Phase sequence measurement indication circuit

The phase sequence of the three-phase power supply has a direct impact on some equipment. For example, if the phase sequence is different, the rotation direction of the three-phase motor will be different; if the phase sequence is wrong,
the measurement of the electric energy meter will be inaccurate. Therefore, it is often necessary to know the phase sequence of the three-phase power supply in advance.
    There are three phase sequence indicators in the figure , all of which can indicate
the phase sequence of the three-phase power supply.
    The phase sequence indicator on the left uses two bulbs and a capacitor
. In the forward phase sequence of U, V, and W, the bulb on the left
is dark and the bulb on the right is bright; while in the reverse phase sequence, the opposite is true
, that is, the bulb on the left is brighter and the bulb on the right is dim.
    The phase sequence indicator in the middle uses a neon lamp and a resistor to replace the two bulbs
in the phase sequence indicator on the left , which greatly reduces power consumption and is easy to use. The neon lamp in the phase sequence indicator is equivalent to an indicator light with an automatic switch: when the phase sequence is forward, the neon lamp does not light up; when the phase sequence is reverse, the neon lamp lights up. This phase sequence indicator either lights up or does not light up. Instructions are clear and reliable.     The phase sequence indicator on the right indicates the same way as the phase sequence indicator in the middle , but the circuit is complicated.