1 Weighing module is known as the heart part of weighing control system and electronic balance. The rapid development of science and technology, by weighing module made of electronic weighing systems and electronic scales have been widely used in all walks of life, the realization of the rapid and accurate weighing of materials. Especially with the emergence of microprocessors, the degree of automation of industrial production processes continue to improve, weighing module has become a necessary device in the process control, from the previous can not be weighed large tanks, hoppers and other weight measurement, as well as crane scales, automotive scales and other measurement control to the mixing and distribution of a variety of raw materials dosage system production process in the automatic detection and control of the amount of powder and granular body feed, etc. are applied to the weighing module.

Weighing electronic material level meter solves the inherent problem of inaccurate measurement caused by solid material surface unevenness, dust, etc. It is widely used in petrochemical, plastics, cement, medicine, feed, food, metallurgy, light industry, building materials, environmental protection and other industries to realize the upper and lower limits of the material level alarm and control.

2 weighing electronic material level meter composition and working principle material level meter is a container of solid material height (weight) changes in real-time detection of the primary instrument. Usually output 4-20mA or 1-5V standard signal and secondary instrumentation or computer system connection can also be through the RS-485 or Modbus/Proftbus/Hart fieldbus way to connect with the computing system. The material level meter is also known as material level transmitter, material level controller, material level meter, material level meter and so on.

Weighing type material level meter consists of several major parts such as silo (or tank, trough, etc.), support body, weighing module, weighing instrument, etc. Among them, the silo and support body are the main parts. Among them, the silo and support body is the mechanical force transfer reset system between the weighed object and the conversion element, including the grain bin that accepts the load of the weighed object, the force transfer reset mechanism, the limit device, etc., which is the main load-bearing part of the weighing electronic material level meter, and plays the role of bearing the weight of the object. The silo and the force transmission mechanism are responsible for accurately transferring the weight of the object to the weighing module. The weighing module (primary instrument) is located between the silo and the supporting body, which converts the weight of the weighed object into the corresponding millivolt electrical signal according to a certain functional relationship, and outputs it to the weighing control instrument (secondary instrument) through the signal cable of the junction box. After processing, the instrument directly displays the weight data of the weighed object and realizes the conversion of the weight data into 4-20mA or 1-5V standard signals; or transmits them to the control terminal by RS-232, RS-485, Modbus/Profitbus/Hart. Weighing control instruments can also be pre-set at different weight values to realize relay output to control the automatic addition and subtraction of materials.

There are many factors to be considered when selecting a weighing module, and the following factors are the main ones to be taken into account in the actual use of weighing modules. Secondly, the sensitivity of the weighing module, the maximum number of divisions, the minimum calibration index value, etc. is also the selection of indicators that must be carefully considered.

3 Use of the environment

Weighing module is actually a quality signal into a measurable electrical signal output device. First of all, we must consider the actual working environment in which the sensor is located, for the correct selection of sensors is critical, related to the sensor can work properly and its safety and service life, and even the reliability and safety of the system. In general, high-temperature environments, such as heavy modules caused by the melting of coating materials, weld joints open, structural changes in the stress of the elastomer and other issues; dust, moisture on the sensor caused by short-circuit effects: in the corrosive environment will cause damage to the sensor elastomers or short-circuit phenomenon; electromagnetic field on the sensor output will produce interference. The corresponding environmental factors to choose the corresponding weighing module in order to meet the necessary weighing requirements.

3.1 Number and range of load cells The choice of the number of weighing modules is based on the purpose of the weighing system, the number of points to be supported by the carrier (the number of points to be supported should be determined according to the principle that the geometric center of gravity of the carrier coincides with the actual center of gravity). Generally speaking, there are a few support points on the selection of several weighing modules load cell range selection can be based on the weighing of the maximum weighing value, the number of sensors selected, the weight of the scale body, the maximum bias load can be generated and the dynamic load factors to determine a comprehensive evaluation. Generally speaking, the closer the range of the sensor is to the load assigned to each sensor, the higher the accuracy of its weighing. However, in actual use, due to the load loaded on the weighing module in addition to the object to be weighed, there are also carrier self-weight, tare, bias load and vibration impact and other loads, so the selection of weighing module, we must consider a number of factors to ensure that the safety and life of the sensor. The following gives an empirical formula that has been verified by a large number of experiments.

3.2 Installation of the weighing module

The installation of the weighing module mainly depends on the type of weighing and installation space to ensure that the installation is appropriate, safe and reliable weighing; on the other hand, the manufacturer's recommendations should be considered. For the sensor manufacturing, the general provisions of the sensor force, performance indicators, installation forms, structural forms, elastomer materials.

