外文翻译--工程机械搅拌设备用称重传感器的选型

工程机械搅拌设备用称重传感器的选型 本文阐述了工程机械搅拌设备称重系统的基本要求和特殊要求，提出了工程机械搅拌设备称重系统选用传感器时需要考虑的几个问题，重点分析了传感器防护结构对工程机械搅拌设备运行可靠性的影响，指出 IP 代码所代表的防护等级不能涵盖工程机械搅拌设备对传感器的全部防护要求。建议不同类型的搅拌设备选用不同防护能力的传感器。 称重系统中选用传感器通常要考虑称重系统的量限、准确度、传感器的安装空间、周围环境对传感器的可能影响、加载的类型以及传感器的寿命等诸方面因素。工程机械搅拌设备的称重 系统也不例外。只是不同的称重系统由于要求不同，工作条件不同，所要考虑的问题侧重点有所不同罢了。 工程机械搅拌设备通常包括混凝土搅拌楼（站）、沥青搅拌站、稳定土拌和厂以及海上混凝土搅拌船等，其中以混凝土搅拌楼（站）最为典型。下面就以混凝土搅拌楼（站）为例进行分析。 1 混凝土搅拌楼（站）对称重系统的基本要求 1.1 准确称量误差对混凝土的强度影响很大，特别是水灰比计量精度，因为强度和水灰比是线性关系。相关国家标准规定，水泥、水、外加剂、掺合料的动态计量精度为 1%，砂、石料的动态计量精度为 2%。 1.2 快速满足搅拌楼站工作循环的要求。 1.3 种类多称量值预选的种类要多，变换要方便，以适应多种配比和不同容量的要求。 1.4 结构简单称量装置要结构简单，牢固可靠，性能稳定，操作容易。 显然，采用传感器电子称重系统较之机械秤更能满足要求。因此，称重传感器在混凝土搅拌楼站中得到了越来越广泛的应用。但是，客观地说，与机械杠杆秤相比，在 “牢固可靠，性能稳定 ”方面，传感器电子称重系统还有很多工作要做。 2 混凝土搅拌楼站中称重传感器的运行条件 与一般用于商贸计量的电子秤的一个很 大的不同之处在于，混凝土搅拌楼站中称重传感器处于相当恶劣的运行条件中，应力环境十分复杂，与一般的电子产品的运行环境相比，有更大的随机性。 2.1 环境温度和湿度 混凝土搅拌楼站通常是露天安装，传感器可能遭受日晒雨淋，温度剧烈变化。而不少工程建设项目是在自然条件相当恶劣的山区或边远地区。所以，必须考虑更大的温度范围，更高的湿度条件。混凝土在生产过程中需要水。在水的输送和称量过程中也会产生不少水气，在一定的小范围内形成较为潮湿的环境。在温控搅拌楼中，则有高温工况和低温工况的不同要求。夏天运行在低温工 况时要通入零度以下的冷风以及加冰搅拌，这时楼内会出现冷凝水，足见楼内湿度之高。 2.2 粉尘 混凝土在生产过程中需要大量的水泥、煤粉灰以及适量的外加剂。这些粉状物在输送和称量过程中会产生粉尘。即使是骨料，在输送过程中也有粉尘产生。这些粉尘有一部分会附着在传感器表面。在粉尘和水气的共同作用下，传感器将受到较为严重的腐蚀。所以，粉料秤传感器的损坏通常要比其他秤的传感器更频繁一些。 2.3 冲击与振动 在进料过程中，砂石料会产生冲击。传感器应能承受 5g 的加速度。在搅拌过程中，会产生持续的振 动，而振动会产生疲劳破坏。 2.4 人为环境 人为环境是产品可靠性设计时必须考虑的因素之一。混凝土搅拌楼一般安装在施工现场。工地上大量使用临时工，其中相当多的临时工文化水平较低，缺少必要的技能。在设备的维修和清洗等工作中，很有可能发生传感器受到高压水的溅射，误操作引起过载等情况。显然，传感器要在这样的环境条件下长期可靠的运行，是要进行一些特殊设计的。 上述基本要求和运行条件可以作为混凝土搅拌楼（站）用称重传感器的选型的依据。 3 混凝土搅拌楼（站）用称重传感器选型时需要考虑的几个问 题 3.1 称重传感器载荷容量的确定 称重传感器载荷容量通常按下式计算 传感器额定载荷 =料斗自重额定称重量 （ 0.60.7） 传感器只数 事实上人们在选择传感器容量时往往还要综合考虑冲击载荷的大小以及选定安全系数 .安全系数的选择又与传感器的灵敏度有密切关系国内外常见的应变式称重传感器灵敏度多数为 2mV/V，但是也有 1mV/V 的，如柱式传感器；也有 3mV/V 的，如部分悬臂梁式传感器和板环式传感器；扭环式传感器则通常是2.85mV/V。目前在搅拌楼上使用的传感器基 本上都是 2mV/V 的。 3.2 称重传感器准确度的选择 传感器准确度的选择以满足称量系统的准确度要求为准，不必片面追求过高的传感器准确度等级。在多只传感器组合使用时，其综合误差按下式计算 r= n 式中， 为单只传感器的准确度， n为组合使用的传感器只数。 目前搅拌楼上常用的 S 型传感器、悬臂梁式传感器、板环式传感器，其线性、滞后、重复性、灵敏度温度影响、蠕变等主要指标绝大多数厂家均优于 0.05%，大多数厂家优于 0.03%，部分厂家优于 0.02%。其单只传感器的综合误差都接近或优 于 0.1%。多只传感器组合后其综合误差就更小了。可以说一般称重传感器生产厂家的产品都能满足要求。 以前，不少搅拌楼生产厂家规定其称重系统的静态精度分别为 0.1%和0.3%。这样，对于使用单只传感器的秤而言，单项指标为 0.05%的传感器就可以满足 0.3%精度的秤的要求。对于使用三只以上传感器的秤而言，单项指标0.05%的传感器也能满足 0.1%精度的要求。 需要指出的是，上述精度是称重系统的静态精度，而混凝土国家标准要求的是动态精度，这是由于原材料不断地向称量机构供料在重力的冲击下称量误差 明显增加。上述 0.1%和 0.3%的静态精度能否保证分别达到 1%和 2%的动态精度还与供料系统的设计有关。 现在，不少厂家规定其称重系统的精度在 0额定称量值的整个称量范围内为水泥、水、外加剂 1%，砂、石料 2%。须知，预拌混凝土国家标准要求的是实物计量精度，而一般计量仪器在 020%范围相对误差较大，因此，还是混凝土搅拌楼（站）的行业标准中规定的 20100%的称量段满足水泥、水、外加剂1%，砂、石料 2%的计量允许偏差更为实际一些。更为合理的精度标注方式是采用衡器行业的术语来表述，即作为累计 料斗秤，应采用自动称量准确度的等级标志 1.0 和 2.0。这类秤的检定项目与用途相适应，既包括物料试验（确定累计误差）也包括静态检定。 其自动称量时的最大允许误差见表一。 在用标准载荷进行静态检定和进行非自动称量时，应满足表二的规定。 通常将 1.0 级秤设计为 1000 分度， 2.0 级秤设计为 500 分度。可以看出，在高量程端 1.0 级秤的误差为 0.15%， 2.0 级秤的误差为 0.3%，并不比以前厂家规定的 0.1%和 0.3%静态精度高。但是在低量程段精度要求确实是提高了。在这种情况下需要确认所选用的传感 器在低量程段能否也满足要求。 按秤的分度数选择传感器最简单的方法就是 1000 分度的秤选用 1000 分度的传感器， 500 分度的秤选用 500 分度的传感器。称重传感器国家标准中准确度就是用分度数来表示的，但是由于多方面的原因，目前大多数生产厂仍用单项指标表示传感器的精度。用户再根据单项精度指标算出综合误差。选用起来麻烦一点。 国外发达国家的混凝土搅拌楼称重系统精度一般用分度数来表示，规定为 000 分度。可能与他们使用高性能混凝土所占比例高有关。 随着经济和技术的不断发展，超高层建筑 、超长桥梁、大型水利工程以及其他暴露在严酷环境中的建筑对混凝土的性能提出了越来越高的要求，混凝土技术也进入了高科技时代，高性能混凝土的应用比例不断提升。生产高性能混凝土除了要正确选用原材料、确定合理的工艺参数外，施工工艺的控制也是十分重要的。混凝土搅拌楼中配料系统的准确度是其中重要的一环。 3.3 传感器结构形式的选择 常用的拉式传感器有形，板环式以及中心十字筋板环式等。中心十字筋板环式传感器精度高、抗偏载性能优异，但是价格较高，通常只在高精度测量场合使用。搅拌楼上常用的是型传感器和板环式传 感器。其中型传感器因其精度高、抗偏载能力强、同时可以带过载保护、量程范围宽等优点用得最多。 常用的压式传感器有悬臂梁式、轮辐式、柱式、桥式、扭环式等。综合考虑精度、量程范围、安装方式、价格等因素，绝大多数搅拌楼生产厂选择了悬臂梁式。 3.4 载荷类型的考虑 混凝土生产主要使用砂、石子、水泥以及水、外加剂、掺合料。几种材料中数石子秤的冲击为最大。在电子秤大家族中，这类冲击不算最大，一般传感器均能承受过载情况。 从笔者调查的情况来看，传感器因过载而损坏的情况时有发生。