C A L I B R A T I O N OF UHF M O I S T U R E M E T E R S

L. I . G o r e n b u r g UDC 681.2.089.6 : 530.93

The uhf moisture meters' calibration characteristics are normally represented by the relationships of the ~ p e K = je(W), where K is the mean value in a general case of an oscillating function and W is the moisture content of the tested material.

Measurement precision is raised either by reducing oscillations, or specifying them, if they are taken into con- sideration. However, this often entails operational difficulties (for instance, when the tested material is thick ~ the testing prolonged).

In measuring moist materials with a small range of moisture content variations it is advisable to use relation- ships of the type Kr = f ( W ) for calibration characteristics when the following condition holds:

1 1 ) 1

h ~,min ~,rnax < --4-- '

where h is the thickness of the tested material , kmin and kma x are the wavelengths in the material with minimum and maximum moisture content respectively. Here Kp. is the value of the function which lies in the "linear" seg- ment in the general case of an oscillating function which is the result of partial waves' interference.

In the above case precision is increased by minimizing the measurement error due to the mismatching of the uhf channel. Moreover, i t is then pessible to measure with thin specimens.

Calibration characteristics of the type Kr. = f ( W ) are used, in particular, for testing the moisture of abrasives, ceramic moulding compounds, whose moisture content variations amount to 1.5 to 3. O%, The measurement error does not then exceed • 0.3% of the absolute moisture content.

Translated from Izmeritel, naya Tekhnika, No. 4, p. 90, April, 1973.

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