英文
Sensor and thickness gauge
Inductive sensor is measured by using electromagnetic induction to the physical quantities such as displacement, pressure, flow rate, vibration, etc., to convert the self-inductance and mutual inductance coil coefficient change, again by circuit . converting voltage or current changes output, implement non-electric quantity to power conversion.
Eddy current sensor is a built in eddy current effect theory of sensor. Eddy current transducer .sensitive coil, when to coil tong with alternating current and make it close to metal conductors, coils magnetic fields produced by will be conductor eddy current magnetic fields produced partly offset by, make the inductance coil amount, impedance and quality factor change. This change of conductor and geometry size, conductivity, the permeability related, also with the geometric parameter, current coil of frequency and coil to be measured distance between conductors concerned. If one of the above parameters to change, the rest are unchanged, it can be made into various USES of sensor can on the surface for metal conductor on objects multi-physical quantity of non-contact measurement.
Eddy current sensor can realize non-contact measure for metal conductors object surface multi-physical quantity, such as displacement, vibration, thickness, rotational speed, stress, hardness parameters. This kind of sensor can also be used to NDT.
Electricity eddy sensing simple structure, frequency response, high sensitivity, wide measurement range, resistance to dry sorrow ability, especially with the advantages of non-contact measurement, therefore in the industrial production and all fields of science and technology has been used widely.
When through the metal body directed flux change, will produce induced current in the conductor, the current in the conductor is self closing, this is the so-called eddy current. Electric vortex produce inevitable consumes part of the energy, thus make produce a magnetic field coil impedance changes, the physical phenomenon called junction effect. Eddy current sensor is using vortex effect, will non-electric quantity convert the impedance of the change and measuring.
Generally speaking, coils of impedance variations and conductor of electrical conductivity, magnetic conductivity, geometric shapes, coils of geometric parameters, exciting current frequency and coil to be measured distance between conductors concerned. If one of the above parameters control changing parameters, and the rest and constant, the impedance will become the varying parameters of a single value function. Like other parameter is changeless, impedance changes can be reflected coil to be measured metal conductors in the distance between size changes.
Induction thickness gauge used for measuring metal strips in rolling of dynamic thickness. inductance L 1 tong in certain frequency ac power UI, get in L 2 inductive voltage u routines. When tested metal strip thickness h the thicker, the resistance in the smaller, the induction eddy current, the greater the strip is coupled to the L2 alternating magnetic field weaken, the greater the in L2 obtained in the inductive voltage u '0 is smaller. So u '0 size reflects the thickness of metal strips h0 this device has no non-contact on-line detection of advantages.
Instrument technology index for:
Measuring scope: 0.010 ~ 5.00 mm
Measuring conditions: strip in rolling, the temperature of the constant change range in + 10%,
Strip the fluctuation in inductance sensor displacements of + 5mm
Measurement error: + 0.00 5mm
Display mode: digital ?
Second, identifying pathways
By the op-amp A 1 component oscillating circuit, the output ac voltage through A 2 amplifier circuit amplification to drive complementary power amplifier circuit, as inductance DLL source. Power amplifier circuit output again two ways feedback signals, all the way back to the inverse amplifier circuit A2 end and the other all the way into the A3 for rectification, then after nine circuit filtered to control T1 tube.
In L 2 obtained in the inductive voltage via A 5 amplification, which is divided into two ways of output. A travelling A6 after rectifying, again with its output voltage directly from the other way output A5 together add to the A7 input for filter and into A8 amplification output (the output voltage, again by analog conversion into digital signals, through decode logic amount in
the digital tube display on thickness h).
Third, underline unit
According to the above pathway can differentiate
Five, the analysis function
(a) signal generator
1. The sinusoidal oscillator: by the op-amp A 1 and R 1, C 1, R 2, C 2 composition RC sinusoidal oscillator series-parallel. R 3, RWl and knot type mosfet T 1 composition negative feedback network, is used in the automatic stable output sine wave signal amplitude. If grade amplifier output amplitude for some reason increase (such as power supply instability, etc.), will make the grid voltage T1 ∣ - uG1 ∣ increase, because T1 work in variable resistor zone, so that the source, the equivalent resistance increases bus-switch oscillating circuit, negative feedback to strengthen output amplitude automatically reduce achieve stability.
2. V oltage and power amplifier circuit: by the op-amp A 2 composition reversed-phase proportion amplifying circuit and its output voltage is driven by T 2, T 3 tube composed of complementary symmetry power amplifier circuit. This is actually made up of op-amp composed of power expansion circuit ?
