Installation technology of ground induction coil

The "ground induction coil" is an oscillating circuit. It is composed of a circular groove on the ground with a diameter of about 1m or a rectangular groove with an equivalent area, and then two to three turns of wires are buried in the groove, which forms an inductive coil buried on the ground. This coil is part of an oscillating circuit, and an oscillating circuit is composed of it and capacitors. The principle is that the oscillation is stable and reliable, The oscillation signal is transferred to the frequency measurement circuit composed of a single chip computer through conversion, and the single chip computer can measure the frequency of the oscillator. When a large metal object, such as a car, passes by, the change of the oscillating frequency is caused by the change of the space medium (the oscillating frequency increases when there is a metal object). This change is taken as the confirmation signal of the car passing the "ground induction coil". At the same time, the time interval between the beginning and the end of this signal can be used to measure the car's moving speed. This is called "ground induction coil". The key technology is that the designed oscillator is stable and reliable, and the frequency changes obviously when a car passes by. Knowledge of ground induction coil
1、 Coil material
Under ideal conditions (without considering the influence of all environmental factors), only the size of area (or perimeter) and the number of turns can be considered for the burial of ground induction coil, and the material of conductor can be ignored. However, in practical engineering, the mechanical strength and high and low temperature aging resistance of the conductor must be considered, and the acid and alkali corrosion resistance must also be considered in some places where the environment is harsh. The detector will not work normally if the conductor is damaged due to aging or insufficient tensile strength. In the actual project, it is recommended to use Teflon high temperature multi strand flexible conductor above 1.0mm.
2、 Coil shape
1. Rectangular installation: Generally, the detection coil should be rectangular. The two long edges are perpendicular to the movement direction of the metal object, and the distance between them is recommended to be 1 m. The length of the long side depends on the width of the road, and the two ends are usually 0.3m to 1m narrower than the road spacing.
2. Installation with an inclination of 45 °: In some cases, when it is necessary to detect a bicycle or motorcycle, the coil can be installed with an inclination of 45 ° to the driving direction.
3. 8 "shape installation: In some cases, when the road is wide (more than six meters) and the chassis of the vehicle is too high, this type of installation can be used to disperse detection points to improve sensitivity. This installation form can also be used for the detection of the sliding door, but the coil must be close to the sliding door.
3、 Number of turns of coil
In order to make the detector work in an optimal state, the inductance of the coil should be kept between 100uH and 300uH. When the coil inductance is constant, the number of turns of the coil has an important relationship with the circumference. The smaller the circumference, the more turns.
Generally, you can refer to the following:
Coil circumference Coil turns
If it is less than 3m, the inductance should be between 100uH and 200uH according to the actual situation
3-6m 5-6 turns
6-10m 4-5 turns
10-25m 3 turns
2 turns above 25m
As there may be various metal substances buried under the road, such as cable pipelines, reinforcement, sewer covers, which will have a great impact on the actual inductance of the coil, the data in the table above is only for users' reference. During the actual construction, the user should use the inductance tester to actually test the inductance value of the ground induction coil to determine the actual number of turns, as long as the final inductance value of the coil is guaranteed to be within a reasonable working range (such as between 100uH and 300uH).
4、 Output leader
When winding the coil, enough length of wire shall be reserved to connect to the loop inductor, and there shall be no connector in the middle. After winding the coil cable, the outgoing cable must be made into a tight twisted pair, which requires at least 20 twists per meter. Otherwise, the output lead without twisted pair will lead into dry winding, which will make the coil inductance value unstable. Generally, the length of output lead shall not exceed 5m. As the sensitivity of the detection coil decreases with the increase of the lead length, the lead cable length should be as short as possible.
5、 Burial method
For coil embedding, firstly use a road cutter to cut grooves on the road surface. Make a 45 degree chamfer on the four corners to prevent sharp corners from damaging the coil cable. The width of the groove is generally 4 to 8 mm, and the depth is 30 to 50 mm. At the same time, cut a slot for the coil lead to the roadside. However, it should be noted that the groove must be clean and free of water or other liquids. When winding the coil, the coil must be straightened, but not too tight and close to the bottom of the slot. After winding the coil, the twisted pair of output leads are led out through the outgoing trunking.
During the winding process of coil, an inductance tester shall be used to actually test the inductance value of the ground induction coil and ensure that the inductance value of the coil is between 100uH and 300uH. Otherwise, the number of turns of the coil shall be adjusted.
After the coil is buried, a loop of nylon rope can be wound on the coil to strengthen protection. Finally, seal the groove with asphalt or soft resin.