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Electronic Process Control

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L-TEC Steel Industry Products is a pioneer and world leader in Scarfing Machines, and the scarfing process. Determined to keep an edge on the growing demands of the steel industry, in both production volume, and quality, L-TEC is continuously making advances in research and development. The Electronic Process Control (EPC) System is one of the newest advances in scarfing development. A combination of gauges, valves, regulators and transducers continuously monitor, regulate, and inform the operator, of the flow of gases to the scarfing machine.

The figure at right illustrates, in simplified form, the process controller system. The pressure at the scarfing unit is the important variable. A pressure tap at the unit senses the pressure, which is conveyed via a signal hose to the P/E unit on the scarfing machine. The P/E unit converts the pneumatic pressure to an analog electrical signal, which is input into the PLC controller. An analog signal is then output by the PLC to an E/P unit. This E/P unit converts the electrical signal to a relative pressure level. This output pressure is input to a P/P unit, which boosts the pressure signal, by a preset ratio factor. The increased pressure signal is of a sufficient pressure and capacity to provide the necessary pilot pressure to the gas regulator. This regulator provides the process supply to the scarfing units.  

The PLC control logic provides several functions, two of which are important in the EPC system operation. The first function is logical in that the desired pressure operation is selected for specific time periods of the various operation sequences (e.g. Scarf cycle, pre-heat, etc.). The second function is as an EPC loop controller, whereby the resulting pressure at the unit is obtained and maintained in the required fashion. In the PLC program, the feedback (P/E measurement) is compared against the working pressure requirement, and correction to the analog output control is made. As a closed loop system, any changes in the steady state pressure by various disturbances can be corrected instantaneously.

EPC_diagram
(Click image to enlarge.)