The principle of the ground coil in the parking lot system and construction considerations

The inlaying of the parking coils in the parking lot system is very important. It can be said that the entire parking lot system is stable. This article starts with the principle of the ground coil and introduces the construction of the coils.

First, the principle of parking lot vehicle detector and geomagnetic coil

1, working principle

The inductive coil vehicle detector is a vehicle detector based on the principle of electromagnetic induction. It usually buries a toroidal coil under the roadbed of the same lane, passing a certain operating current as a sensor. When the vehicle passes the coil or stops on the coil, the iron on the vehicle itself will change the magnetic flux in the coil, causing a change in the inductance of the coil loop. The detector determines the status of the passing vehicle by detecting the change in the inductance. . The detection method of inductance variation generally has two kinds: One is to use the phase latch and the phase comparator to detect the change of the phase; the other is to use the coupling circuit constituted by the loop coil to detect the oscillation frequency.

2, the system composition

Ground-sensing vehicle detectors include geomagnetic coils and detectors. The coils are used for data acquisition. The detectors are used to implement data determination and output corresponding logic signals. The detector is generally composed of a rack, a central processor, a test card, and a connection terminal.

The central processor is a module that calculates the collected signals. It is generally a single-board computer with an embedded operating system, and has strong digital computing, storage capabilities, and a communication interface. Through the scanning of the port, the change time of the level is captured to calculate the corresponding traffic data

When the vehicle passes or is stationary in the detection domain of the induction coil, the inductance through the induction coil decreases, and the function of the detection card is to detect this variation and output the corresponding level accurately. In the detection of high-speed passing vehicles, there may be cases where the length of the vehicle and the vehicle speed are not accurately detected, and the sensitivity of the detector needs to be properly adjusted. Current vehicle detectors generally have multi-level sensitivity adjustable functions.

Second, the role of the sense coil in the parking lot system

In the parking lot system, to determine the role of the ground coil we must first know where the sense coil is installed. The sense coil is generally installed in the following four locations:

1. Entrance ticket box (inlet control machine);

2. One each at the exit gate;

3, export ticket box office (export control machine);

The sense coils used in the industry are generally copper wires. People who have gone through junior high school should know that when a metal object passes through the coil, it will generate current. This principle is used in the parking lot system.

This is why we call it a coil. The coil's production method is relatively simple. It is to surround a certain length of copper wire for several rounds. This explanation is familiar to everyone.

Third, its entrance control machine at the location of the role of the sense of positioning two aspects

1, anti-lost card

Everyone should know that in the standard one-in-one-out system, when a temporary vehicle enters the market, it enters the market through automatic check-in. He only needs to press the button. The sense of the sense of the time is when the vehicle is inducted. You can take a card at any time, not when someone stands up and presses a button to take a card.

2, pressure reader card

In the long distance card reading system (Bluetooth system, license plate recognition system), the sense of place is used to identify the direction of the vehicle;

4. There are two aspects of the role of the entrance gate

1. Anti-dumping car, when the car is in the sense of place, the gate bar will not fall;

2, the car through the drop

The sense of place at the exit control machine is similar to that at the entrance controller. In the remote card reading system (Bluetooth system, license plate recognition system), the sense of place is used to identify the direction of the vehicle.

Fifth, the embedding of geomagnetic coil matters needing attention

The “sense coil” in the parking system is an oscillating circuit. It is constructed in such a way that a circular groove is first created on the ground, about 1 meter in diameter, or an equivalent rectangular groove, and two to three wires are embedded in this groove. This constitutes An inductor coil buried in the earth's surface, this coil is a part of an oscillation circuit, which consists of a capacitor and an oscillation circuit. The principle is stable and reliable oscillation. This oscillation signal is sent to the frequency measurement circuit composed of a single-chip microcomputer and the microcontroller can Measure the frequency of this oscillator. When there is a large metal object such as a car passing, a change in the oscillation frequency is caused due to a change in the space medium (the oscillation frequency increases when there is a metal object), and this change serves as a confirmation signal for the automobile passing through the “sense coil”. The time interval between the beginning and the end of the signal can be used to measure the speed of the car. This is the "sense coil." The key technology is to design the oscillator to be stable and reliable and to have a significant frequency change when the car passes through.

1 coil material

In the design process, usually only the perimeter and number of turns of the inductive coil are considered, and what material is used is often overlooked by designers. When the project is carried out to the implementation stage, the mechanical strength of the wire and the anti-aging problem at high and low temperatures must be considered. In some harsh environments, the problem of acid and alkali resistance must also be considered. However, in the actual use of the conventional wire, the detector will not work if the wire is aged or the tensile strength is not enough to cause the wire to break. Therefore, it is recommended to use more than 1.0mm Teflon high temperature stranded flexible wire.

