JPS5842408B2 - radiation thickness gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation thickness meter that measures the thickness of a steel plate or the like by utilizing absorption of radiation, and in particular includes a circuit for correcting the influence of changes in the material of the object to be measured. This invention relates to a thickness gauge that allows the thickness to be set using a digital switch and the thickness deviation from the set value to be determined.

FIG. 1 shows the basic configuration of a conventional radiation thickness meter.

A radiation source 2 of a radioactive isotope or the like that emits gamma rays or the like is attached to one side of the object to be measured 1 .

Radiation 3 from the radiation source 2 enters the detector 4 after passing through the object to be measured 1 .

An ionization chamber is used as the detector 4, and the radiation becomes an electrical signal proportional to its intensity, which is amplified by a preamplifier 5 and then enters a material correction circuit 7 via a logarithmic amplifier 6.

The difference between the output of the material correction circuit 7 and the output of the thickness setting device 8 is input to a deviation amplifier 9, and the indicator indicates the deviation from the thickness setting value using the output.

The above characteristics of the thickness gauge are closely related to the radiation absorption characteristics.

Absorption when radiation passes through a substance is generally expressed by the following equation.

I-Io e-μX ・・・・・・
...(1) Here ■: Transmitted radiation intensity ■o: Radiation intensity when there is no absorbing material μ - Absorption coefficient This is what I did.

If the material of the object to be measured changes, the absorption coefficient μ in equation (1) changes, so even for the same thickness, the absorption is
It changes like curve C in the figure.

Now, if we express the vertical axis in Figure 2 on a logarithmic scale, we will get a, b in Figure 2.
, c have a linear relationship as shown in Figure 3, which is clear from the (1) 20 relationship.

Therefore, the output of the preamplifier 5 in FIG. 1 has a value proportional to the thickness of the object to be measured 1 after passing through the logarithmic amplifier 6.

The output of the logarithmic amplifier 6 changes according to a straight line a due to changes in the thickness of the object 1 to be measured, and due to changes in the material, the straight line a changes as shown in straight lines S and C.

By supplying this output to a circuit capable of gain adjustment and adjusting the gain according to changes in the material, it is possible to always output the output of the reference material, that is, the relationship shown in FIG. 3a, even if the material changes.

The material correction circuit 7 performs this function.

Figure 4 shows an example of a conventional material correction circuit, in which the operational amplifier 11
The relationship between the input E1 and the output E2 of the resistor R1°Ft2. ,
It changes depending on the value of i'iT resistor VR1.

That is, the gain can be adjusted by changing the variable resistor vR1, which is E2-El.R2/(R1+vR1).

FIG. 5 shows an example of a conventional thickness setting device 8 and deviation amplifier 9.

The thickness setting device 8 is composed of resistors rloO to r400, digital switches 81 to S4, and a DC power supply 13,
In the illustrated example, the plate thickness is set to 0.103 mm, and the thickness can be set up to 3.999 mm by switching the switches 81 to S4.

Sl is used to set the digit of Lmrn, and the DC power supply 13 is applied as shown.

Sl, S2. As shown in the figure, the contacts S3 always switch between the voltages across the two resistors, that is, between contacts 0 and 2, between contacts 1 and 3, and between contacts 2 and 4.

Resistors r100 to r104 j r200-r2□0゜r300-r 3□Otr400'' r4 (+9 is the same resistance within each group, and the resistance value for each group is 1.
If the ratio of 115°1/25 and 1/125 is selected, the contribution to the output voltage E4 will be 1, 0.1, and 0.0 as shown in the figure.
1x.

The value is multiplied by 0.001, and the 4-digit set value can be taken out as the analog quantity E4.

When the operational amplifier 12 is operated as a differential amplifier as shown, its output E5 has a value proportional to the voltage difference between the input E3 and the set value E40i, and has a value corresponding to the thickness deviation.

However, in reality, the output of the logarithmic amplifier 6 in the radiation thickness meter of the above method does not have a linear relationship as shown in Figure 3 due to the influence of scattered radiation, etc., and curves may appear as shown in Figure 6. There are many.

Curve a in FIG. 6 is the relationship when the reference material is used, and curves S and C are the relationships when the material is changed.

Also in Fig. 6, Jx1/x1 and J x 2 /x
2 is always the same value.

Since the material correction circuit shown in Fig. 4 corrects yl and y2, it is sufficient to correct yl within the range of linear relationship at the same rate as J X 1 /X 1. However, for y2 in a range where the slope is gentle, correcting at the same ratio as J x 2 /x 2 results in overcorrection, which has the disadvantage of increasing measurement errors when the material changes.

Conventionally, as a countermeasure for this, when the human power E3 in Fig. 5 has a curved relationship as shown in Fig. 6, the resistors r100''-r104 of the setting device are not set to equal values, but set to different values. A method has been adopted in which a set voltage E4 that matches the curve shown in FIG. 6a is obtained by selecting a suitable voltage or by connecting a compensating parallel resistor to these.

