Discrete logic

Regulatory Control For most batch processes, the discrete logic reqmrements overshadow the continuous control requirements. For many batch processes, the continuous control can be provided by simple loops for flow, pressure, level, and temperature. However, very sophisticated advanced control techniques are occasionally apphed. As temperature control is especially critical in reactors, the simple feedback approach is replaced by model-based strategies that rival if not exceed the sophistication of advanced control loops in continuous plants. 

The discrete logic must have access to operational parameters such as controller modes. That is, the discrete logic must be able to switch a controller to manual, auto, or cascade. Furthermore, the discrete logic must be able to force the controller output to a specified value. 

Sequence Logic Sequence logic must not be confused with discrete logic. Discrete logic is especially suitable for interlocks or per-... 

Discrete logic. Sequence logic can be implemented via ladder logic, and this approach is common when sequence logic is implemented in programmable logic controllers (PLCs). 

Being excellent at discrete logic, PLCs are a potential candidate for implementing interlocks. Process interlocks are clearlv acceptable for implementation within a PLC. Implementation of safety interlocks in programmable electronic systems (such as a PLC) is not universally accepted. Many organizations continue to require that all safety interlocks be hard-wired, but implementing safety interlocks in a PLC that is dedicated to safety functions is accepted by some as being equivalent to the hard-wired approach. 

The potential that the logic within the interlock could contain a defect or bug is a strong incentive to keep it simple. Within process plants, most interlocks are implemented with discrete logic, which means either hard-wired elec tromechauical devices or programmable logic controllers. 

There is a need for advanced discrete-continuous optimization tools that can handle mixed-integer, discrete-logic, and quantitative-qualitative equations to model synthesis and planning and scheduling problems. 

The discrete logic within process plants can be broadly classified as follows ... 

Starting from the discrete logical structure of the reaction lat tice, let us describe a chemical reaction algebraically by employing continuous parameters. In the simplest case we shall investigate the dynamic sublattice of the three-dimensional reaction lattice (single parameter X-model). Thereafter, these basic ideas wiU be generalized in three ways ... 

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