PID control is the most familiar and widely used control scheme. It is a linear combination of proportional, integral and derivative control laws. It combines the advantages of proportional control (fast response), integral control (error elimination), and derivative control (predictive function) while making up for the shortcomings of the other three, making it a relatively ideal composite control law.
How do you configure a PID control scheme in a PKS system?
First and foremost, we still can't do without the famous CM (Control Module).
The CM in the PID control loop contains a total of four functional blocks:
1 AIChannel
One DATAACQ function block (which will later be renamed DDACA)
1 PID function block
1 AOChannel
The AIChannel and DACA function blocks are exactly the same as those in the monitoring loop. The PID function block is the main component in the PID control loop. It is responsible for comparing the detection data processed by the DACA with the target value (i.e., the SP value, the setpoint, which is usually manually input by the operator). Based on the deviation (SP-PV), it performs a composite calculation of proportional, integral, and derivative to obtain the output value (OP value).
The user interface for the PID loop is as follows:
Within the PID function block, you can also select the calculation formula for the PID algorithm, meaning you can recombine the three control methods: P, I, and D.
Algorithm A: The standard PID formula, where proportional, integral, and derivative all act on the deviation value.
Algorithm B: The proportional and integral functions act on the deviation, while the derivative only acts on the change in the PV value. It relatively weakens the function of the derivative and avoids the disturbance to the process caused by the overshoot of the derivative.
Algorithm C: The proportional function acts on the deviation, and both the proportional and differential functions act on the change in the PV value.
Algorithm D: Only has integral action, i.e., a pure integral controller.
Algorithm E: Only proportional action, i.e., pure proportional controller.
Algorithm A and Algorithm B are the two most commonly used algorithms.
The output value is a 0-100% value, which is converted into a 4-20mA signal through the AOChannel (corresponding to a certain channel on the hardware AO card) and sent to the valve positioner in the field to control the valve opening.
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