3.3 Selection of accuracy level of weighing module

The accuracy level of the weighing module technical indicators include nonlinearity, creep, repeatability, hysteresis, sensitivity and so on. In the selection should not blindly pursue high-grade sensors, should consider the accuracy level and cost of electronic scales. In general, the total accuracy of the selected sensor for the nonlinearity, non-repeatability and hysteresis of the sum of the three indicators of the root mean square value is slightly higher than the accuracy of the scale.

4 weighing type material level meter on-site installation

4.1 Field installation characteristics

(1) weighing module installation is difficult, the weight of the silo is relatively heavy, some even up to hundreds of tons. In the entire silo installation (including liner installation) before the completion of the coal connection, weighing module can not be installed.

(2) weighing module installation process, the use of jack jacking technology, to achieve the bin jacking, completed the installation of the sensor.

(3) The installation process is simple, easy to implement the advantages of operation and installation accuracy.

(4) The use of "analog calibration method", debugging high precision, simple, applicable, to meet the requirements of weighing measurement.

4.2 Installation process and key points

(1) Construction process

Weighing module installation location determination a * temporary support production and installation of a weighing module and accessories installation of an electrical circuit wiring check - silo weighing module system simulation debugging a system calibration a put into trial operation data sorting operation.

(2) the main points of the site installation

1) Bin weighing module base elevation determination and temporary support seat installation

In the silo foundation installation is completed, the silo is not in place before (if the silo is in place after the four-point elevation measurement will be difficult), first of all, the need to install the weighing module 4-point position elevation, to determine whether the level of a horizontal plane. Generally recommended control of about 3 ~ 5mm. The height of the temporary support should be 20mm higher than the actual height of the weighing module, so that the weighing module is easy to operate when installed. The temporary support of the weighing module should be installed at the same time as the silo is in place. The temporary support does not need to be fully welded so that it can be removed later.

2) Installation of press type weighing module

Weighing module installation prerequisites, silo on all processes of electric coal work or strong current work must be completed before the sensor installation.

a Determine the location of the weighing module to ensure that the 4 sensors on the silo symmetrical and are hooked force.

b will be 4 jacks (jack type specification selection according to the weight of the silo to determine) were placed on the edge of the temporary support, in 4 positions at the same time to start the jacks, the silo will be slowly jacked up, jacking up the height of the temporary support can be taken out. Move the temporary support away from the position where the weighing module is installed.

c But make sure that the temporary support has a supporting effect on the silo.

d. Install the upper and lower bases of the weighing module and the accessories (with flat washers and copper shims for adjustment), level the upper and lower bases of the load cell with a level meter and the error should not be more than 2mm, weld the upper and lower bases of the weighing module and take out the load cell in the process of welding. After the welding is completed, put the 4 positions of the weighing module in place.

f Remove the temporary support and slowly unload the jacks from the 4 positions at the same time, and slowly place the bins on the installed weighing module.

g Connect the upper and lower kits reliably with the grounding wire. h After the sensor is installed in position, prohibit the electric coal operation when the current flows through the sensor body.

3) Electrical system circuit debugging

Check the wiring weighing detection circuit wiring is correct, Shenyuan circuit insulation is good.

Use precision multimeter to measure the output resistance value of 4 sensors in the silo to see if they are balanced, if not, adjust the precision potentiometer in the sensor compensation junction box to make the output signal of 4 weighing modules balanced. Power up the weighing system circuit.

System calibration

Electrical zeroing of weighing modules

Zeroing of the bin tare

Calibration of weights

Weighing system simulation test

After the instrument calibration is completed, the application parameters of various practical needs are set, and the data records of various tests and adjustments are organized and filed.

It should be emphasized here that in the process of installation, commissioning and use must also pay attention to safety and environmental measures. Any construction must follow its due industry norms and systems.

5 Conclusion

Weighing electronic material level meter, after the actual research and practice in the project, compared with the traditional method, reduce the construction difficulty, reduce labor intensity, shorten the construction period, save the use of large cranes, saving the cost of construction machinery, and improve economic efficiency. At the same time, it ensures the installation and commissioning accuracy of the weighing module, which is highly praised. Therefore, the use and commissioning process in the field must have a clear operational thinking, careful analysis, and actively summarize and accumulate on-site operational experience. If this is the case, can greatly reduce the existing problem of the story, can be for the field commissioning to save the amount of time, for future maintenance to provide convenience.