| 摘要 |
PURPOSE:To improve the sensitivity and safety and to shorten the detection time by subjecting the voltage applied onto the main winding of a single phase capacitor run motor and the phase lead voltage applied onto the auxiliary winding to half-wave rectification then combining both voltages and detecting the phase difference of the combined voltage waveform. CONSTITUTION:When a motor is under overload, the lead angle of voltage applied onto an auxiliary winding will be smaller than the original angle of 90 deg. and the time interval of 0V combined voltage is lengthened. Consequently, when the first inverted pulse width reaches to a predetermined reference, comparison pulse is not produced (Both inputs of a NAND gate G2 does not have 1, 1 simultaneously). Consequently, a time limit CR circuit is charged continuously to boost the input voltage for a NAND gate G3, and when it exceeds over a threshold a stop signal is provided from the NAND gate G3. The output is inverted through a NANO gate G4 and a transistor Q1 is operated while a relay RS is driven thus interrupting the operating circuit and stopping the motor. |