(2) receiving signal amplifier circuit
1. The amplifier circuit, by electromagnetic induction in L2 obtains the ac signal voltage and strip thickness h inversely proportional. The signal voltage from A 5 composed of same phase ratio amplifier circuit amplification. By the magnification RW2 after regulation fixed.
2. Rectifier and filter circuits: by the op-amp A 6 composition high-precision half wave rectifier circuit. By circuits D5, the polarity of the diode D6 knowable, only for the positive half cycle in the input signal, just have the output to negative half cycle signal. Due to the feedback resistance R24 resistance than R23 twice, so the output signal amplitude u06 than input u05 twice.
By the op-amp A7 and R28 and C5 composed with reversed-phase summation proportion amplification of the first-order low-pass active filter circuits. Its two road input signal for op-amp A5 and A6 output signals u05 and u06. By above knowable, u06 amplitude, and u05 twice than
Six, estimation performance
Next face combination-logic circuit performance index back-of-the-envelope calculations. 1, sinusoidal oscillator circuit: its oscillation frequency for
11f 0===4. 82KH z 3-122πRC 2π⨯15⨯10⨯2200⨯10
2. Voltage and power amplifier circuit: because power amplifier circuit output power can be approximately regarded as u 02 amp A 2 output voltage, therefore followed, Amp A 2 and amplifier circuit total voltage magnifacation namely for op-amp A2 inverse ratio for the
R 20A u 2=-5=-=-2 R 410
3. Active filter circuits: op-amp A3 high-precision half wave composed of rectifier circuit output to the positive half cycle of half wave signal u 03, its amplitude and power amplifier circuit output u02 amplitude of the same. Half wave the average dc voltage rectifying output for U 03 = 0.45 U 02. Amp A 4 composition first-order low-pass active filter circuit, its bandpass voltage amplifier multiples of
R 20A u P =-17=-=-2 R 1610
Bandpass cut-off frequency for
1≈4H z 3-62πR 17⋅C 52π⨯20⨯10⨯2⨯10
So U03 through active filter circuit output negative dc voltage
U 04＝A U P ·U 03＝一2 ×0.45U 02＝一0.9U 02
The type of U02 level for amplifier output voltage RMS.
U 04 is voltage mosfet T1 grid of control voltage. UG1 used to change the T1 tubes in the variable resistor RD 3 equivalent resistance, automatic regulation negative feedback strength realize oscillating circuit to stabilize the picture.
4. Receiving signal circuit of the same phase ratio amplifier circuit: op-amp A 5 composition in-phase proportion amplifier circuit voltage magnifacation maximum
