Can the integral operation in PID still be effective in this case?
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The cycle time of the PLC program is set to 100ms, and the calculation cycle of the PID module is also set to 100ms. We fix the actual value and set value of the PID module to maintain an error (this error is known as the residual). If there is only pure proportional action at this point, the OP value remains unchanged—this is easy to understand. If proportional-integral action is present at this time, due to the stabilization of the residual error, the amount integrated over each PID operation cycle remains constant; thus, it does not result in an increasing integral effect over time. Theoretically, each OP output is fixed. May I ask: does the integral action of PID still serve to eliminate residual errors in this case?
The integral action eliminates residual errors; in a closed-loop system, if it is in open-loop mode, the output will reach its maximum or minimum value. The strength of the integral action is determined by the integration rate or integration time constant – the output either increases or decreases depending on the strength of this integral action. Residual error refers to the difference that remains after the system has completed its adjustment, that is, the deviation when time approaches infinity. Error is generally used to indicate the precision of a measuring instrument, though occasionally it is also used to describe the precision of a system.
With a residual error, integration comes into play. The integral action means that when there is a residual error, an output is generated as a result of integration. When this residual error remains constant, the output from the integral term increases over time until it reaches its maximum value. This situation usually occurs due to a fault in the actuator (control valve), which fails to function properly and thus prevents the error from being eliminated.
If the actual value of your PID module is fixed, then what’s the point?