PID automatic control (with diagram)

I especially don’t understand 2, 3, and 4

Personally, I think it is probably: 2 is to control the inlet flow based on the liquid level. 3 Control the inlet flow based on the outlet flow, 4 control the opening degree of the outlet valve based on the outlet temperature and pressure.

I always feel that these will conflict. 2 Can it be done directly by using the level control valve LV, without the need for a flow meter? I’m not sure if that’s feasible 3 If the inlet flow is controlled based on the outlet flow, can the liquid level still be maintained?

I always feel that these will conflict. 2 Can it be done directly by using the level control valve LV, without the need for a flow meter? I’m not sure if that’s feasible 3 If the inlet flow is controlled based on the outlet flow, can the liquid level still be maintained?

The last edit to this post was made by Suspected law-abiding citizen on 2023-2-22 at 17:14. The control logic is roughly as follows: Logic No. 4: The outlet pressure gauge controls the pressure regulating valve, adjusting its opening based on pressure changes. Logics No. 1, 2, and 3: The readings from the outlet pressure gauge and outlet thermometer are combined and fed into the outlet flow meter; these values, along with those from the level gauge, are then sent to the inlet flow meter to control the inlet flow rate. There are issues with the description of this control logic – logical calculations should be represented using the symbol Y. Temperature and pressure compensations should be processed in a compensation module before a signal is generated to be sent to the controller; it’s not appropriate to feed temperature and pressure signals directly into the flow meter. Additionally, the function of flow meter 10302 is handled by ICAQR; it contains a C (control) element, but there are no control signal wires leading to other actuators. It is not appropriate to use the liquid level directly to control the inlet regulating valve LV here. The reason is as follows: Look at the shell side – the inlet is the BW boiler feed water, and the outlet is the LS low-pressure steam. You can consider this to be a small boiler; the water in the shell side is boiling. Under conditions of boiling under pressure, there is something called a false water level phenomenon, where the water level rises even though water is being drained. The specific reason is that drainage causes a sudden drop in pressure, causing the steam to condense rapidly and leading to a sharp increase in liquid level. However, the liquid level at this time is false; if the temperature and pressure reach the design values, this water will evaporate rapidly, causing the liquid level to drop. If adjustments are made based solely on the liquid level in order to remove this false level, then when the temperature and pressure return to normal, the remaining water will evaporate quickly, resulting in a level below the safe threshold and leading to dry burning of the boiler. Therefore, for boiler flow meters, it is not sufficient to rely solely on the liquid level; adjustments should be made taking into account both temperature and pressure.

What should the correct logical representation of 1/2/3/4 look like in a drawing? Could you please draw it for me? I’ll compare it to make it clearer: hug:

This post was last edited by Suspected law-abiding citizen on 2023-2-23 09:57. I don’t have it available right now, and it’s not easy to draw one just like that; I found a control logic for three-transistor regulation of the drum level online for reference – those interested can look into related papers. It can be seen that here, the outlet flow rate, inlet flow rate, and drum liquid level are fed into an additive calculator; through a series of calculations, a control signal is generated to control the inlet flow rate control valve. Instead of sending the outlet flow signal and the level gauge signal to the inlet flow meter in order to control the inlet control valve.

This post was last edited by zxc17834 on 2023-2-23 at 10:13. 1. The water supply system is a simple, strict cascade control system; those who are not familiar with it can learn the basic control methods on their own, as explanations are provided in books. 2. The outlet is a simple pressure control circuit. 3. A temperature and pressure compensation was applied due to the issue related to the selection of the gas flow meter, in order to achieve more accurate measurements. 4. A comparison has been made between the water inlet flow rate and the exhaust gas volume; this can serve as a reference for the boiler’s three-variable control system, and it’s a good opportunity to learn about it together*.