JPS5825289Y2 - Air layer density change compensation device for radiation thickness gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for compensating for errors caused by changes in the density of an air layer due to temperature and pressure in a transmission type radiation thickness meter.

When measuring the thickness of an object using a radiation thickness meter, changes in the density of the air layer between the object to be measured and the radiation source or detector directly result in measurement errors.

In particular, in the case of a transmission-type radiation thickness meter, the radiation source head and the detection head are placed opposite each other with the object to be measured interposed therebetween.
The temperature of each air layer between the radiation source, the detector, and the object to be measured is not equal, and due to the influence of residual heat from drying the object to be measured, this temperature difference can be as much as 5 to 30 degrees, and it is normal for it to change. be.

Since density is inversely proportional to temperature according to the Boyle-Charles law, it is necessary to compensate for the influence of density change due to temperature.

On the other hand, atmospheric pressure fluctuates slowly by about 24 mbar in 24 hours, and the auto-zero mechanism (a mechanism that periodically adjusts the zero point) is generally operated every hour, so the gradual fluctuations mentioned above The effects of atmospheric pressure fluctuations are removed.

However, when checking the stability of the device itself after adjustment and repair, a long run of about 8 hours is performed and the auto-zero mechanism is not operated, in which case a fluctuation of about 6 mbar is expected.

Density is proportional to pressure according to the Boyle-Charles law, so the above 6 mbar fluctuation is relative to standard atmospheric pressure.
This is a fluctuation of 0.6%013 for main fishing.

In order to reduce the influence of changes in air pressure density due to atmospheric pressure fluctuations, it is possible to narrow the distance between the radiation source and the detector, but this may require the use of a shutter mechanism for the radiation source, etc. For example, if the short one is about 33 mm (when the radiation source is Promedium-147), the thickness of this air layer is 33 rIrrn, which is 42 mm in terms of basis weight.
．． 9fAr? corresponds to

In this case, if atmospheric pressure fluctuates by 0.6%, approximately 0.2
61/7-, and in high-precision devices that require a device measurement error of within 0.2 tons, the change in atmospheric pressure during the stability check is checked with a barometer, and correction calculations are performed to ensure the stability of the device. This is inconvenient because it requires a sex test.

Furthermore, since the auto-zero mechanism of the device generally operates every hour, it is not possible to correct sudden pressure changes during this period.

In addition, in general, in this type of device, the object to be measured continuously passes through the detector portion of the device.

Also, the detector part? Although the sensor reciprocates in the direction perpendicular to the object to be measured within the range of the distance to be measured, the pressure change accompanying this movement and the speed of movement are not always constant, and therefore pressure fluctuations occur in the detector section.

On the other hand, since the auto-zero mechanism must be operated at a position where the object to be measured does not exist, pressure fluctuations caused by this speed fluctuation cannot be corrected.

The main purpose of the auto-zero mechanism is to correct dust that adheres to the detector window, attitude changes due to atmospheric pressure at regular intervals, and radiation sources. Changes cannot be corrected.

The present invention was developed with this in mind.The purpose of the present invention is to compensate for errors caused by changes in air layer density due to changes in temperature and pressure, and to improve the measurement accuracy of the air layer density of a radiation thickness meter. To provide a change compensation device.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of the present invention.

In the figure, reference numeral 1 denotes an object to be measured, such as lightweight paper or plastic, which flows continuously in the left-right direction of the figure.

Reference numeral 2 denotes a source-side head, and 3 a detector-side head, which are disposed opposite to each other with the object to be measured 1 interposed therebetween, and during measurement, they reciprocate within the range of the width of the object to be measured in the vertical direction in the figure.

4 is a radiation source, and 5 is an ionization chamber for radiation detection.

6.7 is a temperature sensing element, and in this embodiment, a silicon resistance temperature sensing element is used.

The temperature sensing elements 6 and 7 are the radiation source side head 2 and the detector side head 3.
The thermosensor is provided with its temperature sensing portion protruding from the tube wall on the side of the object to be measured 1.

A pressure detector 8 is attached to the head 2 on the radiation source side.

9 is a high input resistance amplifier that amplifies the output current of the ionization chamber 5, and 10.11 is a temperature sensing element 6. This is a conversion amplifier that converts the resistance change corresponding to the temperature change detected by γ into voltage signals V1 and V2.

12 is a conversion amplifier that converts the pressure detected by the pressure detector 8 into a voltage signal v3.

13, 14, and 15 are variable voltage dividers, each of which connects the radiation source 4.
and the length Ll of the air layer between the object to be measured 1, the length L2 of the air layer between the ionization chamber 5 and the object to be measured 1, and the radiation source 4 and the ionization chamber 5.
Depending on the length L3 of the air layer between each variable voltage dividing terminal 16.
Set 17 and 18.

Reference numeral 19 denotes an adder for adding the signals obtained by the variable voltage dividers 13 and 14.

Reference numeral 20 denotes a deviation amplifier, which includes an adder/subtracter circuit 21, a subtracter circuit 22 that takes the difference between the output VA of the adder/subtractor 21 and the output VB of the high input resistance amplifier 8, and an amplifier 23 that amplifies the output VC of the difference.

