TWI509242B - Non-contact eddy-current detecting device and controlling method thereof - Google Patents

Description

Non-contact eddy current detecting device and control method thereof

The present disclosure relates to a non-contact eddy current detecting device and a control method thereof.

The use of roll-to-roll (R2R) processes to make electronic products is growing, such as flexible printed circuit boards, conductive films, and so on. Among them, the conductive film is rapidly deposited on the substrate, and the uniformity of the impedance of the conductive film directly affects the characteristic performance of the subsequent electronic product, and therefore the impedance of the conductive film formed after deposition must be measured. The device for measuring the conductive film can be divided into a plurality of types, wherein the non-contact measuring device can detect the characteristics and defects of the sample to be tested without destroying the sample to be tested, and the non-contact measuring device There are many types of sensing methods, one of which is to use the eddy current principle for sensing. The principle of Eddy Current is to couple with the sample to be tested through an alternating magnetic field (primary magnetic field), so that the sample to be tested is induced to vortex. The current, the characteristics of the sample to be tested will cause the change of the eddy current flow direction, and the eddy current will form a secondary magnetic field to resist the change of the alternating magnetic field (primary magnetic field), so the coupling characteristics caused by the sample to be tested can be changed. The characteristics of the sample to be tested are detected. However, in the operation of the roll-to-roll machine, the non-contact probe needs to be able to overcome the vibration of the machine up and down and sensitive to temperature changes.

The traditional two-side series probe is connected in series by using two probe coils, but the external connection of the series connection coil is limited by the mechanism, and is suitable for the sheet resistance detection of small-sized samples or large-sized sample edges; when used for large size When the sample is measured, the middle connection between the two sets of probe series coils needs to be lengthened according to the size of the object to be tested. The wire is easy to change due to the dynamic inductance of the dynamic machine table. The change of the inductance value will cause the sheet resistance. Measuring error.

The disclosure relates to a non-contact eddy current detecting device and a control method.

According to the present disclosure, a non-contact eddy current detecting device is proposed. a first end of a first coil is coupled to a second end of a first power amplifier and a first end of a second power amplifier; a first end of the second coil and a second end of the second power amplifier The first end of the first power amplifier is coupled to the first end of the first power amplifier; the first end of the first power amplifier and the first end of the second power amplifier are coupled to the first end of a negative feedback device, the first power amplifier The third end point and the third end of the second power amplifier are coupled to the third end of the negative feedback device; the first of the current detector The end point is coupled to the second end of the first coil and the second end of the second coil, and the second end of the current detector outputs a detection signal.

According to the present disclosure, a non-contact eddy current detecting method is also proposed. The control method includes the following steps. Using a first coil and a second coil to sense an alternating current signal of the object to be tested; and coupling the first coil and the second coil to a first power amplifier and an output of the second power amplifier to form a positive return The input of the first power amplifier and the second power amplifier is controlled by a negative feedback device to have a certain amplitude; the AC signal is generated by a current detector to generate a detection signal of DC.

In order to better understand the above and other aspects of the present invention, a few embodiments are described below, and in conjunction with the drawings, the detailed description is as follows:

FIG. 1 is a schematic diagram showing an example block diagram of an embodiment of a non-contact eddy current detecting device.

FIG. 2A is a schematic diagram showing an example of a positive feedback NMOS implementation.

FIG. 2B is a schematic diagram showing an example of a positive feedback PMOS implementation.

Figure 3 shows an example diagram of the effect of eliminating temperature.

FIG. 4 is a schematic diagram showing the comparison between the prior art and the prior art when the sample test piece is separated from the center of the probe by a different distance.

FIG. 5 is a schematic diagram showing the change of the output signal generated by the prior art single probe for different displacements.

Figure 6 shows the amount of change in the measurement error of the sample vibration after 100 seconds. schematic diagram.

FIG. 7 is a schematic diagram showing a block diagram of an embodiment of a non-contact eddy current detecting method.

Please refer to FIG. 1 , which is a schematic diagram of a block diagram of the non-contact eddy current detecting device 1 . Wherein, the magnetic core 100a (first probe) and the 110a wire form a first coil 10a, the magnetic core 100b (second probe) and the wire 110b form a second coil 10b, and the object to be tested 200 is placed in the first coil 10a and the second coil Between 10b, the first coil 10a and the second coil 10b may be symmetric, and the first coil 10a and the second coil 10b may be collectively referred to as the probe 10. The output of the first power amplifier 120a is coupled to the first end of the first coil 10a and is output to the input of the second power amplifier 120b (first end point); the output of the second probe second power amplifier 120b (the second end) Point) coupled to the first end of the second coil 10b, and outputting the input end (first end point) of the first power amplifier 120a, the first power amplifier 120a and the second power amplifier 120b form a positive feedback, positive feedback forming The self-oscillation of the circuit causes the first coil 10a and the second coil 10b to be in the same oscillating circuit and operates at the same oscillating frequency; the output current of the power amplifier 120 drives the probe 10 to generate an alternating magnetic field (ie, a primary magnetic field). The alternating magnetic field passes through the object to be tested 200, and the object to be tested 200 induces an eddy current (which is an alternating current signal), and the magnitude of the eddy current and the conductive characteristics of the object to be tested 200, for example, electrical conductivity, magnetic permeability, thickness, Defects...etc. In addition, the eddy current induced by the object to be tested 200 radiates a secondary magnetic field to resist the alternating magnetic force generated by the probe 10. A change in the field (ie, a magnetic field). The two coils are respectively connected to independent power amplifier circuits (for example, the first power amplifier 120a and the second power amplifier 120b), thereby reducing the influence of the oscillation frequency of the coil inductance caused by the machine pulling (equivalent to vibration) on the eddy current error. .

