CN102608199A

CN102608199A - Signal conditioning circuit of ACFM (Alternating Current Field Measurement) digital detector

Info

Publication number: CN102608199A
Application number: CN2012100566903A
Authority: CN
Inventors: 任尚坤; 李兵
Original assignee: Nanchang Hangkong University
Current assignee: Nanchang Hangkong University
Priority date: 2012-03-06
Filing date: 2012-03-06
Publication date: 2012-07-25

Abstract

The invention provides a signal conditioning circuit of an ACFM (Alternating Current Field Measurement) digital detector, comprising a signal input circuit, a program control gain amplification circuit, a band-pass filtering circuit, a gain adjustable amplification circuit, a true effective value conversion circuit, a signal output circuit, an MCU (Micro-programmed Control Unit) interface and a self-adapting clock signal. The signal conditioning circuit is characterized in that: the signal input circuit is connected with the program control gain amplification circuit; the program control gain amplification circuit is connected with the band-pass filtering circuit; the band-pass filtering circuit is connected with the gain adjustable amplification circuit; the gain adjustable amplification circuit is connected with the true effective value conversion circuit; the true effective value conversion circuit is connected with the signal output circuit; the MCU interface is connected with the program control gain amplification circuit and the band-pass filtering circuit; and the self-adapting clock signal is connected with the band-pass filtering circuit. The signal conditioning circuit has the technical effects that: the defects that the applicability of the existing ACFM signal conditioning circuit is poor, the measurement type is single, the measurement precision is not high and the digital control cannot be realized are overcome; the signal conditioning circuit has the characteristics of wide applicable range, high detection precision, digital controllability and stable and reliable work, and can be applied to the signal conditioning circuit of the ACFM digital detector with the high cost performance.

Description

The signal conditioning circuit of ACFM digitizing detector

Technical field

The present invention relates to a kind of signal conditioning circuit, relate in particular to a kind of signal conditioning circuit of ACFM digitizing detector.

Background technology

In recent years, on EDDY CURRENT and Magnetic Flux Leakage Inspecting basis, a kind of new Dynamic Non-Destruction Measurement grows up---disturbed magnetic field detection technique (Alternating Current Field Measurement is called for short ACFM).This techniques make use conductive material is under the exchange current effect, and the defect crack of material will change the faradic distribution around it, thereby change ferromagnetic test specimen surface induction DISTRIBUTION OF MAGNETIC FIELD.Through the variation of surface measurements induced field, and, confirm the length and the depth characteristic of crack defect according to the inverting of mathematical model.

Ferromagnetic component in use under the effect of stress corrosion, fatigue load, internal work medium or operate outside environment, is prone to produce surface crack at fluting, cavity, stress raiser and weld seam and heat-affected zone thereof.Crack defect is a kind of main damage form of hardware, and crack size is an important parameter of estimating the member safe reliability.Can detect defectives such as crackle when member is carried out Non-Destructive Testing fast, easily and accurately, and can carry out accurately quantitatively characterizing, for the fracture defect of prevention member with prevent that the generation of great serious accident is significant.

Traditional lossless detection method detects and the magnetic detection like infiltration, and its detection sensitivity is higher, but it has relatively high expectations to component surface, need carry out cleaning works such as paint removal to the surface, when having increased a large amount of check mans and workload; Ultrasound detection is then because the coarse injustice of component surface and acoustic coupling is relatively poor, makes relatively difficulty of accurate detection by quantitative; EDDY CURRENT has realized non-contact detecting, need not couplant, but because influence the detection signal factor more, and is high to testing staff's competency profiling, is prone to cause fail to judge or judge influence detection quality by accident.The disturbed magnetic field detection technique is a kind of new detection technique; This method detection speed is fast, precision is high; Qualitative and quantitative analysis is once accomplished, and can realize non-contact detecting, need not to clear up the paint and the coating of metal surface; Simultaneously need not demarcate test block, have the incomparable advantage of traditional lossless detection method.Developing new disturbed magnetic field detector will have broad application prospects.

In 20 end of the centurys, the technical software company of Britain (TSC company) just pilot development the pertinent instruments that detects based on disturbed magnetic field, the beginning exploration is applied to the detection of offshore platform.But because this instrument costs an arm and a leg, measuring accuracy awaits to improve, and also is not applied in China.At present; At home according to report; At the used signal conditioning circuit of the ac magnetic field detection system of laboratory development, exist poor for applicability, measuring that kind is single, measuring accuracy is not high and have can't numerically controlled shortcoming, is inappropriate for the high-end detecting instrument of preparation high performance-price ratio.

