Power phase sequence display circuit

Any power supply and distribution department should have a phase sequence detection device to ensure the stability of the power supply phase sequence. Any irreversible electromechanical product
itself should also have a phase sequence detection device to determine whether the power phase sequence meets the requirements before the host is put into operation. The three- phase power supply phase sequence indication circuit is as shown in the figure.
    When the forward phase sequence is used, the voltage on R3 is rectified by UR1, and then charged to C2 through Ri. When the voltage on C2 reaches the
starting , EL1 lights up. , emits green light. Cz is discharged through EL1; when the voltage on C2 is lower than a certain value. EL1 goes out, Cz is
recharged, after a while EL1 lights up again, C2 is discharged again... and so on, the green neon lamp EL1 keeps flashing
. Similarly, when the reverse phase sequence is used, only the red neon lamp EL2 keeps flashing. By adjusting the time constants of RL, C2 and Shu and G, you can adjust the flashing frequency of the neon lamp.