INTRODUCTION

Improvement in the effectiveness and quality in the modern technological processes employed in the manufacture of aluminum and its alloys cannot be achieved unless the temperature can be measured to an accuracy of ± 0.5 – 1%.

In static processes, where there is a calm object surface, measurements of errors to this order of magnitude have been achieved by contact means using a thermocouple.

In dynamic processes, such as casting, rolling, extrusion etc., accurate continuous temperature control is possible using non-contact, in particular optical, methods. The advanced characteristics of the instruments used in this type of pyrometry (such as high speed, sensitivity, etc.), make it possible to measure relatively low temperatures.

The use of optical pyrometry methods in the aluminum industry is, however, associated with a number of fundamental difficulties, such as:

the variable emissivity and transmission of intermediate media intervening between the pyrometer and the measured object in the course of measurements; the influence of the light reflected from external radiation  sources; and the fluctuation of objects within the field of view of the optical pyrometer allowing only partial object sighting.

The harsh operating environment of the optical pyrometer – the wide temperature changes, dust and humidity, and the action of variable and permanent electro-magnetic fields – introduces secondary destabilizing factors that need to be corrected by various technical  solutions. All this makes modern optical pyrometry more complicated and therefore more expensive.