However, when there is a material change, the output E5 does not have a constant value for the same thickness change, that is, a deviation, and an error occurs.

In addition, since the setting device in Fig. 5 uses the lO backward method,
There was a drawback that the number of resistors and the number of contacts of the changeover switch were increased.

It is an object of the present invention to eliminate all the drawbacks of the above-mentioned conventional techniques and to provide a radiation thickness meter with a simple circuit configuration and less error.

That is, as shown in the block diagram of FIG. 7, the output of the logarithmic amplifier 6 is further supplied to the linearization circuit 20, and the material correction is performed by changing the curve relationship in FIG. 6 to a linear relationship similar to that in FIG. BCD (Binary coded decimal system) that allows you to easily and completely perform the process, and requires less than half the number of parts.
This allows the thickness of the method to be set, and the main points will be explained below.

FIG. 8 shows an example of the material correction circuit according to the present invention, in which a linearization circuit is added to correct the curve of the output of the logarithmic amplifier 6, and the operational amplifier 14 amplifies the input E1 as it is.
R6+V R2)/R5 times the output E2 is produced.

The operational amplifiers 15 and 16 are examples of circuits added in accordance with the present invention to correct characteristic curves, and their operation will be explained with reference to FIG.

FIG. 9 is a graph showing the relationship between the material correction circuit input (vertical axis) and the thickness of the object to be measured (horizontal axis). Curve A is supplied to the operational amplifier 14 through the resistor R5 in the circuit of FIG. It shows the zero relationship between the input and the thickness of the object to be measured.

As in the case of FIG. 6, curve A is curved.

In FIG. 8, if R7=8 and R9=RIO are selected, in the range where the input voltage E1 is higher than the first set value -Vl, the output of the correction operational amplifier 15 becomes higher than the ground potential and the diode D1 is cut off, and the output e
1 does not occur.

Similarly, when the input E1 is higher than the second set value -v2, the output e2 of the correction operational amplifier 16 is not generated.

When the thickness of the object to be measured increases and the input F1 becomes lower than Vl, Dl becomes conductive and an output e1 is generated.

Similarly, when the input E1 becomes lower than -v2, e2 occurs.

The output e1. Since e2 enters the operational amplifier 14 through R1□ and R1□, it is added to the signal entering through R1.

In other words, if the material correction circuit input becomes lower than the first set value -vl due to an increase in the thickness of the object to be measured, etc., the output e1
occurs as shown in Figure 9 and joins curve A, and curve B
becomes.

Furthermore, when the material correction circuit input becomes lower than the second set value -V2, a correction voltage e2 is generated and added to curve B, forming curve C.

In this way, the relationship between the thickness of the object to be measured and the material correction circuit input approaches a linear relationship.

The number of correction operational amplifiers can be increased or decreased depending on the degree of characteristic curve.

The first feature of the present invention is that by adding the above-mentioned bending correction circuit or straightening circuit to the input side of the material correction circuit as shown in FIG. It is possible to linearize the relationship and prevent errors caused by material correction.

Further, the present invention has the advantage that it can be easily implemented by simply adding the linearization circuit shown in Figure 8 to an existing radiation thickness gauge.

vR2 in FIG. 8 is a variable resistor for material correction.

When an input linearized as shown by curves B or C in FIG. 9 enters the operational amplifier 14 in FIG. 8, its output E2 has a linear relationship with respect to the thickness as shown in FIG. 10a.

If the material changes, the relationship will be b or c, but by setting VR2 according to the material, it is possible to always output the relationship a.

In other words, since it is only necessary to prepare one set of thickness setting devices 8 that match this linear relationship a, B
A CD system can be adopted.

Although in FIG. 8, the addition of the correction voltages e1 and e2 and the material correction using vR2 are performed using one operational amplifier, the same effect can be obtained even if the addition of the correction voltages e1 and e2 and the material correction using vR2 are performed using separate operational amplifiers. Included in the range.

The second feature of the present invention is that, as described above, the relationship between the thickness of the object to be measured 1 and the output of the material correction circuit 7 is a linear relationship, so it is not necessary to correct the bending in the thickness setting device 8. This means that it is now possible to use the BCD method, which has fewer parts.

Figure 11 is the same as Figure 5, from 0.000mm to 3.99
Thickness setting device 8 and deviation amplifier 9 that can set up to 9mm
This is a configuration example.

Switches 81 to S4 are BCD type digital switches, and have a length of 1 mm and 0.1 mm, respectively.

This is for setting digits of 0.0171Lm and 0.001.

Although an example of the resistance value of each resistor rll to 14B is illustrated,
As long as the resistance ratio does not change, you can choose one with a different value.

i1 to i4 are currents proportional to the values set for each digit.

