from ALSE chambers which are designed to absorb RF energy.) The low absorption permits a high EM field strength with moderate input power.
A reverberation chamber is basically a cavity resonator. The electrical and magnetic fields form standing waves in the chamber. The chamber uses what are called tuners (stirrers) to reduce this effect and to create a voluminous EM field. Tuners are large metallic reflectors that can be moved around to produce different boundary conditions. The lowest usable frequency of a reverberation chamber depends on the size of the chamber and the design of the tuner. The size of the EM field or RF test volume created in the reverb chamber is rather large and allows for larger systems to be fully immersed in the EM field.
Other EMC tests to consider with an automotive system include tests that emulate other electrical phenomena in a vehicular environment, such as electrostatic discharge (ESD) and electrical transients.
EMC test labs are typically accredited to the ISO 17025 standard by a third-party accreditor. Additional standards can also apply, including pre-compliance and test plan development services.
The post Basics of Electronics Testing for Automotive Interiors appeared first on Test & Measurement Tips.
Filed Under: Test & Measurement Tips