For tested objects with different materials and different testing distances, different types of proximity sensors should be chosen to make them have a high performance price ratio in the system. Therefore, the following principles should be followed in selecting the products.

1.1.When the tested object is a metal material, the high-frequency oscillatory proximity sensor should be selected, which is the most sensitive to the testing of iron-nickel and A3 steel.

For aluminum, brass and stainless steel, its testing sensitivity is low.

1.2. Capacitive proximity sensors shall be used when the tested object is nonmetallic, such as wood, paper, plastics, glass and water.

1.3. For remote testing and control of metals and non-metals, photoelectric or ultrasonic proximity sensors shall be selected.

1.4. When the tested object is metal with low requirement on testing sensitivity, the magnetic proximity sensor or Hall type proximity sensor with low price can be selected.