At the beginning we discuss a few models of electrothermal devices intended for the measurements of thermal parameters of materials, components or devices. A solution to the task of optimal control of furnace batch temperature is presented. On the basis of a multisectional thermal system model with equivalent delays, the solution to the reactor batch optimal temperature control is found. Next we show how the optimal feedback gain matrix can be reduced to suboptimal form of lower dimensions. We also demonstrate an implementation of suboptimal controller in the form of a predictive temperature controller with variable cascade configuration. The effects of the predictive reactor temperature control are demonstrated for a few measuring devices.