time£º2018-10-16 16:34 source£ºshelok pressure transmitter

Using a vacuum pressure transmitter to adjust the frequency

Abstract: The problem of how to efficiently collect the bottom oil of the tanker in the railway tank trucks is calculated. If the residual oil of each tanker is 5kg, the number of oil-removing vehicles in the previous year will be 6741, and 33.7 tons of oil will be lost in one year. Product. In this case, the method of collecting the oil by the pump is adopted. However, during the operation, because the pump running speed cannot be controlled, strong vibration often occurs, which seriously damages the operation of the pump and affects the effect of oil collection. To this end, this paper will propose a solution to this problem, and introduce the methods and theories in detail.

First, the reason why the pump is equipped with frequency conversion

When the residual bottom oil of the tank car is swept by the oscillating rotor pump, since the diameter of the sweeping hose is small, when the whole liquid flows, the vacuum of the pump inlet is too high, which causes the problem of pump vibration and noise increase. The swept rotor pump is used for gas-liquid mixing. Therefore, the cavitation performance of the pump must be considered. When the tank bottom oil is too much, the sweep hose is full and the pump inlet vacuum is high. When the vacuum exceeds the pump cavitation point. The vibration and noise of the pump will increase. Therefore, the swinging rotor pump needs to adjust the running speed of the motor at any time in order to control the vacuum of the pump inlet, to achieve smooth pump operation, improve efficiency, and reduce noise. In this case, the inverter and the three gauge pressure transmission are configured. Adjust with the PID controller.

Second, the principle of PID controller

The PID controller (Proportion Integration Differentiation proportional-integral-derivative controller) is composed of a proportional control unit P, an integral control unit I and a differential control unit D, and collects the collected data by the parameters K, Ti, and Td, respectively. The preset empirical values are compared, and the result of the comparison is calculated to generate a new value as an input signal. The purpose of this new input value is to stabilize the system within a certain range of set reference values, which makes the system more accurate and more stable. PID control system is characterized by simple principle, convenient use and strong applicability.

1. The specific meaning of PID. The proportional control unit P is characterized by rapid response, but there is a static difference to the controlled object having self-balancing. Increasing the integral adjustment unit I plays a positive role in eliminating the static difference, but reduces the response speed of the system. In order to solve this problem, it is necessary to respond to the deviation before the occurrence of the deviation, and also to judge and control the variation trend of the deviation, and then increase the differential control unit D. In summary, in order to achieve the control effect, the PID controller should be selected. PID is named after the algorithm of proportional, integral and differential functions. These three parameters are the key to achieving high performance algorithms. These three algorithms are:

1.1 Proportional control unit: proportionally reflects the deviation of the system. Increasing the proportional coefficient can reduce the steady-state error of the system, improve the control accuracy of the system, and speed up the response. However, too large a scale factor will cause the stability of the system to decline, and even the system is unstable.

1.2 integral control unit: mainly to make the system eliminate the steady-state error and improve the steady-state performance of the system. The strength of the integral action depends on the integral time constant T, the smaller the T, the stronger the integral action, and vice versa, the weaker the effect. The integral action reduces the stability of the system and slows the dynamic response. Therefore, the integral link is usually used in combination with the other two regulators.

1.3 Differential control unit: The differential action reflects the trend of the deviation signal and is predictive. Appropriate differential adjustment can improve the dynamic performance of the system and reduce the adjustment time. However, excessive differential regulation is unfavorable to system interference.

2. Set the PID parameters of the instrument. The process PID is used for the control of pressure process variables. The proportional link produces a control effect proportional to the deviation to reduce the deviation; the integral link is mainly used to eliminate the static difference. The larger the integration time, the weaker the integral effect, the shorter the integration time, the stronger the integral action; the differential link passes the deviation The change trend predicts the change of the deviation signal, and generates a control signal for suppressing the variation change before the deviation becomes large, thereby accelerating the response speed of the control.

PID parameter adjustment principle:

Adjustment of the proportional parameter. First increase the proportional gain from a small value such as (0.20) until the feedback signal begins to oscillate, then reduce the feedback signal by 40-60%, and set the larger value of the proportional coefficient P to cause the system to be unstable and frequently oscillate; Small, and will reduce the sensitivity of the system. Appropriate setting of the scale factor will make the system sensitive enough but not too sensitive. The delay of a certain time is adjusted by integrating the integral time and adjusting the differential parameters. The integration time is from a larger value (such as 20.00s) until the feedback signal begins to oscillate, and then increases by 10-50% to stabilize the feedback signal. If the adjustment of the proportional and integral parameters still does not meet the ideal control requirements, and the system requires high overshoot and dynamic error, it is necessary to increase the differential unit (some systems require time lag, only need to add this parameter), you can pass Adjust the differential time parameters, from small to large when initial debugging, and gradually adjust the method until the system is stable.

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