R +R 2168+10A u 5=1+W2=1+=8.8 R 2210
When RW2 = 0, AU5 = 2.
5. Rectifier (A6) and filtering (A7) circuit diagram shown : the waveform knowable, op-amp A7 composition reversed-phase summation first-order active low-pass filter circuit the equivalent input electric pressure for u 05 + u 06 the total wave rectifier negative signal, the average dc voltage is namely
U 05+U06 ＝0.9U 05 f C ==
Type in U 05 is op-amp A 5 output ac voltage RMS. Active filter circuit embodied with voltage amplifier multiples of 1
A u P7=-R 2820=-=-2 R 2610
So active filter circuit output dc voltage
U 07＝A UP7×0.9U 05＝一1.8U 05 Bandpass cut-off frequency for
11f 0==≈4H z 2πR 28⋅C 52π⨯20⨯103⨯2⨯10-6
6. The output stage amplifier circuit: the output stage is composed by the op-amp A 8 inverse ratio, the voltage amplifier circuit for magnifacation
R 3110A U3=-=-=-0. 79、 R 30//(RW3+R 33) 30//（22+0. 1）
When RW3 = 0, then
R 3110A U8=-=-=-100 （max) R 30//R3330//0. 1
So, the voltage magnifacation has magnified adjustment range, in order to achieve the latter stage frequency-field after being measured strip thickness corresponding to the digital display needed simulation voltage range
中文
传感器与测厚仪
电感式传感器是利用电磁感应把被测的物理量如位移，压力，流量，振动等转换成线圈的自感系数和互感系数的变化，再由电路转换为电压或电流的变化量输出，实现非电量到电量的转换。
电涡流式传感器是一种建立在涡流效应原理上的传感器。电涡流传感器的敏感元件是线圈，当给线圈通以交变电流并使它接近金属导体时，线圈产生的磁场就会被导体电
涡流产生的磁场部分抵消，使线圈的电感量、阻抗和品质因数发生变化。这种变化与导体的几何尺寸、导电率、导磁率有关，也与线圈的几何参量、电流的频率和线圈到被测导体间的距离有关。如果使上述参量中的某一个变动，其余皆不变，就可制成各种用途的传感器，能对表面为金属导体的物体进行多种物理量的非接触测量。
电涡流式传感器可以实现非接触地测量物体表面为金属导体的多种物理量，如位移、振动、厚度、转速、应力、硬度等参数。这种传感器也可用于无损探伤。
电涡流式传感结构简单、频率响应宽、灵敏度高、测量范围大、抗干忧能力强，特别是有非接触测量的优点，因此在工业生产和科学技术的各个领域中得到了广泛的应用。
当通过金属体的磁通量变化时，就会在导体中产生感生电流，这种电流在导体中是自行闭合的，这就是所谓电涡流。电涡流的产生必然要消耗一部分能量，从而使产生磁场的线圈阻抗发生变化，这一物理现象称为涡流效应。电涡流式传感器是利用涡流效应，将非电量转换为阻抗的变化而进行测量的。360毕业设计网友情提供---www.bysj360.com
一般讲，线圈的阻抗变化与导体的电导率、磁导率、几何形状，线圈的几何参数，激励电流频率以及线圈到被测导体间的距离有关。如果控制上述参数中的一个参数改变，而其余参恒定不变，则阻抗就成为这个变化参数的单值函数。如其他参数不变，阻抗的变化就可以反映线圈到被测金属导体间的距离大小变化。
感应测厚仪用来测量金属带材在压延时的动态厚度。电感L 1通以一定频率的交流电源ui ，在L 2上得到感应电压u 。。当被测金属带材厚度h 越厚时，其电阻越小，在带材上感应涡流越大，耦合到L 2上的交变磁场削弱越大，在L 2上得到的感应电压u 0就越小。所以u 0大小反映了金属带材的厚度h 0该装置具有无接触式在线检测的优点。
仪器的技术指标为：
测量范围：0.010～5.00mm
测量条件：带材在压延时的温度变化范围恒定在±10%，带材在电感传感器中的上下位移为±5mm
测量误差：±0.00 5mm
显示方式：数字显示0.000
采样时间：
本书只讨论测量部分的原理电路，
二、找出通路
由运放A 1组成振荡电路，其输出交流电压通过A 2放大电路放大后去驱动互补功率放大电路，作为电感L l 的信号源。功率放大电路输出再分两路反馈信号，一路反馈到放大电路A 2的反相端，另一路送入A 3进行整流，再经九电路滤波后去控制T 1管。
在L 2上得到的感应电压经A 5放大后，分两路输出。一路经A 6整流后，其输出电压再与直接从A 5输出的另一路一起加到A 7的输入端进行滤波，再送到A 8放大后输出(输出的电压，再由模拟量转换成数字量信号，通过译码电路在数码管上显示厚度h 值) 。
三、划出单元
根据上述通路可划分出下列各单元电路：信号源发生部分可分为RC 串并联正弦波振荡电路、反相比例放大电路、互补时称功率放大电路、高精度整流电路、有源滤波电路。信号接收放大部分可分为同相比例可调放大电路、高精度整流电路、有源滤波电路和放大电路。
