一般的防水透气材料由高分子防水透气薄膜和阻燃布复合而成。高分子防水透气薄膜内有微小的孔隙，孔的直径为零点几到几十μm。雨水水珠直径的平均值如表1所示。从表1 中看出，高分子防水薄膜的孔隙直径比水滴直径小很多，甚至不到水滴直径的千分之一，所以在常温状态下，水以液态形式存在时，是不可能通过防水透气材料进入传感器内部的，而空气分子的直径比防水透气材料的孔隙直径小很多，可以透过，基于此该种材料就能达到防水透气的目的。1.3 防水透气材料的选择

防水透气材料主要分为以下四大类：高密织物、层压织物、涂层织物和膨化织物。

本文探讨的传感器用防水透气材料是由聚四氟乙烯薄膜膨化拉伸扩展而成的，被拉伸的聚四氟乙烯膜在三维方向均形成了网状结构。优异拉伸技术能够使微孔直径保持在0.3 ～ 1.2 μm，远远小于水珠直径，阻水性能优异，小轻雾也不能通过；同时微孔直径又远大于气体分子；所以该种材料具备防水功能的同时，也能允许气体分子轻松通过；材料使用温度范围为（-55 ～ 200）℃，可满足大部分压力传感器的工作温度要求。

1.4 防水透气材料在表压传感器上的应用
General waterproof and breathable materials are composed of polymer waterproof and breathable film and flame retardant cloth. There are tiny pores in the polymer waterproof and breathable film, and the diameter of the pores is a few tenths to dozens μ m。 The average value of rainwater droplet diameter is shown in Table 1. From Table 1, it can be seen that the pore diameter of the polymer waterproof film is much smaller than the diameter of the water drop, or even less than one thousandth of the diameter of the water drop. Therefore, at normal temperature, when water exists in liquid form, it is impossible to enter the sensor through the waterproof and breathable material, while the diameter of the air molecule is much smaller than the pore diameter of the waterproof and breathable material, and it can be penetrated. Based on this, this material can achieve the purpose of waterproof and breathable. 1.3 Selection of waterproof and breathable materials



Waterproof and breathable materials are mainly divided into the following four categories: high-density fabrics, laminated fabrics, coated fabrics and puffed fabrics.



The waterproof and breathable material for sensors discussed in this paper is formed by the expansion of polytetrafluoroethylene film. The stretched polytetrafluoroethylene film forms a network structure in the three-dimensional direction. Excellent stretching technology can keep the micropore diameter within 0.3~1.2 μ m. It is far smaller than the diameter of the water droplet, with excellent water resistance, and the minimum light fog can not pass; At the same time, the diameter of micropores is much larger than that of gas molecules; Therefore, the material has waterproof function and can also allow gas molecules to pass easily; The temperature range of the material is (- 55~200) ℃, which can meet the working temperature requirements of most pressure sensors.



1.4 Application of waterproof and breathable material on gauge pressure sensor