SPECIAL FOCUS MILITARY & AEROSPACE EMC design considerations
As a developer of AC and DC transducers for military and aerospace applications, American Aerospace Controls ensures its technologies have full design compliance with EMC standards. Here, the company explains why, and looks into the applications for its products
A
C and DC current, frequency and voltage measurements for military
and aerospace applications are conducted in some of the harshest environments, yet still require high-reliability operation for support of mission-critical systems. The conditions faced by military and aerospace related AC and DC current monitoring applications may mean they are plagued by the undesirable presence of electromagnetic interference (EMI) and radio frequency interference (RFI), both of which can lead to measurement uncertainty. Electrical current moving through cables, connectors, PCB traces and RF signals emitted by transmitters, radios and other electrical equipment can all become sources of undesirable EMI or RFI. RF noise generates RF currents and voltages that can radiate and induce electrical coupling between conductors, sometimes through insulating materials and dielectrics. Conducted RF voltages and currents can also interfere with interconnected devices and systems, even if cables are bundled with or in close proximity to them. At their heart, interference anomalies occur because the RF noise and desired operating signals exist within the same frequency ranges. The effects can range from system
performance inconsistencies and measurement errors, reduced device functionality or shutdown. Or, worst-case scenario, can result in permanent damage. To ensure reliable and continuous AC
and DC current transducer operation, devices and components must conform to an array of electromagnetic compatibility (EMC) standards that ensure standards- compliant devices operating within a specific application do not otherwise interfere with components. As an example, the MIL-STD-461
standard covers the requirements and test limits for electromagnetic interference (emission and susceptibility) of electronic, electrical, and electromechanical equipment for military applications. Products that meet MIL-STD-461 have been rigorously tested to determine that the radiated or conducted signals they
12 MARCH 2014 | DESIGN SOLUTIONS
might produce will neither interfere with, nor damage, other system components. Similarly, the DO-160 standard outlines
a set of standard environmental test conditions and corresponding test procedures used to assess the operational performance of avionics electronic hardware. Each standard is divided into sections relating to specific areas, such as temperature and altitude effects. For electronic components, this also includes measures of magnetic effect, voltage spikes, conducted audio and RF signals, and electronic emissions. A military and aerospace related customer specifying an AC or DC current sensor will often be well-versed in the specific standards to which their devices must conform. These standards, in turn, will dictate how the equipment or device must be tested to ensure full compliance.
PRODUCT DESIGN American Aerospace Controls is an ISO9001 and AS9100C designer and manufacturer of AC and DC voltage, current, frequency and power transducers. Over the years, the company has evolved its sensing technologies for full design compliance with EMC standards, as well as those set forth by DO-160 and various MIL and EN specs. When designing AC and DC current
and frequency transducers for operation within military or aerospace
Over the years, the company has evolved its sensing technologies for full design compliance with EMC standards, as well as those set forth by DO-160 and various MIL and EN specs
environments, AAC engineers work firstly on reducing, suppressing and containing device emissions, as well as isolating the transducer from external environmental interferences. This is done in a number of ways: by
adding EMI shielding within the device to minimise or eliminate emissions; by careful control of PCB layout and connectors to reduce emissions, cross-coupling and induced transients; via the incorporation of a metal housing as a Faraday cage to isolate the device from external signals; by adding EMI filters onto electrical connectors to suppress EMI; and by adding EMI filters and transient protection on both the input and output of the device. As an example, the company’s Series S1028 AC current level detector is designed to measure AC currents from 0–250A within a frequency range of 360 to 650kHz. This is used in flight situations to monitor many different systems within the plane or helicopter – including monitoring power supplied to the
landing gear, radar systems, cabin and galley heating elements, braking systems and cockpit controls. Its EMC performance complies with portions of the DO-160E standard as it applies to commercial avionics electronic components. The Series S1048 DC current level detector is designed to measure DC currents and has trip points of ±1 ADC (S1048-1) and ±3.3 ADC (S1048-3.3). The device is used to monitor the same types of systems and complies with the same EMC and DO-160 standards. AAC ensures the full EMC compliance
of its AC and DC transducer technologies through extensive in-house testing expertise and customer specified design requirements at the earliest stages of transducer design. Tests include thermal cycling and powered burn-in soaks, with data acquisition monitoring throughout testing, ensuring product quality and reliability.
American Aerospace Controls
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