Automatic control system is being and developed on the basis of artificial control.
So, first introduced in automatic control, artificial operation, the first analysis and compare with the automatic control, the analysis and understanding of the automatic control system is helpful.
Figure 1 & ndash;
2 is a liquid storage tank, in the production of the frequently used as a general in the middle of the container or tank.
Once upon a time a process to the material continuously shed groove, and the liquid in the tank and sent to the next working procedure for processing or packaging.
When the inflow Qi (
Or outflow Q)
Severe fluctuations can cause the tank liquid level fluctuation, when overflow or time.
The simple solution to this problem, based on storage tank liquid level indicator, operation means to change the outlet valve opening to control, as shown in figure 1 & ndash;
When the liquid level rise, will export the valve opening is big, the more liquid level rise, the larger the valve open;
On the other hand, when the liquid level drops, the outlet valve, turn down the liquid level drops, the more the smaller valve shut up.
In order to make the liquid level has ample room to rise and fall, choose indicating value of the glass tube liquid level meter in the middle of a point for the normal work of liquid level height, by changing the outlet valve opening and keep liquid level on the level, so as not to appear in the storage tank level is too high to overflow trough, or make the liquid in the tank fit and accident phenomenon.
To sum up, the operator's work has three aspects, as shown in figure 1 & ndash;
Detection with eyes looking glass tube liquid level meter,
In the liquid level height, and tell the brain through the nervous system.
, command, according to the eyes to see the level of thinking and comparing with the requirements of the liquid level value, it is concluded that the size of the deviation and the positive and negative, and then according to the operation experience, after thinking, decision making orders.
Perform according to the command from the brain, by hand to change the valve opening, to change the outlet flow Q.
, keeping level on the required height.
Eye, brain, hand three parts, respectively for the testing, operation, and perform three action, to complete the measurement deviation, control valves, o to correct deviation of the process.
Due to manual control is limited by a person's physical, so the control on the speed and accuracy can meet the needs of the large modern production.
In order to improve the control precision and reduce the labor intensity, can use an automated device to replace the manual operation, so that it changed from manual control to automatic control.
Liquid storage tank and automatic device together form a automatic control system, as shown in figure 1 & ndash;
For persons involved in the eye, brain, hand three organs of the task, automatic device generally should also include at least three parts, respectively used to simulate the function of the eyes, brain and hands.
As shown in figure 1 & ndash;
3, automatic device of three parts, respectively is: (
Function is to measure the liquid level measuring element and the transmitter and the liquid level height can be converted to a specific, uniform output signal (
Such as air pressure signals or voltage, current, etc. )
Automatic controller it receives signals from transmitter, comparing with the process need to keep the liquid level height deviation, fruit with a specific signal,
Air pressure or current)
And calculated result, according to a operational rule: then this result with a specific signal value to change the valve opening.
Actuator control valve, it with normal valve function, except that it automatically according to the signal value from controller to change the valve opening.
Obviously, this set of personnel is operated in the automatic device with manual control part of the eye, brain, hand function, therefore, it can fulfill the task of automatic control in the holding tank liquid level height.
In the composition of the automatic control system, besides must have the automation device, will also have to be controlled by the control unit of production equipment.
In the automatic control system, will need to control the process parameters of production equipment or machine is called a controlled object, referred to as 'objects.
Figure 1 & ndash;
3 the liquid storage tank is shown in the liquid level control system of the controlled object.
Chemical production of a variety of columns, reactor, heat exchanger, pumps and compressors as well as a variety of containers, storage tank are common controlled object, even a gas pipeline can also be a controlled object.
In sophisticated production equipment, such as distillation, absorption tower, etc. , on a device may have several control systems.
When determining the controlled at this moment, is not always the production equipment of the whole device.
, for instance, a rectification tower, often need to control tower top temperature, pressure, etc. , the bottom and the need to control temperature, column reactor level, etc. , sometimes also need to control in central feed flow, you need to cooperate work flow meter
and control valve system, in this case, there is only one of the tower and control is a control system of the corresponding portions of the controlled object.
For example, in the discussion of feed flow rate control system, the controlled object refers to only feed tube and valve, etc. , rather than the column itself.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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