Moore Industries has been continuously running its NET Concentrator System (NCS) data acquisition system at temperatures hovering around the boiling point of water for more than two years in an environmental chamber.
According to Moore Industries, conventional testing and life-test procedures are not enough when products are intended for use in severe operating conditions, such as in the Middle East.
The NCS is intended for use as a remote control and data acquisition system in unheated and un-air conditioned enclosures, so it has to endure wide temperature extremes.
According to Moore Industries, The MTBF (Mean Time Between Failures) for the NCS, determined in accordance to the Bell Core reliability model, exceeds 300,000 hr@25°C.
Moore Industries is using the Highly Accelerated Life Test (HALT) concept, which calculates equipment life based on increased environmental stress at higher temperatures.
Running at 90°C provides a factor of 6.5; that is, every hour running at 194°F (90°C) is equal to running 6.5 hours at normal ambient temperatures. Fortunately, meeting the test specs was not difficult.
Moore Industries’ products are designed for operation at ambient temperatures of -40oC to +85oC, so the test is just barely above its maximum design temperature.
HALT lets Moore Industries demonstrate performance of the NCS outside its specified environmental operational envelope. The idea is that any failures induced that way might be consequently eliminated by design, thus creating a product with more margins to failure.
Therefore, Moore Industries has been running a continuous HALT on the NCS since February 2005, at temperatures from 90 to 105°C (194 to 221°F), with open air applications in the Middle East in mind.
The NCS reached a HALT-calculated MTBF of 123,240 hr in April 2007, and remains in continuous test. The HALT accumulates about 50,000 hours per year, so the full test has less than four years to go before reaching 300,000 hr. Moore Industries intends to reach 300,000 hours, and may be beyond.
Having actually operated Moore Industries’ product at these high temperatures should give its customers more confidence. HALT demonstrates that Moore Industries’ MTBF calculations and design verifications are valid so far.
The specs for the NCS HALT are:
Ambient Temperature: 90oC (194°F)
Test Commenced:
February 8, 2005
Models Installed:
EIM, CPM, AIM, TIM, DIM, ROM
Operation Mode: Temperature inputs are monitored via EIM on-line and data is logged on a daily basis.
MTBF status:
790 days times 24 hr = 18,960 h
According to the Arrhenius equation, the acceleration fac 90oC is 6.5.
This means a demonstrated MTBF of 123,240 hr has accumulated as of April 8.