Immersion heater for domestic hot water - has inbuilt electronic temp. control and safety circuits

摘要

The cylindrical tank (1) contains a vertical heating element (3), a pressure sensor (7) and a temp. sensing probe (6). The probe (6) contains two electric temp. sensors (4,5). The pressure switch (7) operates if the tank dries out. On the base of the tank are a mains connection box (9) and a temp. setting control (8). The output of one (5) of the sensors is compared with a reference voltage; the comparator disables the supply if the maximum safe temperature is exceeded. The other sensor (4) output is compared with the setting control (8) output; the second comparator output switches the supply to the element on and off via a triac. Both sensor outputs are fed to a circuit which disables the supply if the wiring to the sensors become open-circuit or short-circuit.