When utilization ac magnetic field detection technique was carried out Non-Destructive Testing, detection signal was very faint, all was that millivolt level and signal to noise ratio (S/N ratio) are low usually.Signal conditioning circuit is very important ingredient in detecting instrument, relates to the signal to noise ratio (S/N ratio) of effective raising detection signal, and is that back level processing provides stable signal gain.

Summary of the invention

The object of the present invention is to provide a kind of signal conditioning circuit of ACFM digitizing detector, overcome the various drawbacks that signal conditioning circuit exists in the present ac magnetic field detection.

The present invention realizes like this; It comprises signal input circuit, programme-controlled gain amplifying circuit, bandwidth-limited circuit, Gain Adjustable amplifying circuit, real effective change-over circuit, signal output apparatus, MCU interface and self-adaptation clock signal; It is characterized in that signal input circuit connects the programme-controlled gain amplifying circuit; The programme-controlled gain amplifying circuit connects bandwidth-limited circuit; Bandwidth-limited circuit connects the Gain Adjustable amplifying circuit, and Gain Adjustable amplifying circuit connection real effective change-over circuit, real effective change-over circuit connect signal output apparatus, the MCU interface connects the programme-controlled gain amplifying circuit and is connected bandwidth-limited circuit with bandwidth-limited circuit, self-adaptation clock signal; Said programme-controlled gain amplifying circuit uses low noise integrated operational amplifier and can control enlargement factor by MCU; Said bandwidth-limited circuit can be by MCU program and the control of self-adaptation clock signal dual mode; Described self-adaptation clock signal comprises sinusoidal wave circuit and square-wave, phase locking frequency multiplying circuit and the bandwidth-limited circuit of becoming.

Technique effect of the present invention is: overcome current ACFM signal conditioning circuit poor for applicability, measure that kind is single, measuring accuracy is not high and can't numerically controlled shortcoming; It is wide to have the scope of application; Accuracy of detection is high; Digital controllable, the stable and reliable operation characteristics can be used for the signal conditioning circuit of the ACFM detecting instrument of high performance-price ratio.

Description of drawings

Fig. 1 is an electric functional-block diagram of the present invention.

Fig. 2 is the electric functional-block diagram of self-adaptation clock signal of the present invention.

Embodiment

Below in conjunction with accompanying drawing and specific embodiment the present invention is elaborated.

As shown in Figure 1; The present invention includes signal input circuit 1, programme-controlled gain amplifying circuit 2, bandwidth-limited circuit 3, Gain Adjustable amplifying circuit 4, real effective change-over circuit 5, signal output apparatus 6, MCU interface 7 and self-adaptation clock signal 8; It is characterized in that signal input circuit 1 connects programme-controlled gain amplifying circuit 2; Programme-controlled gain amplifying circuit 2 connects bandwidth-limited circuit 3; Bandwidth-limited circuit 3 connects Gain Adjustable amplifying circuits 4, and Gain Adjustable amplifying circuit 4 connects that real effective change-over circuit 5, real effective change-over circuit connect signal output apparatus 6, MCU interface 7 connects programme-controlled gain amplifying circuits 2 and is connected bandwidth-limited circuit 3 with bandwidth-limited circuit 3, self-adaptation clock signal 8; Its principle of work is that low noise programme-controlled gain amplifying circuit carries out the prime amplification to the feeble signal of signal input circuit; Programmable amplifier is selected low noise integrated operational amplifier for use; The enlargement factor of amplifier can be selected suitable enlargement factor according to the situation of workpiece to be checked by the MCU programmed control.BPF. is also selected integrated adaptive bandpass filter spare for use; This BPF. realizes that the control mode of bandpass filtering has two kinds: MCU controls and accepts the self-adaptation clock signal; Dual mode makes the centre frequency of BPF. can follow variation along with the variation of pumping signal; Therefore can be suitable under the different materials attribute conditions the different bandpass filtering demands that detect frequency.Said programme-controlled gain amplifying circuit uses low noise integrated operational amplifier and can control enlargement factor by MCU, and said bandwidth-limited circuit can be by MCU program and the control of self-adaptation clock signal dual mode.

As shown in Figure 2, the self-adaptation clock signal comprises sinusoidal wave circuit and square-wave 9, phase locking frequency multiplying circuit 10 and the bandwidth-limited circuit 3 of becoming, and at first imports sinusoidal signal 11 through a sinusoidal wave circuit and square-wave 9 that becomes, and becomes sinusoidal excitation signal with square-wave signal frequently.Signal is afterwards realized the fixedly frequency multiplication output of multiple of signal through a phase locking frequency multiplying circuit 10, has promptly exported the needed clock control signal of BPF..The adjustable gain amplifying circuit can make the input signal of back level real effective change-over circuit be in suitable amplitude range the control of the amplitude of input signal within the specific limits.Through high-precision true rms value convertor circuit, AC signal is become direct current signal, thereby can obtain desirable detection signal characteristic curve.This signal conditioning circuit scope of application is wide, accuracy of detection is high, working stability is reliable, can be used as the signal conditioning circuit of the ACFM detecting instrument of high performance-price ratio.

