Position: This article is about weight sensor selection for the Concrete mixing equipments.
in this page engineering mechanical mixing equipment weighing system, the basic requirements and specific requirements, the proposed construction machinery mix equipment weight sensor system used to consider several issues, the focus of the sensor protective structure on the operation of mechanical mixing equipment reliability the impact of IP code that represent a level of security not covered mechanical equipment works full protection of the sensor requirements. Proposals of different types of mix equipment selection of different defensive capabilities of the sensor.
Weight sensors are used in the weighing system to consider the amount of limited weighing accuracy of the sensor installation space, the environment may affect the sensor, loading and the type of sensor, such as the life span of various factors. Mixing mechanical engineering equipment weighing system is no exception. Weighing system is different because of different requirements, the working conditions are different, to consider the issue of just focusing on different.
Mixing mechanical engineering equipment usually include concrete mixing floor (stations), asphalt mixing station, stabilized soil mixing concrete mixing plant and sea vessels, which concrete mixing plant (stations), the most typical. Below the concrete mixing plant (station) as an example for analysis.
1.A concrete mixing plant (station) on the basic requirements of weighing systems
1.1 accurate error on the great strength of concrete, particularly the water-cement ratio measurement precision, because the water-cement ratio and strength of a linear relationship. Relevant national standards require that the cement, water, additives, the admixture of dynamic measurement accuracy of ± 1%, sand, stone dynamic measurement accuracy of ± 2%.
1.2 floor, stirring rapidly to meet the requirements of recycling stations.
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 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 weight sensor in the floor concrete mixing stations have been increasingly wider range of applications. However, an objective that the mechanical lever scales compared with the "solid and reliable, stable performance," the sensor electronic weighing system has much work to do.
2 floor, concrete mixing stations weight sensor operating conditions
And the general measurement of electronic commerce for a large scale of the difference is that concrete mixing stations in the weight sensor floor in quite poor operating conditions, stress environment is complex, and the general electronic products compared to the operating environment, greater randomness.
2.1 ambient temperature and humidity
Concrete mixing station is normally open floor installation, the sensor may be subject to the sun and the rain, temperature changed dramatically. And many construction projects is very bad natural conditions in the mountains or remote areas. Therefore, consideration must be given a greater temperature range and higher humidity conditions. Concrete in the production process need water. In the delivery of water and also in the process of weighing a lot of water vapor, in a certain small area within a relatively humid environment. Stir in the temperature control in the House, there are high-temperature and low-temperature conditions for the status of the different requirements. Low-temperature operation in the summer when the state-all well below freezing and the cold wind stirring Jianing, when the building will be a condensed water is well demonstrated building high humidity.
2.2 dust
Concrete in the production process requires a large amount of cement, coal ash, as well as appropriate additives. These powder in the transportation and weighing process will produce dust. Even the aggregate, in the course of transmission have also generated dust. Some of these dust sensor will be attached to the surface. Dust and water vapor in the common role, the sensor will be more serious corrosion. Therefore, powder weight sensor damage than other scales are usually more frequently sensors.
2.3 Shock and Vibration
In the feed process, the aggregate impact will be. Sensors should be able to bear 5 g acceleration. Stir in the process, will have a sustained vibration, and vibration fatigue damage will have.
2.4 man-made environment
Man-made environment is the product reliability of the design of one of the factors that must be taken into account. Concrete Mixing floor general installed at the construction site. Large-scale use of temporary workers on the site, including a considerable number of temporary low level of education, lack of the necessary skills. Mixing equipment maintenance and cleaning work, the sensor may be in the high-pressure water sputtering, misoperation caused overload, and so on. Clearly, the sensor in this environment under the conditions of long-term reliable operation is to carry out some special design.
The basic requirements and operating conditions can be used as mixing concrete floor (stations) by weighing the basis for the selection of the load cell sensor.
3 Concrete Mixing House (stations) by weight sensor selection, the need to consider several issues
3.1 sensors determine the load capacity
weight sensor payload capacity usually Anxiashijisuan Rated load sensor = + rated themselves Hopper said weight (0.6 ~ 0.7) × only a few sensors
In fact people in the choice of sensor capacity, but also often considered the size and impact load selected safety factor. Safety factor of choice closely related to the sensitivity of the sensor. Domestic and foreign common strain load sensor sensitivity majority of 2 mV / V, but there are 1 mV / V, such as the column sensor; also 3 mV / V, as some cantilever sensor and sensor plate Central; twisting Central sensor usually 2.85 mV / V. Mixing upstairs in the use of sensors are basically 2 mV / V.