五、分析功能
(一) 信号源发生电路
1．正弦波振荡器：由运放A 1和R 1、C 1、R 2、C 2组成RC 串并联正弦波振荡器。R 3、R Wl 和结型场效应管T 1组成负反馈网络，用于自动稳定输出正弦波信号幅度。若功放级
输出幅度由于某种原因 增加(如电源不稳等) ，将使T1的栅极电压∣-u G 1∣增加，由于T 1工作于可变电阻区，因此源、漏极间等效电阻增加，负反馈加强使振荡电路输出幅度自动减小达到稳定。
2．电压和功率放大电路：由运放A 2组成反相比例放大电路、其输出电压驱动由T 2、T 3管组成的互补对称功率放大电路。这实际上是由运放组成的功率扩展电路。电阻R 4、R 5组成电压并联负反馈，为电感传感器L 1提供较为稳定的交流电源电压，提高测量精度。
3．整流和滤波电路：由运放A 3，和D 3、D 4组成高精度半波整流滤波电路。根据D 3、 D 4在电路中的极性可知，只有整流电路输入为负半周时，才有输出，得到正半周信号。由于R 13=R14, 故输出和输入幅值相等。
由A 4和R 17、C 1组成带有反相比例放大的一阶低通有源滤波电路，其输出为负向直流电压，作为振荡器T 1的栅极电压u G1，自动控制振荡电路负反馈的强度，稳定输出幅度。
(二) 信号接收放大电路
1．放大电路，通过电磁感应在L 2上获得交流信号电压与带材厚度h 成反比。此信号电压由A5组成的同相比例放大电路进行放大。其放大倍数由R W2调节后固定。
2．整流和滤波电路：由运放A 6组成高精度半波整流电路。由电路中二极管D 5、D 6的极性可知，仅在输入为正半周信号时，才有输出为负半周信号。由于反馈电阻R 24阻值比R 23大一倍，故输出u 06信号幅度比输入u 05大一倍。
由运放A 7和R 28、C 5组成具有反相求和比例放大的一阶低通有源滤波电路。其两路输入信号为运放A 5和A 6的输出信号u 05和u 06。由上述可知，u 06幅度比u 05大一倍，而两路输入电路R 26=R27，故输入信号求和叠加为u 05+u06，相当于反相全波整流信号。其波形如图12．3．4所示。其幅度仍为A 5。放大后的输出幅度u 05M 、C 5和运放构成的一阶低通有源波，其输出变成直流信号。
3．输出，级放大电路：由运放A 8构成反相比例放大电路作为缓冲输出级，调节R W3可改变放大倍数，与第一级放大倍数配合调节，使输出电压值经模—数转换后的数字显示值与厚度尺寸一致。另一方面这级电压负反馈使输出电阻减小，使后级模-数效转换电路的输入电阻不影响这级输出电压。
六、估算性能
下面对各级电路性能指标作粗略估算。
1、正弦波振荡电路：其振荡频率为
11f 0===4. 82KH z 3-122πRC 2π⨯15⨯10⨯2200⨯10
2．电压和功率放大电路：由于功放电路输出电u 02可近似看作运放A 2输出的跟随电压，因此；运放A 2和功放电路总的电压放大倍数即为运放A 2的反相比例系数为
R 20A u 2=-5=-=-2 R 410
3．有源滤波电路：运放A 3组成的高精度半波整流电路输出为正半周的半波信号u 03，其幅值与功率放大电路输出u 02的幅值相同。半波整流输出的平均直流电压为U 03=0.45U02。运放A 4组成一阶低通有源滤波电路，其通带电压放大倍数为
R 20A u P =-17=-=-2 R 1610
通带截止频率为
11f C ==≈4H z 3-62πR 17⋅C 52π⨯20⨯10⨯2⨯10
故U 03通过有源滤波电路输出负的直流电压为
U 04＝A U P ·U 03＝一2 ×0.45U 02＝一0.9U 02
上式中U 02为功放级输出的电压有效值。
电压U 04是场效应管T 1的栅极控制电压。u G1用来改变T 1管在可变电阻区的等效阻值R D3，自动调节负反馈强度实现振荡电路的稳幅。
4．信号接收电路的同相比例放大电路：运放A 5组成同相比例放大电路的电压放大倍数最大为
R +R 2168+10A u 5=1+W2=1+=8.8， R 2210
当R W 2＝0，A U5＝2。
5．整流(A6) 和滤波(A7) 电路：由图12．3．4所示波形可知，运放A 7组成反相求和一阶有源低通滤波电路的等效输入电 压为u 05+u06的全波整流负信号，其平均直流电压即为
U 05+U06 ＝0.9U 05
式中U 05是运放A 5输出的交流电压有效值。
有源滤波电路的诵带电压放大倍数为
R 20 A u P7=-28=-=-2 R 2610
故有源滤波电路输出的直流电压
U 07＝A UP7×0.9U 05＝一1.8U 05
通带截止频率为
11 f 0==≈4H z 2πR 28⋅C 52π⨯20⨯103⨯2⨯10-6
6．输出级放大电路：输出级由运放A 8组成反相比例放大电路，其电压放大倍数为
R 3110 A U3=-=-=-0. 79 R 30//(RW3+R 33) 30//（22+0. 1）
当R W 3＝0，则
R 3110A U8=-=-=-100 （max) R 30//R3330//0. 1
因此，电压放大倍数具有放大调节范围，以达到后级模数转换后对应为被测带材厚度的数字显示所需要的模拟电压范围。
英文
Sensor and thickness gauge
Inductive sensor is measured by using electromagnetic induction to the physical quantities such as displacement, pressure, flow rate, vibration, etc., to convert the self-inductance and mutual inductance coil coefficient change, again by circuit . converting voltage or current changes output, implement non-electric quantity to power conversion.
