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Interpretation of weighing junction box

Views: 6     Author: Site Editor     Publish Time: 2023-07-06      Origin: Site

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The weighing junction box is a device that outputs one signal after adjusting the signals of multiple load cells. It is divided into analog junction box and digital junction box. The analog junction box is a device that outputs a voltage signal after connecting the signals of multiple load cells in parallel. The digital junction box is a device that converts the signals of multiple load cells into digital and analog, and outputs digital signals through serial communication.

Weighing junction boxes are widely used in mass measurement. In particular, some large scales need to install multiple load cells to complete the measurement, such as truck scales, platform scales, hopper scales and other scales, etc. need to install 4 or more load cells to complete the measurement work. In order for the host computer instrument to process the weighing signal, it is generally necessary to use a weighing junction box to synthesize multiple load cell signals into one signal. Therefore, the weighing junction box is an indispensable equipment for various weighing instruments.

Principle and application of weighing junction box:

The junction box is the connection part between the load cell of Ningbo Saintbond intelligent floor scale and the display instrument. It plays the role of connecting and transmitting the signals of two important parts of the weighing system. Generally speaking, the junction box of the floor scale is mostly made of metal materials. The side of the box is arranged with a sealing joint for passing through the signal cable. The common junction box is flat and rectangular. The metal material can ensure that it has a certain anti-interference performance and is more durable. The types of different junction boxes have also changed, and the common application types are analog and digital.

The principle and application of the junction box of the electronic platform:

Analog Junction Box:

The junction box used by the analog weighbridge is analog, which can be connected to analog load cells and analog weighing display instruments. No matter how many load cells are used in the scale, they are generally connected in full parallel, and each load cell must be connected in parallel to work. The ratio of the sensitivity of the load cell to its output impedance is required to be equal, but in the actual production of the component, the difference between the sensitivity and the output impedance is inevitable, which will lead to an error in the weighing result of the weighing system, so the junction box The function is also to make the output of each load cell consistent. Therefore, from this point of view, the junction box is equivalent to a passive resistance network, and adjusting an adjustable resistance is equivalent to changing the output impedance of the load cell connected to it, so that the load cell can realize full parallel operation.

Digital Junction Box:

Weighbridge equipment is constantly developing towards digitalization, and naturally its junction box is also constantly improving. The digital junction box converts the analog signal generated by the analog load cell into a digital signal, and transmits the data to the weighing display instrument after processing. According to the difference in circuit structure, this type of junction box is divided into single A/D and multi-channel A/D forms. Single A/D is to connect multiple analog load cells to an A/D conversion circuit, and multi-channel A/D The junction box is equipped with multiple analog load cell inlets and a power communication port. It has multiple A/D conversion communications and can be connected to multiple load cells on the weighing platform. The digital junction box is an essential part of the digital weighbridge.

Selection and wiring method of weighing junction box:

At present, there are two kinds of Ningbo Saintbond intelligent weighing junction boxes on the market. One is to combine the signal lines together, and connect one or two potentiometers on the power line of each load cell to adjust the power supply voltage of the load cell. Eliminate corner differences. Another is to connect a potentiometer at the load cell signal output end, connect two resistors in series, and change the output resistance, so as to achieve the purpose of eliminating the angle difference.

1: Overview of the use of the junction box, because the consistency of the load cell is not necessarily ideal when the load cell leaves the factory, coupled with the environmental factors in the field use and the limitations of the installation method, it will bring imbalance problems to the parallel group scale of multiple load cells. In order to solve the above problems, the junction box must be selected to adjust the ratio of the load cell coefficient to the load cell output impedance (mV/V/Ω) to be close to the same, so as to ensure the balance of the entire scale body.

Adjust the level of the mechanical table. For more than four load cells, due to various reasons, the mechanical table and the foundation are more or less deformed. The longer the use time, the more serious the deformation, resulting in inconsistent force on the load cell, only rely on the potentiometer The compensation cannot be compensated, so the height of the load cell should be adjusted first, within the range of the difference (20-40) kg, and then compensated by the potentiometer until it is basically the same. This is an iterative process, due to the mechanical table Deformation, adjusting one corner may affect two corners, or even three corners, only trial and error.

2: Junction box model and naming, junction boxes can generally be divided into: BJ-4/6/8 and other series. JB-4: five-hole junction box with four wires, suitable for electronic scales or systems that use 4 load cells in combination; JB-6: seven-hole junction box with six wires, suitable for electronic scales or systems that use 6 load cells in combination; BJ- 8-SS: Nine-hole junction box with eight wires, suitable for electronic scales or systems with 8 load cells combined; for electronic scales or systems with more than 10 load cells, the connection can be realized through the combination of multiple junction boxes.

For example: BJ-4-SS, BJ-6-SS, BJ-8-SS junction box Features: BJ-4-SS is used for parallel connection of four load cells, BJ-6-SS is used for parallel connection of six load cells, integrated Resistive mesh for four-corner adjustment, HBM* shielding method for EMC protection (according to EN45501), expandable to more than six load cells (only applicable to BJ-6-SS), protection class IP65 (according to EN60529), stainless steel chassis.

3: Technical overview of Ningbo Saintbond intelligent junction box: 1) Stainless steel or aluminum alloy shell, special sealing joint, durable and good sealing. 2) High-precision, low-drift resistors and potentiometers are used to ensure the accuracy and stability of the system. 3) The load cell connection and signal cable connection are equipped with special terminals to ensure reliable connection. 4) Welding holes for welding wires are reserved next to each terminal post, which can be used for both welding and insertion wiring, and can be selected independently. 5) There is a code mark next to the wiring welding point, which is convenient for users to connect.

4: Junction box installation and debugging

4.1: Junction box installation, fix the junction box at a suitable position on the scale body. Open the top cover of the junction box. Pass the load cell cable and instrument signal cable through the corresponding interface of the junction box, connect all the cables according to the wiring diagram shown in the figure, and tighten all the nuts after completion. Use sealing rubber gasket or plasticine to block the unused interface, and tighten the nut at the same time. Connect the outer shield of all cable wires to the grounding post of the junction box.

4.2: Junction box debugging, according to the output signal size of the load cell, refer to the wiring diagram given in the figure below, and adjust the corresponding potentiometer. (Note: Do not over-adjust the potentiometer) After debugging, cover the upper cover of the junction box and tighten it with screws. )

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