| 摘要 |
<p>1533834 Touch responsive switching systems W F HAMILTON 16 June 1977 [16 June 1976] 25204/77 Heading G1N In a hum type pick-up touch switch false switching due to mains supply variations are obviated. In Fig. 1 reference detector 20 produces an output signal at 28, proportional to the amplitude of the A.C. line signal on 26, which is fed as a reference signal to comparator 54. Thus a change in the amplitude of the line signal which also produces a change in true signal picked up by touch plate 30, will not produce a false switching since the two signals applied to the comparator inputs both change by the same amount. When the touch plate 30 is touched the pick-up signal at 56 increases, the signal at 54 remaining the same causing an increase in the voltage across capacitor 68 so that trigger circuit 24 changes state, the latter being operable in synchronism with the line signal. Sensitivity of the comparator is continuously updated by the feedback path including FET 60 connected as a shunt. In an alternative arrangement Fig. 3 (not shown) touch plate 30 is connected to a peak detector of the same form as 20 of Fig. 1 and the output thereof is connected to one input of a comparator. The other input of which is connected to the output of a similar peak detector to the input of which is connected the A.C. line. Alternatively Fig. 4 (not shown) the touch detector and reference detector use C-MDS invertors each detector being provided with a feedback and the output of the touch detector is connected to the D input of a trigger circuit to the reset input of which is connected the output of the reference detector. Thus a change in amplitude of the line signal causes the trigger circuit to be inhibited.</p> |
