PROBLEMS WITH AUTOMATION AND MECHANIZATION

RADIO-FREQUENCY MOISTURE METERS FOR BULK MATERIALS

�9 A. I. Alekhin and A. D. Zavgorodnii

D]3C~666.3:543.712

Industry does not produce radio-frequency moisture meters for bulk materials. The Ukrainian Scientific-Research Institute for Refractories has developed and is now making rf rapid moisture meters for molding and bulk materials to be used for process control in the production of refractories and the raw material as well for quality control of the fin- ished products. Despite variations in the chemical composition, the meter can determine the moisture content of any bulk material and molding material that do not contain metallic in- clusions and lumps larger than 5 mm. One measurement of the moisture content takes less than 1 min.

Principal metrological characteristic range of moisture-content measurements is 0 to 15%; error is i 0.25% (absolute) at a 0.95 confidence coefficient.

The schematic diagram of the meter is shown in Fig. i. It is based on an amplitude microwave method of measuring the moisture content in the 3-cm range [i]. The operating principle of the meter is based on the known dependence of the dielectric loss tangent of the material on its moisture content: The absorption of radio-frequency waves of the given mate- rial placed in a closed waveguide is measured.

The meter functions as follows: microwaves from the oscillator section 1 (the section has a stabilized voltage power supply) travels in the hollow waveguide through decoupling 2 and tunable 3 attenuators and then through an appropriate transformer to a demountable measuring section 4, where a cell containing the sample material of a given density is placed. Depend- ing on the moisture content of the material, the radio waves are attenuated in the cell and enter the input transducer 5 of the wattmeter 6.

The moisture meter has been metrologically certified and pressed into service for process control and certification of output. Inspections are made of the molding materials for dianas brick used to line glass-melting furnaces and the coke furnace batteries of open-heath and electric steel-melting furnaces, molding material for the lining of steel-pouring ladles, chamotte masses, MSh-39, 42 aluminosilicate mortar, and PShGT chamotte-aiumina powders.

The use of standard domestic highly stable component parts and elements has ensured that that the radio-frequency moisture meter is very reliable during operation under production conditions. In view of its relatively low production cost and small size (1200 • 200 • 300 mm) this moisture meter can be recommended for widespread use in enterprises and organizations that need to make highly accurate measurements of the moisture of bulk materials.

The use of radio-frequency meters for two years in four enterprises producing refractories has confirmed the superior operating characteristics of the meters.

At the present time the Ukrainian Scientific-Research Institute for Refractories is in- stalling such moisture meters in enterprises of the Ukrogneupor Company.

LITERATURE CITED

i. P.R. Ismatuiiaev, "Microwave moisture meters for cotton and cotton materials'" Izmer. Tekh., No. i, 50 (1986).

Ukrainian Scientific-Research Institute for Refractories. Translated from Steklo i Keramika, No. 8, p. 31, August, 1992.

0361-7610/92/0708-0395512.50 �9 1993 Plenum Publishing Corporation 395