Electronic temp. limitation switch for boiler, heater etc. - uses differential amplifier to compare detected and preset temps.

摘要

The switch has a difference stage obtaining the difference between the signal from a temo sensor and the selected required temp limit. The output of the difference stage is supplied to an amplifier, which responds to this difference being zero to initiate disconnection. A thermoelement (4) is used as the temp sensor, coupled between one input of an operational amplifier (5) and the centre-top of a resistive voltage divider (R1,R2). The latter also has a variable tap-off (R13) for setting the required temp. limit coupled to the other input of the operational amplifier (5). Pref. an IC oscillator (11) controls a transistor (T1) connected in series with a resistor (R6) between the first input of the operational amplifier and earth, for periodic short-circuiting of this input. The output of the operational amplifier (5) is coupled via a transformer with the switching element (RS).