304 Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Structured Text
Condition/State Action Taken
Prescan See Prescan in the Function Block table.
Normal Execution See Tag.EnableIn is true in the Function Block table.
Postscan See Postscan in the Function Block table.
Example
The SOC instruction is a specialized function block that is used in applications
where energy is transferred between two sections through a spring-mass system.
Typically in these types of applications, the frequency response of the process itself
can be characterized as shown in the bode diagram A below:
The SOC instruction implements a first order lag filter followed by a PID
controller to implement a transfer function with an integration, a second order
zero, (lead,) and a first order pole (lag.) With this instruction, PID tuning is
simplified because the regulating terms are arranged so that you have WLead and
ZLead as inputs to the SOC instruction, rather than Kp, Ki, and Kd values. The
transfer function for the SOC instruction is:
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