The principle of multihead weigher and its technical characteristics of rotary metrological verification

Author: Smartweigh–Multihead Weighter

The technical improvement of rotary metrological verification and its multihead weigher principle 1. The current situation of the metrological verification method of rotary mixing machinery 1.1 The traditional rotary metrological verification method is used in the metrological verification of fibrous raw materials such as decorative building materials, grain, oil, food, mining, etc., or when manipulating seasonings online. . The more typical ones are: electronic belt scales, flushing plate flowmeters, nuclear scales, and round wheel feeding scales. This measurement verification method has its own characteristics, but the limitations are very large.

The processing technology of the electronic belt scale is introduced in detail, and the steps are as follows: The electronic belt scale integrates the load data signal and the transformation rate (transmission belt speed ratio) data signal on the total area of ​​the enterprise (weighing section) to obtain the total flow value. Manipulable targets. Detailed introduction of the processing technology of the electronic belt scale Note: The amount of raw materials to be pulled out is changed according to the speed ratio of the drag-and-pull transmission belt. Size, the load on the drive belt is all stable. Compared with other feeding methods, this method has a good actual effect of metrological verification and linearity.

Schematic diagram of the measurement verification circuit of the electronic belt scale Note: The feeding and weighing functions are completed on two transmission belts respectively. 1.2 The rotary measurement verification method is used in the continuous mixing machine. equipment, concrete rotary mixer, bitumen rotary mixer. As far as the precision of metrological verification is concerned, at this stage, this kind of equipment cannot be generalized with intermittent. Therefore, the rotary mixing method is not favored by many customers, which is also one of the reasons.

Scientific demonstrations can show that the mixing and processing processes decided by these two measurement verification methods have their own usable places, and the use of rotary mixing should not be jeopardized by temporary technical limitations. At this stage, in our country, rotary mixing machines are all measured by volume method or electronic belt scale/spiral scale. In the 1970s, the continuous mixing processing technology was introduced from Europe to develop and design. So far, it has been like this, and there has been no improvement from beginning to end. In fact, these two measurement verification methods can achieve high precision in European applications. For example, Schenck's transmission belt batching scale in France has a dynamic seasoning accuracy of 2%.

But in my country, it is not good, because it depends on the restraint of basic industrial production such as machinery and equipment manufacturing and raw materials in my country. At this stage, the measurement and verification accuracy of electronic belt scales used in the road field in my country is generally only about 5%, which is no different from the capacity measurement verification, and the long-term reliability is weak. two. Continuously Weighing Reforms——The multihead weigher (English Loss-in-weight) of the differential signal medicine reduction (weightless state) scale was first used in the whole process of industrial production in the 1990s for continuous metrological verification.

Multihead weigher gradually replaces electronic belt scales, spiral scales, and even accumulative scales. As a new and upgraded measurement verification method, it is gradually applied to more and more raw materials. 2.1 Basic concept: Take the weighing bucket and the feeding organization as the whole scale body, continuously sample the net weight data signal of the scale body according to the instrument panel or the software of the upper computer, and measure the change ratio of the net weight in unit time as the instantaneous speed The total flow, and then technically solved according to the filtering technology of various hardware and software, can be used as a manipulation target.“specific total flow”. The acquisition of this total flow is very critical and is the basis for the accurate measurement and verification of the multihead weigher.

A classic method is described in detail in the figure: the multihead weigher measurement verification method, and then the FC feeds back the optimization algorithm according to the PID opinion, carries out the operation calculation of the total flow close to the overall target, and outputs the adjustment data signal to operate the soft starter and other vibrating feeders. control panel. 2.2 The specific application of the differential signal multihead weigher: From the basic principle, it can be seen that it will not be harmed by the mechanical equipment changes of the scale body and the feeding structure. It only measures the net weight error (difference weight), and Compared with the traditional dynamic metrological verification method, its advantages are obvious. When the control target is the total flow (t/h, kg/min), and the raw material has good transportability, and the metrological verification precision is required to be high, the weightless state method can be used as the best plan for metrological verification.

2.2.2 Production process of multihead weigher: Production process of multihead weigher 2.2.3 Matters that must be paid attention to in the design scheme of multihead weigher, factors that affect the precision: multihead weigher has the characteristics of static data scale and dynamic scale. Therefore, in the design scheme System software, stipulate: 1. The appropriate transport rate range is generally 60% to 70% of the rated transport capacity in specific work. If the communication and exchange speed change is used, it is best to respond to the stress frequency of 35-40Hz. This ensures a wide range of adjustments.

