In industrial production, the principle and common problems of multihead weigher

Author: Smartweigh–Multihead Weighter

With the improvement of the continuous and precise metrological verification control regulations for raw materials, especially solid raw materials, a new type of metrological verification equipment——The weightless state metrological verification machinery and equipment came into being in the 1990s. The multihead weigher continuously and precisely measures the raw material according to the change in the net weight of the raw material on the scale body. The emergence of multihead weigher slowly replaced the original electronic belt scale, spiral scale and even total scale.

As a new and upgraded measurement method, it has been widely used in metallurgical industry, mining, chemical plant and chemical fiber energy industry. The weighing service platform, the feeding bin and all the machinery and equipment functioning on the weighing service platform are used as the whole weighing body, and the sensor continuously transmits the net weight change on the weighing body to the multihead weigher manipulator (the manipulator is the key of the multihead weigher Part of the solution, all manipulation and resolution are performed by it). The control instrument calculates the net weight elastic coefficient of the scale body per unit time according to the data signal as the specific instantaneous total flow, and then compares it with the set overall target total flow.

After PID calculation, output 4-50mA current data signal, change the output frequency of the feeding motor inverter, and then change the motor speed ratio, so that the specific feeding amount is as close as possible to the set overall target total flow, so as to achieve accurate The destination of the feed. In order to better complete the continuous feeding and measurement verification precision of the multihead weigher, a large hopper for continuous feeding and a fully automatic valve for feeding feeding must be set on the feeding bin. There is an upper limit value (recharge_terminated) and a lower limit value (recharge_started) in the control meter.

When the net weight on the scale reaches the lower limit value, a signal will be sent to open the reloading valve, the reloading valve will be opened, the raw materials in the warehouse will be lowered to the loading bin according to the conductive flexible connection, and the net weight on the scale will increase. When the net weight on the scale reaches the set reload amount, here in the whole process, the pass motor operates from beginning to end, which means that the pass is continuous. For raw materials with poor circulation, light weight and light weight, it is not easy to add a part of the net weight to the scale body in a short period of time after the gate valve is closed.

At this time, if the multihead weigher carries out PID control according to the data signal transmitted by the sensor, the net weight change detected by the sensor during this period will be reduced, resulting in inaccurate data signal loss frame manipulation. Therefore, there is also a feed time delay (timer 2) in the control instrument, which starts timing from the closing of the gate valve. During the period from the beginning of feeding to the end of the feeding time delay, the feeding motor will maintain the frequency before feeding, that is to say, the multihead weigher is operating at a fixed frequency - static data manipulation.

When the feeding time is over, the multihead weigher automatically restores the real-time control, that is, operates the feeding motor according to the data signal sent by the sensor. The operation process of the multihead weigher is carried out in this way. In order to better ensure the linearity of the multihead weigher, in addition to the key main parameters, there are also the following main parameters in the control instrument: SetP (proportional coefficient p value); integration time value; SetD (differential signal time d value); Caltime (current total flow sampling time); Calcount (current total flow sampling time); flow monitoring target; limit E (tolerable deviation range of flow monitoring); high_net weight (high material level value); low_net weight (moderate load-maximum value (frequency limit); load minimum value (minimum frequency); sample total flow 1 (dynamic correction total flow value 1); sample total flow 2 (dynamic correction total flow value 2 ); sample total flow 3 (dynamic correction total flow value 3); working mode (working mode selection); mass selection (large batch (quantitative analysis) function selection); flow coefficient (the main parameter of total flow calibration); Ratio factor (raw material ratio calibration main parameter).

4 Frequently Asked Questions in Multihead Weigher Design Schemes. In order to better improve the linearity of the multihead weigher, the following aspects should be considered in the design scheme: 1) Select a suitable application frequency and keep the frequency between 35HZ and 40HZ as the best. When the frequency is too low, the reliability of the system software is poor; 2) The selection of the sensor measurement range is appropriate, the application range is 60%~70%, and the data signal conversion range is large, which is beneficial to improve the linearity; 3) The mechanical system design scheme should ensure that the raw materials Good circulation, short feeding time.

Feeding should not be excessively frequent, and it is generally prescribed to feed every five to ten minutes; 4) The paired transmission device should ensure stable operation and excellent linearity. 5Multihead weigher installation and application common problems: In order to better ensure the accuracy of multihead weigher, the following key points must be paid attention to in the whole process of installation and application: 1) The weighing platform must be fixed and firm, the sensor is an elastic deformation component, be affected by external vibrations. Work experience shows that the most taboo thing about applying multihead weigher is the harm of natural environment vibration; 2) There should be no cyclone in the natural environment, because in order to better improve the weighing precision, the selected sensor is very smart, so all common faults All will affect the sensor; 3) The left and right conductive soft connections should be soft to prevent the influence of the left and right equipment on the multihead weigher.

The most ideal raw material at this stage is smooth, soft and strong satin; 4) The less the connecting distance between the large hopper and the upper hopper, the better. Especially for raw materials with strong adhesion, the longer the connection distance between the large hopper and the upper silo, the more raw materials adhere to the wall thickness. When the chemical substances on the wall thickness adhere to a certain level, once they fall, it will have a great impact on the multihead weigher; 5) Try to avoid contact with the outside, and the net weight of the outside on the scale must be maintained. 6) The feeding rate should be fast, so it is necessary to ensure smooth feeding during the whole feeding process.

For raw materials with poor circulation, in order to better avoid railway bridges, the best solution is to add mechanical stirring in the warehouse. The bigger taboo is that the cyclone gets rid of the arc, but the mixing cannot be carried out all the time. The most ideal is to keep the whole process of mixing and feeding consistent, that is, to keep the same with the feeding valve; 7) The lower limit value and upper limit value of auxiliary materials are set as far as possible, and the guideline for setting is the table of raw materials in the silo. The apparent density here is basically the same between the two quantities.

This can be obtained by carefully observing the frequency transition of the soft starter. When the apparent density of the raw materials in the silo is basically the same, the frequency basis of the soft starter does not change much. The appropriate setting of the lower limit value and the upper limit value of the feeding can improve the linearity in the whole feeding process, because it has already been said that the multihead weigher is in static data control during the feeding process, if the left and right soft starters before and after feeding The frequency basis will not change, and the measurement accuracy in the whole process of feeding is guaranteed.

In addition, when the bulk density is basically the same, try to avoid the frequency of feeding, that is, feeding a large amount of raw materials at one time as much as possible. The two are divergent and should be considered as a whole. This is also important to ensure the accuracy of the entire feeding process; 8) The setting of the feeding time delay is as far as possible.

The specific guidelines for setting are to ensure that all raw materials are on the scale, and the less set-up time the better. I've heard that the multihead weigher is in static data manipulation within the feed time delay, so the less time the better. This time can also be carefully observed.

During the adjustment period, you can first set the time delay longer, and observe how long the total weight of the scale can be stable without fluctuation (not increase) after each replenishment (the total weight of the scale decreases smoothly). Then this time is the appropriate feeding time delay. 6. Results.

Introduction: This paper introduces in detail the principle of multihead weigher and some common problems in the whole process of design and application, especially some key points in the whole process of application. It is a precious work experience, and I look forward to helping you With some help, the multihead weigher can be used better. Only by attaching great importance to this critical point can the linearity of the multihead weigher be ensured and high-quality goods produced.

Author: Smartweigh–Multihead Weighter Manufacturers

Author: Smartweigh–Linear Weighter

Author: Smartweigh–Linear Weigher Packing Machine

Author: Smartweigh–Multihead Weighter Packing Machine

Author: Smartweigh–Tray Denester

Author: Smartweigh–Clamshell Packing Machine

Author: Smartweigh–Combination Weighter

Author: Smartweigh–Doypack Packing Machine

Author: Smartweigh–Premade Bag Packing Machine

Author: Smartweigh–Rotary Packing Machine

Author: Smartweigh–Vertical Packaging Machine

Author: Smartweigh–VFFS Packing Machine