SIMATIC PID Temperature Control Manual

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Control Zone (CONZ_ON, CON_ZONE)
If CONZ_ON = TRUE, the controller operates with a control zone. This means that
the controller operates according to the following algorithm:
• If PV exceeds SP_INT by more than CON_ZONE, the value LMN_LLM is
output as the manipulated variable (controlled closed-loop).
• If PV falls below SP_INT by more than CON_ZONE, the value LMN_HLM is
output as the manipulated variable (controlled closed-loop).
• If PV is within the control zone (CON_ZONE), the manipulated variable takes
its value from the PID algorithm LMN_Sum (automatic closed-loop control).

Note
The changeover from controlled closed-loop to automatic closed-loop control
takes into account a hysteresis of 20% of the control zone.