To get electronics and radio applications on board in the aviation industry, electrical engineers need familiarity with engineering standard RTCA DO-160 (DO-160), which governs all testing aspects of commercial airlines and airborne equipment for the Federal Aviation Administration (FAA).
Standardized testing aims to reproduce the environments that would be seen on the aircraft, for example, temperatures, vibrations, or the electromagnetic environment. D160 is divided into test sections. Sections 4 through 14 as well as 24 and 26 focus on environmental test conditions, which cover temperature, altitude, humidity, vibration, and other attributes which challenge the mechanical durability of electronics products. Sections 15 through 25 (aside from section 24) would center on radio frequency (RF) and electromagnetic interference (EMI) categorizations for certification.
Does a product need to be tested on every section of the standard document? A test section is determined to be applicable based on the product’s placement on the airframe (whether internal or external, for instance) and the product’s criticality to the safety of the aircraft. A test product may have to demonstrate effectiveness on each one of the sections or just a subset.
Like Department of Defense (DoD) standard MIL STD 416G, which tests for electrical interference on installations on the ground or on ships, a large portion of DO-160 does the same for electronics in the air. The substantial difference between the two requirements is that aviation testing includes the mechanical stresses from environment on the product design.
These evaluations are described in the guidance and are mostly straightforward: extreme changes in temperature, high humidity, shock and crash durability, explosion proofness, accelerated corrosion, waterproofness, and blowing sand and dust resistance.
Of course, many of these apply more to external equipment exposed to the elements, or those system elements most critical to the flight of the plane. If your test equipment is a coffee pot hot plate, for example, it wouldn’t be exposed to blowing sand, nor would it be subject to that test in D160.
RF Emission and Susceptibility
The backbone of D160 for electrical engineering is the emissions and susceptibility testing guidance. No matter what the criticality of the electronics product, it still must be assessed for the radio frequency energy it emits, and its performance when exposed to radiated frequencies from nearby sources.
The testers will direct various levels of RF energy onto your product through either radiated susceptibility — through antennas — or conductive susceptibility, where an injection transformer probe would be inserted into the device and into each individual bundle of I/O or power lines to show that the system can handle the exposure.
For a more detailed description of the setup of equipment for emissions and susceptibility tests inside Farraday test chamber, see the recent post about MIL Standard 416.
image credits: InterferenceTechnology.com
Other Electrical Tests in DO160
For other electrical effects covered in the aviation document, see Quell’s summary pages for schematics, breakdown of requirements, and common test values.
Magnetic Effect – One initial test is for the magnetic effect, and judges what impacts the equipment will have on the true north of a compass. Even though today’s navigation is achieved through GPS and hall effect sensors, D160 evaluators still use an actual compass to assess how close to the object it takes to change the bearing by one degree.
Power Input – Power input testing looks at power surges, frequency transients, and current harmonics originating from the design during performance. Power input is the single largest test section within D160, partially because there’s so many different variables of input power, from your basic DC to a single-phase AC to a three-phase AC.
Constant Frequency – Constant frequency (CF) — whether the product is intended to operate at 400 hertz or 800 hertz or anywhere in between — generates a lot of variety in the power input section as well. Many cases require different criteria and different methods of reproducing each of the potential phenomena. For devices under testing that operate with a range of frequencies, the test setup may use increments of 20 hertz to demonstrate that your system will handle the entire spectrum.
Voltage Spike – A voltage spike is a power line transient from a switching effect. For example, a 600 volts operation might generate a 10-microsecond-wide pulse with a less than two microsecond rise. Such small spikes do cause quite a bit of failures in D160 testing.
Audio Frequency – Conductive interference on AC or DC power lines can cause a low frequency ripple. Testers would reproduce that ripple voltage on the input power line to your device range of 10 Hz to 150 kHz to see how the product responds to those phenomena.
image credits: InterferenceTechnology.com
Power Lines and I/O lines
D160 scrutinizes not only your device but also its input power lines and I/O or communication lines for energy effects. Coupling tests might wrap I/O lines with wire to simulate an electrical field or a magnetic field and measure to what degree this changes output signal. Or tests can use voltage transients to see if the cabling of your system causes communication issues.
Cabling and connectors used in testing should be exactly the same as those intended for use in deployment. With over a million units sold to aviation and electronics customers, Quell offers EMI protection for a wide range of common connectors and are a low-cost and effective way of reducing interference in power and communication lines in both testing and on the plane.