比如控制系 统出故障，造成大量物料倾泻而下，造成过载。也有使用过程中人为因素造成的过载，特别是小量程传感器因操作者踩踏秤架而过载损坏的事时有发生。因此传感器的过载能力、传感器有无过载保护对称重系统的可靠运行还是有一定影响的。 传感器的性能指标中有两项与此有关，一是允许过负荷，一是极限过负荷。 允许过负荷是指卸去这一负荷后，传感器的性能指标不变。极限过负荷是指在这一负荷下传感器不会产生有害的永久性机械变形。 一般传感器的允许过负荷为 150%，极限过负荷在 200%300%之间。有些带过载保护的传感器则可能超 过着一范围。如莆田传感器厂的 CFCKN-1 型传感器因其特殊设计，允许过负荷高达 500%。此类传感器在频繁过载的情况下也能可靠地工作。 3.5 传感器的防护等级 传感器的防护等级通常用 IP 表示。一般传感器厂家均称自己的产品达到IP67 水平，少数厂家的部分产品达到 IP68 水平。 我们知道， IP 代码所表示的是电压不超过 72.5kV 电气产品的外壳防护等级。国家标准 GB4208-93 外壳防护等级中规定， IP67 是指产品能防尘、防短时间浸水影响； IP68 是指产品能防尘、防持续潜水影响。需要指出 的是，这样的防护中未包括机械损坏、锈蚀、潮湿等外部影响或环境条件。涉及这类保护通常由有关产品标准规定。称重传感器与一般的电器产品和二次仪表产品不同的是，它同时还是一个受力构件，在运行中不断地受到力的作用并产生变形。此外还有可能受到震动、冲击或撞击这样的机械损伤，粉尘和水气共同作用下的较为严重的腐蚀以及在非常潮湿的环境条件下运行。这与 GB4208-93 规定的试验条件有很大的不同。 曾碰到这样的情况：某矿山的矿石秤上选用了进口传感器，某大型钢厂的钢包秤上选用了一种国际知名品牌的传感器，均是焊接密封，非 常漂亮，达到了IP68 级。但是在现场实际使用寿命都很短。在不得已的情况下，试用了莆田传感器厂的产品。结果出乎他们的意外，使用寿命都超过了进口传感器。其中在某大型钢厂钢包秤上的传感器已运行了 7 年，至今还在运行中。 在这两个例子中，说穿了主要是防护上的区别。一是有外壳还是没有外壳；二是焊缝设计。三是密封材料。 一般说来，有外壳的设计优于无外壳的设计；在焊缝设计方面则要尽可能避免焊缝受力。在无法避免的情况下，则要校核焊缝强度，特别是疲劳强度。疲劳引起的细微裂纹是导致潮气进入，传感器失效的重要原因。前面 提到的某国际知名品牌焊接密封传感器在现场使用寿命短的原因就是过分依赖焊接密封，内部应变片仅薄薄一层面胶密封，一旦焊缝裂纹，传感器就在潮气的作用下迅速失效。在密封材料方面需要提醒的是，能通过 IP67 半小时浸水试验的传感器未必能通得过传感器标准中的 12 周期湿热试验。应该说传感器标准中规定的湿热试验更符合传感器的使用环境要求，其严酷程度并不低于 IP67。 受价格竞争的影响，不少传感器厂取消了保护外壳，拉式传感器尤甚。目前国内生产的 S 型传感器、板环式传感器几乎都取消了外壳。 确实，在很多场合这样 做没有什么问题。但是在混凝土搅拌楼这样的环境条件下，未必是最好的选择。我厂为三峡工程搅拌楼设计生产的 CFCKN-1 型外壳焊封传感器使用寿命长达十年。我们所看到的美日欧混凝土搅拌楼上用的拉式传感器多数也是带保护外壳的。他们认为传感器应是半永久性器件，使用寿命应不低于 10次。 多年来的实践证明， CFCKN-1 型传感器与普通 S 型传感器相比，至少有以下几个优点： 外壳厚，防机械损伤，特别是防以外撞击能力强； 焊缝深，耐蚀穿时间长； 过载保护间隙也在外壳内，不会因粉尘积聚或杂物受堵； 称重传感 器合理的外壳设计是称重装置 “牢固可靠、性能稳定 ”的重要保证，选型时不可不认真考虑。 3.6 不同类型搅拌楼对称重传感器选型的细分 大中型水利工程的混凝土搅拌楼、城市商品混凝土搅拌楼、小型水利工程和县级公路建设中使用的混凝土搅拌楼在规格大小、使用连续时间、安装地点的环境条件都有很大的不同，所生产的混凝土性能要求也有很大差别。因此，对传感器的可靠性、防护等级等性能事实上也有不同的要求，应区别对待。对连续运行时间长、环境条件恶劣以及生产高性能混凝土的搅拌楼应选择可靠性、防护等级高的传感器。其余的则可适当 降低要求。对于运行在海上的混凝土搅拌船，则还需要考虑防盐雾的要求，这里就不再一一细说了。 Mechanical mixing equipment works with the selection of load cell This paper engineering machinery mixing equipment weighing system and the basic requirements for special requirements, proposed construction machinery mixing equipment weighing system used to be considered when the sensor several issues, the focus of sensor protective structure on the construction machinery mixing equipment reliability of operation, pointing out that the code generation IP Table protective levels can not cover mechanical mixing equipment works full protection of the sensor requirements. Recommendations different types of mixing equipment selection of different defensive capabilities of the sensor. Weighing System sensors normally used in the weighing system to consider the amount of limited accuracy, sensor installation space, the environment may affect the sensor, load and the type of sensor, such as the life span of various factors. Engineering machinery mixing equipment weighing system is no exception. The weighing system is different because of different demands, different working conditions, to be considered by focusing on different issues only. Engineering machinery mixing concrete mixing equipment usually include floor (stations), the asphalt mixing plant, stabilized soil mixing concrete mixing plants and ships at sea, mixing them with concrete floor (stations) the most typical. Below the concrete mixing plant (stations) as an example for analysis. 1 concrete mixing plant (station) on the basic requirements Weighing System 1.1 accurate weighing error on the strength of concrete is strongly influenced, in particular water-cement ratio measurement precision, because strength and water-cement ratio is linear. The relevant national standards, cement, water, additives, the admixture of dynamic measurement accuracy of 1%, sand, stone dynamic measurement accuracy of 2%. 