The loop of the negative feedback device 300 is comprised of a differential amplifier 130, a detector 140, an error comparator 160, and an amplitude voltage modulator 170. The output of the power amplifier 120 is subtracted by a set of differential amplifiers 130 and sent to the detector 140 for conversion to a DC signal. The error comparator 160 compares the DC voltage output by the reference voltage generator 150 with the DC signal difference of the detector 140. Afterwards, the amplitude voltage modulator 170 outputs to the third terminal of the power amplifier 120, that is, the third terminal of the first power amplifier 120a and the second power amplifier 120b, and the loop of the negative return device 300 controls the amplitude of the oscillating voltage of the probe 10. Controlled by the fixed value. According to the feedback control theory, when the differential amplifier 130, the detector 140 and the error comparator 160 are multiplied by the gain, the coil voltage amplitude is approximately equal to the reference voltage generator voltage divided by the amplitude voltage modulator 170 gain, and the coil current amplitude is equal to The coil voltage amplitude is divided by the coil resistance. The voltage setting of the reference voltage generator 150 may change due to the intensity of the eddy current signal of the object to be tested. For example, if the eddy current signal to be measured is weak, the reference voltage generator 150 may be adjusted to generate a higher voltage; if the eddy current signal is to be measured The strong, adjustable reference voltage generator 150 produces a lower voltage.

The eddy current of the coil current change is converted by the current detector 180 into the DC detection signal SD, and the length of the line connecting the first 10a and the second coil 10b to the current detector 180 is not to be measured. The size of the object 200 needs to be adjusted whole.

FIG. 2A is a positive feedback embodiment of the present disclosure, wherein the magnetic core 100a (first probe) and the wire 110a are represented by L1, the magnetic core 100b (second probe) and the wire 110b are represented by L2, and the power amplifier 120a and 120b is formed by using NMOS transistors Q1 and Q2, respectively, for example, to match the transistor; and the differential amplifier 130 inputs signals VD1 and VD2. When the temperature rises, the threshold voltage Vt of the first-stage NMOS transistors Q1 and Q2 decreases as the temperature rises, and Vt varies by -2mV/°C with temperature, so the Q1 and Q2 gate currents I _D and according to formula (1) I _D =1/2 μ _n C _ox (W/L)(V _GS -V _t ) ² .....................(1).

Will rise at the same time. Where μ _n is the electron mobility, C _ox is the oxide capacitance, W is the channel width, and L is the channel length. The differential amplifier compares the offset temperature to the drift of the Q1 and Q2 bungee currents, so it has nothing to do with the temperature. As shown in Figure 3, the temperature effect is offset, that is, ±2.5% from the left of the figure to ± on the right side of the figure. 0.35%. Figure 2B shows an embodiment of a PMOS power amplifier. The mode of operation is similar to that of an NMOS and will not be described again.

FIG. 4 is a schematic diagram showing a comparison between the prior art and the prior art when the sample test piece is separated from the center of the probe by a different distance. The displacement relationship of the object to be tested in the vertical direction is displayed. The left side of the figure is the prior art, and some of the obstructions have large errors due to distance changes, such as the points indicated by the arrows on the way. The right side of the picture shows the experimental data of our invention, and there is no shortcoming of the left figure. FIG. 5 is a schematic diagram showing the change of the output signal generated by the prior art single probe for different displacements. There are 5 test piece resistances, each with different conductivity, showing the effect of horizontal displacement on the object to be tested. Where the x-axis is different in conductivity For the sample, the y-axis is the output signal SD voltage value, and the symbol in the figure is the distance d from the center of the object to be tested, that is, d is the distance between the probe and the object to be tested. The SD value is expected to vary with d, the smaller the better. Figure 6 is a schematic diagram showing the amount of change in the measurement error of the sample vibration after 100 seconds. Shows the effect of sample vibration on the object to be tested. Under vibration, an error of ±1.5% can still be maintained. A schematic diagram showing an example block diagram of one of the non-contact eddy current detecting methods.

