With the comprehensive advancement of technology in the field of automotive electronics and electrical appliances, electronic truck scales have been widely used in various industries. However, most of today's electronic truck scales are used and repaired in the open air, so it is often inevitable that they will encounter electromagnetic interference and other external factors such as thunderstorm lightning, which affect the system operation. Common phenomena include: meter hop count and drift. Grounding is an important method to suppress electromagnetic interference and avoid lightning strikes. It is also an important part of interference shielding and improving system safety, and plays an important role in electronic truck scales.
1. The concept of "land"
Generally speaking, "ground" refers to the reference potential point, which is not necessarily the potential point of the earth. Since the earth itself is a conductor and its capacitance is extremely large, the earth's potential is constant. For this purpose, the earth's potential can be used as a reference potential - zero potential.
2. Method for grounding electronic truck scale
(1) Suspension grounding: It means that the working place of the electronic truck scale is insulated from the earth system, so that the interference on the grounding system will not enter the equipment and improve the working reliability of the equipment. This method is most commonly used on electronic weighing instruments.
(2) Single-point grounding: A certain point is used as a grounding point in the whole circuit, and other units are connected to this grounding point.
(3) Multi-point grounding: means that each grounding point in the equipment or system is directly connected to the ground plane closest to it.
3. Application of electronic truck scale grounding
In the design and installation of all-electronic truck scales, from the perspective of the actual structural layout and anti-interference and safety of the project, mixed grounding is often used, that is, the suspension grounding and single point are adopted according to the power and level of each equipment in the weighing instrument and the sensitivity of the equipment. Grounding and multi-point grounding methods are used in combination to take advantage of each grounding method. To achieve better results. Let's take an example of an all-electronic truck scale.
Suppose an electronic truck scale consisting of a weighing platform, multiple load cells, connected external devices such as printers, computers, large screens, etc. According to the use of one or more grounding methods, we will analyze and explain them one by one.
3.1 Grounding platform
Since the weighing platform of the truck scale is generally outdoors, it is easy to inductively charged and subjected to lightning strikes, etc., it is easy to introduce static electricity when the vehicle is weighed and lowered, and it is also easy to be charged when the insulation of the sensor is broken. In addition, the weighing platform is also a sensor. The junction box and the sensor transmission line are protected from direct interference. The good grounding of the weighing platform plays an important role in the safety and operational reliability of the sensor and the junction box. Therefore, multi-point grounding is an ideal grounding method. In addition, due to the direct contact between the sensor and the weighing platform, the metal part of the sensor is connected to the ground to achieve multi-point grounding. In this way, the accumulation of static electricity of the scale body can be effectively eliminated, and equipment damage caused by lightning induction can be prevented.
3.2 Sensor Grounding
The sensor is a highly sensitive unit, which is highly susceptible to static electricity and electromagnetic radiation. The sensor is also in the same environment as the weighing platform. It is extremely likely to be struck by lightning. Therefore, in combination with the above reasons, the grounding of the sensor is generally grounded at multiple points. The elastic body and the mounting structural component are grounded nearby, and one end of the shielding wire of the signal transmission line is grounded through the elastic body, and the other end is connected to the junction box housing in the junction box, and is connected to the weighing platform through the junction box housing or grounded. Since the connection between the junction box and the sensor is relatively short and the grounding point is close, the ground loop is not formed at the grounding point of the sensor, so the interference is effectively suppressed under the premise of ensuring the safety of the device.
3.3 junction box grounding
The junction box is the intermediate link between the scale body and the weighing instrument. The reliability of the grounding directly affects the signal transmission between the scale body and the meter. Therefore, the grounding of the junction box is also a very important part. The junction box can generally be connected to the scale body through the outer casing, and sometimes the junction box is also overlapped with the scale body to improve the grounding reliability, increase the safety of the equipment and the shielding effect of the junction box housing.
3.4 Grounding of shielded wires
Sensor transmission line, computer communication line and large screen connection cable. Since the connection lines of these transmission lines are long, the shielding effect of the shielding lines has a great effect on preventing interference caused by electromagnetic induction. The shielding function of the shielded wire is completely grounded. It is not grounded or the grounding is unreliable. The shielded wire is not only useless, but will become a source of interference. Shielded wires are usually connected to the ground by a single-point grounding method; this prevents two devices from forming a ground loop through the shielded wires and causing interference to the transmission lines. However, it is also feasible to make a two-point connection of the shielded wire. Firstly, the venting path of the interference signal on the shielded wire is increased. In addition, in the case where the grounding effect at both ends is good, the interference of the statical accumulation is greatly reduced due to the increase of the release loop. The generation of the source, even if the ground loop is formed, the current on the ground loop is extremely weak, and it is difficult to cause interference to the transmission line. The two-point grounding actually increases the grounding reliability of the shielded wire and enhances the shielding effect.
3.5 Instrument Grounding
The instrument grounding is actually divided into two parts: first, the instrument housing and the metal structural member and the metal casing of each connector are grounded. Generally, the ground wire is connected to the ground of the power supply by a single point grounding, and then grounded through the power ground. Secondly, the circuit board, components, etc., are usually suspended in the instrument. This connection ensures that external interference does not enter the inside of the meter, and at the same time prevents the power of the meter housing from causing safety hazards.
As mentioned above, the grounding of the instrument case and so on is grounded by the power cable. This requires the weighing instrument to pay attention to the ground wire connection when laying the power cable. The way the power supply is not grounded or unreliable is extremely wrong. Not only does it have security problems, but also the interference protection of the instrument will bring great problems.
3.6 External equipment grounding
It is common for electronic truck scales to connect to external devices such as large screens, computers, and printers. These external devices require a good power grounding when composing a weighing system. When connecting these external devices, especially when connecting the printer to the computer, poor grounding can directly cause problems such as digital jitter, drift, and error message prompts on the weighing instrument. This is because printers and computers, etc., their internal signal ground and ground (power ground) are connected together. If the power supply is not grounded, the interference signal coupled on the power line ground will pass through the printer or computer. The signal ground is introduced into the signal ground inside the instrument, which destroys the original suspended state of the instrument, causing interference of the instrument ground wire and affecting the normal operation of the instrument. Therefore, when connecting an external device, the external device power supply must be well grounded.
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