1.2 Quick meet mixing station duty cycle requirements. 1.3 variety that money to the type of pre-selection, to facilitate the transformation to adapt to a variety of different ratio and capacity requirements. 1.4 simple structure weighing devices to simple structure, solid and reliable, stable performance, easy operation. Clearly, the use of electronic weighing system sensor machinery weighing more than meet the requirements. Therefore, the load cell floor in the concrete mixing stations to be more widely used. However, objectively speaking, compared with the mechanical lever scales in the solid and reliable, stable performance, as a sensor electronic weighing system has much work to do. 2 concrete mixing stations floor in the load cell operating conditions For commerce and the general measurement of electronic scales a great difference is, in concrete mixing stations floor load cell in a very adverse operating conditions, stress environment is very complex, and the general electronic products compared to the operating environment, a greater randomness. 2.1 ambient temperature and humidity Concrete mixing station is normally open floor installation, sensor may be subject to the sun and rain, temperature dramatic changes. And many construction projects are in very bad natural conditions in the mountains or remote areas. Therefore, we must consider greater temperature range and higher humidity conditions. Concrete in the production process needs water. In the delivery of water and weighing process and also have a lot of water in the gas, in some form within relatively small humid environment. Stir in the temperature control in the House, there are high-temperature and low-temperature conditions of the different requirements of condition. Running in the summer when low-temperature condition to the zero-below cold wind and 加冰 stirring, then building a condensed water will be well demonstrated high humidity building. 2.2 dust Concrete in the production process requires a large amount of cement, coal ash and the appropriate amount of admixture. These were in the transportation and powder weighing process will produce dust. Even the aggregate, in the course of transmission have also dust. Some of these dust sensor will be attached to the surface. The dust and water vapor in the common role, the sensor will be more serious corrosion. Therefore, the damage powder weighing sensors usually weigh than the other sensors more frequently. 2.3 Shock and Vibration In the feed process, the impact of aggregate will have. Sensors should be able to bear 5 g acceleration. Stir in the process, will have sustained vibration, and vibration would have fatigue damage. 2.4 man-made environment Man-made environment is the product reliability design one of the factors that must be considered. Concrete Mixing floor installed at the construction site in general. Large-scale use of temporary workers on site, of which a considerable number of temporary low level of education, lack of the necessary skills. In terms of facilities, such as the maintenance and cleaning work, the sensor may be in the high-pressure water sputtering, misoperation caused overload, and so on. Clearly, the sensor should be in such an environment and a long-term reliable under the conditions of the operation is to carry