Influence of relative humidity on relay performance
Under high humidity, especially high temperature and humidity conditions:
The corrosion rate of metal parts increased significantly. For example, the corrosion rate of iron and steel parts is very low in the dry atmosphere containing 0.1% SO2. When the relative humidity reaches 70%, the corrosion rate immediately increases by more than 100 times. The critical humidity of common metal (the lowest relative humidity that can significantly increase the corrosion rate of metal) is generally 60-70% (which is equivalent to the normal use environment humidity condition of relay).
When the open or closed relay is wet, the insulation will be significantly reduced, and the leakage will increase dramatically. In addition, when the relative humidity is over 80%, mold and insects propagate rapidly, which is easy to grow mold on the organic materials that are not resistant to mold, thus affecting the product performance. For example, mildew on the surface of insulating paint and laminated plastic reduces the surface resistance by 10%.
In dusty environment, the relative humidity is high, and the dust is easy to absorb water, which makes some soluble impurities dissolve in the water and become electrolyte. The corrosion micro battery is formed between the dust and the metal to accelerate metal corrosion. For the unsealed relay, the coil failure is often caused by the disconnection caused by this "electrolytic corrosion".
When the moisture content is over 1000 ppm, the contact resistance will change irregularly. For some unsealed relays which are used in high temperature and high humidity conditions, special three proofing (anti humidity, anti mildew and anti bacteria) treatment should be carried out for their insulating parts.
In other environmental conditions, such as salt spray, oil spray, noise field, constant acceleration, etc., the internal structure of the relay is damaged similar to other electrical components. For example, salt spray or other harmful gases have serious corrosion on parts of electrical products.
When selecting relays, users must have some knowledge of the above situations.