3.2 sensor accuracy of choice
Sensor accuracy of weighing options to meet the requirements of the accuracy of the system, is not one-sided pursuit of high levels of sensor accuracy. In the multi-sensor combination used only when its integrated error Anxiashijisuan
Δ r = δ / √ n
Where, δ single sensor for the accuracy of the combination use of the n is only a few sensors.
Currently stirring upstairs popular S-type sensor, the cantilever sensor, the sensor plate ring, linear, delay, reproducibility, sensitivity temperature, creep, and other major weight indicators are better than the vast majority of manufacturers 0.05%, the majority of manufacturers gifted at 0.03 percent, some manufacturers better than 0.02%. Its single integrated 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 generally weight sensor manufacturers can meet the requirements of the products.
Previously, many manufacturers stirring floor with their static accuracy of the weighing system, respectively 0.1% and 0.3% respectively. Thus, the use of single sensor scale, the individual indicators was 0.05% of the sensors to meet the 0.3% accuracy of weighing requirements. Those who use more than three scales sensor, the 0.05% target individual sensors can also meet the requirements of 0.1% accuracy. Needs to be pointed out is that the accuracy of the weighing system is static accuracy, and the requirements of national standard concrete is a dynamic precision, this is because the raw materials for the body to the material in weighing the impact of the gravity weighing errors increased significantly. Above 0.1% and 0.3% respectively, the ability of static accuracy of 1% and 2% of the dynamic accuracy with the system for the design of these materials.
Now, many manufacturers provisions of the accuracy of its weighing systems rated at 0 ~ that money within the weighing of cement, water, additives ± 1%, sand, stone ± 2%. Information, ready-mixed concrete requirements of the national standard measurement accuracy is kind, and the general measurement instruments in the range 0 to 20% relative error is larger, or mixing concrete floor (stations), the industry standard stipulated in the 20 ~ 100% of the said meet the volume of cement, water, additives ± 1%, sand, stone ± 2% of the more practical measures to allow some deviation. More reasonable accuracy Weighing tagging method is used to express the terms of trade, that is, as a cumulative hopper scales should be used in automatic weighing accuracy of 1.0 and 2.0 grade mark. Verification of such scale projects and the use of the adaptation, including both materials testing (identified cumulative error) also includes static test. Usually 1.0 scale designed for 1,000 points, 2.0 hopper scale for the design of 500 points. Can be seen in the high-end range of error of 1.0 scale was 0.15%, 2.0 scale error is 0.3 percent, not manufacturers than before provisions of 0.1% and 0.3% static high accuracy. But in the low range of accuracy is indeed improved. Under such circumstances the need to confirm the choice of sensor in the low range can also meet the requirements of paragraph.
Scales by the sub-degree sensor choose the simplest way is to weigh 1,000 points in the selection of the sensor 1,000 points, 500 points of the sub-scales of 500 selected sensors. weight sensor accuracy in the national standard is used to express the degree, but due to various reasons, most production plants still use single indicator that the sensor accuracy. According to the accuracy of individual users to calculate indicators of error. Selection of trouble with that. Developed countries floor of the concrete mixing with the general accuracy of weighing system to the degree that, in the 1,000-degree. They may be related to the use of high-performance concrete of the high proportion. As the economy and the continuous development of technology, ultra-high-rise buildings, long bridges, large-scale water conservancy projects, as well as other exposed to the harsh environment in the construction of concrete performance in an increasingly high demand, concrete technology has also entered the high-tech age, Application of high-performance concrete ratio on the rise. In addition to production of high-performance concrete correct selection of raw materials, determine a reasonable parameters, the control of the construction process is also very important. Stir ingredients in the concrete floor, the weighing load cell accuracy of the system is important. 3.3 Selection of the sensor structure Used a pull-type sensor S-shaped plate Cross center ring and ring reinforcement plates, etc.. Cross centre ring reinforcement plate high precision sensors, anti-containing partial 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, wide range of benefits, such as the use of maximum. Pressure sensors used a cantilever-type, Spoke, column, bridge, such as ring-twisting. Considered accuracy, range of installation, price and other factors, the vast majority of mixing plant floor, the cantilever-type choice.
