Ceramics-Silikáty 31, (4) 365 - 369 (1987)

Popisovaný adaptér je použitelný u všech pecí vybavených dvoupolohovou regulací konstantní teploty a termočlánkovým, měřidlem (čidlem) teploty. Zapojuje se do série tohoto termočlánku (obvykle PtRh 10-Pt, Ni-NiCr); v tomto obvodu pak generuje zvolenou rychlosti "chybové" napětí, které se k regulačnímu termočlánku přičítá nebo odečítá. Tak lze dosáhnout lineárního růstu, nebo naopak poklesu termoelektrické síly regulačního termočlánku zvolenou konstantní rychlostí, a tedy i přibližně lineárního růstu, nebo poklesu teploty pece. Adaptér tak rozšiřuje použití komerčních pecí i pecí konstruovaných individuálně a možnosti naprosto reprodukovatelného ohřevu, nebo chlazení zvolenou rychlostí prakticky lineárním programem.

The regulators of conventional laboratory furnaces operate on the two-position principle, thus allowing only the preset temperature to be maintained. To ensure reproducible firing conditions, such primitive regulation must be supplemented with a reproducible linear heating up and possibly also cooling. The control device described is connected in series with the control thermocouple in the furnace (Fig. 1). generating, at a preset speed, the "error" voltage E_ad which is added to (on heating up) or subtracted (on decreasing the temperature), from the voltage of the thermocouple, E_th, so that always E_th ± E_ad = E(t₀) (cf. Fig. 2a, b).The sign ⁺ holds for heating up, the ⁻ for cooling down, E(t₀) is the final temperature (for cooling, E(t₀) = 0). A schematic diagram of the adapter is shown in Fig. 3. It is based on operational amplifier OZ of high input resistance, which works in feedback with input resistor R; and the integrating capacitor C_i. The resistors R₁, R₂, R₃ determine defined and adjustable rates of decreasing the voltage on the integrator. Switch S serves to preset the initial voltage E_ad. Zero voltage on the adapter and thus also the end of a temperature rise (constant temperature schedule) is indicated by a LED. Z is the source of the necessary supply voltages and U_ref is the reference stabilized voltage. The dynamic properties of the system depend on the properties of the two-position furnace controller and on the position of the control thermocouple. If this is placed close to the heating coil and if the temperature is measured by a separate thermocouple in the area of the furnace muffle, the record of the temperature rise or fall is perfectly smooth and continuous. The linearity of the program depends only on a slight non-linearity of the dependence of temperature on the thermoelectric voltage of the thermocouple.