Abstract: the main and deputy control fluid control laws and positive, the choice of the reaction information produced by excellent
flow meter, flow meter manufacturer to offer you the quotation.
1.
Control law of the choice of the cascade control system in the main, choice of the control law for the deputy controller principle is different.
(
1)
Main controller usually use pid control law is the purpose of the cascade control system for high accuracy stable main variables.
The main variable is.
More flow meter manufacturers choose model price quote you are welcome to inquire, the following is the main and deputy control fluid control law and is, select the details of the reaction.
1.
Control law of the choice of the cascade control system in the main, choice of the control law for the deputy controller principle is different.
(
1)
Main controller usually use pid control law is the purpose of the cascade control system for high accuracy stable main variables.
Main variables are main controlling index of production process, it is directly related to the quality of the product or production, craft is strict with it.
In general note variable does not allow more than poor.
So the main controller usually chooses pid control law, in order to realize the main variables of poor control.
Sometimes, objects, control channel capacity lags behind relatively large, such as temperature or component object, in order to overcome the lagging capacity, can choose pid control law.
(
2)
Deputy controller generally adopts the proportion control law in the cascade control system, stable variable is not an end, the purpose of the set pair of variable is the guarantee and improve the quality of the main variable control.
Under the effect of interference, in order to maintain the main variables is changeless, vice variables will change.
Vice variables of a given value is the changes over the output of the main controller.
So, in the process of control, are generally not very strict to the requirement of pair of variables, allowing it to fluctuate.
Therefore, deputy controller generally adopts the proportion control law.
In order to be able to fast track, zui okay with integral action, because the integral action can make tracking becomes slow.
Deputy controller differential function is not needed, because when deputy controller with differential function, once a slight change of the main controller output, is likely to lead to dramatically change control valve, which is unfavorable to the stability of the system.
2.
Controller, the choice of the reaction according to the different situation, the main and deputy controller direction selection method is as follows: (
1)
The assistant controller in cascade control system the choice of direction, is according to the process safety requirements, such as the selected actuator gas, gas close type, according to make vice control circuit a principle to determine negative feedback system.
Therefore, deputy controller of the direction and object properties, gas, gas close type of actuator, its selection method and the simple controller of control system are, selection of reaction in the same way, don't consider the role of the main controller direction at this moment, only the output of the main controller as deputy controller is given.
Figure 8 - for example
1 -
2 of tube type heating furnace temperature a deputy circuit of temperature cascade control system, if in the gas source is interrupted, stop the supply of fuel oil, to prevent burning stove, then actuators should choose gas valve open, is & other;
Throughout the &;
Direction.
When greater amounts of fuel, furnace temperature & theta;
2 (
Deputy variables)
Is increased, therefore, deputy object is & other
Throughout the &;
Direction.
In order to make the deputy loop constitute a negative feedback system, assistant controller T2C should choose & other;
Throughout the &;
Direction.
Only in this way can, when the interference effect of furnace temperature rises, the output of the T2C is reduced, thus gets off valve on small, reduce the amount of fuel, furnace temperature drop.
As shown in figure 8 - again
1 -
As is shown in rectifying tower kettle for the cascade control system of temperature and steam flow, if the thinking process, select actuators for the gas valve is closed.
So, in order to make the deputy loop is a feedback control system, assistant controller of FC direction should be chosen for & other;
Throughout the &;
Role.
At this moment, when the steam pressure fluctuations and make the steam flow rate increases, the deputy controller output will increase to make the valve down,
As a gas valve)
To ensure the people into the reboiler heating steam is not affected by or less by the steam pressure fluctuations.
So, give full play to the deputy loop to overcome the steam pressure fluctuations this interference for quick action, improve the quality of the main variable control.
(
2)
Cascade control system in the choice of main controller direction according to the following methods: when the main and deputy variables on the increase,
Or decrease)
If by the process analysis, to reduce main and deputy variables (
Or increase)
And is consistent with the requirements of control valve movement direction, main controller should choose & other;
Throughout the &;
Role;
On the other hand, was elected & other;
Throughout the &;
Role.
Can be seen from the above methods, the main controller in cascade control system is completely determined by process conditions the choice of direction, and the gas, gas close type of actuator and deputy controller direction completely unrelated.
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