Device for sensing the operative status of electrical equipment

A device for sensing the energization condition of an electrical apparatus including an AC-DC converter circuit from at least one power line to the apparatus, comprising:

• means in series circuit with the power line for the electrical apparatus for detecting the current waveform of current therein;
• first amplitude detector means responsive to the detected current waveform, the first amplitude detector means including a first terminal, rectifier means, capacitor means and first voltage divider means coupled to provide to the first terminal an integrated mean absolute value signal varying with the integrated mean absolute value of the detected current waveform;
• a second amplitude detector means responsive to the detected current waveform, the second amplitude detector means including a second terminal, rectifier means, and second voltage divider means coupled to provide to the second terminal a peak value signal varying with the peak absolute value of the detected current waveform;
• comparator means responsive to the mean value signal and peak value signal for indicating the existence of an energized condition for the electrical apparatus when there is greater than a selected ratio between the peak value and mean value signals, the comparator means including differential amplifier means coupled to receive signals from the first and second terminals and to provide an output signal when the voltage at the second terminal is greater than that at the first terminal, the ratio of voltages at the second and first terminals being selected to provide an output signal from said differential amplifier means only when an impulse peak signal arising from operation of the AC-DC converter is superposed on the power line signals;
• and
• means responsive to said comparator means for providing a steady state indication of the energization condition of the electrical apparatus.

A system for distinguishing the full energization condition of an electrical unit including an AC-DC converter from a standby condition in which alternating current is drawn without activation of the AC-DC converter to superpose a pulse peak on the alternating current waveform, comprising:

• means coupled in circuit with the electrical unit for sensing the current waveform thereat;
• means responsive to the ratio between the peak level of the absolute value of the sensed current and the mean level of the absolute value of the sensed current for providing a pulse output for each half-cycle in which greater than a selected ratio exists;
• means responsive to the pulse outputs from the ratio responsive means for generating a control voltage whose amplitude is responsive to the number of pulse outputs received in a predetermined time;
• and
• means responsive to the control voltage for generating a steady state output signal when the control voltage is in excess of a predetermined level.