(57) An electric heater assembly comprises at least one electric heater, each of which
incorporates at least one sensing means (8) for use in detecting a cooking vessel
(9) on a cooking plate (7) overlying the heater. The sensing means (8) is provided
for the purpose of effecting selective energising and/or de-energising of one or more
electric heating elements (3) in the or each heater. The or each sensing means (8)
comprises an electrically conductive sensor loop. The or each sensor loop is connected
to a circuit (100) comprising a non-oscillatory resonant circuit (102, 103), for the
or each sensor loop, driven by an oscillatory circuit (101) such that the or each
resonant circuit is operated at within ± 15 percent of its resonant frequency, the
resonant circuit not forming part of the oscillatory circuit (101). A transformer
(104, 105, 106), associated with the or each sensor loop (8), has a first winding
(105) connected in the resonant circuit and a second winding (106) connected to, or
integral with, its associated sensor loop (8). Means (110, 111) is provided to monitor
change in a parameter associated with electric current in and voltage across the or
each resonant circuit (102, 103) as a result of placement and/or removal of a cooking
vessel (9) on and/or from the cooking plate (7) and to effect selective energising
and/or de-energising of one or more electric heating elements (3) in the or each heater.
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