JPS61225683A - Automatic gain/bias adjusting type dose rate meter - Google Patents

Abstract

PURPOSE:To achieve a higher accuracy of calculating dose rate, by combining the correction of an input exponential value produced by adding a constant thereto with the correction by gain and bias of an amplifier within a dose rate meter. CONSTITUTION:An input proportional to the logarithmic value of a dose rate is subjected to two corrections, the one by multiplying the logarithmic value constant times by a gain and a bias of an amplifier within a dose rate meter 7 and the other by adding a constant thereto and additional correction is done for any leaked current attributed to a resistance 3 and a capacitor 2 between a cable A between a radiation detector 1 and a preamplifier 4 and the ground. In other words, the current signal outputted from the detector 1 is amplified with an amplifier 4 and the amplification of the current signal thereof is done with a logarithmic amplifier 5, which outputs a voltage proportional to the logarithmic value of the input signal to be inputted into a dose rate meter 7, which is made up of a CPU, a memory and an input/output section. The output voltage signal of the amplifier 5 is converted into a dose rate by a software. The three resulting correction values are determined by a specified correction factor calculating formula based on the three irradiations at a reference dose rate and then the dose rate is shown on a display 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a radiation measuring device, and particularly to an adjusting means suitable for adjusting the gain and bias of a dose rate measuring system that is periodically adjusted.

[Background of the invention]

Previously, Corona Publishing Basic Atomic Energy Course 2 "Radiation" 188
Configure the measurement system with analog circuits as described on page 1.
To adjust the gain and bias of the measurement system, the gain resistor and bias resistor are alternately operated many times using a variable resistor so that the output command value matches the target value.
No consideration was given to ease of adjustment.

Digital radiation measurement by other companies is just a count rate meter that counts the number of pulses, and no new method has been published for the dose rate meter of the present invention.

Conventionally, the voltage signal input from the preamplifier (proportional to the logarithm of the dose rate) was adjusted to the correct dose rate using the gain and bias inside the dose rate meter. This error to be corrected may also be caused by an error that adds a nearly constant value to the dose rate measurement system. This is due to leakage current and deterioration of the detector over time, and requires calibration during periodic inspections while the radiation measurement system is in use. Conventionally, this error was corrected using the gain and bias of the amplifier inside the dose rate meter, which made it impossible to accurately match the dose rate. (K2
See diagram. ) [Purpose of the Invention] The purpose of the present invention is to easily adjust the gain and bias by inputting the simulated signal (or actual irradiation) three times to facilitate maintenance when calibrating a radiation measurement device using a simulated signal (or actual irradiation). It is an object of the present invention to provide a dose rate meter that enables automatic gain and bias adjustment that can dramatically shorten adjustment work time during inspection.

Furthermore, the purpose of this automatic adjustment is to improve the accuracy of measurement.

[Summary of the invention]

Conventionally, it was only possible to perform corrections that were proportional to the logarithm of the dose rate, and for the next input, multiplied the logarithm by a constant using the gain and bias of the amplifier, and added a constant value. The correction value was determined by repeating the irradiation, but this was not always calibrated accurately.

In the present invention, the conventional two methods are used as means for calculating the dose rate.
The dose rate can be calculated with high accuracy by simultaneously performing two corrections and a correction that adds a fixed value to the input index value (value indicating the dose rate). Furthermore, by providing calculation formulas, these three correction values can be determined by three irradiations at the reference dose rate, thereby greatly simplifying the adjustment.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

Figure 1 shows the radiation measurement system. First, a radiation detector 1 such as an ion chamber outputs a weak current of about IQ-11 to 10-'A when radiation (especially r-rays) is incident thereon. The output current of the radiation detector 1 is proportional to the intensity and dose rate (mR/h) of the radiation incident on the radiation detector. Since this output current is weak and has a very wide range of values, it is difficult to send it directly to the site where the detector is installed or to the place where monitoring is performed. Therefore, the current signal output from the detector 1 is usually amplified by a preamplifier 4.

Amplification of this current signal is performed by a log amplifier. The log amplifier 5 outputs a voltage (for example, θ˜10V) proportional to the logarithm value of the input current signal. This voltage is input to the dose rate meter 7 placed at the monitoring location.
8°, which is expressed as the radiation dose rate irradiating the detector 1. Furthermore, a high voltage of several hundred V is applied to the radiation detector 1 in order to generate a staining current due to the incidence of radiation. Therefore, the current signal carried on the cable connecting the detector 1 and the preamplifier 5 is easily influenced by the resistance 3 and capacitor 2 to ground caused by the cable, connector, etc. Because a high voltage is applied to this resistance between the ground and the ground, a small amount of current flows through it. This minute current (leakage current) causes an error in radiation measurement.

