How to choose a weighing system

How to choose a weighing system

With the continuous popularization of automation equipment, many enterprises are gradually transforming their production processes into automation. So, how should we choose the measurement aspect in automation? The following explanation is provided in a simple and understandable way, hoping to be helpful.
A complete weighing system generally consists of three parts: weighing sensors, weighing junction boxes, and weighing instruments; However, some sites may not require on-site display, so weight transmitters can also be chosen; The specific selection can be determined according to the on-site situation; The specific selection methods for weighing systems include the following aspects:

accuracy
The accuracy requirements for a single weighing sensor when it is deployed are basically in accordance with the national standard C3 (i.e. 1/3000), but this is the accuracy of a single weighing sensor. In practical application scenarios, it may require the combination of three or more weighing sensors, and on-site interference needs to be considered, such as some vibrations in production lines, wind force after outdoor installation, etc. Therefore, the accuracy that may be achieved in practical applications is 1/1000 or 1/2000, but this depends on the environment on site; In other situations where high precision is required, such as C6 or C10, the installation location of these sensors should consider the possible interference during design, which is also an important factor in sensor selection.
range
There is also a fixed algorithm for the range requirements when selecting sensors
The formula is as follows:
C=K-0K-1K-2K-3（Wmax+W）/N
K-0- Insurance coefficient, generally ranging from 1.2 to 1.3
K-1- Impact coefficient
K-2- Center of gravity offset coefficient of the scale body
K-3- Wind pressure coefficient
Wmax - Refers to the net weight of an object
W - Self weight of the scale body
N - Number of support points adopted by the scale body
C - Rated range of a single sensor
Generally, some coefficients may not have specific quantities when calculating, so there is a simple calculation method for weighing: (Wmax+W) 1.5/N; The net weight of the material plus the weight of the scale body multiplied by a safety factor of 1.5 divided by the number of support points; This calculation method is relatively simple.
For example:
Material weight 6t; The weight of the tank is 2t; 4 pivot points; So the calculation method is: (6+2) * 1.5/4=3, and the selected weighing sensor range is 3t.

texture of material
The materials of general weighing sensors and module components can be divided into two categories, namely alloy steel and stainless steel. When selecting these two materials, attention should be paid to distinguishing them, mainly based on the following points:
(1) Cost
Generally, alloy steel is cheaper than stainless steel, so when considering the price without considering the actual usage environment on site, alloy steel material can be given priority
(2) Actual situation on site
Generally speaking, if there are no corrosive liquids or gases on site, alloy steel material can be selected. However, if there are any of the above objects on site, stainless steel material should be chosen as much as possible, and even 17-4PH material may be required in some situations.
When selecting materials, it is advisable to consider the actual usage and environment on site as much as possible before making the choice.

Module category:
The module components of general weighing sensors are divided into two categories, namely static load weighing modules and dynamic load weighing modules. There is now a dynamic static integrated weighing module, but this new type of weighing module generally has a higher cost, so when choosing, you can choose according to your own abilities
When selecting the dynamic and static weighing modules, consideration should be given to whether the on-site tank is equipped with mixing and whether the feeding method during material feeding is horizontal. Horizontal feeding will generate horizontal impact force on the tank.
If there is no mixing and the feeding method is not horizontal, then a static load weighing module can be selected; Otherwise, a static load weighing module needs to be selected.
From the perspective of usage scope and stability, the dynamic load weighing module is suitable for high-speed dynamic weighing occasions, such as material measurement and logistics transportation on production lines. The static load weighing module is suitable for static weighing applications such as large equipment, tanks, etc., such as petrochemicals, food processing, etc.
When choosing between dynamic and static load weighing modules, it is necessary to comprehensively consider the actual application scenarios. If high-precision and high stability dynamic weighing is required, a dynamic load weighing module can be chosen; If large equipment, tanks, and other static weighing situations are needed, static load weighing modules can be selected.
explosion-proof
When choosing a weighing system, it is also necessary to determine whether the on-site usage environment requires explosion-proof selection, and the explosion-proof requirements vary in different occasions, which should be noted when selecting.
Selection of Instruments
In general, the combination of a system in the field includes not only weighing sensors but also instruments and transmitters. The usual combination is a weighing junction box and weighing instruments. However, if there is no need for display on site, a weight transmitter can also be selected when transmitting data to the DCS system through a communication protocol. The specific method is shown in the following figure:

When making a choice, we should understand what kind of effect we want, whether it is on-site display or direct signal transmission, and then make a decision after determining this.
Selection of Instrument Appearance
Instruments are generally divided into several types: embedded, desktop, and rail mounted
Embedded: As the name suggests, it is a panel type instrument that can be embedded into an electrical cabinet. When selecting this instrument, the instrument manufacturer should be contacted to obtain the opening size diagram, and the opening should be made according to the opening size diagram to prevent incorrect opening positions or hole sizes.
Desktop type: refers to an instrument placed on the desktop, which is generally used for on-site data viewing such as weighing scales and platform scales without communication transmission. It can see the weight in real time during weighing.
Rail type: refers to the instrument installed on the rail inside the electrical cabinet or stainless steel cabinet. When selecting this type of instrument, the size of the rail should be determined with the manufacturer.

nstrument power supply
There are currently two main types of instrument power supplies: 24V and 220V; When selecting, it is necessary to confirm the on-site power supply with the manufacturer to prevent selection errors.
Instrument communication
The current mainstream communication methods are basically divided into two types: analog and Modbus; Modbus has more detailed classifications, and there are also other classifications for communication methods. We will not elaborate too much and will publish them separately later.
When choosing, we should first determine which communication protocol the PLC system we have chosen is compatible with, and then select the corresponding instrument based on the adapted communication protocol.
The above are the precautions to be taken when selecting a weighing system, and there are some specific issues that will not be elaborated too much. The weighing selection varies depending on the environment of each usage site. The above nine categories are basically applicable to the selection of the vast majority of scenarios.