Instrumented level and flow cascade control

I didn’t understand your question; there are already two parameters, so what do you want to convey?

The deviation in the secondary loop is relatively large; it is necessary to examine the control curve and adjust the PID parameters if needed

From the perspective of the process control flow, it is the liquid level control in the reflux tank that regulates the tower top reflux. The feedback loop has a large deviation; it is likely due to the relatively long integration time set for the feedback loop.

. In level and flow cascade control, there is no strict correspondence between the level and the flow rate； In cascade control for liquid level and flow rate, it is only possible to achieve full stability in one of them (the primary controller); when necessary, the two parameters can be allowed to fluctuate within specified ranges (for uniform adjustment).

The Pv and SV deviations in the feedback loop are too large

This post was last edited by jlshnlhj on 2024-5-30 09:19. The adjustment of the p and i parameters should be carried out with reference to the trend curve. Using instantaneous values won’t work. In this loop, d is set to 0 to turn off differentiation.

Not long ago, such control was implemented; previously, cascade control was used, which resulted in large fluctuations in flow rate. Later, only a PID control system was used for flow regulation, with the flow value being determined by a program calculation. This approach prevented flow rate fluctuations and enabled effective control of the liquid level. The operating conditions here are as follows: Materials A and B enter the distillation tower where they undergo reaction simultaneously with distillation. The heavier components exiting the bottom of the tower go to the heavy-component tank, while the lighter components coming from the top of the tower are sent to the finished product tank. It is necessary to control the liquid level in the tower bottom; this is achieved by regulating the flow rate of the distilled and heavy components through the pump that circulates the liquid in the tower bottom. Flow rate = (A+B) * distribution coefficient * (bottom of tower liquid level / set value for bottom of tower liquid level). The value obtained is then used as the set value for the PID controller. Assuming that there are 12 control loops for regulating the bottom of tower liquid level, if the calculated flow rate is denoted as F, then g_bsc.SwAM = ON; (*Set the 12 loops to automatic mode*) g_bsc.SV = F; (*Assign the calculated flow rate value as the set value for the control loops.*) *) Assuming the distribution coefficient is 0.6, the current liquid level is 1200 while the controlled liquid level is 1000. If a total of 100 kilograms per hour of materials A and B are fed in, then 60 kilograms per hour will emerge from the bottom of the tower. Since the current liquid level is too high, the set flow rate is changed to 72 kg/h. By performing a material balance, it is possible to determine the approximate value of the distribution coefficient; accuracy isn’t required here. In this way, the traffic remains stable, without any fluctuations. The value assigned to SV is a number between 0 and 1. If the range of the flow meter for feed AB differs from that of the flow meter for the outlet flow from the reactor bottom, it must first be converted to engineering units, and then converted to a value between 0 and 1 based on the range of the flow meter for the outlet flow from the reactor.