【Q&A Question 222】2018.08.16
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【Q&A Question 222】 August 16, 2018: Why is differential control not generally used for regulating pressure and flow rates, while it is often employed for regulating temperature and composition? For controlled parameters such as pressure and flow rate, the time constant of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which significantly affect the quality of regulation. Therefore, differential control is not used. In contrast, for systems where the time constants of both the measurement loop and the control loop are larger, such as those related to temperature and composition, the leading effect of differential control yields good results. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Correct: 3 wealth, Incorrect: 1 wealth ； Mass posting of posts – rated based on the lowest score ； Replies that are unrelated to the answer are considered spam and will be deleted immediately. For management purposes, if you need to view content from a few days ago, please go to https://bbs.hcbbs.com/home.php?mod=space&uid=3862647&do=thread&view=me&from=space through the summary post below
For regulated parameters such as pressure and flow rate, the time constant T0 of their control loops is small; hence, even slight disturbances can cause rapid changes in these parameters. If a differential control strategy is used, it can lead to oscillations in the instruments and the system, which has a significant impact on the quality of regulation. If T0 is very small, using a negative derivative can yield good results. For adjustable parameters such as temperature and composition, the time constants of both the measurement channels and the control channels are large; as a result, even in the presence of slight disturbances, the changes in these parameters occur slowly, allowing the use of differential laws. By utilizing differentiation and lead action, the inertia of the parameter being regulated can be overcome, thereby improving the quality of regulation.
For regulated parameters such as pressure and flow rate, the time constant To of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which significantly affect the quality of regulation. Therefore, a differential control law is not used. For systems with large time constants in the measurement channels and control mechanisms related to temperature, composition, etc., using the leading effect of differential laws can yield good results.
Distinguished by the lag of the adjusted parameters
For regulated parameters such as pressure and flow rate, the time constant T0 of their control loops is small; hence, even slight disturbances can cause rapid changes in these parameters. If a differential control strategy is used, it can lead to oscillations in the instruments and the system, which has a significant impact on the quality of regulation. If T0 is very small, using a negative derivative can yield good results. For adjustable parameters such as temperature and composition, the time constants of both the measurement channels and the control channels are large; as a result, even in the presence of slight disturbances, the changes in these parameters occur slowly, allowing the use of differential laws. By utilizing differentiation and lead action, the inertia of the parameter being regulated can be overcome, thereby improving the quality of regulation.
For regulated parameters such as pressure and flow rate, the time constant To of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which significantly affect the quality of regulation. Therefore, a differential control law is not used. For systems with large time constants in the measurement channels and control mechanisms related to temperature, composition, etc., using the leading effect of differential laws can yield good results.
Differentials are primarily responsible for inertia and lag; the regulation of pressure and flow is a direct reflection of the volume flow rate of the medium； The regulation of temperature and composition generally relies on indirect means; for example, adjusting temperature requires changing the pressure or flow rate of the fuel gas, and this must be done based on the efficiency of combustion, which inevitably results in delays. Therefore, temperature regulation basically involves differentiation.
For regulated parameters such as pressure and flow rate, the time constant of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which have a significant impact on the quality of regulation. Therefore, differential control is not used. However, for systems where the time constants of the measurement loops and control loops for parameters such as temperature and composition are larger, the leading effect of differential control can yield good results.
For regulated parameters such as pressure and flow rate, the time constant T0 of their control loops is small; hence, even slight disturbances can cause rapid changes in these parameters. If a differential control strategy is used, it can lead to oscillations in the instruments and the system, which has a significant impact on the quality of regulation. If T0 is very small, using negative differentiation can yield good results. For parameters such as temperature and composition, whose measurement channels and control channels have large time constants, any interference results in slow changes in these parameters; therefore, the differential principle can be applied. By utilizing differentiation and lead action, the inertia of the parameter being regulated can be overcome, thereby improving the quality of regulation.
For regulated parameters such as pressure and flow rate, the time constant To of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which significantly affect the quality of regulation. Therefore, a differential control law is not used. For systems with large time constants in the measurement channels and control mechanisms related to temperature, composition, etc., using the leading effect of differential laws can yield good results.
For regulated parameters such as pressure and flow rate, the time constant of the control loop is small, and the load changes rapidly; in such cases, both differential and integral actions can cause oscillations, which have a significant impact on the quality of regulation. Therefore, differential control is not used. However, for systems where the time constants of the measurement loops and control loops for parameters such as temperature and composition are larger, the leading effect of differential control can yield good results.