What is Anti interference technology of explosion proof electronic scale

With the rapid development of electronic technology, the world has entered the information age. The wide application of electronic technology makes the application of electronic and electrical equipment more and more complex, and the electromagnetic environment more and more bad. The large and medium power transmitter has a disastrous interference to the explosion-proof electronic scale with high sensitivity test of non corresponding channels, which makes the explosion-proof products unable to work normally, the performance is reduced or even damaged.

This kind of interference source comes from the outside, which is an electromagnetic phenomenon damaging the network signal. The electromagnetic energy of this kind of interference is transmitted to sensitive equipment such as test instruments through some media, and the explosion-proof weighing electronic scale expresses "response" in some form, and produces "effect" of interference, such as oscilloscope image distortion, stray signal particles, poor image contrast and geometric figure bending, etc. this process and result is called electromagnetic interference effect. Obviously, electromagnetic interference has been a huge obstacle in the development of testing technology. In order to ensure the normal work of the explosion-proof weighbridge or truck scale, we must study and analyze the electromagnetic interference, study the technical means to limit and suppress all kinds of interference, improve the anti-interference ability of the test environment, and reasonably design the electromagnetic test environment of the electronic weighing laboratory.

1:Conducted interference

This kind of interference propagates along the conductor, such as wires, transmission lines, inductors and capacitors are all transmission channels for conducting interference.

From the interference source, it has noise without any information and useless signal with information. If the spark generated at the moment when the power switch is turned on may interfere with a sensitive circuit. A signal with information is a useful signal in its corresponding channel. If it enters into other channels, although the signal with information is useless, it can cause interference to other instruments. Therefore, any explosion-proof electronic scale weighing scale may become an interference signal source.

The path of conducting EMI is called the transmission channel of EMI. The interference source is transmitted to the input through the line, which generates the corresponding interference voltage and current in the test instrument circuit. So it is necessary to analyze the transmission path between EMI source and explosion-proof electronic scale circuit.

To sum up, the causes of conductive interference are interference source, transmission channel and explosion-proof electronic scale. Therefore, anti-interference must be solved from these three aspects.

1.1:Treatment and solution of interference source

The transformer and coil in the cabinet and on the circuit board of the instrument are the devices that produce strong magnetic field. When designing and arranging, they should be shielded or far away from the receiving circuit. The power supply equipment that has no effect on the network system and has interference must be cancelled. 

Besides the high frequency amplification, input and oscillation circuits in explosion-proof electronic scales, there are circuits with the same or close frequency, which are a kind of conducted interference source causing self-excited oscillation and must be far away from them in design and layout.

1.2:Processing of transmission channel

In the control network of explosion-proof electronic scale, it is necessary to isolate the wires, components or component return lines with interference sources from the wiring and receiver return lines connected to the receiving network; use thick isolation wires and isolation sleeves to reduce the capacitance coupling between stages; in the control circuit, the transmission wires should be as short as possible, and special attention should be paid to this problem for high-frequency circuits, and parallel arrangement of conductors should be avoided For the input and output wires of the amplifier, it is necessary to avoid too close distance and parallel arrangement, so as to avoid causing feedback cross link and self-excited oscillation; if several sets of independent function control boards in the same chassis share a set of power supply, they must be equipped with high-frequency and low-frequency bypass decoupling capacitors at the same time, so as to eliminate interference.

1.3:Treatment of interference of test instrument

The equipment, components and control circuit board of explosion-proof electronic scale system should basically not use low-level product components when selecting electronic components. The sensitivity of technical indicators only needs to ensure that they can work stably and reliably. If the receiving circuit is sensitive to electromagnetic field, it can be equipped with basically enclosed shielding to cancel the receiver power supply that is not needed when the system is working.

2:Radiation interference

Radiated interference is a kind of interference source which propagates through space in the form of electromagnetic wave according to the characteristics of electromagnetic wave. The obvious difference between radiated interference and conducted interference is that the former is the interference with wire devices as the transmission channel, while the latter is the interference of electromagnetic wave propagating in free space.

There are two conditions to form a radiation interference source: first, there is a source of electromagnetic wave, and then the electromagnetic wave energy is radiated out. The common device does not necessarily radiate electromagnetic wave, its structure must be open, and the relevant size and wavelength of electromagnetic wave must be in the same order of magnitude. Of course, the antenna of radio equipment is the most effective equipment to radiate electromagnetic waves. In addition, if the wires, structural parts and components can meet the radiation conditions, they can play the role of transmitting antenna, that is to say, they produce antenna effect.

2.1:Solutions to radiation interference

Just like the method of solving conducted interference, the solution of radiated interference must start from three aspects: radiated interference source, transmission path and receiver.

How to reduce the impact of radiation interference of emission explosion-proof electronic scale on non channel receiver, we can deal with the interference source from the following aspects: the method of processing and solving conduction interference source is also suitable for solving radiation interference, we can also change the antenna emission direction and polarization direction of explosion-proof electronic scale, and configure the corresponding filter at the output end of transmitter to filter The frequency that interferes with the receiver.

From the perspective of communication technology, the smaller the loss of the transmission channel, the better, so that the useful signal attenuation is small, so that the receiving quality is high. However, from the perspective of the interference generated by the receiver, it seems contradictory to expect that the loss of the transmission channel can be greater, and the useless signal or electromagnetic radiation noise can be completely lost. Of course, we can also increase the length of the transmission channel, so that the loss can be increased to reduce the radiation interference, but this kind of increase in the cost of equipment is rarely used. The conventional method is to set the shield on the channel between the radiation interference source and the explosion-proof weighbridge, which can obviously reduce the radiation interference. If it is a direct wave, a blocking layer can be added to the transmission channel to cut the wave

Cut off the radiation interference path of the receiver.

For the sensitivity of explosion-proof electronic scale weighing scale, the same contradiction exists. For communication, the higher the sensitivity, the better, so that the receiving distance can be far. But from the interference point of view, on the contrary, the lower the sensitivity is, the better, and the lower it is, the better it will be if there is no radiation interference at all. The conventional method of anti radiation interference is to add a filter at the input end of the receiver to filter out the corresponding interference frequency. Or change the receiving direction of the antenna, so that the antenna of the receiver and the interference source has different polarization and the antenna is not facing the interference source, so as to reduce the interference, which is similar to dealing with the conducted interference.

Anti interference is a comprehensive science with both theory and technology. It involves the calculation method of electromagnetic interference, the detection method of radio system interference, the basic concept and principle of electromagnetic compatibility, the suppression technology of electromagnetic interference and many other aspects of knowledge. This paper only makes a simple description from the perspective of practical application. If there is anything wrong in this paper, please give us your advice.