3.4 consider the type of load
Concrete production mainly uses sand, gravel, cement and water, additives, and admixture. Several materials in a few stone weighing the impact is the greatest. In the big family of electronic scales, such is not the greatest impact, the general sensor can bear. Overload situation. From the author of the survey, which contains sensors for the damage to occur from time to time. For example, control system failures, resulting in a large number of materials and disposal, causing overload. Also in the process of using human factors caused the overload, especially the small range sensor for the operator stampede Scale Frame and overload damage things happen from time to time. Therefore Guozainaili sensor, the sensor system weighing whether Overload Protection for the reliable operation of a certain influence. Sensor performance indicators and there are two related, first, to allow a load limit First overload. Overload refers to allow stepped down after this 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% overload limit of 200% to 300% between. 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 percent. Such frequent overload sensor in the case can reliably work.
3.5 grade sensor protection
Sensors with a level of security usually IP said. General sensor manufacturers said their products have reached the level of IP67, a few manufacturers of the products meet IP68 level.
We know that the IP code is expressed by the voltage does not exceed 72.5 kV electrical products protective casing grades. National Standard "GB4208-93 shell level of security", refers to products IP67 dust, water-short; IP68 dust refers to products, sustained-impact diving. Needs to be pointed out is that this protection does not include mechanical damage, corrosion, moisture, and other external influences or environmental conditions. Involved in such protection is usually provided by the relevant product standards. weight sensor and general electrical products and secondary products of different instruments, it is also one of the components, and are subject to the operation of power and the role of the deformation. There is also likely to be vibration, shock or impact the mechanical damage, and dust and water vapor under the common role of the more serious corrosion and in a very humid environment under the conditions of operation. This GB4208-93 and under experimental conditions are quite different.
I have encountered such a situation: a weigh-mine ore imports on selected sensor, a large-scale steel mills on a selection of well-known international brands sensors, are welded, sealed and very beautiful, to IP68 level. But the actual life in the field are short. In the last resort circumstances, the trial of the sensor Putian plant products. The accident came as the result of their service life in excess of imports sensor. In which a large scale steel ladle on the sensor has been in operation for seven years, are still in the running. In these examples, to put it bluntly, is the difference between protection. First, there are still no shell casing; second weld design. Third, it is sealing materials.
Generally speaking, the design is better than no shell casing design in the design of weld seam will have to avoid as much as possible by force. In unavoidable circumstances, will have to check weld strength, in particular the fatigue strength. Fatigue cracks are caused minor tidal lead entering the sensor failure of an important reason. Mentioned before an international famous brands welding sensor at the scene sealed the short life of the reasons for the excessive reliance on the welding is sealed, the internal strain gages only a thin plastic seal level, once the weld cracks, moisture sensors in the role of rapid failure. In the sealed materials need to be reminded that the half-hour through IP67 immersion sensor may not be able to test-too sensor in the standard 12 cycles Damp Heat Test. It should be noted that sensor standards set out in the hot and humid test more in line with the environmental requirements in the use of sensors, which is not lower than the level of IP67 harsh.
By the impact of price competition, many sensors cancelled for the protection of plant cover, particularly pull-type sensor. At present the domestic production of S-type sensors, sensor plate ring almost all shell removed. Indeed, on many occasions there is nothing wrong with doing so. But in the concrete mixing equipment under such conditions, may not be the best choice. I plant for the Three Gorges Project mixing plant design and production of CFCKN-1 shell welded shut sensor life up to 10 years. We have seen the United States, Japan and Europe concrete mixing upstairs with the majority of the pull-type sensor is with the protection of the shell. They believe that should be a semi-permanent sensor device, life should not be lower than 106.
Over the years of practice has proved that CFCKN-1 S-type sensor and sensor ordinary compared to a minimum the following advantages:
① thick shell, anti-mechanical damage, in particular the strong anti-collision outside;
② deep weld corrosion resistance to wear a long time;
③ Overload Protection Gap also cover, not the accumulation of dust or debris by blocking;
Weighing sensor design is a reasonable case weighing device "solid and reliable, stable performance," an important guarantee for selection, must be seriously considered.
3.6 on the floor, mixing different types of load cell breakdown Selection
Large and medium-sized water conservancy projects of concrete mixing equipment, the Town of concrete mixing plant, the small county road construction projects and the use of concrete mixing plant in the size specifications, the use of continuous-time, the installation locations to the environmental conditions are very different from the production Concrete performance requirements also vary considerably. Therefore, the reliability of the sensor, the performance such as the level of security in fact also have different requirements, should be treated differently. The continuous operation a long time, harsh environmental conditions as well as production of high-performance concrete mixing plant should choose reliability, a high level of security sensors. The remaining requirements can be appropriately reduced. The operation in the sea of concrete mixing ship, it would need to consider the requirements of anti-salt spray, here is no longer a January 1 elaborate.
