Method 4.8.18 tests low-temperature conditioning and capacitance change with temperature for mica dielectric capacitors. In the first part (4.8.18.1), capacitors are placed in a chamber maintained at -55C +/- 3C with rated voltage applied for 48 +/- 4 hours, with circulating air.
In the second part (4.8.18.2), capacitance is measured at the temperatures and in the order shown in the applicable table, to characterize how capacitance changes across the operating temperature range.
This test ensures that mica capacitors maintain their capacitance within specified tolerances across the full military operating temperature range of -55C to the maximum rated temperature.