The measurement of temperature of the steel in a reheat furnace and control from this indication has been an aspiration of furnace operators since the radiation pyrometer was first developed.

However, the signal from a radiation pyrometer not only indicates the temperature of the steel but also includes reflected radiation from the other sources in the furnace such as flame and refractory.

This has severely limited the adoption of direct steel temperature measurement throughout the industry.

The most common way of adjusting for this unwanted radiation has been to incorporate an "emissivity”-adjusting adjusting rheostat in the system. However, since the relationship between steel temperature and "furnace" temperature varies with production rate and other factors, the success of this method has been limited.

Most recently, a system consisting of a thermocouple to measure "furnace" temperature and radiation pyrometer to measure "steel" temperature has been developed. These two signals are fed into a microprocessor and the resulting output is then a reasonable indication of the surface temperature of the steel.

There are several reheat furnaces in operation, where they are not only measuring steel temperature but controlling form this signal, the "application engineering" of such systems is not without pitfalls. To ensure a successful installation one should rely upon someone with experience in these systems and not just the instrument manufacturer.