Critical Power Immunity Testing of DC Powered Equipment
Reliable operation of on-board electrical equipment under all circumstance is a critical requirement to ensure the safety of passengers and crew. This is true for both AC powered and DC powered equipment. With the continued growth of on-board electrical systems, the amount and types of equipment that needs certification and compliance testing for power anomalies increases every year. In this month’s blog we will discuss compliance testing of DC powered products but much of the same issues apply to AC powered products which we will cover in a future blog post.
Test Standards
The requirements that electrical equipment has to meet are controlled by standardization bodies or governments. For commercial aviation, the governing body is the US based Radio Technical Commission for Aeronautics or RTCA for short. (www.rtca.org).
The RTCA is a private association and a private public partnership between a large group of companies involved with aviation technologies. RTCA publications cover many aspects of safety and design but the one of interest for this month’s blog is the DO160 standard. This standard covers many aspects of equipment operation and verification, including Section 16 which deals with power immunity.
DO160 Rev G, section 16
Currently at revision G, the DO160 standard is constantly updated to cover new developments and technologies that find their way in new airplane designs. Section 16 of the standard covers environmental conditions and test procedures for power input.
Figure 1: RTCA/DO160 Test Standard
Table 1: Proprietary Test Standards
- Required maximum DC output voltage. This is often considerably higher than the nominal test voltage.
- Voltage slew rate. DC transient testing typically requires voltage slew rates that conventional DC power supplies cannot support. AC sources with DC mode however support high voltage slew rates as they are designed to support high frequency AC and have no output capacitance.
- Maximum DC current supported. At lower than nominal input voltage, some EUT may draw more current which the power source used must be able to deliver.
Figure 1: DO160-Table 16-3 DC Rise and Fall Times
Table 2: Other Aviation Test Standards