Automation Recipes - 2: PLC Logics and HMI Screens for 4-20 mA Sensors Automation

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This booklet is the second in a series focused on automation recipes using PLC (Programmable Logic Controller) and HMI (Human Machine Interface). It targets readers with basic PLC programming knowledge who seek advanced, real-world solutions. In modern programming, developers utilize "Design Patterns" to address recurring problems effectively. This series replaces the term "design pattern" with "automation recipe" for clarity. The chapters detail a reusable automation recipe applicable to any PLC-HMI project involving electric motors, optimized for SCADA systems. This volume specifically covers measuring and monitoring quantities from 4-20 mA current sensors. The first section examines measurement types for physical quantities like pressure, level, flow, electric current, and temperature. The second section focuses on developing combined software for PLC and HMI, analyzing two function blocks: Conv4_20mA, which converts analog signals to engineering units, and AnalogSts, which monitors the analog signal's status based on parameters like set-point and alarms. Relevant display screens for value monitoring and parameter adjustments are also detailed, along with auxiliary subroutines, VirtualAI and Init. The final section applies these concepts to a practical level control case in a wastewater pumping station, utilizing the Horner OCS, which integrates multiple functions into a single product. The author, experienced with vario