GB1333345A - Immersion heater - Google Patents

Abstract

1333345 Automatic control of temperature K GASS ERB 28 April 1972 [28 April 1971] 19875/72 Heading G3R [ Also in Division B1] An immersion heater 2 in a mixing device (see Figs. 1-8, not shown, and Division B1) is supplied with current through a diac 17 which triggers an alternating current thyristor 19. At a predetermined temperature the circuit to diac 17 is interrupted by a contact thermometer 7 whereby the thyristor 19 blocks passage of current to the heater, should the contact thermometer 7 fail, another 7' closes at a higher predetermined temperature whereby the voltage applied to diac 17 becomes insufficient and the heating circuit is interrupted. Simultaneously a tube 22 triggers thyristor 23, so that if thyristor 19 has become permanently interconnected, a resistance 24 heats up and melts an adjacent fuse wire 25, which alsocan be arranged to melt by direct heat from the treated liquid. In a modification the induction coil 11 of the mixing device is in series with the heater 2 and the contact thermometer 7 is replaced by a thermistor, see Fig. 10, (not shown). In another Fig.11 (not shown) in which the phase cutting angle is negligible to eliminate radio interference, the thyristor 19 is always inter-connected and the contact thermometer 7' is also replaced by a thermistor the regulating resistance (33) of which is in tandem with that (29) of the heating current circuit. In yet another, (Fig. 12, (not shown) a conjunction transistor (40) is used as trigger for a thyristor (27).