Analyzed the common problems and solutions of multihead weigher

Author: Smartweigh–Multihead Weighter

Introduction: This paper is divided into two parts: The first part mainly describes the introduction and principle of the automatic control system of the multihead weigher. The second part mainly introduces the analysis and solutions to the common problems of multihead weigher in detail. The introduction and principle of a multihead weigher automatic control system.

The multihead weigher (English Loss-in-weight) is a continuous multihead weigher that was used in industrial production in the 1990s. With the new upgrade of metrological verification methods, multihead weigher is gradually applied to more and more raw material metrological verification. With the rapid development of electronic equipment control system, a new electronic computer control system was selected according to the characteristics of multihead weigher, and the metrological verification precision can be increased to 0.1%~0.2%.

Due to the choice of continuous weightless state measurement verification, it can ensure that the material is mixed in proportion, and the necessity of mixing is reduced, the production process is simplified, and the measurement verification is more accurate. The key multihead weigher manufacturers are: French Schenck Company, Cloth Dabenla Company, French Pioneer Company, etc. The principle of the multihead weigher is continuous weight loss, that is, a certain amount of raw materials are maintained in the weighing bin; the weighing bin uses a weight sensor to weigh the net weight conversion per unit time, and the net weight conversion is based on the transport motor. It is carried out at a specific feeding speed; the weighing bin and transportation organization, as a kind of the whole scale, can continuously sample the data of the scale according to the instrument panel or host software, measure the total flow per unit time of net weight conversion, and then according to various hardware software processed by the filtering technology to obtain the manipulation target“specific total flow”, and then adjust the main parameters by PID according to the control board, the manipulation calculation is close to the overall target, and the adjustment data signal is output to manipulate the soft starter, so as to achieve the purpose of converting the total flow of raw materials. The 300,000-ton polypropylene equipment W804a-E is a multihead weigher, and the raw materials must be measured continuously and accurately, that is, there must be a certain amount of raw materials in the scale.

The weightless scale has three motors, of which the smallest motor W804a-E is the extruder screw conveying motor, that is, the feeding motor. Top or side motors are percussion motors to reduce sticking of raw materials or railway bridges. D804A-E The motor at the bottom of the storage hopper is a raw material mixing motor to reduce the adhesion of raw materials.

The upper end of the D804A-E storage hopper has a feeding port with a capacity grid travel switch, which is used for feeding to operate the cylinder valve (butterfly valve). The concentration of smoke and dust can prevent explosion accidents. Everything is ready. The valve is closed. When the preservative must be added, the dosing door is opened and the valve is opened. There are two small emerald circles next to the multihead weigher on the computer screen, reminding the high and low net weight of the multihead weigher, not to control the opening and closing of the opening valve, it is just a reminder.

According to the program flow, the upper and lower limits of the net weight of the raw materials are operated. The D804 opening valve is opened and closed, and the motor of the stirring device is started and stopped; according to the net weight of the multihead weigher, continuous and accurate measurement is performed to ensure that there is enough smell in the scale. The modules that operate the multihead weigher are: weighing equipment module VSE, input and output module VEA, and field operation module VLG. According to the specific situation of our factory, when designing the scheme, the more popular network communication method is selected, and the PLC control system software has added modules and network communication protocols relative to network communication.

The operation chooses the modular design method. The automatic control system is composed of a variety of different modules, and the different control modules are connected according to their own computer interfaces to exchange data and information. The management program was written in the original factory, and it was put into the processing chip. According to the notebook of the supporting equipment mobile phone software EASYSERVEVPC, it communicated with the system software control module according to serial communication, and the main parameters were modified. The main parameters of the site can also be displayed and modified according to the optional actual operation module VLB. The actual operation is relatively simple and convenient, avoiding the complicated process in the process of program writing and modification.