Eddy current sensor is a built in eddy current effect theory of sensor. Eddy current transducer .sensitive coil, when to coil tong with alternating current and make it close to metal conductors, coils magnetic fields produced by will be conductor eddy current magnetic fields produced partly offset by, make the inductance coil amount, impedance and quality factor change. This change of conductor and geometry size, conductivity, the permeability related, also with the geometric parameter, current coil of frequency and coil to be measured distance between conductors concerned. If one of the above parameters to change, the rest are unchanged, it can be made into various USES of sensor can on the surface for metal conductor on objects multi-physical quantity of non-contact measurement.
Eddy current sensor can realize non-contact measure for metal conductors object surface multi-physical quantity, such as displacement, vibration, thickness, rotational speed, stress, hardness parameters. This kind of sensor can also be used to NDT.
Electricity eddy sensing simple structure, frequency response, high sensitivity, wide measurement range, resistance to dry sorrow ability, especially with the advantages of non-contact measurement, therefore in the industrial production and all fields of science and technology has been used widely.
When through the metal body directed flux change, will produce induced current in the conductor, the current in the conductor is self closing, this is the so-called eddy current. Electric vortex produce inevitable consumes part of the energy, thus make produce a magnetic field coil impedance changes, the physical phenomenon called junction effect. Eddy current sensor is using vortex effect, will non-electric quantity convert the impedance of the change and measuring.
Generally speaking, coils of impedance variations and conductor of electrical conductivity, magnetic conductivity, geometric shapes, coils of geometric parameters, exciting current frequency and coil to be measured distance between conductors concerned. If one of the above parameters control changing parameters, and the rest and constant, the impedance will become the varying parameters of a single value function. Like other parameter is changeless, impedance changes can be reflected coil to be measured metal conductors in the distance between size changes.
Induction thickness gauge used for measuring metal strips in rolling of dynamic thickness. inductance L 1 tong in certain frequency ac power UI, get in L 2 inductive voltage u routines. When tested metal strip thickness h the thicker, the resistance in the smaller, the induction eddy current, the greater the strip is coupled to the L2 alternating magnetic field weaken, the greater the in L2 obtained in the inductive voltage u '0 is smaller. So u '0 size reflects the thickness of metal strips h0 this device has no non-contact on-line detection of advantages.
Instrument technology index for:
Measuring scope: 0.010 ~ 5.00 mm
Measuring conditions: strip in rolling, the temperature of the constant change range in + 10%,
Strip the fluctuation in inductance sensor displacements of + 5mm
Measurement error: + 0.00 5mm
Display mode: digital ?
Second, identifying pathways
By the op-amp A 1 component oscillating circuit, the output ac voltage through A 2 amplifier circuit amplification to drive complementary power amplifier circuit, as inductance DLL source. Power amplifier circuit output again two ways feedback signals, all the way back to the inverse amplifier circuit A2 end and the other all the way into the A3 for rectification, then after nine circuit filtered to control T1 tube.
In L 2 obtained in the inductive voltage via A 5 amplification, which is divided into two ways of output. A travelling A6 after rectifying, again with its output voltage directly from the other way output A5 together add to the A7 input for filter and into A8 amplification output (the output voltage, again by analog conversion into digital signals, through decode logic amount in
the digital tube display on thickness h).
Third, underline unit
According to the above pathway can differentiate
Five, the analysis function
(a) signal generator
1. The sinusoidal oscillator: by the op-amp A 1 and R 1, C 1, R 2, C 2 composition RC sinusoidal oscillator series-parallel. R 3, RWl and knot type mosfet T 1 composition negative feedback network, is used in the automatic stable output sine wave signal amplitude. If grade amplifier output amplitude for some reason increase (such as power supply instability, etc.), will make the grid voltage T1 ∣ - uG1 ∣ increase, because T1 work in variable resistor zone, so that the source, the equivalent resistance increases bus-switch oscillating circuit, negative feedback to strengthen output amplitude automatically reduce achieve stability.
2. V oltage and power amplifier circuit: by the op-amp A 2 composition reversed-phase proportion amplifying circuit and its output voltage is driven by T 2, T 3 tube composed of complementary symmetry power amplifier circuit. This is actually made up of op-amp composed of power expansion circuit ?
