Geomagnetic sensor--new type of vehicle detection sensor

Geomagnetic sensors can be used to detect the presence of vehicles and identify vehicle models. Compared with the commonly used geomagnetic coil (also known as ground induction coil) detector, this sensor that uses the influence of the earth's magnetic field when the vehicle passes through the road to complete vehicle detection has the advantages of small installation size, high sensitivity, small construction volume, long service life, and small damage to the road surface (wired installation only requires a 5 mm wide gap in the road surface, and wireless installation only requires a hole with a diameter of 55 mm and a depth of 150 mm in the road surface. When installed on the hanger or side of the detection point, the road surface does not need to be damaged). It will definitely play a very important role in the information collection of intelligent transportation systems.

The current status of vehicle detection sensors

With the rapid development of the economy, the investment in infrastructure is increasing, and one of the manifestations is road construction. However, due to the generally long road construction cycle, its growth is far behind the sharp increase in vehicles, making the traffic situation worsening, which has almost become a common problem in all cities. The effective solution to change the current traffic situation is to establish a complete traffic monitoring system in the urban traffic management department. The main goal of the traffic monitoring system is to adapt to changes in dynamic traffic conditions. That is, by collecting traffic data and transmitting it to the traffic management center, the center will analyze it. According to the analysis results, the center can better control traffic by controlling vehicle access and signal lights; the center can also use this data to take prompt measures in the event of a traffic accident. At the same time, the management center can transmit the collected traffic data to the driver, which helps to ease traffic congestion and optimize driving routes. The use of traffic monitoring systems can improve the capacity of existing roads, coordinate the handling of sudden traffic incidents, ease traffic congestion, and thus improve traffic conditions. The data acquisition system plays a very important role in the traffic monitoring system, so it is necessary to study data acquisition systems with higher application value. Vehicle detection sensors are a key part of the data acquisition system, and the performance of the sensor plays a decisive role in the accuracy of the data acquisition system. Traditional traffic data collection is done by laying ground induction coil sensors on the road surface. This method has the following disadvantages:

1. The coil must be buried directly in the lane during installation or maintenance, which will hinder traffic;

2. The cut of the buried coil softens the road surface and easily damages the road surface;

3. During construction, the coil may be cut off accidentally or due to need, which often makes the coil unusable;

4. The induction coil is easily affected by freezing, salinity or busy traffic;

5. The life of the induction coil is generally two years, after which the road surface must be destroyed and re-laid. Other sensors such as ultrasonic sensors are easily affected by the environment. When the wind speed is above level 6, the reflected wave drifts and cannot be detected normally; people or objects passing under the probe will also generate reflected waves, causing false detection; dust and ice fog at the infrared sensor working site will affect the normal operation of the system.

Moreover, the above sensors all identify the type of vehicle based on the length of the vehicle and cannot identify loaded vehicles.

In the future intelligent transportation system, traffic data collectors will cover streets and roads on a large scale, thereby giving full play to the advantages of data collection. The detection accuracy of the sensor is very important for the generation of regional monitoring solutions, so replacing the existing backward sensor system with an advanced, stable and accurate sensor system has become an urgent problem to be solved.

In addition, due to the large investment in the construction of highways, the policy of loaning for road construction and charging to repay the loan has long been deeply rooted in the hearts of the people. However, the toll stations on the highways have greatly reduced the traffic capacity of the highways. There are examples of non-stop toll collection abroad. In China, non-stop toll collection is also the development direction of this toll collection system. In non-stop toll collection, the data collector is required to automatically identify the vehicle model so as to charge the corresponding fees according to different vehicle models. This requires the data collector to not only detect the traffic flow, but also accurately identify the type of passing vehicles. The existing data collection system usually identifies the vehicle model based on the length of the vehicle, cannot identify the loaded vehicle, and cannot meet the requirements of charging according to the weight of the vehicle in the toll collection system.

Geomagnetic sensing technology and its advantages

The earth's magnetic field is basically constant within a few kilometers, but large ferromagnetic objects will cause huge disturbances to the earth's magnetic field. Geomagnetic sensors can distinguish changes in the earth's magnetic field by 1 part in 6000, and when a vehicle passes by, the impact on the geomagnetic field will reach a fraction of the geomagnetic intensity. Therefore, the use of geomagnetic sensors to detect vehicles has extremely high sensitivity. Geomagnetic sensors detect vehicles by detecting the disturbances caused by the earth's magnetic field when the vehicle passes by. It is widely used abroad.

The advantages of geomagnetic sensors are:

1. Easy installation and maintenance, no need to close the lane, little damage to the road surface, no need to damage the road surface when installing on the detection point hanger or side, only need to check the geomagnetic sensor during maintenance; the detection point is not easily damaged and is not affected by the movement of the road surface;

2. The geomagnetic sensor uses the changes in the earth's magnetic field when a ferromagnetic object passes by to detect, so it is not affected by the climate;

3. By setting the sensitivity, the size of ferromagnetic objects can be identified, and the type of vehicle can be roughly determined;

4. It has no response to non-ferromagnetic objects, thus effectively reducing false detections.