Severe Environment Testing: Providing Safety Qualifications for COTS DesignsNovember 19, 2019 by Brian Niehoff, Samtec
This article introduces Severe Environment Testing (SET), a safety testing standard that bridges the gap between a full MIL-STD product and a COTS product to provide additional confidence in the safety of a COTS product.
Electrical interconnects are used in a wide variety of industries and within a myriad of storage and operating conditions. Because of this, many end-users require extensive testing on the interconnects to ensure they function as intended in the end application. Severe Environment Testing (SET) was developed to give designers the confidence needed to design them into their systems.
Origination of the SET Initiative
Commercial-off-the-shelf (COTS) products are nothing new; however, it is relatively new for the military/aerospace, automotive, industrial, and medical industries to utilize them. Typically, these industries require additional testing that isn’t normally conducted on COTS products. The intent of SET is to bridge the gap between a full MIL-STD product (for military/aerospace) and a COTS product. SET provides system designers and engineers the additional confidence that a COTS product will work in their application.
Figure 1. The SET approval badge.
Severe Environment Testing
SET was developed using VITA 47.0 – 47.3 and takes several of the common qualification tests involving low-level circuit resistance (LLCR), humidity, temperature cycling, dielectric withstanding voltage (DWV), and mechanical shock and vibration. SET takes these standard qualification tests and adds requirements to them, thereby demonstrating the capability of the connector for severe environments. For a better understanding of SET testing, see the SET report example (PDF).
Table 1. Areas of Samtec's Design Qualification Testing
Mating/unmating/durability demonstrates the capability of the connector set to perform as designed, even when the conditions it is subjected to are not ideal. Mating/unmating/durability are common in standard qualification tests, but with SET, the conditions have been intensified. In a standard mating/unmating/durability test, the relative humidity (RH) will be set at a range of 90 – 98% for a duration of 10 days with 25 mating and unmating cycles. For SET, the RH is set to 100% with 250 mating and umating cycles.
Another critical aspect of any environmental testing involves ensuring the performance of the connector set when exposed to temperature shock. The temperature cycling test (also known as thermal shock testing) assesses the connector’s ability to withstand extreme temperature changes. This test is important when a system’s operating conditions can change within a matter of minutes.
Normally, a thermal shock test takes a connector set from -55°C to +85°C through 100 cycles with a 30-minute dwell at each temperature. The SET version of this test increases the temperature range to -65°C to +125°C through 500 cycles with a 30-minute dwell at each temperature. During the course of this test, the parts are tested for low-level circuit resistance (LLCR) to look for increases in resistance through the system.
Mechanical Shock/Random Vibration/LLCR and Event Detection
The overall goal of mechanical shock/random vibration testing is to measure a connector set’s performance under exposure to a series of mechanical shocks and random vibrations. Whereas the standard version of this test uses a 100G peak shock for six milliseconds, half-sine, the SET version uses 40G peak shock for 11 milliseconds, half-sine. LLCR is used before and after the test to gauge the effects of the test and look for changes in the contact system resistance.
The standard random vibration test uses 7.56gRMS for two hours per axis; the SET version of this test uses 12gRMS, 5 – 2000Hz for one hour per axis. During this test, event detection is used to continuously monitor the contact set for discontinuities during the vibration test.
Electrostatic discharge (ESD) is not typically tested for electrical connectors; in severe environments, however, there are times when system designers need to know how the components will handle ESD. During an ESD test, the connector is tested mated and unmated with visual inspections before and after testing to determine if damage occurred. For this test, a visual inspection is sufficient to determine if the connector passed. Connectors are passive devices, with no active components, and the only damage that could occur would be to the plating.
This test is based on EN61000-4-2 from VITA 47. The ESD events range from 0kV to 15kV as discharged through a 150 – pf capacitor through a 330-ohm resistor. The connectors are exposed to 5kV, 10kV, and 15kV (10 times at each level), and they are then visually inspected for damage.
DWV at Altitude
Dielectric Withstanding Voltage (DWV) is a common electronics test, but testing at an altitude of 70,000 ft adds to the difficulty of the test. In a typical DWV test, the connectors are tested by applying the testing voltage for 60 seconds. The part is considered to pass if there were no electrical arcs at its testing voltage (.75 x a part’s breakdown voltage).
For DWV at Altitude, the test is conducted in an altitude chamber to simulate an altitude of 70,000 feet with a test voltage at 300VAC. Assuming the connector sets do not electrically breakdown, they are considered to have passed the test.
SET is Expanding to Additional Product Series
The Severe Environment Test was developed by Samtec for engineers and designers seeking additional qualification data for COTS products being used in severe environments. These tests go beyond the standard qualification tests conducted on COTS items and demonstrate the capability of connectors to operate in severe environments.
Samtec recently began the roll-out of Severe Environment Test reports for several different product series, and by the end of 2019 the company should have 8 - 10 series SET qualified.
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