2 coil shape

1. Rectangular installation

Usually the search coil should be rectangular. The two long sides are perpendicular to the direction of movement of the metal objects. The distance between them is recommended to be 1 meter. The length of the long side is determined by the width of the road, which is usually 0.3 meters to 1 meter narrower than the distance between the roads.

2. Tilted 45° to install

In some cases when it is necessary to detect a bicycle or a motorcycle, consider installing the coil at an angle of 45° to the direction of travel.

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 the detection points and increase the sensitivity. This type of mounting can also be used for sliding door detection, but the coil must be close to the sliding door.

3 turns of the coil

In order to operate the detector under optimum conditions, the inductance of the coil should be maintained between 100uH-300uH. With the coil inductance constant, the number of turns of the coil has an important relationship with the perimeter. The smaller the perimeter, the more loops there are. Generally refer to:

Since there may be buried under the road with various metal materials such as cable lines, steel bars, and sewer covers, these will have a great influence on the actual inductance of the coil, so the data in the above table is for reference only. During actual construction, the user should use the inductance tester to actually measure the inductance of the ground inductance coil to determine the actual number of turns of the construction, as long as the final inductance of the coil is within a reasonable working range (eg, between 100uH and 300uH).

4 output leads

When winding the coil, leave a sufficient length of wire to connect to the loop inductor and ensure there is no connector in the middle. After winding the coil cable, the outgoing cable must be made in a tightly twisted form, requiring a twist of at least 1 m 20 times. Otherwise, untwisted output leads will pull in, making the coil inductance unstable. The output lead length should generally not exceed 5 meters. Since the sensitivity of the detection coil decreases as the length of the lead increases, the length of the lead cable must be as short as possible.

5 Burial methods

The coil is first embedded in a slot cutter on the road. Perform 45-degree chamfering on the four corners to prevent sharp corners from damaging the coil cable. Groove width is generally 4mm ~ 8mm, depth 30mm ~ 50mm. At the same time, a slit for the coil lead to the curb must also be cut. However, it should be noted that the grooves must be clean and free of water or other liquids. When winding the coil, the coil must be straightened, but do not stretch too tight and close to the bottom of the groove. After winding the coil, the twisted output lead is led out through the lead-out slot.

Note: The sensitivity of the vehicle detector coil decreases as the length of the lead increases, so the length of the lead cable should be as short as possible (usually should not exceed 5 meters), untwisted output leads must cause crosstalk, and the vehicle detector coil The instability of the inductance value causes the vehicle detector to malfunction.

In the winding process of the coil, an inductance tester should be used to actually measure the inductance of the ground inductance coil and ensure that the inductance of the coil is between 100uH and 300uH. Otherwise, the number of turns of the coil should be adjusted. After the coil is buried, a nylon rope can be wound around the coil to enhance protection. Finally cut the groove with asphalt or soft resin.

6 Precautions

6.1 coil material: standard 1.0 square high temperature tinning line.

6.2 There must not be a large amount of metal within a range of 1 meter around, such as manhole cover, storm drain cover, etc.

6.3 There shall be no more than 220V power supply lines within a range of 1 meter.

6.4 When multiple coils are used, the distance between the coil and the coil must be greater than 2 meters, otherwise they will interfere with each other.

6.5 The standard 3 meter wide road, vehicle detector coil size is 2 meters long and 1 meter wide, 45 degrees, 10 centimeters long chamfered corners. As shown below:

6.6 The distance between the coil and the roadside is about 50 centimeters, and the coils are vertically overlapped with 4 to 8 turns, with a total length of 40 to 80 meters (including lead wires).

6.7 buried trunking cutting parameters: width 4mm, depth 50-80mm, depth and width should be uniform, should try to avoid suddenly deep shallow, suddenly wide and narrow situation. As shown below:

6.8 Coil should be in the same balance position as the barrier or control machine.

6.9 The two wires drawn from the coil should be twisted with a density of no less than 20 knots per meter. Untwisted output leads will cause interference. The output lead length is recommended not to exceed 5 meters. Since the sensitivity of the detection coil decreases as the length of the lead increases, the length of the lead cable must be as short as possible.

6.10 After the well is laid down, apply cement, asphalt, epoxy resin and other materials to seal and solidify the notch. For the above three kinds of materials can be used on the cement pavement, asphalt or epoxy resin can be used for asphalt pavement, and the use of asphalt sealing should pay attention to the coil.

6.11 There must be no debris in the cut groove, especially if it cannot have any hard objects. Clean it first.

6.12 The slot of the detector coil of the vehicle should be cut into the area of ​​the safety island to prevent the lead from being exposed on the road surface.

6.13 When winding the coil, you must straighten the coil, but do not stretch too tightly and close to the bottom of the groove. Do not create staggered layers. After winding the coil, the twisted output lead is led out through the lead slot.