In conventional analog dose rate meters, the output voltage from the preamplifier 5 is input, and the voltage amplified by the amplifier is displayed on an output display with a logarithmic scale of dose rate. At this time, be sure to adjust the gain and bias of the amplifier of the dose rate meter to show the correct dose rate. This principle will be explained using FIG. 2. In FIG. 2, the horizontal axis represents the true irradiation dose rate that irradiates the radiation detector 1, and the vertical axis represents the displayed dose rate shown on the output display of the analog dose rate needle. In principle, the dash-dotted line in the figure is the relationship that should exist, but due to the aforementioned leakage current, it becomes like the solid line in the figure. This makes it impossible to measure the low dose rate range, so adjust the gain and bias of the amplifier in the dose rate meter so that it is close to the dashed-dotted line. Adjusting the gain and bias cannot be done simply, so irradiation is performed at the dose rate within the measurement range using a simulated radiation source (a radiation source that generates the radiation dose rate that should be the standard) many times. The relationship should be close to the one-dot chain line. The complexity of this calibration has been one of the major drawbacks of the prior art. Furthermore, even if this calibration was performed many times to minimize the error, it was not possible to measure accurately as shown by the broken line in the figure.

This phenomenon also occurs due to aging of the detector l. As the radiation detector 1 (an ion chamber type detector such as an ion chamber) is used, the gas sealed inside is gradually consumed by ionization, and a weak current flows due to the high voltage applied. A phenomenon similar to leakage current occurs.

In the present invention, the dose rate meter 7 is a central processing unit (CPU).

It consists of a main storage section (memory) and an input/output section, and converts the voltage signal from the preamplifier 5 into a dose rate using software.
The dose rate is displayed on the display 8. The method of converting this dose rate will be explained below. Assume that the irradiation dose rate is t-D, the output current from the detector is (■), and the output voltage of the preamplifier is V.

True dose rate and output current I are proportional to formula 9 (1) % formula % (1) However, A is a constant, B is a correction coefficient, and the output voltage V of the preamplifier 4 is the amplification of the log amplifier 5. Since it is caused by V-p x tog I 10q ”・(
2) However, p is a constant (amplifier gain) and q is a constant (amplifier bias).Since the dose rate meter of the present invention calculates the dose rate as it is, (
Using equations 1) and (2), V=pXtogI+q =pxLog(AXD+B)+q...(3)
There is a relational expression. That is, then the equation (4) becomes nXV-)m D=lO+t (5).

In the present invention, the calculation of equation (5) is performed using a dose rate meter, and n.

The correction coefficients for m and L are determined to be optimal.

Next, a method for determining the m, n, and to correction coefficients will be explained. First, the three dose rates Dt, D! Irradiation was performed at tDs, and the displayed dose rate at that time was t-M1, Ml.

If Ms, then from equation (5) zog(Mi A)=nxVt+m
・-(6) tOg (Mlt) = n
x Vz +m ・”(7) LogcMs-t
3=nxV3+m - (a) However, m, n, l
is the correction coefficient before adjustment.

Furthermore, if the correction coefficients after adjustment are mQ, ng, and 16, then tag (DB -2o) = nQ X Vt +m6
- (9) Log (Dz Ao) = no
X Vz +mo −(10)Log(D3−
to)=noXVx+mo·-(xl). Here, if Ms > Mz > Mt and 20 is small, Ms, Ml)t, (7), g3
), (10), From equation (u), Log Mz =
n X Vz +m...(12)! ,
og Ms =: n X Vs +m =
(13) AOg Dz = n6 X Vz +mo
...(14) tog Ds ” no X
Vs +mo (15). This 4
Solving the two equations, tOgDs AogD2 no = x n =
(16) togM3-LozM2 ... (17) becomes (9), (12), (16), (
17) Using formula, to = D t 10C-(
18) where OC=[:tog(Mx 7)+m]+m.

becomes. By performing the above calibration (calculation of correction coefficients), calibration can be performed more easily and accurately than in the past.

Using Figure 3, we can calculate the above at 1.10', 10'm/
The case of calibration using h will be explained. The horizontal axis is the true irradiation dose rate,
If the displayed dose rate is plotted on the vertical axis, the solid line in the figure before calibration is a solid line, and the dashed line in the figure can be changed by calibration using equations (16), (17), and Cl8). Here, Da =
Use M3 = 10'' D2 = Mx = 10' D 1'' 1 + M t = 5 x 10'. However, n and m in formulas (16), (17), and (18).

t is a correction coefficient for the solid line. Therefore, the calculated n
By using , ), m(,, Lo, it is possible to easily perform calibration with high accuracy as shown by the broken line in the system.

〔Effect of the invention〕

According to the present invention, errors caused by leakage current and aging of the detector, which could not be corrected accurately in the past, can be easily and accurately calibrated (man-machine-friendly), resulting in the effect of significantly improving performance and maintainability. be.

[Brief explanation of drawings]

Figure 1 shows the radiation measurement system, Figure 2 shows the conventional correction diagram,
FIG. 3 is an explanatory diagram of correction according to the present invention. 1... Radiation detector, 2... Cable capacitance,
3... Resistance to ground, 4... Preamplifier, 5...
- Log amplifier, 7... Dose rate meter, 8... Dose rate display.

Claims (1)

[Claims] 1. In a dose rate meter that calculates the dose rate by inputting a signal proportional to the logarithm of the output ionizing current from an ionization chamber radiation detector, there is a part that adds a constant to the input, and a part that adds a constant to the input, and a part that multiplies the input by a constant. 1. A gain/bias automatic adjustment type dose rate meter, characterized in that the dose rate meter has a part for adding a constant to an input index value, and a part for adding a constant to an input index value separately from the two parts. 2. The dose rate meter according to claim 1, characterized in that it is provided with means for calculating the three correction constants once after irradiation at three different dose rates. Automatic bias adjustment type dose rate meter.