It is also because of the poor reliability of the system software when the transport rate is too low. 2. The measurement range of the sensor is moderate. In other words, the sensor also uses 60%~70% of its measurement range according to the formula. The data signal has a wide range of transformation, which is extremely beneficial to improve the precision. 3. The mechanical system design plan should ensure that the raw materials have good circulation, and also ensure that the feeding time is short, and the feeding should not be excessively frequent. Generally, it is stipulated that the feeding should be done every 5-10 minutes.

The transmission device of the supporting facilities should ensure stable operation and good linear shape. 2.2.4 Application prospect: With the rapid development of electronic device control system, the multihead weigher is based on the selection of new technologies, and the accuracy of metrological verification is increased from 0.3% to 0.5%. The key to this new technology is the use of digital display weight sensors.

2.2.4.1 Application of digital display weighing sensor: In order to better integrate into the necessity of dynamic and accurate measurement, it is particularly important to be used as a system software key-in sensor in weighing equipment. Especially in the place where the system must be intelligent, the immediate or indirect data of the sensor is indispensable. At this time, the precise measurement uncertainty and the precise measurement rate are usually a pair of differences, and it is difficult to take into account the two. The specific situation is selected as a compromise. In the weighing industry, many traditional digital analog sensors are produced and used in my country at this stage, and the output of the pulse signal is small.

Taking a weight sensor with a large total output and the basic principle of resistor strain force as an example, the general large output is 30-40mV. Therefore, the data signal is easily affected by radio frequency, and the transmission distance of the cable is also short, generally within ten meters. In the container weighing equipment (silo scale batching scale), service platform weighing equipment or scale bridge (electronic truck scale or rail scale) using several sensors in series, the data system software can be used to complete“self-calibration”.

This is due to the multi-channel digital sensor system software, there is no matching resistance problem. The customer enters the detailed address, weighing and sensitivity of each sensor, and the scale can be fully automated.“four corners”or“edge”Balanced, no need to constantly adjust the letter again and again. In the system simulation, after several sensors are wired together, the characteristics of each sensor can no longer be distinguished from others. When calibrating, the standard weight should be released on each sensor and the voltage divider in the terminal should be used. Carry out adjustment.

Because there is a paired t-test when adjusting, it is repeated several times. In the data system software, each individual sensor is allowed to be checked individually. Therefore, the time to correct the total cost of the system software with digital sensor is only 1/4 of the system simulation.

Can be done using data system software“self-diagnosed”, that is, the diagnosis program flow continuously checks whether the data signal of each sensor is terminated, whether the output is significantly exceeded, etc. If there is a problem, a message or alarm is automatically displayed on the dashboard or control panel control panel, and customers can use the keys on the control panel to find each sensor, identify the cause of the problem individually and perform common troubleshooting. This kind of judgmental diagnosis and common fault clearing work is obviously a key advantage for customers, and it is difficult to forget and reduce costs in the simulation of analog sensor system software.

In the weighing industry, the resolution of the displacement coefficient SPWM of the typical simulation sensor system software is 16 bits, and there are 50,000 available counts; while the screen resolution of each sensor in the data system software is 20 Bit, there are 1,000,000 available counts. Therefore, a system software with 4 digital sensors can produce a screen resolution of 4,000,000 counts. The advantages of this kind of high pixel are especially suitable for places where the weight of the scale frame is very large and the net weight of the weighed object is small.

For example: in the seasoning weighing equipment, sometimes a certain type of raw materials in the secret recipe only accounts for a small proportion, but the accuracy requirements are still very high. This is also difficult to accomplish in traditional system simulation. three. The application of rotary mixer and the impact of market prospects Because the measurement and verification of rotary mixer in China remains in the traditional way, the application prospect of marketing and promotion of multihead weigher will be very broad. , The continuous mixing process of bitumen has a subversive change, and the precise control of the total flow can produce a very ideal mixture.

Because the rotary mixer has a simple structure and low maintenance costs, once the product mix ratio is strictly controlled, it will change the current situation of the low market share of the rotary mixer. In particular, the production-increasing machinery and equipment required in the fields of road and hydropower engineering has positive significance, and the multihead weigher is a key improvement to improve the precision of metrological verification.

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