out some special design. These basic requirements and operating conditions can be used as concrete mixing plant (stations) by the load cell selection basis. Three concrete mixing plant (stations) to use when weighing sensor to be considered by the Selection Problems 3.1 weighing sensor payload capacity determination Weighing sensor payload capacity usually Hopper sensor rated load = + rated themselves that weight (0.6 0.7) only a few sensors In fact people in the choice of sensor integrated capacity even when they consider the size and impact load selected safety factor. Safety factor with the choice of sensor sensitivity closely related. Domestic and foreign common strain load sensor sensitivity majority of 2 mV / V, but there are 1 mV / V, such as column sensor； Also 3 mV / V, as some cantilever sensor and sensor plate Central； Twisted ring sensor usually 2.85 mV / V. Stir upstairs in the use of sensors are basically 2 mV / V. 3.2 weighing the choice of sensor accuracy The choice of sensor accuracy of the weighing system to meet the accuracy requirements, is not one-sided pursuit of the high level sensor accuracy. In multi-sensor combination used only when its integrated error r = / n Where, only a single sensor accuracy, the use of combinations of n is only a few sensors. Currently stirring upstairs popular S-type sensor, the cantilever sensor, the sensor plate ring, linear, hysteresis, repeatability, and temperature sensitivity effects of creep, and other key indicators vast majority of manufacturers are is better than 0.05%, the majority of manufacturers better than 0.03%, some manufacturers better than 0.02%. Its integrated single sensor error of close to or better than 0.1%. Multi-sensor combination only after its integrated error even smaller. It can be said that the general load cell manufacturers of products to meet the requirements. Previously, many manufacturers stirring floor, its provisions static accuracy of the weighing system, respectively 0.1% and 0.3% respectively. Thus, the use of single-sensor weighing only, individual indicators of 0.05% of the sensor will satisfy 0.3% precision weighing requirements. The use of three over the weigh-sensor, single indicators 0.05% sensors can also meet 0.1% accuracy requirements. It must be pointed out is that the accuracy of the weighing system is static precision, while the concrete is the national standards require dynamic accuracy, which is due to the constant weighing of raw materials for the material in the body of gravity weighing the impact of errors increased significantly. Above 0.1% and 0.3% respectively, the ability of static accuracy reached 1% and 2% of the dynamic accuracy for feeding system with the design. Now, many manufacturers provisions of the accuracy of its weighing system in the 0-rated weighing that money within the cement, water, additives 1%, sand, stone 2%. Notes, ready-mixed concrete national standards require that physical measurement accuracy, and general measurement instruments 0 20% of the relative error greater, or concrete mixing plant (station) provides the industry standard in the 20 100% of the weighting of the meet cement, water, additives 1%, sand, stone 2% of the more practical measures to allow some deviation. A more reasonable approach is the use of precision weighing instrument tagging industry terminology to express that as a cumulative hopper scales should be used in automatic weighing accuracy of the grading marks 1.0 and 2.0. Such scale test