| 摘要 |
A missing phase detector circuit which monitors the ac three-phase output voltages of power equipment or sources and produces an output signal in the event a missing ac phase is detected. The circuit reduces the monitored phase voltages to low values and produces an ac ripple voltage waveform where each ripple represents a phase. An analyzer circuit examines the ac ripple voltage waveform for its zero crossings and produces a pulsed dc waveform where the width of the pulses is normally small. If any of the pulses is found to be wide, indicating a missing phase, a positive high signal is output by an AND gate. This output signal may be used to initiate illumination of a "Missing Phase" indicator or it may be used for equipment control purposes. Provision is made to prevent a false output signal when there is no input power. The circuit is not sensitive to frequency, power factor or unbalanced loads. Brown-outs (low ac voltages) do not affect the analyzer portion which looks only at ac ripple zero crossing points and not at amplitudes. The circuit components are low power, low in stress and few in number. Thus the circuit has high reliability.
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