Cascade control
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There is a reactor whose temperature is kept constant, while the pressure gradually increases as the temperature changes. Once the temperature reaches the set value, it is necessary to lower the temperature. However, there is a large temperature lag in this single-loop system. I was thinking of incorporating pressure control into a cascade control system, but since the pressure is not constant, isn’t cascade control inappropriate in this case?
Yes, if the pressure isn’t constant, cascade control might not be very suitable. In cascade control, the slower process affects the faster one, and as pressure changes, the temperature of the reactor also changes, which leads to instability in cascade control. It is recommended to use other control strategies to solve this problem. .
It has to be variable in order to be used for control; if it’s fixed, it can’t be used for control. If the relationship between pressure and temperature is linear, wouldn’t it be better to simply use pressure as the main control variable?
The process is not described clearly; generally speaking, pressure is not the main means of regulating temperature, but only has an impact on it.
A prerequisite for forming a cascade control system is that the secondary controlled variable has an effect on the primary controlled variable; if there is no such effect, a cascade control system cannot be established. The secondary controlled variable has an impact on the primary controlled variable, and: 1. The secondary controlled variable is measurable ； 2. It has a certain level of sensitivity ； 3. There is a one-to-one correspondence ； 4. It is preferable to have a linear relationship of influence ；