The adjustment circuit 21 is a circuit that adjusts the reference thickness setting signal VD, the density change compensation signal VE due to the air layer pressure, and the density change compensation signal VF due to the air layer temperature, which is the output signal of the adder 19. .

Next, the operation of the above configuration will be explained.

The radiation emitted from the radiation source 4 is transmitted through the air layer from the radiation source 4 to the object to be measured 1, the object to be measured 1, and from the object to be measured 1 to the ionization chamber 5.
The light passes through the air layers up to the point where the light is attenuated on each path depending on the product of the density of the air layer or the object to be measured and the length of the path, and then enters the ionization chamber 5.

The ionization chamber 5 generates an ionization current according to the incident radiation,
This becomes an output current and is output.

On the other hand, the temperature θ1 of the air layer from the radiation source 4 to the object to be measured 1 is detected by the temperature sensor 6, the temperature θ2 of the air layer from the ionization chamber 5 to the object to be measured 1 is detected by the temperature sensor 7, For each detected value,
Temperature converters 10 and 11 measure the change Jθ from the reference temperature θO.
1. A voltage signal V1. proportional to lθ2. If V2 is obtained and the voltage is divided according to the lengths LI and L2 of each air layer using variable voltage dividers 13 and 14, compensation signals L]! JθI, Lz
, lθ2 is obtained.

These are added by the next adder 19, and the sum output VF2L+, Jθ] +L2. Obtain lθ2.

Further, the pressure of the air layer from the radiation source 4 to the ionization chamber 5 is detected by the pressure detector 8, and the pressure converter 12 obtains a voltage signal v3 proportional to the change JP from the reference pressure Po.

If the variable voltage divider 15 divides the pressure according to the length L3 of the air layer, a compensation signal V for the pressure of the air layer is generated from the voltage dividing terminal 18.
E=L3, get AP.

In the addition/subtraction circuit 21, this compensation signal VE and the compensation signal VF are subtracted and added to the reference thickness setting signal VD, respectively, and the sum signal VA is subtracted from the output VB of the high input resistance amplifier 9 in the subtraction circuit 22. .

The difference signal VC is amplified by an amplifier 23 to compensate for changes in density due to the temperature and pressure of the air layer, and is output as a thickness deviation signal Io from the correct reference thickness.

In the above embodiment, the temperature of each air layer is measured at one location, so strictly speaking it is not an average temperature, but the temperature is measured on the tube wall of the source side head 2 and the detector side head 3 on the side of the object to be measured 1. Since the temperature is detected by a temperature-sensitive body with a protruding temperature-sensing section, salinity close to the average temperature of each air layer can be detected.

Therefore, it can be said that the compensation for the density change of the air layer as described above is quite accurate.

Note that in order to obtain the average temperature, for example, a large number of temperature sensing bodies may be provided at different distances from the object to be measured to determine the temperature distribution.

Alternatively, instead of the average temperature, the temperature may be measured as a more or less uniform temperature by, for example, purging the air layer.

In addition, in the above embodiment, the air layer on the radiation source side was used as the length L from the radiation source 4 to the object to be measured 1, but if the radiation source 4 is sealed inside the radiation source head 2, the radiation source 4 to source side hand 2
Since the density of the air layer L4 up to the irradiation window 30 is constant, in this case, the air layer portion (length L5) from the radiation source side hand 2 to the measured object 1, excluding this air layer portion, is This may be the part covered by compensation.

Moreover, it goes without saying that the pressure detector 8 may be provided in the head on the detector side.

As explained above, the present invention provides a temperature sensing body on each measured object side of the radiation source side head and the detector side head, and also provides a pressure detector on the radiation source side head or the detector side head. The density change of the air layer due to temperature and pressure is compensated in proportion to the thickness of each air layer and the temperature and pressure. Since the moving speed of the reciprocating motion of the head and the air pressure fluctuation due to the fluctuation of the speed are compensated for, errors caused by changes in the density of the air layer due to temperature and pressure can be accurately compensated for.

According to the present invention, it is possible to realize an air layer density change compensation device for a radiation thickness meter that can compensate for errors caused by changes in air layer density due to temperature and pressure fluctuations and improve measurement accuracy. .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention. 1...Measurement object, 2...Radiation source side head, 3...Detector side head, 4...Radiation source, 5... ...Detector (ionization chamber), 6,7...
...Temperature sensor, 8...Pressure detector, 9...
...High input resistance amplifier, 10,11...Temperature conversion amplifier, 12...Pressure conversion amplifier, 13゜1
4.15... Variable voltage divider, 19... Adder, 20... Deviation amplifier, VD...
Reference thickness signal.

Claims (1)

[Scope of utility model registration request] In a radiation thickness meter, a temperature detection means is provided on the side facing the object to be measured of the radiation source side head and the detector side head which are arranged opposite to each other with the object to be measured interposed therebetween, and the temperature detection means on the radiation source side or the detection side. A pressure detection means provided on the head, first and second converters that convert pressure and temperature detection values of the detection means into electrical signals, and a signal of the first converter is detected by the detector. The radiation thickness meter is equipped with an arithmetic circuit that adds the signal of the second converter to the detected value of the detector, and compensates for density changes due to pressure and temperature of the air layer. Change compensator.