project in line with the purposes, including both materials testing (determining the accumulated error) also includes static test. Automatic Weighing at its maximum allowable error in Table 1. Criteria used in a static load test and non-automatic weighing, should meet the requirements in Table 2. Usually 1.0 weigh design for the 1000 points, 2.0 Balance of design for 500 points. We can see that the range in the high-1.0 scale error is 0.15%, 2.0 Balance of error is 0.3%, not manufacturers than before provisions of 0.1% and 0.3% static high accuracy. But in the low range of accuracy is indeed increased. Under such circumstances the need to confirm the selection in the low range of the sensor can also meet the requirements. According to weigh the degree of choice of the simplest sensor is 1,000 points method of selection of 1000 at the weigh-in sensors, 500 hours of the weigh-selection 500 points of the sensors. National standards in weighing sensor accuracy is to use the degree to express, but because of various reasons, most production plants that still use single indicator sensor accuracy. According to individual users to calculate indicators integrated precision error. Choose up trouble point. The concrete mixing of foreign developed countries floor general with precision weighing system to the degree that, in the 1000 Indexing. They may be related to the use of high-performance concrete high proportion of the. As the economy and the continuous development of technology, ultra-high-rise building, long bridges, large-scale water conservancy projects, as well as other exposed to the harsh environment in the construction of concrete performance raised higher and higher demands, concrete technology has also entered the high-tech age, the proportion of high-performance concrete continuous improvement. In addition to producing high-performance concrete correct selection of raw materials, determine a reasonable process parameters, the construction technology of control is also very important. Stir ingredients in the concrete floor, the accuracy of the system is important. 3.3 sensor structure forms of choice Commonly used a pull-type S-shaped sensors, the plate center ring and ring cruciate tendons, such as plate. Cross center ring reinforcement plate high accuracy sensors, anti - partial contains excellent performance, but higher prices are normally only used in high-precision measurement occasions. Mixing upstairs is commonly used S-type sensors and sensor plate Central. S-type sensor which its high accuracy, anti - partial-carrying capacity, at the same time can bring overload protection, the wide range of use of the advantages of the largest. Popular pressure sensor of a cantilever beam, Spoke, column, bridge, such as ring-twisting. Considered accuracy, range of installation, price and other factors, the vast majority of production plants to choose stirring floor of the cantilever. 3.4 load type of consideration Concrete production mainly uses sand, gravel, cement and water, additives, admixture. Several materials weigh the impact of a few stone as the greatest. In the large family of electronic scales, such is not the greatest impact, the sensor can generally bear overload situation. From the author of the survey, the sensor overload and damage due to the situation from time to time. For example, a control system fault, causing heavy material disposal and the next, causing overload. Also the use of human factors during the overload, especially the small