The net weight of the raw materials in the weighing material warehouse is converted into electronic signals according to the weight sensor and sent to the weighing equipment module VSE. The weighing equipment module VSE compares and identifies the net weight of the raw materials according to the preset upper and lower limit values. Operate the feed sluice to intermittently feed the weighed material bin. In addition, the weighing equipment module VSE compares the measured specific feed rate (total feed flow) with the preset feed rate, and adjusts the feed equipment according to the control board and controller (PID) to achieve Accurately track presets for specific feed rates. The feed water gate opens the feed port, locks the feed speed with the control data signal, locks the feed flow with the control data signal, locks the feed flow with the control data signal, and locks the feed flow with the control data signal. locking.

Second, the analysis and solution to the common problems of multihead weigher. The 2.1multihead weigher fluctuates a lot. The precise measurements have fluctuated a few times since it started operating in 2005, and unlike the large error of the presets, at the bottom of the multihead weigher, it has fluctuated a lot over the years.

(1) If there are fluctuations when adding solid preservatives manually, the feeding port at the upper end of the D804A-E storage hopper must be opened, otherwise N2 will enter the multihead weigher, which will endanger the weighing measurement verification, thus causing the multihead weigher to fluctuate. (2) If the solid preservative has just been added, the first thing to check is whether the water inlet valve is closed; whether the travel switch touches everything is normal; whether the gas supply to the gate valve is all normal; whether the pneumatic valve is closed; If it is normal, check whether the result fluctuates. (3) If there is a sudden fluctuation when everything is running normally, first check whether there is dirt around the multihead weigher; check whether there are lumps or railway bridges in the scale; check whether the multihead weigher transport motor is running normally; check whether the screw transport parts of the machine are running normally ; Check to see if the opening is running normally.

After checking, clear the multihead weigher according to the above requirements, and recalibrate the multihead weigher. 2.2 The precise measurement of the multihead weigher is lower or higher than the predetermined value. In October 2008, the multihead weigherW804B with a measurement range of 0~115kg/h encountered difficulties when the preset value reached 50kg/h, and the precise measurement value of the instantaneous speed was sometimes stable at 40kg/h, which caused great harm to production. Shut down immediately.

In the case of the default value of 50kg/h, the Schenck scale is running well, and it is suspected that it is caused by other factors, and the following inspections are carried out. Check that the operation of the transport motor of the multihead weigher is normal, the screw of the transport extruder has no abnormal phenomenon, and there is no dirt blockage. The material level of the weightless scale is stable, and the standard air pressure value is normal.

The wiring of the weight sensor is not loose, and the data signals of the weight sensor are all normal. None of the above inspections found common causes of failure. I recalled that the screw conveying part of the extruder was disassembled when the multihead weigher was updated and renovated not long ago. When dismantling the screw conveying section of the extruder, it is likely to cause a change in net weight.

Perform static data verification of the multihead weigher again. After booting, everything runs normally. The precise value is basically the same as the preset value. After the analysis, the multihead weigher specifies high precision for the weighing part and the transportation part. All conversions must be verified again. , so as to ensure that the precise value is accurate. 2.3Multihead weigher often close failure. W804B is often closed in November 2009. The alarm information content shows the content of the common fault alarm information SC05, which is used for alarming common faults in external malignant events. The electrical equipment staff inspected the server cabinet between the power distribution equipment and found that the leakage switch jumped, which occurred many times. Frequent gaps and high openings are mostly common faults at night; after inspection, it is found that the frequent gaps and high openings are caused by the overload of the multihead weigher, but check that the multihead weigher transport motor rotates normally and there is no dirt blockage.

In order to reduce the weight better, the lower limit of the original weightless scale is 40kg~50kg, which is changed to 30kg~40kg, and the raw material weightless scale is changed to 10kg. Three overviews. The weight scale control system design scheme is effective, reliable in operation, accurate in measurement verification and low in equipment failure rate. The effect has laid a good foundation for the second phase of the project, and the market prospect of its development trend is very impressive.

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