JPS58176508A - Method and device for calibrating meter in optical thickness gage - Google Patents

Abstract

PURPOSE:To obtain a measurement output signal with high accuracy, by converting the detection signal of the light transmitted through a sample logarithmically and calculating the calibration conditions of a DC amplifier for said output from the coefft. of absorption and reflectivity. CONSTITUTION:The light from a light source 10 transmits through an object 14 to be measured and is made incident to a photodetector 12. The detection signal thereof is inputted through a primary DC amplifier 16, a logarithmic converter 18 and a DC amplifier 20 to an AD converter 22 and the thickness of the sample is displayed on a display 26. On the other hand, the coefft. of absorption, reflectivity and the average value and deviation rate of the measured value are calculated by a CPU26 from the output signal from the converter 22. The calibration conditions of the DC amplifier 20 are calculated from the measured values of the coefft. of absorption and reflectivity of plural samples and a correction is applied to the amplifier 20, whereby the measurement output of high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for calibrating an optical thickness needle using infrared rays, ultraviolet rays, lasers, or the like.

In general, an optical thickness needle is constructed by placing an object to be measured between a light source and a photodetector, and when the light from the light source passes through the object to be measured, it is damaged by absorption and scattering, and the amount of attenuation is affected. Using the fact that it is a function of the thickness of the object to be measured, the thickness t of the object to be measured is
-It is something to be measured.

However, there is a drawback that measurement errors occur when the object to be measured reflects light.

Traditionally, this type of optical thickness gauge has been
T-meter calibration means have been proposed and implemented, and the following methods are typically known.

(1) Calibration method β4i that does not linearize the detection signal from the photodetector! This is a calibration technique used in thickness gauges using a photodetector, and the detection signal tube is not linearized by a photodetector, but is calibrated by approximating a t-line between two points on an exponential curve. In this case, there is a problem in that as the setting point is deviated from, a large error occurs.

(2) Detection using a photodetector [Calibration method using linearization processing using a logarithmic amplifier By connecting and arranging a logarithmic amplifier in the middle of the circuit, it is possible to linearize the detection signal with respect to the thickness. , there is a drawback that large calibration errors occur because reflectance cannot be processed. In addition, by using two samples of known thickness and repeatedly adjusting the zero adjustment and span adjustment of the calibration DC amplifier many times by trial and error, the processing of 1 reflectance was
However, proper calibration is generally difficult because it requires theoretical and empirical judgment, and even if calibration is performed, it not only takes a considerable amount of time but also requires calculating the average value of a large number of samples. There is one point in which the calibration precision f cannot be improved because it cannot be used.

Generally, the measurement principle of an optical thickness meter is expressed by a linear equation based on Beer's law.

Vl: Vloel-μt...(
1) However, ■1: Detection signal vlo: Measured voltage when the optical path is open μ: Measured)・
Extinction coefficient t of constant: Thickness of the object to be measured In the above equation (1), it is the same as that of the conventional radiation type thickness meter, and the calibration using the above-mentioned conventional calibration method (2) is also straightforward. However, it was confirmed that the optical thickness needle was clearly affected by reflection, resulting in a large measurement difference. Therefore, by modifying the above equation (1) by t, the following equation holds true as the reflectance 'Irr.

V1= Vlo (1-r)e-μ' -----(
2) Although it was confirmed that high-accuracy measurement was possible by applying the above formula (2), it became difficult to determine one calibration condition.

Therefore, the inventors of the present invention have conducted various studies to overcome all the problems of the conventional optical thickness gauge calibration method described above, and have determined that the detection signal from the optical detector and output device can be converted into a primary DC intensifier. The optical thickness is amplified by a logarithmic converter and a DC amplifier, and then linearized and calibrated via a logarithmic converter and a DC amplifier, and then displayed via an A/D converter and subjected to arithmetic processing by JdCPUK. In a measurement system using a needle, when calibrating, the extinction coefficient and reflectance of the object to be measured are calculated by transmitting the primary DC amplifier output or logarithmic converter output directly to the CPUK via the A/D converter using a changeover switch. By doing so, it is possible to accurately calculate the calibration conditions of the DC amplifier and obtain a high aFt measurement output signal.

