The gamma ray density gauge, one of the industrial instruments applying isotope, has such special features as non-contact measurement, high accuracy and adaptability to automatic control. Since the demand for this instrument is increasing in this country, its study is being pursued in many laboratories and makers. The writer has also studied the characteristics of this gauge. Described in this paper is its fundamental characteristics, optimum scale range, applications and influence of the physical condition of the material to be measured.

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A thermistor has a large temperature coefficient of resistance and fit hot resistance, and yet is small in size. If such thermistor is used in place of the hot wire of hot wire anemometer, therefore, it is possible to obtain a simple but high-sensitivity instrument. However, it has been difficult to compensate its ambient temperature. The writer manufactured for trial a thermistor anemometer employing the idea of temperature compensation. In the constant resistance method, it has become possible to make the temperature compensation using the resistance compensation shown in Eq. 13 or 14 by means of the fundamental circuit of Fig. 3. As a direct reading type anemometer using the constant current method, the relation between wind speed and Ig. was obtained by Eq. 20 and then it was confirmed that this relation coincided with that between the results of actual measurement and experiment(Fig. 10). It was alstudied to what extent the discrepancy among the resistance values of detecting thermistor and compensating thermistor, constant B and various characteristics of dissipation constant is permissible when using the circuit shown in Fig. 12(a) as a method for temperature compensation(Eqs. 26, 31, 34 and Fig. 14). As shown in Fig. 16, the meter circuit needs the resistance compeation of Eq. 36. If such adaptor as shown in Fig. 20 is attached to the thermistor, it becomes possible to measure high speed wind. Concerning the direction of detecting part, the data shown in Figs. 23 and 24 were obtained.

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In order to improve the inspection characteristics of A.I.M., further experiments were carried out to avoid the influences of air bubbles and liquid surface in ampules, and considerably good results were obtained by applying the liquid surface masking using the optical system in vertical method. On the basis of these experiments, a new model of the machine(Model-4) was developed.
The new model was proved to have also good characteristics as expected through several experiments. Furthermore, for the purpose of improving the correspondency to the visual inspection by S.I., two new decision methods, i.e., 2 signal decision method and twice inspection method, were investigated and a little more improvements were achieved. The inspection characteristics of this Model-4 so far developed is considered at this stage to be almost satisfactory for practical use and the detailed analysis on the inspection results leads the author to the conclusion that further improvement is hardly expected other than that on the influences of colored particles and mechanical vibrations.

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