Application and parameter adjustment of automatic

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The use and parameter adjustment of the automatic air filling system of the shield machine

the automatic air filling system of the Herrick shield machine is used to keep the air pressure in the soil silo close to a constant value. It is an automatic pressure control system. In order to make the control system achieve the desired control effect, the parameters of PI (proportional integral) regulator, which affects the dynamic performance of the system, must be set correctly. At the same time, the shield machine works in a harsh environment, and the spring fatigue and diaphragm aging of the gas filling system will cause changes in the parameters of the regulator, resulting in abnormal system control. Therefore, the parameters of the regulator should be adjusted frequently in use

1. Working principle of automatic gas filling system

the control principle of automatic gas filling system is shown in Figure 1

pressure transmitter 1 converts the actual air pressure in the silo into standard air pressure signal x (0.02 ~0.1mpa) and sends it to regulator 4

the regulator compares the measured value x sent by the transmitter with the set value w (0.02~0.1mpa) to obtain the deviation. According to the deviation size and change trend, P1 regulator control is widely used in various fields. After calculation, it outputs the corresponding control signal Y to positioner 3

the positioner compares the regulating signal Y (0.02~0.1mpa) sent from the regulator with the valve position signal sent from the regulating valve to judge whether they match the expected relationship. If it matches, the positioner will keep the opening of the regulating valve unchanged. Otherwise, the air pressure to the regulating valve 2 will change greatly through the action of the internal amplifier of the positioner, so as to overcome the friction that can eat all bags directly or throw away the valve rod, and eliminate the influence of the uneven force of the regulating valve, so that the regulating valve acts until the two signals match, so as to ensure that the valve position is correctly positioned according to the signal sent by the regulator

2. Usage

the control module of automatic gas dispensing system (see Figure 2) includes display panel and manual operation station. The manual operation station and regulator are German (Samson type422, type 423) products. The pipeline connection between the manual operation station and the regulator is shown in Figure 3. The X and w values on the display panel are different from the X and w values on the regulator. The X and w values on the regulator are standard air pressure signals (0.02~0.1mpa), while the X and w values on the panel are the actual pressure value and the expected pressure setting value of the silo after the X and w values on the regulator are converted by bellows and lever machinery

the use steps can be summarized as follows:

(1) open the relevant air circuit and check whether the outlet pressure of pressure reducing valve 5 and pneumatic triplet 6 in Figure 1 is 0.14 MPa ± 0.01 MPa and 0.4 MPa ± respectively. It is strictly prohibited to process steel bar diameters, numbers and mechanical speeds that exceed the mechanical regulations by 0.01 MPa, so as to ensure that the pipe circuit is free of leakage and blockage

(2) check whether the wint/wet selector switch is in the wint position when SCM integrates the latest oilfield chemicals and technologies to participate in the meeting. If it is, it indicates that the set value w of the regulator is set by knob 5 in Figure 2. If it is in the w position, it indicates that the set value w of the regulator is given by the outside of the operation station, and the set value w in this system is set by knob 5

(3) turn the manual/automatic switch to the manual operation position:

(4) adjust the knob 7 in Figure 2 to make the control system work, and adjust the YH value until the actual value indicator needle (red) slowly approaches the set value (green needle)

(5) in the process of adjusting YH, the automatic operation output signal Ya is also rising slowly. When ya=yh, turn the manual/automatic switch to the automatic operation position, which can reduce the system impact

(6) observe the dynamic response characteristics of the system. If the actual value fluctuates within the range of the set value, it indicates that the system is in a normal working state. Otherwise, readjust the control parameters of the PI regulator

3. Parameter adjustment method

the control goal of the automatic aerating system is to keep the pressure of the silo constant, and at the same time, the system is required to have a high ability to suppress disturbances. Therefore, differential control is not used, and only PI (proportional integral) control mode is used. Regulator parameter adjustment means that when the control law has been determined in the form of PI, by adjusting the parameters of PI regulator, the dynamic characteristics of the control loop can meet the expected index requirements and achieve the ideal control objectives

PI parameters can be adjusted by trial and error method. According to the empirical formula and the characteristics of the automatic gas filling system, the following adjustment steps of proportion first and then integration are carried out for the parameters

first set the proportional part, that is, set the integration time TN to the maximum (20 min), then gradually change the proportional coefficient Kp from small to large, and observe the changes of the regulator output signal and the adjusted parameters at the same time. If the adjustment process is to attenuate oscillation, KP should be continuously reduced; If the adjustment process is amplitude oscillation, KP should be increased until the adjustment process becomes equal amplitude oscillation. At this time, the system still has static error, and the static error is still in a large range, so the control purpose can not be achieved by using the proportional regulator alone, and the next step of integral adjustment should be carried out

set the integral system. First, set the dish TN to a smaller value, and slightly reduce the KP obtained in the first step, such as 0.8 times the original value. Then gradually increase TN and observe the system response curve, so that the static error can be eliminated while the system maintains good dynamic performance. In this process, KP and TN can be changed repeatedly according to the quality of the response curve, in order to get a response curve with fast response and small overshoot. (end)

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