Prime low noise gain amplifying circuit adopts low noise instrument amplifier and numerical control pot to realize, wherein the digital potentiometer GPIO end that meets DSP carries out programmed control and changes its resistance value, thereby reaches the effect of change enlargement factor.Amplify accordingly by programmed control corresponding to the different detection material properties.

BPF. adopts integrated control BPF. able to programme, and its centre frequency and passband width can be controlled through programming.The control mode that adopts in the design has two kinds: MCU programmed control and self-adaptation clock signal controlling.Under the MCU program control mode; The clock pin of BPF. and F value are provided with pin with the Q value and all are connected with the control pin of DSP; Control the centre frequency and the passband width of bandpass filtering by the program of MCU according to the frequency of pumping signal, be fit to instrumentation and use.Under the self-adaptation clock control pattern signal; Need provide the self-adaptation clock signal to BPF.; The generation circuit of self-adaptation clock signal becomes circuit and square-wave by sine wave and the phase locking frequency multiplying circuit constitutes; Adopt the hysteresis comparator circuit to add squaring circuit and realize the sinusoidal wave square wave that becomes, and keep the dutycycle of square wave 50%.Adopt the phase locking frequency multiplying circuit that square-wave signal is carried out exporting the clock signal as BPF. after the frequency multiplication, the selection of F value and Q value manually wire jumper is provided with flexibly, is applicable to the laboratory study use.

Back gain per stage adjustable control circuit adopts low noise integrated operational amplifier to add accurate adjustable resistance and realizes, its objective is the output gain of whole signal conditioning circuit is controlled, to adapt to the variation characteristic of two-way detection signal in the ACFM testing process.

The true rms value convertor circuit adopts integrated high precision true rms value convertor chip to realize, and improves the filter network design of accuracy of detection, guarantees signal detection accuracy.

The signal conditioning circuit of the ACFM digitizing detecting instrument of the present invention's design adopts low noise integrated amplifier and bandwidth-limited circuit, and noise level is far smaller than discrete component.Bandwidth-limited circuit with respect to low-pass filter circuit for low-frequency disturbance particularly power frequency disturb and to have better inhibition effect, improve the signal to noise ratio (S/N ratio) of signal greatly.The low noise amplifying circuit of prime adopts stored program control system, can satisfy the demand of amplifying detection signal under the different materials attribute.Design of Bandpass is two kinds of control modes, and auto adapted filtering control is used applicable to the laboratory, and MCU control can be used in instrumentation control.Under two kinds of control models, the centre frequency of BPF. all can change according to the variation of exciting signal frequency, and the demand that excitation frequency changes in the time of therefore can satisfying the different materials workpiece sensing is applied widely.Adopt high-precision true rms value convertor circuit; The magnitude of AC signal can be changed into the magnitude of direct current signal; Help appearing of detection signal characteristic curve, and also can reduce the requirement of data acquisition circuit, also help digitized processing signal.

Claims

1. the signal conditioning circuit of an ACFM digitizing detector; It comprises signal input circuit, programme-controlled gain amplifying circuit, bandwidth-limited circuit, Gain Adjustable amplifying circuit, real effective change-over circuit, signal output apparatus, MCU interface and self-adaptation clock signal; It is characterized in that signal input circuit connects the programme-controlled gain amplifying circuit; The programme-controlled gain amplifying circuit connects bandwidth-limited circuit; Bandwidth-limited circuit connects the Gain Adjustable amplifying circuit, and the Gain Adjustable amplifying circuit connects the real effective change-over circuit, and the real effective change-over circuit connects signal output apparatus; The MCU interface connects programme-controlled gain amplifying circuit and bandwidth-limited circuit, and the self-adaptation clock signal connects bandwidth-limited circuit.

2. the signal conditioning circuit of ACFM digitizing detector according to claim 1 is characterized in that said programme-controlled gain amplifying circuit uses low noise integrated operational amplifier and can control enlargement factor by MCU.

3. the signal conditioning circuit of ACFM digitizing detector according to claim 1 is characterized in that said bandwidth-limited circuit can be by MCU program and the control of self-adaptation clock signal dual mode.

4. the signal conditioning circuit of ACFM digitizing detector according to claim 1 is characterized in that described self-adaptation clock signal comprises sinusoidal wave circuit and square-wave, phase locking frequency multiplying circuit and the bandwidth-limited circuit of becoming.