It has been found that the above problems can be solved.

Therefore, one object of the present invention is to provide a measurement system using an optical thickness meter configured to linearize a detection signal using a logarithmic converter, then set calibration conditions using a DC amplifier, and perform high fW thickness measurement. An object of the present invention is to provide a method for calibrating an instrument in an optical thickness needle, which can immediately calculate calibration conditions for a DC amplifier from measured signals of a plurality of samples and perform highly accurate manual or automatic calibration.

Round 1 to achieve the above object In the present invention, the amount of light transmitted from the light source to the object to be measured is detected, the obtained detection signal is amplified and linearized through a logarithmic converter, and then A In a measurement system that uses an optical thickness needle that measures the thickness of a workpiece by A/D conversion, the signal obtained by amplifying the detection signal tube or logarithmically converting the signal is directly @A/D converted to measure the thickness. The present invention is characterized by calculating the extinction coefficient and reflectance of a known sample, and manually or automatically setting calibration conditions for DC amplification of an output signal converted to EI based on these calculated values.

In the instrument calibration method described in StJ, the calibration conditions are set when the logarithmically converted output signal is DC amplified.
It is preferable to use IIIN Kintake.

In addition, when carrying out the above calibration method, a light source and a photodetector are arranged opposite to the object to be measured, and a primary DC amplifier, a logarithmic converter, a DC amplifier, and an A/D are connected to the output line of the photodetector. In a measurement system using an optical thickness needle connected to a display via a converter, a DC amplifier and an A
/l) Connect a V changeover switch between the converter and connect the output line of the primary DC #1 and logarithmic converter directly to /D.
It is preferable to configure it so that it is connected to CPUK* via a converter.

Next, a method for calibrating an optical thickness gauge according to the present invention will be described in detail below in relation to an apparatus that implements Jin's method.

Figure 1 shows a block circuit diagram of an apparatus for carrying out the method of the invention, ie in Figure 1 reference numeral 10 designates a light source, for example consisting of an infrared lamp. This light source 10
A photodetector 12t is provided opposite the light source 10 and the photodetector 12, and an object to be measured 14tl is provided between the light source 10 and the photodetector 12. Therefore, the detection signal detected by the photodetector 12 is transmitted to the primary DC amplifier 16, the logarithmic converter 18, and the DC amplifier 520'.
A/l) converter 22 via the A/l) converter 22.

The thickness of the object to be measured 14 is measured, and the measured value is displayed on the display 24 as appropriate. In addition, the signal received by the A/D converter 22 is used to calculate the average value and deviation rate of the extinction coefficient μ, reflectance r, and the measured values of the bare metal using the CPU 26, thereby expanding the function as a measurement system. I'm trying.

The measurement system described above can be constructed in the same manner as a measurement system using an infrared thickness gauge that can employ conventional general calibration techniques. However, in the present invention, in order to calculate appropriate values of the extinction coefficient and reflectance of the measured object 14, which may cause errors, from the detection signal from the photodetector 12, an amplifier 2 (IA/D converter) is used at ti. Interview with 22
A changeover switch 28t is provided and configured to directly supply the output signal of the logarithmic converter 18 or the output signal of the primary amplifier 16 to the A/D converter 22.

Next, we will explain how to calibrate instruments in a measurement system consisting of ^d configurations, and how to calibrate each configuration. This will be explained with reference to an original output characteristic curve diagram.

Diagram M2 shows the output characteristic curve SV of the photodetector 12. In this case, t′1. , L characteristic curve, the following relationship holds based on the above-mentioned Hair's law.

