Steuerung und Überwachung der Sicherheit einer Flüssigkeitsheizanlage, worin die elektrischen Heizelemente als Sensor gebraucht werden

The electronic system comprises a microcontroller which provides for the automatic temperature adjustment of solids or liquids, with the heating element being utilized as temperature sensor. Depending on the number of available heating elements, the electronic circuit is expanded with a basic circuit which is built up from two relays with make-and-break contacts by means of which the heating element can be employed for the original purpose or can be connected as a temperature sensor in a measuring bridge. Due to extensive continuous test activities by the microcontroller, the realized system design is very well protected against uncontrolled heating. Also malfunctions in the microcontroller cause the heating activities to be stopped immediately. This renders an excess temperature cut-out switch redundant. Due to the alternating switching order, the two relays are loaded equally over time, which prolongs their lives significantly. The number of switching actions is further limited by performing a number of measurements during heating, so that it can be calculated after how much time the desired temperature will be reached. Just before this time has passed, a small number of measurements are carried out to achieve the final temperature within the desired tolerance. The electronic system makes both the conventional temperature sensor and the heat content sensor redundant. Further, the electronic system can measure the thickness of lime deposition on the heating elements and, depending on the measurement, give a service alarm or cut out the appliance completely.