Aerospace contactors are high-performance, high-capacity circuit controls designed for aerospace applications. They are used to switch large amounts of electrical power via multiple contacts and can operate at 400 Hz. Pole and throw configurations for aerospace contactors can be single- pole, single- throw (SPST); single-pole, double-throw (SPDT); double-pole, single-throw (DPST); or double-pole, double throw (DPDT). Contacts are either normally open (NO) or normally closed. A normally-open aerospace contactor has contacts that are open or disconnected in their non-actuated (normal) position. Power to the load is shut-off when the coil is de-energized. The coil circuit can be powered from an alternating current (AC) or direct current (DC) source. Aerospace contactors that are normally closed (NC) have contacts that are closed or connected in their non-actuated (normal) position.
Selecting Aerospace Contactors
Selecting aerospace contactors requires an analysis of product specifications, environmental parameters, and mounting styles. Product specifications include number of poles, maximum switching current, maximum AC switching voltage, maximum DC switching voltage, and frequency. Aerospace contactors can operate at 50 Hz, 60 Hz, and/or 400 Hz. Additional specifications to consider include resistive and rupture load ratings, contact voltage drop, mechanical and electrical life limits (cycles), meant-time between failure (MTBF), contact bounce time, and reliability. Environmental parameters include operating temperature, altitude, shock, and vibration. Some aerospace contactors mount on a printed circuit board (PCB, PC board) or connect to wiring via a standard socket or plug. Others mount on a DIN rail, bracket, or flange. DIN is an acronym for Deutsches Institut für Normung (DIN), a German national organization for standardization.
Aerospace contactors must be able to withstand the severe environmental conditions of high-voltage power generation and distribution systems. Intrinsically safe (IS) is an adjective for equipment and wiring that is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most ignited concentration. In terms of features, aerospace contactors with a time delay can provide delay-on-make, delay-on-break, single-shot, recycling, and interval timing functions. Hermetically-sealed products are designed to prevent contamination or the ingress of water. Latching contactors stay in position until actively actuated to another position. Aerospace contactors that provide visual guidance for power and signal monitoring are also available.
Certifications and Approvals
Aerospace contactors differ in terms of product certifications and approvals. Guidelines for contactors and relays are maintained by the National Electric Manufacturers Association (NEMA) and the International Engineering Commission (IEC). The NEMA rating indicates the continuous current rating at rated voltages. The IEC rating indicates thermal current ratings. Aerospace contactors that meet U.S. military specifications (MIL-SPEC) and U.S. military standards (MIL-STD) are available. Standards for aerospace contactors include MIL-HDBK-21 7E , MIL-R-6106, MIL-C-83383, and MIL-PRF-6106.
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