Issues regarding proportion, integration, and differentiation in DCS systems

There are issues with the settings: the values for integration and differentiation are too sensitive, resulting in large fluctuations

Caused by improper adjustment of the PID

Proportional (P) control Proportional control is the simplest form of control. The output of its controller is proportional to the input error signal. When only proportional control is used, there is a steady-state error in the system output. Integral (I) control: In integral control, the output of the controller is proportional to the integral of the input error signal. For an automatic control system, if there is a steady-state error after it reaches steady state, then such a control system is said to have a steady-state error, or simply referred to as a system with steady-state error. To eliminate steady-state error, an “integral term” must be introduced into the controller. The integral term represents the time-dependent integration of the error, and as time increases, this integral term grows. In this way, even if the error is small, the integral term increases over time, which drives the output of the controller to increase and further reduces the steady-state error until it becomes zero. Therefore, a proportional-plus-integral (PI) controller enables the system to have no steady-state error after reaching stability. Differential (D) control: In differential control, the output of the controller is proportional to the derivative of the input error signal (i.e., the rate of change of the error). Automatic control systems may experience oscillations or even instability during the process of correcting errors. The reason is the presence of components with high inertia or components that introduce delay, which have the effect of suppressing errors; their changes always lag behind those of the errors. The solution is to make the change in the error-suppression effect \"proactive\", that is, when the error approaches zero, the error-suppression effect should be zero. In other words, it is often not sufficient to include only the \"proportional\" term in the controller; the function of this term is merely to amplify the magnitude of the error. What is needed now is the addition of a \"derivative\" term, which can predict the trend of error changes. Thus, a controller with both proportional and derivative terms can bring the control action to zero, or even to a negative value, in advance, thereby preventing severe overshoot of the controlled variable. Therefore, for controlled objects with high inertia or lag, a proportional-plus-differential (PD) controller can improve the dynamic characteristics of the system during the regulation process.

If continuous production is not involved, it is generally necessary to manually adjust the instrument parameters to values near the set points first, and then switch to automatic mode. This way, a steady state can be reached quickly; otherwise, it will be troublesome. Tebi is for those with strong non-linearity.

Could you share the method for setting proportional-integral-derivative controls? In the settings, what do 100% and 200% mean for the ratio? What is the numerical meaning of integrals and derivatives as well? 4# zhongmingh

Generally, the integration constant is set to a small value while the differentiation constant is set to a large value; this results in small fluctuations when automation is used, whereas large fluctuations occur otherwise! It’s just personal experience

For setting parameters, in most cases only P and I need to be set; the use of D is generally not recommended. Generally, control valves are regulated using parameters such as liquid level, pressure, and temperature. Different measurement parameters have distinct set ranges, and these ranges must be adjusted gradually based on the actual operating conditions. 1# Ah Xuan