環(huán)形線圈檢測原理

1、英 文 翻 譯系 別專 業(yè)班 級學(xué)生姓名學(xué) 號指導(dǎo)教師 The principle of toroidal coil detection Toroidal coil length is 2 m, width depends on the lane width, usually covering a lane of 50% 60%, should not be less than 0.5 m. Know by electromagnetic field theory, any current-carrying conductor will be produced in the surroundi

2、ng magnetic field, for the length of l type, number of turns for the N of solenoid coil, coil in the magnetic field strength. The self inductance is: L = LSL0N2Al (1)Type: the relative permeability of LS is medium, air LS to 1; L0 = 4 x 10-7 hm - 1; A. to coil around the area. Because of toroidal co

3、il can not completely equal to solenoid, considering the nonuniform1.Design principle and the hardware of the systemThe system design principle and hardware system design principle as shown in figure 1. Toroidal coil through feeder connection to the isolation transformer, on the other side of the is

4、olation transformer and a capacitance in parallel, LC parallel resonance of this LC parallel resonant frequency can be obtained according to the formula (1) 1. F = 12 PLC (1) : L) for the circular coil and the total inductance of feeder; C) for parallel capacitor; F) as the resonance frequency. Can

5、be seen by the formula, the factors influencing the frequency f only L and C, so in certain cases, C ring coil and the total inductance of feeder determines the frequency of oscillation. The numerical values of similar products at home and abroad for reference, at the same time, to determine the veh

6、icle detector coil oscillation frequency is between 20 100 KHZ range. Circular coil inductance is 80 120 lh, feeder inductance for 019 H# m - 1, plus the influence of other factors, the length of the feeder in within 300 m, in order to make the total inductance is less than 1 000 lh. Isolation trans

7、former primary coil and secondary coil number of turns for the 1 b1, it makes the total inductance coil and feeder truthfully from primary reflection to the secondary, isolation effect, prevent damage of external interference of the internal circuit.Diagram 1.the system principle design of schematic

8、 diagram In the design of the phase-locked loop circuit composed of MM74HC4046M role is to provide a current source for LC oscillation, its frequency locking range between 20 to 100 kHz. Phase-locked loop is mainly composed of the phase comparator, voltage-controlled oscillator, low pass filter of 3

9、 parts, its basic structure as shown in figure 2. Follow the LC oscillator frequency oscillation frequency and the frequency to the EPLD. The phase comparator is a signal control delay of digital storage network. Its claim to the input signal duty cycleIs not high, allowed to enter asymmetric wavefo

10、rm, it has wide capture range, and wont lock in the harmonics of the input signal. It provides digital error signal and the signal (impulse) phase locking 2 kind of loseOut, when to lock in the phase comparator keep zero phase shift between two input signals. MM74HC4046M part design of the circuit s

11、hown in figure 3.Diagram 3.the peripheral circuit design 14 feet LC oscillation signal, four feet to the output of the vco. The phase-locked loop circuit adopts the voltage-controlled oscillator is RC type, must be an external capacitor C1 (6, 7 feet) and the resistor R4 (11 feet) as a charge and di

12、scharge device. When the phase lock loop (PLL) to track the frequency width of input signal requirement need external resistor R3 (12 feet). Because of the VCO is a current controlled oscillator, charging current of timing capacitor C1 and from 9 feet is directly proportional to the control voltage

13、of the input, the oscillation frequency of the VCO is proportional to the voltage control. When the VCO control voltage is zero, the output frequency of the lowest; When the VDD input control voltage is equal to the power supply voltage, output frequency increases linearly to the highest output freq

14、uency. VCO oscillating frequency range is determined by the R3 and R4 and C1. Because of its charging and discharging are performed by the same capacitor C1, therefore, the output waveform is symmetrical square wave. R4 determines the maximum oscillation frequency of the VCO, R3 determines the minim

15、um oscillation frequency of the VCO 3. This can be designed to test the four-way signal, composed of XC9536XL - 7 vq44c EPLD circuit can into the CK1 CK4 is 4 line circle oscillation frequency input, SEL signals for choice, to choose the input coil. T0 for 1 and 3 coil oscillation frequency input, T

16、1 for # 2 and # 4 coil oscillation frequency input. Serial communication using RS - 485 standard, it USES the difference balance data transmission, the common mode signal has excellent inhibition ability, not only long transmission distance, reliable communication, and use a single + 5 v or + 3 v po

17、wer supply, logic level compatible with the traditional digital logic TTL 5. This design USES MAX488EESA chip, using the + 5 v power supply full duplex mode, the highest rate of up to 0125 MBPS. MAX488EESA with SST89C58 interface circuit as shown in figure 5. Vehicle inspection plate using 12 V powe

18、r supply, through 7805 into 5 V voltage for the use of single-chip microcomputer and oscillation circuit, and convert 5 V to 313 V for the use of EPLD. And suppress the high frequency interference in power supply and ground magnetic beads, and USES the capacitor filter, the digital earth and simulat

19、ed with the method of one-point earthing, and in 7805 the output increase tablets filter part of single-chip processor, restrain oscillation of crosstalk of single chip microcomputer.Diagram 4.serial line circuit2.The coupling oscillation circuitCoupling oscillation circuit using the three-point cap

