The upper and lower limit water levels and upper and lower limit alarm water levels are set in the sedimentation tank. Its control process is when the water reaches the limit, the water level detection send signals to PLC, PLC started rising frequency converter and frequency signal output to the frequency converter, when the frequency converter has reached 50 hz if the water level is still at the lower limit position, PLC signal switch of sewage pump 1 # switch to run the power frequency, delay after a period of time by the frequency converter to start the sewage pump 2 #. In contrast, when the water reaches limit position stop sewage pump 1, PLC signal frequency drop, if because of the water pump or other causes water level below the lower or upper limit water level alarm, water level detector send alarm signal to PLC, the PLC output start alarm circuit (alarm lamp and ring), to prompt the operator to check the reason.
Aerator and submersible water pump are the core equipment of sewage treatment, need to use frequency converter to aerator blower (roots fan) and submersible water pump speed, blower frequency conversion control: sewage treatment aerobic partial dissolved oxygen concentration has a great impact on the treatment results, dissolved oxygen concentration is too low, sewage can not meet the standard; If the dissolved concentration is too high, it will not only waste electric energy, but also may make the activated sludge floating up so that the effluent cannot reach the standard. The purpose of the blower and frequency converter is to control the dissolved oxygen concentration of CASS tank to be stable at a constant value.