Issues with the PID block of Deltav
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As shown in the figure above, this is part of an introduction to the PID function block of Deltav. Does anyone who is familiar with this topic know how to interpret the part marked in red – that is, \"when to use the PV from the downstream function block as BKCAL_IN so that its OUT can track the PV from the downstream system\"? I’m not quite sure about this! The text mentions that when both the upstream and downstream components are PID blocks, if \"Dynamic Integral Limit\" is selected in the FRSIPID_OPTS option of the main PID block, then the secondary PID should choose \"use PV for BKCAL_OUT\" so as to automatically adjust the integral value of the main PID based on the performance of the secondary PID. This statement is difficult to understand; those who know how to explain it would be appreciated, thank you!
Okay, not bad, not bad; come down and learn *.
In single-loop PID control, this pin does not need to be connected; what is mentioned here actually refers to the case of cascade control. In cascade control, the OUT of the main loop is connected to the SP of the secondary loop. By reconnecting the BKCAL_OUT of the secondary loop to the BKCAL_IN of the main loop, this return connection enables a disturbance-free switchover when the secondary loop is incorporated into the cascade configuration.
It’s clearly stated in the image you sent as well: the BKCAL_OUT value of the secondary circuit tracks the PV value of that same secondary circuit.