(2) receiving signal amplifier circuit
1. The amplifier circuit, by electromagnetic induction in L2 obtains the ac signal voltage and strip thickness h inversely proportional. The signal voltage from A 5 composed of same phase ratio amplifier circuit amplification. By the magnification RW2 after regulation fixed.
2. Rectifier and filter circuits: by the op-amp A 6 composition high-precision half wave rectifier circuit. By circuits D5, the polarity of the diode D6 knowable, only for the positive half cycle in the input signal, just have the output to negative half cycle signal. Due to the feedback resistance R24 resistance than R23 twice, so the output signal amplitude u06 than input u05 twice.
By the op-amp A7 and R28 and C5 composed with reversed-phase summation proportion amplification of the first-order low-pass active filter circuits. Its two road input signal for op-amp A5 and A6 output signals u05 and u06. By above knowable, u06 amplitude, and u05 twice than
Six, estimation performance
Next face combination-logic circuit performance index back-of-the-envelope calculations. 1, sinusoidal oscillator circuit: its oscillation frequency for
11f 0===4. 82KH z 3-122πRC 2π⨯15⨯10⨯2200⨯10
2. Voltage and power amplifier circuit: because power amplifier circuit output power can be approximately regarded as u 02 amp A 2 output voltage, therefore followed, Amp A 2 and amplifier circuit total voltage magnifacation namely for op-amp A2 inverse ratio for the
R 20A u 2=-5=-=-2 R 410
3. Active filter circuits: op-amp A3 high-precision half wave composed of rectifier circuit output to the positive half cycle of half wave signal u 03, its amplitude and power amplifier circuit output u02 amplitude of the same. Half wave the average dc voltage rectifying output for U 03 = 0.45 U 02. Amp A 4 composition first-order low-pass active filter circuit, its bandpass voltage amplifier multiples of
R 20A u P =-17=-=-2 R 1610
Bandpass cut-off frequency for
1≈4H z 3-62πR 17⋅C 52π⨯20⨯10⨯2⨯10
So U03 through active filter circuit output negative dc voltage
U 04＝A U P ·U 03＝一2 ×0.45U 02＝一0.9U 02
The type of U02 level for amplifier output voltage RMS.
U 04 is voltage mosfet T1 grid of control voltage. UG1 used to change the T1 tubes in the variable resistor RD 3 equivalent resistance, automatic regulation negative feedback strength realize oscillating circuit to stabilize the picture.
