SDI'S MODEL 1527 ACCELEROMETER
This report documents tests conducted on Silicon Designs, Inc. (SDI) Model 1527 MEMS accelerometers to determine their sensitivity to total dose gamma radiation. The Model 1527 was chosen for this test is because this one accelerometer model, once qualified, can perform the functions of all SDI analog accelerometers. In particular the Model 1527 has the performance needed for tactical navigation, but it also shares the same architecture as SDI’s Model 1521, which was previously built and qualified for a military space application.
SDI develops and manufactures miniature accelerometers useful in a wide range of military and commercial systems, including measuring shock, vibration, impulse and other changes in velocity of aircraft, spacecraft and weapons. SDI accelerometers are used on more than 13 US and NATO missiles, and the Model 1527 can be made in full scale ranges of 2, 5, 10, 25, 50, 100, 200 and 400g, all of which are expected to have similar performance after exposure to gamma radiation and are pin compatible allowing easy range changes during development.
The tests consisted of six steps:
Fabricate a lot of 1527 accelerometers using current standard production methods;
Measure their pre-radiation performance;
Divide the units into six groups of three parts each;
Expose each group at Oregon State University to six different total-dose levels of gamma radiation: 10K, 25K, 50K, 100K, 200K and 350K rads (Si);
Measure the post-radiation performance of the Model 1527 accelerometers for general instrumentation uses; and
Measure the post-radiation performance of the Model 1527 accelerometers for tactical navigation uses.
Three tests were intended to concentrate on measuring the adverse effects of gamma radiation to the accelerometers. First, the standard production calibration test was run to measure each unit’s normal characteristics as general-purpose instrumentation accelerometers. The second test evaluated each unit’s performance for navigation use at +1 and -1g to calculate bias and scale factor shifts, measured its output for eight hours at a constant 30°C temperature. The third test measured each accelerometer’s output at +1 and -1 g over a temperature scan from 25 to 85°C, then to -40°C, and then back to 25°C to calculate bias and scale factor over temperature. Plots of the output compensated for temperature were then generated to compare with the actual applied accelerations.
The test results show that all the units met all requirements as instrumentation accelerometers before and after radiation. The two navigation performance tests show that the scale factor is only slightly affected by radiation. All but one of the units showed a bias that remained within specification for all radiation levels. Only one unit produced a bias shift of approximately 6 mg, about 0.024% of full scale, after 350K rads of radiation, and the unit retained its prior performance for tactical navigation.
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