range sensor for the operator stampede Scale Frame and overload damage things happen from time to time. Therefore sensor, sensors whether Weighing System Overload Protection for the reliable operation of a certain influence. Sensor performance indicators have two with this, first allowing overload, first limit overload. Allow overload refers to shed the load, sensor performance indicators unchanged. Limit overload refers to the load sensor does not produce harmful permanent mechanical deformation. General overload sensor allows for 150%, and overload limit in 200% 300%. Some of the sensor with overload protection are likely to exceed the scope of one. Sensors such as Putian factory CFCKN-1 - because of their special sensor design, allowing the load as high as 500%. Such frequent overload sensor in the case can reliably work. 3.5 sensor protection rating Sensor IP protection levels that are usually used. General sensor manufacturers said their products have reached IP67 level, a small number of manufacturers of some products to IP68 level. We know that the IP code is expressed by not more than 72.5 kV voltage electrical products protective shell of grading. National standards GB4208-93 shell protection levels, IP67 means the product can dust, and against short-term immersion； IP68 means the product can dust, and against continued diving impact. It must be pointed out is that such protection does not include mechanical damage, corrosion, or external influences such as humid environmental conditions. Usually involving such protection provided by the relevant product standards. Weighing sensors and general electrical products and secondary products of different instruments, it is also a force component in the operation of constantly being produced and the role of deformation. There is also likely to be shock, impact or impact such a mechanical damage, dust and water vapor to the more common under severe corrosion and in extremely humid conditions running. This is GB4208-93 under the test conditions are quite different. Have encountered such a situation: a weigh-ore mines on selected imports sensor, a large steel ladle weigh on the selection of an internationally renowned brands sensors, are welded, sealed and very beautiful, to IP68 level. But in actual life very short scene. In the last resort circumstances, the trial of Putian sensor plant products. The accident came as the result of their service life in excess of imports sensor. One in a large steel ladle weigh on the sensor has been in operation for seven years, are still running. In these two examples, the fact is the protection of distinction. First, there were still no shell casing； Second, weld design. Third, sealing materials. Generally speaking, the design is better than no shell casing design； The design of the weld seam should be avoided as far as possible by force. In the unavoidable circumstances, will have to check weld strength, in particular the fatigue strength. Fatigue cracks are caused minor tidal lead entry, the important reasons for sensor failure. The aforementioned welding of a world-renowned brand sensor at the scene sealed the reasons for the short life of excessive reliance on the welding is sealed, the internal strain tablets only a thin plastic seal level, once weld cracks, moisture sensor on the role in the rapid failure. In sealing materials need to be reminded that, through IP67 half-hour soaking test sensors may not be able to know, sensor-standard damp heat in the 12-cy