In electric motors, phase sequence in 3 phase configuration is very important. Change in phase sequence may cause trouble in machines.
Here is 1 a circuit which indicates the change in 1 phase sequence by a beeper or an LED. Transistors Tl, T2 and T3 are used. to square the 3 phase waveforms. The resistor value should be such that the transistor gets fully saturated when the base voltage becomes 10V. During negative cycle, the diode at the base keeps the reverse voltage below 0.6V. It is assumed that if the phase sequence is correct, the red phase lags the yellow-phase by l20° and the green-phase lags the red-phase by 120°. Any change from this sequence produces a beeping sound.
Transistor T4 is not only used for phase inversion but also to decrement the slope of the rising and falling edge (i.e to decrement the rise time of g the square wave). Output of this transistor is fed to the clock input of t the flip(IC 7476). Thus, during every cycle the phase sequence is checked. For the clock, squared waveform of the yellow—phase is used. Other phases are inverted during squaring operation. So at the falling edge, transistor T3 is cut-off and T2 is in saturation: Collector of T2 is connected to the input J and`K of lC1b. So at the clock edge we get low at both the inputs. Collector of T3 is connected to K input of ICla and J of IC1b resulting in high output at the clock pulse. At the rising edge of the clock we get J low and K high for ICla. So it gets reset and gives high at Qi. Similarly, when V the J and K inputs of IC1b are high the Y flip-flop is set. The Q output of IC1ai and Q output of IC lb are O Red and fed Ig at the base of T5 in order to switch on the alarm. In place of the alarm, an LED can also be used as an indicator. As long as the phase sequence is correct, both Q of ICla and Q of lClb are high and the transistor SK100 remains in off state.
Whenever thc phase sequence changes, both the outputs become low and turn on transistor T5. The beeper circuit comprises of a low frequency oscillator and a high frequency oscillator. The low frequency oscillator, which oscillates at l0 Hz, makes the high frequency oscillator enable and disable. The high frequency oscillator produces 3kHz output and a beeping sound in the speaker. lf a relay driven circuit is used, the system can be turned off when the phase change occurs.
Here is 1 a circuit which indicates the change in 1 phase sequence by a beeper or an LED. Transistors Tl, T2 and T3 are used. to square the 3 phase waveforms. The resistor value should be such that the transistor gets fully saturated when the base voltage becomes 10V. During negative cycle, the diode at the base keeps the reverse voltage below 0.6V. It is assumed that if the phase sequence is correct, the red phase lags the yellow-phase by l20° and the green-phase lags the red-phase by 120°. Any change from this sequence produces a beeping sound.
Transistor T4 is not only used for phase inversion but also to decrement the slope of the rising and falling edge (i.e to decrement the rise time of g the square wave). Output of this transistor is fed to the clock input of t the flip(IC 7476). Thus, during every cycle the phase sequence is checked. For the clock, squared waveform of the yellow—phase is used. Other phases are inverted during squaring operation. So at the falling edge, transistor T3 is cut-off and T2 is in saturation: Collector of T2 is connected to the input J and`K of lC1b. So at the clock edge we get low at both the inputs. Collector of T3 is connected to K input of ICla and J of IC1b resulting in high output at the clock pulse. At the rising edge of the clock we get J low and K high for ICla. So it gets reset and gives high at Qi. Similarly, when V the J and K inputs of IC1b are high the Y flip-flop is set. The Q output of IC1ai and Q output of IC lb are O Red and fed Ig at the base of T5 in order to switch on the alarm. In place of the alarm, an LED can also be used as an indicator. As long as the phase sequence is correct, both Q of ICla and Q of lClb are high and the transistor SK100 remains in off state.
Whenever thc phase sequence changes, both the outputs become low and turn on transistor T5. The beeper circuit comprises of a low frequency oscillator and a high frequency oscillator. The low frequency oscillator, which oscillates at l0 Hz, makes the high frequency oscillator enable and disable. The high frequency oscillator produces 3kHz output and a beeping sound in the speaker. lf a relay driven circuit is used, the system can be turned off when the phase change occurs.
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