4. Receiving signal circuit of the same phase ratio amplifier circuit: op-amp A 5 composition in-phase proportion amplifier circuit voltage magnifacation maximum
R +R 2168+10A u 5=1+W2=1+=8.8 R 2210
When RW2 = 0, AU5 = 2.
5. Rectifier (A6) and filtering (A7) circuit diagram shown : the waveform knowable, op-amp A7 composition reversed-phase summation first-order active low-pass filter circuit the equivalent input electric pressure for u 05 + u 06 the total wave rectifier negative signal, the average dc voltage is namely
U 05+U06 ＝0.9U 05 f C ==
Type in U 05 is op-amp A 5 output ac voltage RMS. Active filter circuit embodied with voltage amplifier multiples of 1
A u P7=-R 2820=-=-2 R 2610
So active filter circuit output dc voltage
U 07＝A UP7×0.9U 05＝一1.8U 05 Bandpass cut-off frequency for
11f 0==≈4H z 2πR 28⋅C 52π⨯20⨯103⨯2⨯10-6
6. The output stage amplifier circuit: the output stage is composed by the op-amp A 8 inverse ratio, the voltage amplifier circuit for magnifacation
R 3110A U3=-=-=-0. 79、 R 30//(RW3+R 33) 30//（22+0. 1）
When RW3 = 0, then
R 3110A U8=-=-=-100 （max) R 30//R3330//0. 1
So, the voltage magnifacation has magnified adjustment range, in order to achieve the latter stage frequency-field after being measured strip thickness corresponding to the digital display needed simulation voltage range
中文
传感器与测厚仪
电感式传感器是利用电磁感应把被测的物理量如位移，压力，流量，振动等转换成线圈的自感系数和互感系数的变化，再由电路转换为电压或电流的变化量输出，实现非电量到电量的转换。
电涡流式传感器是一种建立在涡流效应原理上的传感器。电涡流传感器的敏感元件是线圈，当给线圈通以交变电流并使它接近金属导体时，线圈产生的磁场就会被导体电
涡流产生的磁场部分抵消，使线圈的电感量、阻抗和品质因数发生变化。这种变化与导体的几何尺寸、导电率、导磁率有关，也与线圈的几何参量、电流的频率和线圈到被测导体间的距离有关。如果使上述参量中的某一个变动，其余皆不变，就可制成各种用途的传感器，能对表面为金属导体的物体进行多种物理量的非接触测量。
电涡流式传感器可以实现非接触地测量物体表面为金属导体的多种物理量，如位移、振动、厚度、转速、应力、硬度等参数。这种传感器也可用于无损探伤。
电涡流式传感结构简单、频率响应宽、灵敏度高、测量范围大、抗干忧能力强，特别是有非接触测量的优点，因此在工业生产和科学技术的各个领域中得到了广泛的应用。
当通过金属体的磁通量变化时，就会在导体中产生感生电流，这种电流在导体中是自行闭合的，这就是所谓电涡流。电涡流的产生必然要消耗一部分能量，从而使产生磁场的线圈阻抗发生变化，这一物理现象称为涡流效应。电涡流式传感器是利用涡流效应，将非电量转换为阻抗的变化而进行测量的。360毕业设计网友情提供---www.bysj360.com
一般讲，线圈的阻抗变化与导体的电导率、磁导率、几何形状，线圈的几何参数，激励电流频率以及线圈到被测导体间的距离有关。如果控制上述参数中的一个参数改变，而其余参恒定不变，则阻抗就成为这个变化参数的单值函数。如其他参数不变，阻抗的变化就可以反映线圈到被测金属导体间的距离大小变化。
感应测厚仪用来测量金属带材在压延时的动态厚度。电感L 1通以一定频率的交流电源ui ，在L 2上得到感应电压u 。。当被测金属带材厚度h 越厚时，其电阻越小，在带材上感应涡流越大，耦合到L 2上的交变磁场削弱越大，在L 2上得到的感应电压u 0就越小。所以u 0大小反映了金属带材的厚度h 0该装置具有无接触式在线检测的优点。
仪器的技术指标为：
测量范围：0.010～5.00mm
测量条件：带材在压延时的温度变化范围恒定在±10%，带材在电感传感器中的上下位移为±5mm
测量误差：±0.00 5mm
显示方式：数字显示0.000
采样时间：
本书只讨论测量部分的原理电路，
二、找出通路
由运放A 1组成振荡电路，其输出交流电压通过A 2放大电路放大后去驱动互补功率放大电路，作为电感L l 的信号源。功率放大电路输出再分两路反馈信号，一路反馈到放大电路A 2的反相端，另一路送入A 3进行整流，再经九电路滤波后去控制T 1管。