According to another aspect of the present disclosure, a non-contact eddy current detecting method is proposed. Referring to FIG. 7 , a schematic block diagram of an embodiment of a non-contact eddy current detecting method is illustrated. The present disclosure utilizes the first and second coils to sense an alternating current signal 802 of the object to be tested, and the alternating current signal is an eddy current; The first and second coils are coupled to the outputs of the first and second power amplifiers respectively to form a positive feedback 804; the first and second power amplifiers are controlled by a negative feedback device to have an amplitude at a fixed value 806. The AC signal is generated by the current detector and the detection signal is DC 808; the negative feedback device is composed of a differential amplifier, a detector, an error comparator and an amplitude voltage modulator. Among them, the differential amplifier eliminates the temperature effect, and the error comparator moderately adjusts the error between the object to be tested and the reference voltage, so that the amplitude modulator can provide a certain amplitude to the power amplifier.

The device and method disclosed in the present invention form a positive feedback by a symmetric non-contact eddy current probe through a symmetrical coil and an amplifying circuit, and generate a self-oscillating circuit, and compare the output signals through a differential amplifying circuit to reduce the influence of the common mode temperature drift. At the same time, two sets of power amplifiers are used in the circuit to respectively provide the coil current of the corresponding probe to reduce the influence of the interference and vibration of the coil line.

The disclosure uses two magnetic cores to respectively drive the coils of the magnetic cores to reduce the length of the coil windings, and the two power amplifier circuit outputs are compared by a set of differential amplifiers and sent to the detector. The differential amplifier reduces the influence of the two power amplifiers on the temperature drift. The two sets of coils and the two power amplifiers on the two magnetic cores form a positive feedback self-oscillation circuit, and the self-oscillation circuit makes the two probes in the same oscillation circuit and works in the same The oscillating frequency, the two probes are respectively connected to the independent power amplifier circuit, which reduces the influence of the oscillating frequency change caused by the oscillating frequency change of the coil inductance, and reduces the influence of the common mode temperature drift by the differential amplifier.

In conclusion, the present invention has been disclosed in the above embodiments, but it is not intended to limit the present invention. A person skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

1‧‧‧ Non-contact eddy current testing device

10‧‧‧ probe

10a, 10b‧‧‧ first and second coils

100a, 100b‧‧‧ first and second magnetic core

110a, 110b‧‧‧first and second conductors

120‧‧‧Power Amplifier

120a, 120b‧‧‧ first and second power amplifiers

130‧‧‧Differential Amplifier

140‧‧‧Detector

150‧‧‧reference voltage generator

160‧‧‧Error Comparator

170‧‧‧Amplitude voltage controller

180‧‧‧current detector

180‧‧‧current detector

200‧‧‧Test object

300‧‧‧negative feedback device

SD‧‧‧Detection signal

Claims (12)

A non-contact eddy current detecting device includes: a first coil, a first end of the first coil coupled to a second end of a first power amplifier and a first end of a second power amplifier; a second coil, the first end of the second coil is coupled to the second end of the second power amplifier and the first end of the first power amplifier; a negative feedback device, the first power amplifier An end point and a first end of the second power amplifier are coupled to a first end of the negative feedback device, a third end of the first power amplifier and a third end of the second power amplifier a third end point coupling of the negative feedback device; and a current detector, the first end of the current detector being coupled to the second end of the first coil and the second end of the second coil, The second end of the current detector outputs a detection signal. The non-contact eddy current detecting device of claim 1, wherein the second end of the first power amplifier is output to the first end of the second power amplifier, and the second power amplifier is further The second endpoint outputs to the first end of the first power amplifier to form a positive feedback. The non-contact eddy current detecting device according to claim 1, wherein the first coil and the second coil are symmetric. The non-contact eddy current detecting device of claim 1, wherein the negative feedback device further comprises: a differential amplifier receiving the first end of the first power amplifier and the first a signal of a first end of the power amplifier; a detector for receiving an output of the differential amplifier; an error comparator for inputting a DC voltage to the error comparator; and an amplitude voltage modulator for receiving The error comparator compares the DC voltage with a reference voltage, and outputs an amplitude signal coupled to the third terminal of the first power amplifier and the third terminal of the second power amplifier. The non-contact eddy current detecting device according to claim 4, wherein the amplitude signal is a certain value. The non-contact eddy current detecting device according to claim 4, wherein the reference voltage is generated by a reference voltage generator. The non-contact eddy current detecting device according to claim 4, wherein the differential amplifier, the detector, the error comparator and the amplitude voltage modulator form a negative feedback. The non-contact eddy current detecting device according to claim 1, wherein the detection signal is caused by a current change of the first coil and the second coil. The non-contact eddy current detecting device according to claim 1, wherein the detection signal includes a conductive property of the object to be tested. The non-contact eddy current detecting device according to claim 6, wherein the reference voltage generated by the reference voltage generator is determined by a detection signal strength of one of the objects to be tested. The non-contact eddy current detecting device according to item 2 of the patent application scope, The positive feedback causes the first and second probes to be in the same oscillation circuit and operates at the same oscillation frequency. A non-contact eddy current detecting method includes: using a first coil and a second coil to sense an alternating current signal of a test object, wherein the first coil and the second coil are respectively coupled to a first power amplifier An output of a second power amplifier is coupled to form a positive feedback; the first power amplifier and the second power amplifier are controlled by a negative feedback device to have a certain amplitude; and the AC signal is detected by a current The device generates a detection signal that is DC.