Environmental Protocol
International test methods specify cyclic temperature and humidity profiles to evaluate the resistance of electrotechnical products to moisture-induced degradation. The standard iec 60068-2-38 defines a composite temperature cyclic test designed to reveal defects in sensor housings.
Test Procedure
Laboratory technicians subject test specimens to ten temperature cycles that oscillate between twenty-five and sixty-five degrees Celsius while maintaining relative humidity above ninety percent. Unlike steady-state humidity tests, iec 60068-2-38 incorporates sub-zero excursions to ten degrees below zero Celsius during several of the cycles. This rapid transition to freezing temperatures causes any moisture that has penetrated the housing to freeze and expand.
The resulting mechanical stress accelerates the failure of micro-seals, joint interfaces and potting materials.
Moisture Condensation
The cyclic nature of the temperature transitions promotes continuous condensation on the surface of the electronic assembly under test. Because the relative humidity remains high during the cooling phases, water vapor condenses into liquid inside any unsealed voids within the instrument. This condensation leads to surface tracking, corrosion of circuit traces and severe degradation of insulation resistance between conductive terminals.
Manufacturers of industrial pressure transmitters use this severe test to verify that their potting and sealing techniques can withstand harsh outdoor deployments.
Pass Criterion
Evaluation of the test specimen involves measuring critical electrical parameters before, during and after the exposure cycle. Following the completion of the iec 60068-2-38 routine, the test sensor must maintain its dielectric strength and insulation resistance within specified limits. Any physical degradation, such as cracks in the enclosure or corrosion on the connector pins, constitutes a failure of the qualification process.