在L 2上得到的感应电压经A 5放大后，分两路输出。一路经A 6整流后，其输出电压再与直接从A 5输出的另一路一起加到A 7的输入端进行滤波，再送到A 8放大后输出(输出的电压，再由模拟量转换成数字量信号，通过译码电路在数码管上显示厚度h 值) 。
三、划出单元
根据上述通路可划分出下列各单元电路：信号源发生部分可分为RC 串并联正弦波振荡电路、反相比例放大电路、互补时称功率放大电路、高精度整流电路、有源滤波电路。信号接收放大部分可分为同相比例可调放大电路、高精度整流电路、有源滤波电路和放大电路。
五、分析功能
(一) 信号源发生电路
1．正弦波振荡器：由运放A 1和R 1、C 1、R 2、C 2组成RC 串并联正弦波振荡器。R 3、R Wl 和结型场效应管T 1组成负反馈网络，用于自动稳定输出正弦波信号幅度。若功放级
输出幅度由于某种原因 增加(如电源不稳等) ，将使T1的栅极电压∣-u G 1∣增加，由于T 1工作于可变电阻区，因此源、漏极间等效电阻增加，负反馈加强使振荡电路输出幅度自动减小达到稳定。
2．电压和功率放大电路：由运放A 2组成反相比例放大电路、其输出电压驱动由T 2、T 3管组成的互补对称功率放大电路。这实际上是由运放组成的功率扩展电路。电阻R 4、R 5组成电压并联负反馈，为电感传感器L 1提供较为稳定的交流电源电压，提高测量精度。
3．整流和滤波电路：由运放A 3，和D 3、D 4组成高精度半波整流滤波电路。根据D 3、 D 4在电路中的极性可知，只有整流电路输入为负半周时，才有输出，得到正半周信号。由于R 13=R14, 故输出和输入幅值相等。
由A 4和R 17、C 1组成带有反相比例放大的一阶低通有源滤波电路，其输出为负向直流电压，作为振荡器T 1的栅极电压u G1，自动控制振荡电路负反馈的强度，稳定输出幅度。
(二) 信号接收放大电路
1．放大电路，通过电磁感应在L 2上获得交流信号电压与带材厚度h 成反比。此信号电压由A5组成的同相比例放大电路进行放大。其放大倍数由R W2调节后固定。
2．整流和滤波电路：由运放A 6组成高精度半波整流电路。由电路中二极管D 5、D 6的极性可知，仅在输入为正半周信号时，才有输出为负半周信号。由于反馈电阻R 24阻值比R 23大一倍，故输出u 06信号幅度比输入u 05大一倍。
由运放A 7和R 28、C 5组成具有反相求和比例放大的一阶低通有源滤波电路。其两路输入信号为运放A 5和A 6的输出信号u 05和u 06。由上述可知，u 06幅度比u 05大一倍，而两路输入电路R 26=R27，故输入信号求和叠加为u 05+u06，相当于反相全波整流信号。其波形如图12．3．4所示。其幅度仍为A 5。放大后的输出幅度u 05M 、C 5和运放构成的一阶低通有源波，其输出变成直流信号。
3．输出，级放大电路：由运放A 8构成反相比例放大电路作为缓冲输出级，调节R W3可改变放大倍数，与第一级放大倍数配合调节，使输出电压值经模—数转换后的数字显示值与厚度尺寸一致。另一方面这级电压负反馈使输出电阻减小，使后级模-数效转换电路的输入电阻不影响这级输出电压。
六、估算性能
下面对各级电路性能指标作粗略估算。
1、正弦波振荡电路：其振荡频率为
11f 0===4. 82KH z 3-122πRC 2π⨯15⨯10⨯2200⨯10
2．电压和功率放大电路：由于功放电路输出电u 02可近似看作运放A 2输出的跟随电压，因此；运放A 2和功放电路总的电压放大倍数即为运放A 2的反相比例系数为
R 20A u 2=-5=-=-2 R 410
3．有源滤波电路：运放A 3组成的高精度半波整流电路输出为正半周的半波信号u 03，其幅值与功率放大电路输出u 02的幅值相同。半波整流输出的平均直流电压为U 03=0.45U02。运放A 4组成一阶低通有源滤波电路，其通带电压放大倍数为
R 20A u P =-17=-=-2 R 1610
通带截止频率为
11f C ==≈4H z 3-62πR 17⋅C 52π⨯20⨯10⨯2⨯10
故U 03通过有源滤波电路输出负的直流电压为
U 04＝A U P ·U 03＝一2 ×0.45U 02＝一0.9U 02
上式中U 02为功放级输出的电压有效值。
电压U 04是场效应管T 1的栅极控制电压。u G1用来改变T 1管在可变电阻区的等效阻值R D3，自动调节负反馈强度实现振荡电路的稳幅。
4．信号接收电路的同相比例放大电路：运放A 5组成同相比例放大电路的电压放大倍数最大为
R +R 2168+10A u 5=1+W2=1+=8.8， R 2210
当R W 2＝0，A U5＝2。
5．整流(A6) 和滤波(A7) 电路：由图12．3．4所示波形可知，运放A 7组成反相求和一阶有源低通滤波电路的等效输入电 压为u 05+u06的全波整流负信号，其平均直流电压即为
U 05+U06 ＝0.9U 05
式中U 05是运放A 5输出的交流电压有效值。
有源滤波电路的诵带电压放大倍数为
R 20 A u P7=-28=-=-2 R 2610
故有源滤波电路输出的直流电压
U 07＝A UP7×0.9U 05＝一1.8U 05
通带截止频率为
11 f 0==≈4H z 2πR 28⋅C 52π⨯20⨯103⨯2⨯10-6
6．输出级放大电路：输出级由运放A 8组成反相比例放大电路，其电压放大倍数为
R 3110 A U3=-=-=-0. 79 R 30//(RW3+R 33) 30//（22+0. 1）
当R W 3＝0，则
R 3110A U8=-=-=-100 （max) R 30//R3330//0. 1
因此，电压放大倍数具有放大调节范围，以达到后级模数转换后对应为被测带材厚度的数字显示所需要的模拟电压范围。