1=I(1-r)e-μ' -----(31, however, l: Detection current Io: Detection current when the optical path is an oven r: Reflectance of the object to be measured μ: Absorption of the object to be measured Coefficient t: Thickness of the object to be measured FIG. 3 shows the output characteristic curve of the primary DC amplifier 16.
The characteristic curve obtained in this case has the following relationship based on the above equation (3) I/C. This relationship is expressed by the above formula c2
) is the same as

V1= Vlo (1-r) @-μt −・・−(4
) FIG. 4 shows the output characteristic curve of the logarithmic converter 18. The characteristic curve obtained in this case is fully logarithmically converted according to the above equation (4), and the following equation holds: V2 = A LoPVl
o + A top(1-r)-A(toPe)μt-
--(5) However, 1 person: Converter constant Therefore, in the present invention, a sample of known thickness is used as the object to be measured, and the changeover switch 2 is set to 1.
The output signal of the next DC amplifier 616 or the logarithmic converter 18 is directly converted into a signal via the A/D converter 22, and the CPU 2
6, the extinction coefficient μ and reflectance r are calculated, and the zero adjustment and span adjustment of the DC amplifier 20 connected to the output side of the logarithmic converter 18 are performed manually or automatically. In this case, if at least 412 types of samples with known thickness ζ are prepared, the calibration conditions can be set with sufficient accuracy through the above-mentioned calibration work.

That is, first, when setting the calibration conditions based on the output signal of the primary DC amplifier 16, the output signal of the primary DC amplifier 16 is determined by the above equation (4).

In this case, there are three unknowns: vIC1+r+J', but since Vlo (voltage when open) can be found by measurement, it can be easily determined by using two or more samples tPz of known thickness, extinction coefficient μ, reflectance r, and It can be calculated.

In addition, when setting the calibration conditions based on the output signal of the logarithmic converter 18, the output signal of the logarithmic converter 18 is determined by the above formula 6).
The relationship between v2 and electric current is a linear equation (straight line). By transforming the above equation 6), the following equation can be obtained.

・・・-〇-3) In the above formula η), A# 2.3026 °°°°°σ)-・φ・・
(2) h, the regression line S is determined from two or more sets of data (V2.t), and the extinction coefficient μ and reflectance r can be determined from the obtained a and b using the following equations.

2.5026μ=−−λ−························································································ι The characteristics are as shown in FIG. 5, and the following relationship holds true.

Vao: l (AtopVto+B) 10s...
,,,(11) Therefore, as shown in FIG. The signal can be displayed on the display 24.

As is clear from the embodiments described above, according to the present invention,
Using at least 42 samples of known thickness, the detection signal from the photodetector is subjected to 11th DC multiplication or logarithmic conversion, and the obtained signal is directly A/DJ converted to calculate the extinction coefficient μ and reflectance r. By doing so, the calibration conditions using DC amplification can be appropriately set.

Furthermore, these calibration conditions can be set with a simple configuration and can be reliably achieved manually or automatically.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made within the scope d of the present invention.

[Brief explanation of the drawing]

Figure 1 is a block circuit diagram of a measurement system showing an embodiment of the method for calibrating an optical thickness needle according to the present invention, and Figures 2 to 6 show the operating characteristics of each component of the circuit shown in Figure 1. FIG.

Claims (1)

[Claims] (1) Detect the amount of light transmitted from the light source to the object to be measured, amplify the obtained detection signal, perform linear conversion through 5ft logarithmic conversion, and then perform A/D conversion to determine the thickness of the object to be measured. t-
11' In a measurement system using an optical thickness needle, the detection signal is amplified and then logarithmically converted and the resulting signal is directly A/D converted to completely calculate the extinction coefficient and reflectance using a sample of known thickness. An instrument calibration method using an optical thickness gauge r (21% Scope of Permission Required In the instrument calibration method described in item 1, the calibration conditions when amplifying the logarithmically converted output signal tube DC are the zero adjustment and span adjustment of the DC amplifier connected after the logarithm converter. A method for calibrating an optical thickness gauge using an optical thickness gauge. ■ A light source and a photodetector are arranged opposite to the object to be measured, and a primary DC amplification gain, a logarithmic converter, and a DC amplifier are connected to the output line of the photodetector. In the gauge-j system that applies an optical thickness needle that is connected to a display via a dial and an A/D converter,
A total of 41 selector switches between the DC amplifier and A/D converter
An instrument calibration device for an optical thickness gauge, characterized in that the output lines of the ML, the primary DC amplifier, and the logarithmic converter are directly connected to the CPUK via an A/Di converter tube.