IP is the abbreviation of Ingress Protection. IP level is the protection grade of electrical equipment enclosure against ingress of foreign matter. Waterproof Level of electronic measuring instruments reflects their freedom from dampness and dusts at the same time. It is unavoidable for them to be exposed to heavy dampness and terrible dusty environments, especially when they are used in the open air. The capability of an instrument to be free from water or damp air is of vital importance to the normal operation and lifespan of the instrument. Therefore, the international standard IEC529 was established and is well recognized throughout the world. IPxx protection grade is comprised of two digits.The first digit denotes the level against the ingress of dust or foreign matter. The second denotes the level against the ingress of damp or water. The larger the number , the higher the level.

The first x denotes the protection leve against dust as follows:

Level 0: Without protection 
Level 1: Free from solid objects larger than 50mm
Level 2: Free from solid objects larger than 12mm 
Level 3: Free from solid objects larger than 2.5mm 
Level 4: Free from solid objects larger than 1.0mm 
Level 5: Preventing the gathering of harmful dusts and motes 
Level 6: Free from dusts and motes completely.

The second digit denotes the protection level against water as follows: