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【multihead weigher】How does multihead weigher work in industrial production and what problems should be paid attention to in use

2022/09/15

Author: Smartweigh–Multihead Weighter

In modern industrial production, the continuous and accurate metering control requirements for materials, especially solid materials, are increasing, and the multihead weigher is born. The multihead weigher continuously and accurately measures the material according to the change of the weight of the material on the scale body, and gradually replaces the original belt scale, spiral scale, and even accumulative scale. The chemical fiber energy industry has been more and more widely used. So how does multihead weigher work in industrial production, and what problems should be paid attention to in use? Let's take a look with Zhongshan Smart weigh editor! ! ! Working principle of multihead weigher in industrial production Multihead weigher realizes metrology by controlling the weight loss during operation.

Firstly, the discharging device and weighing hopper are weighed, and according to the weight loss per unit time, the actual feeding rate is compared with the set feeding rate, so as to control the discharging device so that the actual feeding rate always accurately conforms to the set feeding rate. Fixed value, in the process of feeding in a short time, the discharge device uses gravity to make the control signal stored during the work work according to the volumetric principle. During the weighing process, the weight of the material in the weighing hopper is converted into an electrical signal by the weighing sensor and sent to the weighing instrument. The weighing instrument compares and discriminates the calculated material weight with the pre-set upper and lower weight limits. The feeding gate is controlled by PLC, and the material is fed into the weighing hopper intermittently. At the same time, the weighing instrument compares the calculated actual feeding rate (discharge flow) with the preset feeding rate, and uses PID adjustment to control the discharging device, so that the actual feeding rate accurately tracks the set value .

When the feeding gate is opened to feed into the weighing hopper, the control signal locks the feeding rate, and volumetric discharging is performed. The weighing instrument displays the actual feeding rate and the accumulated weight of the discharged material. Multihead weigher is also known as reduction method weighing scale or reduction scale. It is mainly composed of five parts: closed feeding vibrating machine, closed feeding vibrating machine, tension sensor, measuring bin and microcomputer control system.

The feeding vibrating machine feeds the measuring bin, and the unloading vibrating machine discharges the measuring bin. The unloading vibrating machine and the measuring bin are supported by three tension sensors. These three are the metering part of the system.

This scale is used for continuous metering of solid materials. The combination of several such scales is the batching metering equipment. Precautions for using multihead weigher in industrial production In order to improve the control accuracy of multihead weigher, the following points should be considered in the design: 1) Select an appropriate frequency of use, and it is best to keep the frequency of use at 35Hz~40Hz, when the frequency is too low , the stability of the system is poor; 2) The sensor range is properly selected, and it is used in 60%~70% of the range, and the signal variation range is wide, which is conducive to improving the control accuracy; 3) The mechanical structure design should ensure that the material has good fluidity, and at the same time ensure that the material is replenished The time is short, and the feeding should not be too frequent. Generally, it is required to feed once every 5min~10min; 4) The supporting transmission system should ensure stable operation and good linearity.

5 Precautions during the installation and use of the multihead weigher: In order to ensure the accuracy of the multihead weigher, the following details must be paid attention to during the installation and use: 1) The weighing platform must be fixed firmly, the sensor is an elastic deformation element, and the external vibration It will interfere with it. Experience tells that the most taboo of multihead weigher is the vibration of the environment during use; 2) There should be no airflow in the environment, because in order to improve the weighing accuracy, the selected sensor is very sensitive, so Any disturbance will interfere with the sensor; 3) The upper and lower soft connections should be light and soft to avoid interference with the multihead weigher caused by the lower and lower equipment. The most ideal material currently used is smooth and soft silk thick; 4) The connection distance between the large silo and the upper hopper is as short as possible, especially for those materials with relatively strong adhesion, when the large silo and the upper hopper are connected. The longer the connection distance between the hoppers, the more materials adhere to the pipe wall. When the material on the pipe wall adheres to a certain extent, it will be a very big disturbance to the multihead weigher once it falls; 5) Minimize For the connection with the outside world, the external weight acting on the scale body must be kept constant, in order to reduce the influence of external force on the scale body; 6) The feeding speed should be fast, so it must be ensured that the feeding process is unloading. smoothness. For materials with poor fluidity, in order to prevent them from bridging, the best solution is to add mechanical stirring in the large silo. The biggest taboo is the airflow breaking the arch, but the stirring cannot run all the time. The ideal is to maintain the stirring and feeding process. Consistent, that is, keep in sync with the feeding valve; 7) The lower limit value of the feeding material and the upper limit value of the feeding material should be set appropriately. The guiding idea of ​​the setting is that the bulk density of the material in the hopper is basically the same between these two quantities. .

This can be obtained by observing the frequency change of the frequency converter. When the bulk density of the materials in the hopper is basically the same, the frequency of the frequency converter basically changes little. Appropriate setting of the lower limit value and upper limit value of the feeding can improve the control accuracy during the feeding process, because it has been said that the multihead weigher is in static control during the feeding process. If the frequency of the inverter before and after feeding can be kept basically The measurement accuracy of the feeding process is basically guaranteed. In addition, in the case of ensuring that the bulk density is basically the same, try to reduce the number of feedings, that is, try to feed more materials each time.

The two contradict each other and should be considered in a coordinated manner. This is also the key to ensuring the accuracy of the feeding process; 8) The feeding delay time should be set appropriately. The guiding ideology of the setting is to ensure that all materials have fallen on the scale body, and the shorter the setting time, the better . It has already been said that the multihead weigher is in static control during the feed delay time, so the shorter the time, the better.

This time can also be obtained by observation. During the debugging period, the delay time can be set longer first, and observe how long the total weight on the scale body will not fluctuate (won’t become larger) after each feeding ends. Stabilize (the total weight on the scale body decreases steadily). Then this time is the appropriate feed delay time. The above is to share with you about how multihead weigher works in industrial production, and what issues need to be paid attention to in use. I hope it will be helpful to you.

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