【Daily Question 20090206】Automatic pressure and flow regulation does not require differentiation, while temperature regulation often makes use of differentiation
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【Daily Question 20090206】Why is the differential law generally not used in the automatic control of pressure and flow? And for temperature regulation and composition adjustment, is the differential law commonly used? Summary: For pressure and flow, the time constant T of the controlled variable is small, and the load changes rapidly; in such cases, the differential action can cause oscillations, and the integral action should not be too strong either, as this would also lead to oscillations, having a significant impact on the control quality. Meanwhile, the time constants of the temperature and composition variables are large, and differential control has a leading effect, which enables better regulation quality. This post was last edited by 13897295006 on 2009-2-7 17:00]
In pressure and flow measurement, there is no inertial lag, whereas in temperature and composition control, a certain amount of time is required for the changes to take effect, resulting in process inertial lag; therefore, differential control is used for advanced regulation
This is because parameters such as temperature and composition respond slowly, in other words, there is a reaction lag. The role of differentiation is to address this lag; by introducing differentiation, regulation takes place in advance, that is, it constitutes advanced control.
For pressure and flow rate, the time constant T of the process variable is small, and the load changes rapidly; in such cases, the differential action can cause oscillations, and the integral action cannot be too strong either, as that would also lead to oscillations, having a significant impact on the control quality. Meanwhile, the time constants of the temperature and composition variables are large, and differential control has a leading effect, which enables better regulation quality.
The differential regulation law states that the output of the regulator is proportional to the rate of change of the input deviation. It is used to overcome the effects of time constants and capacity lag in the regulated object. The characteristic constant is the differentiation time; the greater the differentiation time, the stronger the differentiating effect, and too large a value can also cause oscillations.
The time constant T of the pressure and flow control objects is small, and the load changes rapidly; thus, the differential action can cause oscillations. Meanwhile, the time constants of the temperature and composition variables are large, and differential control has a leading effect, which enables better regulation quality.
Why isn’t the differential law generally used in the automatic regulation of pressure and flow? And for temperature regulation and composition adjustment, is the differential law commonly used? For pressure and flow rate, the time constant T of the process variable is small, and the load changes rapidly; in such cases, the differential action can cause oscillations, and the integral action cannot be too strong either, as that would also lead to oscillations, having a significant impact on the control quality. Meanwhile, the time constants of the temperature and composition variables are large, and differential control has a leading effect, which enables better regulation quality.