Most modern control systems employ a PLC (Programmable Logic Controller) as a means to control motors, pumps, valves, and various other equipment used in a process. Computer-based HMI (Human Machine Interface) products provide how to process personnel interact with the PLC control system. A well-designed combination of PLCs and HMI's can be a solid foundation for your process automation needs. In detail, the first section of this booklet, dedicated to the application domain, analyzes the two types of sequencer: twin for the operation of two machines, one of which is always on standby or parallel to start/stop a certain number of machines, generally of the same size, installed in parallel. The second section deals with the development of combined software for both PLC and HMI. The logic of the two functional blocks (UDFB), Mot2Seq and Mot6SEq, and the related display screens, for local monitoring and setting configuration and timing parameters, are illustrated. Finally, the third section shows the application of the concepts developed in a real level control case in a wastewater pumping station.