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MIL-STD 202 Moisture Resistance Testing

The moisture resistance test helps evaluate the resistance of component parts to the deteriorative effects of high-humidity and heat conditions. Most tropical degradation results from moisture ingress on vulnerable insulating materials, and from surface wetting of metals and insulation. This test differs from the steady-state humidity test, and is more effective in  its employment of temperature cycling. It provides alternate periods of condensation and drying essential to developing corrosion processes.

Increased effectiveness is also obtained by use of a higher temperature, which intensifies the effects of humidity. The test includes low temperature and vibration sub cycles that act as accelerants to reveal decay. As a result, the decay can be detected by the measurement of electrical characteristics or by performance of a test for sealing. Application of a polarizing voltage across insulation investigates the possibility of electrolysis, which can promote eventual dielectric breakdown.

This test also provides for electrical loading of certain components. This is to determine the resistance of current-carrying components, especially fine wires and contacts, to electro-chemical corrosion. Results obtained with this test are reproducible and have been confirmed by investigations of field failures. This test has proven reliable for indicating those parts which are unsuited for tropical field use.

Keystone Compliance is an enclosure testing lab with significant MIL-202G moisture resistance and MIL-202H moisture resistance knowledge. Our test engineers have an in-depth knowledge of the requirements of ingress protection testing. Below is a summary of Method 512.7, as derived from the MIL-202 moisture resistant section. It also includes information from the MIL-STD 202G moisture resistance and MIL-STD 202H moisture resistance .

What Test Equipment is Needed in a Moisture Resistance Testing Lab?

Ingress protections labs require a test chamber which can meet the temperature and humidity cycling necessary for water enclosure testing. The material used to fabricate the platforms and standoffs, which support the specimens, must be non-reactive in high humidity. Wood or plywood cannot be used because they are resiniferous, neither can materials containing formaldehyde or phenol. Provisions should be made to prevent condensate from the chamber ceiling dripping onto the test specimens.

During the periods when the humidity is ascending or descending, the chamber door should not be opened. If the chamber door must be opened, it should be opened during the 16th – 24th hour of an individual cycle. While the chamber is at 25°C, the chamber door should be opened only for a short period of time, to maintain relative humidity.

Steam, or distilled and demineralized, or deionized water, having a pH value between 6.0 and 7.2 at 23°C are used to obtain the specified humidity. No rust or corrosive contaminants should be imposed on the test specimens by the test facility.

What is the Procedure for the Best Moisture Resistance Testing?

Test items are mounted by their normal means, in the position they would normally be mounted when used. However, items should not touch each other, so that they each receive essentially the same degree of humidity. Materials are then subjected to 10 continuous cycles. During at least 5 of the 10 cycles, a low temperature sub cycle and, if applicable, a vibration sub cycle is performed.

During step 7, there is a one-two part sub cycle. 1 – 4 hours after step 7 begins, the specimens are either removed from the humidity chamber, or the temperature is reduced. Specimens are then conditioned at -10°C ±2°C with uncontrolled humidity, for 3 hours minimum. When a separate cold chamber is not used, specimens must be held at -10°C (plus or minus 2 degrees) for the full 3 hours.

If the second step of the sub cycle is not applicable, specimens return to 25°C at 80 percent relative humidity minimum. It is kept there until the next cycle begins. For the second part of the sub cycle, within 15 minutes of completion of part one, specimens are vibrated for 15 minutes. The humidity during this step remains uncontrolled and the temperature should be at room ambient.

The vibration requires a simple harmonic motion having an amplitude of 0.03 inch. The frequency is varied uniformly between the approximate limits of 10 and 55 hertz (Hz). The entire frequency range, from 10 to 55 Hz and return to 10 Hz, is traversed in approximately 1 minute. After this step, the specimens return to 25°C at 80 percent relative humidity minimum and are kept there until the next cycle.

Interruptions like equipment failure, or power interruptions may occur during IP code testing. When only one accidental test interruption occurs before completion of the cycle, the cycle is repeated and the test continues. Accidental interruptions during the last cycle require a repeat of the cycle plus an additional uninterrupted cycle. Any intentional interruption, or any accidental interruption of greater than 24 hours requires a complete retest.

How are the Final Measurement for Water Ingress Protection Testing made?

After step 6 of the final cycle, or step 7 if the sub cycle is performed during the tenth cycle, the specified measurements are made. They are made only after a temperature of 25°C (plus or minus 2 digress), and a RH of 80 percent minimum is maintained for 1.5 – 3.5 hours. Due to the difficulty in making measurements under high humidity conditions, specific precautions may be needed for individual items.

Upon removal from the humidity chamber, final measurements are made within 1 – 2 hours after the final cycle. During final measurements, specimens should not undergo any means of artificial drying.

After the drying period, in which test materials are conditioned for 24 hours at ambient conditions, measurements can be made. Measurements may be made during the 24 hour conditioning period. However, any failures which occur will be considered failures and will not be retested later.

What Moisture Resistant Laboratory Should You Trust for Moisture Enclosure Ingress Testing?

Keystone Compliance has been recognized as one of the best moisture resistance labs in the country. We employ experienced test engineers, who understand the requirements of moisture resistance compliance testing.

Are you looking to get a moisture resistance certification for your product? We are equipped to provide IP code certifications for commercial, military, and aerospace products. Contact us to learn why so many manufacturers rely on Keystone Compliance to meet their compliance testing needs.