Since the sum of 11 to i4 corresponds to the thickness setting value, if the voltage of the current source 18 is selected so that the signal current i when the actual thickness is equal to the setting value is equal to the sum of 11 to i4,
The output E of the operational amplifier 17 becomes zero.

When the signal current i changes in accordance with the change in thickness, the output E5 of the operational amplifier 17 takes on a value corresponding to the deviation.

The thickness setter of FIG. 5 requires 37 resistors, while the thickness setter of FIG. 11 suffices with 14 resistors.

If the characteristic curve is corrected using the method shown in FIG. 5, the number of required resistors will further increase.

Note that Fig. 11 shows the method of directly subtracting the current of the setting device from the signal current, but the total current of 11 to 14 is converted to voltage once and then converted to a differential amplifier as in Fig. 5. The same effect can be obtained by adding it.

Further, in FIGS. 5 and 11, the setting circuit up to 3.999 mm is shown, but it goes without saying that a thicker value can be set by adding one digit of resistor and contact.

Furthermore, even if the thickness unit and number of digits change, it is of course possible to create a setting device using the same concept.

According to the present invention, even if the radiation absorption characteristics deviate from the exponential relationship, the material can be corrected without causing errors, and a thickness setting device with a small number of parts can be manufactured. There is.

As described above, according to the present invention, it is possible to provide a radiation thickness meter with a simple circuit configuration and less error.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of a conventional radiation thickness meter, Figs. 2 and 3 are graphs showing changes in absorption characteristics when the material of the object to be measured changes, and Fig. 4 is a block diagram showing the basic configuration of a conventional radiation thickness meter. Figure 5 is a diagram showing an example of a material correction circuit, Figure 5 is a diagram showing an example of a conventional thickness setting device and deviation amplifier, and Figure 6 is an example of the relationship between the thickness of the object to be measured and the actual output of the logarithmic amplifier. 7 is a block diagram of the radiation thickness meter of the present invention, FIG. 8 is a diagram showing an example of the material correction circuit according to the present invention, and FIG. 9 is an explanatory diagram of the operation of the circuit of FIG. FIG. 10 is a graph showing the relationship between the output of the material correction circuit and the thickness of the object to be measured according to the present invention, and FIG. 11 is a diagram showing an example of the thickness setting device and deviation amplifier according to the present invention. 2... Radiation source, 4... Detector, 6...
... Logarithmic amplifier, 7 ... Material correction circuit,
8... Thickness setting device, 9... Deviation amplifier, 10... Indicator.

Claims (1)

[Scope of Claims] 1. A detector that converts radiation transmitted through an object to be measured into an electrical signal, a logarithmic amplifier that amplifies the signal, and is supplied with the output of the logarithmic amplifier, and is configured to detect the material of the object by adjusting the gain. A material correction circuit that corrects changes, a thickness setting device,
In a radiation thickness meter comprising a device for outputting the output of the material correction circuit and a deviation from the set value by the thickness setting device, a linearization circuit inserted between the output of the logarithmic amplifier and the input of the material correction circuit is provided. The linearization circuit includes at least one correction operational amplifier whose input is the output of the logarithmic amplifier, and a diode connected in series between the output of each correction operational amplifier and the input of the material correction circuit. including,
In a range where the output of the logarithmic amplifier is higher than the set value set for each correction operational amplifier, the corresponding diode is cut off and the output is blocked; When the output of the amplifier becomes low, the corresponding diode is conductive and the output is added to the input of the material correction circuit, thereby determining the relationship between the thickness of the object to be measured and the input of the material correction circuit. A radiation thickness gauge characterized by linearization. 2. A detector that converts radiation transmitted through the object to be measured into an electrical signal, a logarithmic amplifier that amplifies the signal, and a material that is supplied with the output of the logarithmic amplifier and that compensates for changes in the material of the object by gain adjustment. A correction circuit, a thickness setting device,
In a radiation thickness meter comprising a device for outputting the deviation of the output of the material correction circuit from the value set by the thickness setting device, a linearization circuit inserted between the output of the logarithmic amplifier and the input of the material correction circuit is provided. The linearization circuit includes at least one correction operational amplifier whose input is the output of the logarithmic amplifier, and a diode connected in series between the output of each correction operational amplifier and the input of the material correction circuit. including,
In a range where the output of the logarithmic amplifier is higher than the set value set for each correction operational amplifier, the corresponding diode is cut off and the output is blocked; When the output of the amplifier becomes low, the corresponding diode is conductive and the output is added to the input of the material correction circuit, thereby determining the relationship between the thickness of the object to be measured and the input of the material correction circuit. A radiation thickness meter characterized in that the thickness setting device is linearized and further comprises a binary coded decimal type digital switch provided for each digit.