Control circuit for electric storage heater - prevents unwanted charging with low outside temps. lying outside switching characteristics

摘要

The control circuit has a charging limiting signal (E3, E4) adjustable between two reference voltages (OV and -5V). The upper (Eo) and the lower (Eu) levels of the control signal (U2) pass through a voltage equal to one of the reference voltages. A voltage limiter (3) limits the control signal below the lower level to the first ref. voltage (OV). An adder (5) connected to the limiter's output processes the charging limiting signal and the control signal. A comparator (7) coupled to the output of the adder compares the adder's output with the first ref. voltage to generate a release or disable signal. The voltage limiter is an operational amplifier with a diode connecting its output to its inverting input, which is also coupled via a resistor to the first ref. voltage. The release signal initiates the charging of the storage heater but does not appear if the low outside temp. lies outside the transfer characteristics.