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Special Application of Electronic Weighing Module in Production Process
The electronic weighing module is the combination of the weighing sensor and the bearing structure, which is actually a special application structure of the sensor. It is widely used in the accurate measurement of batching system and filling system. Compared with the traditional electronic truck scale, the weighing module has the characteristics of flexible assembly, low price, free from site restrictions, and convenient maintenance.
In addition to the above applications, the electronic weighing module can also be used in other special occasions in the production process. The weighbridge will share with you:
1、 Accurate measurement for liquid storage tank
At present, most of the metering devices used for liquid storage and irrigation materials in the chemical industry are flowmeters, metering pumps, level meters and other products. Flowmeters are characterized by high measurement accuracy, convenient installation and debugging, and are generally installed on the inlet and outlet pipes of storage and irrigation materials to measure the instantaneous flow and cumulative flow of pipeline fluids. They are mostly used in flow measurement and control systems, but their shortcomings are that the measurement accuracy is greatly affected by installation conditions and temperature changes, To calculate the weight of materials in the storage tank, it is necessary to connect the inlet and outlet flowmeters to the totalizer or DCS system. Its accuracy is affected by various factors. At present, electromagnetic flowmeters, mass flowmeters, ultrasonic flowmeters and other products are most widely used in the market, but the products are expensive and difficult to calibrate, which is rarely used by general enterprises.
The metering pump is generally used to measure the outgoing flow of the storage and irrigation materials, but it cannot measure the storage weight of the materials inside the storage and irrigation, and the price is very expensive, which limits the use of the production process.
In the early days, bell jar type liquid level gauge was also used to measure the weight of storage and irrigation materials, which is characterized by high measurement accuracy and is not affected by temperature changes. Based on the static pressure measurement principle, the static pressure at the bottom of the storage tank is measured and the sectional area of the tank is measured in advance. The weight of the material is calculated by the formula: P=F/S. The requirements for the pressure transmitter are very high, and the installation is more complex. More difficult is the strict requirements for the processing accuracy of the tank. The sectional area of the column is required to be kept to a certain extent. Any deviation will directly affect the measurement accuracy, and it is only suitable for use in open containers, It is rarely used now.
In recent years, the weighing module has been widely adopted by enterprises as the accurate measurement of storage and irrigation materials. It is characterized by convenient installation, low price, no limitation of site and storage and irrigation shape, high measurement accuracy, easy calibration, and can be used for the measurement of storage and irrigation materials in and out of the warehouse, as well as process flow control. Generally, three or four weighing modules can be selected according to the shape and installation mode of the storage and irrigation, It is especially suitable for quantitative feeding system.
2、 Used for level measurement and control during production
There are many devices used for level measurement in the production process, such as differential pressure level meter, ultrasonic level meter, magnetostrictive level meter, floating ball level meter, etc. However, due to their own characteristics, these products have some problems to varying degrees, such as differential pressure level meter, which is difficult to measure the level of high viscosity medium due to the influence of material properties, The ultrasonic liquid level is difficult to measure the liquid level of oil products and some organic chemicals due to the influence of the dielectric constant of the materials. The measuring piece of the magnetostrictive liquid level gauge is composed of a guide rod and a float. The guide rod should not be too long, otherwise it is easy to deform and affect the float to slide up and down. At the same time, the guide rod is easy to shake in the tank when the tank is equipped with an agitator or when materials enter the tank, which limits its application. The float level gauge is a mechanical level gauge, No continuous signal output, rarely used in process control.
The weighing module can play a great role in the level measurement system in some special occasions. For example, for the level measurement in an open container, only one or two modules need to be installed at the bottom of the tank to accurately measure the level of the tank. When selecting the weighing module to measure the level, a sensor with an output of 4-20 m A or a weighing module plus a weight transmitter need to be selected. During the commissioning, there is no need to calibrate with weights, but only need to calibrate the zero point according to the empty filling of the level, The calibration of the instrument can be completed by calibrating the output current at any point greater than 50% of the total range according to the level height ratio. After the calibration, the output current of the instrument is basically linear with the level height.
3、 Used for liquid density measurement and control in reactor
In the salt chemical industry and lithium chloride production process, it is often necessary to control the two parameters of liquid level and density in the reaction kettle. How to detect the density of liquid when the control level is fixed is a headache for process technicians. Using online densitometers, ordinary products are difficult to overcome the impact of high temperature and pressure, and the price is also very expensive, the measurement accuracy is not high, and it is not easy to calibrate, which has a certain impact on continuous production.
This problem can be well solved by using electronic weighing modules. The selection principle of weighing modules is basically the same as that of the batching system and the filling system. Three or four weighing modules are installed according to the shape of the reaction kettle. The current is converted into 4~20mA through the weight transmitter as the input signal for system display and control. When the liquid level in the reaction kettle is fixed, the current weight of raw brine is used as the density zero point for calibration, The initial density value is set through the display instrument or DCS system. When the weighing module detects that the weight in the reactor has risen to a certain value, if it rises more than 20% (the liquid level must be guaranteed), the weight value of this point can be calibrated as the density value of the second point. At this time, the output current is basically linear with the density value. In order to ensure the accuracy of each point, the liquid density must be sampled before calibration, At this time, the liquid level signal of the reaction kettle is used as the control signal of the feed valve of the reaction kettle for automatic adjustment of the liquid level parameters, and the output signal of the weight transmitter is used as the control signal of the discharge valve of the reaction kettle for automatic adjustment of the density parameters, so that the entire system realizes the automatic adjustment function of the continuous production process.
The weighing module is used as the density detection device, which has the advantages of low cost, convenient installation and high detection accuracy. Compared with other types of densitometers, it has unparalleled advantages.