20、acitance feedback oscillation circuit, as shown in figure 2. Two reverse connection diagram, the regulator tube suppress sinusoidal oscillation output signal in the range of 5 + 5 v, the former vice edge coupling transformer turn ratio is 1:1, diode P6KE12CA is used to eliminate the moment caused by

21、 the electrostatic voltage. Sinusoidal oscillation signal into the signal after a comparator LM339 plastic shaping and amplifying circuit, and then output to the counting unit of the microprocessor. According to the actual need, can increase the channel multiplex detection, draw only one here.環(huán)形線圈檢測

22、原理環(huán)形線圈長為2m,寬度視車道寬度而定,通常是覆蓋一個車道的50%60%,不應(yīng)小于0.5m。由電磁場理論知道,任何載流導(dǎo)線都將在其周圍產(chǎn)生磁場,對于長度為l、匝數(shù)為N的螺線管型線圈,線圈內(nèi)磁場強度均勻。其自感量為:L=LSL0N2Al(1)式中:LS是介質(zhì)的相對磁導(dǎo)率,空氣的LS為1;L0=410-7hm-1;A為線圈的環(huán)繞面積。由于環(huán)形線圈不能完全等同于螺線管,考慮引入磁場的不均勻修正因子F1,于是環(huán)形線圈的自感量L可表示為:L=F1LSL0N2Al(2)由式(2)可知,環(huán)形線圈的自感的大小取決于線圈的周長、環(huán)繞面積、匝數(shù)及周圍的介質(zhì)情況。當(dāng)有車輛通過環(huán)形線圈時,車體上的鐵金屬底板產(chǎn)生自成

23、閉合回路的感應(yīng)電渦流,此渦流又產(chǎn)生與原有磁場相反的新磁場,導(dǎo)致線圈總電感量變小,使調(diào)諧頻率偏離原有數(shù)值。該頻率偏離信號經(jīng)波形整形為矩形波后作為計數(shù)脈沖,在固定的時間窗口采樣計數(shù)脈沖便可間接得到探測振蕩器的頻率的變化。如果將無車輛通過時的空載頻率用f0表示(頻率本底),將有車輛通過時的實載頻率用fx表示,差值為$f=fx-f0,對應(yīng)的脈沖計數(shù)差值為$。由于道路(路面變形等)、氣環(huán)境的變化和線圈老化以及變形等干擾因素的影響均會使空載頻率f0發(fā)生漂移,故每10min需對f0動作漂移補償,重新標(biāo)定一次f0。1.系統(tǒng)設(shè)計的原理及硬件系統(tǒng)系統(tǒng)的設(shè)計原理及硬件系統(tǒng)設(shè)計原理見圖1。環(huán)形線圈通過饋線連接到隔離變

24、壓器一端,隔離變壓器的另一端與一個電容并聯(lián),組成LC并聯(lián)諧振, 此LC并聯(lián)諧振的頻率可根據(jù)公式(1)求得1。f=12PLC(1)式中:L)為環(huán)形線圈與饋線的總電感量;C)為并聯(lián)的電容;f)為諧振頻率。由公式可以看出,影響頻率f的因素只有L和C,故在C一定的情況下,環(huán)形線圈與饋線的總電感量決定了振蕩頻率。同時借鑒國內(nèi)外同類產(chǎn)品的相關(guān)數(shù)值,確定車輛檢測器線圈的振蕩頻率在20100kHz范圍之間。環(huán)形線圈的電感量為80120LH,饋線的電感量為019 H#m-1,加上其它因素的影響,饋線的長度設(shè)在300 m以內(nèi),以使總電感量小于1 000LH。隔離變壓器初級線圈與次級線圈匝數(shù)之比為1B1,它使線圈和

25、饋線的總電感量如實的從初級反映到次級,起隔離的作用,防止外界的干擾損壞內(nèi)部電路。 圖1 硬件系統(tǒng)設(shè)計原理圖 本設(shè)計中由MM74HC4046M組成的鎖相環(huán)電路的作用是為LC振蕩提供電流源,其頻率鎖定范圍在20 100 kHz之間。鎖相環(huán)主要由相位比較器、壓控振蕩器、低通濾波器3部分組成,它的基本構(gòu)成見圖2。 振蕩器頻率跟隨LC振蕩頻率,并將此頻率送到EPLD。相位比較器是一個由信號的上升沿控制的數(shù)字存儲網(wǎng)絡(luò)。它對輸入信號占空比的要求不高,允許輸入非對稱波形,它具有很寬的捕捉頻率范圍,而且不會鎖定在輸入信號的諧波。它提供數(shù)字誤差信號和鎖定信號(相位脈沖)2種輸出,當(dāng)達到鎖定時,在相位比較器的2個輸人信號之間保持零度相移。MM74HC4046M的部分設(shè)計電路見圖3。圖3 MM74HC4046M的外圍設(shè)計電路其中14腳接LC振蕩信號,4腳為壓控振蕩器的輸出端。本電路鎖相環(huán)采用的是RC型壓控振蕩器,必須外接電容C1(6,7腳)和電阻R4(11腳)作為充放電元件。當(dāng)鎖相環(huán)(PLL)對跟蹤的輸入