Pneumatic valve positioner and pneumatic actuator

Pneumatic valve positioner and pneumatic actuator

Mathematical model of electric pneumatic valve positioner and pneumatic actuator

The electric pneumatic regulating valve positioner is used in conjunction with the pneumatic diaphragm actuator. The positioner converts a standard signal of 4~20 Am into a standard pressure signal of 0.2~1 Pa to change the displacement of the valve stem of the pneumatic actuator. The valve stem displacement is then fed back to the input end of the positioner through a mechanical feedback part, forming a closed-loop system with negative feedback [2-3]. The difference between the electric pneumatic valve positioner and the pneumatic valve positioner introduced earlier is the device for inputting signals. The device for inputting pressure signals into pneumatic valve positioners is a bellows, while the device for inputting pressure signals into electric pneumatic valve positioners is a torque motor, resulting in different input torques for the two types of positioners. Based on the input-output relationship function of the former, the input signal of the pneumatic valve positioner to the output torque part equation (1) is transformed into the output torque equation (2) of the electric pneumatic valve positioner, and the relationship between the input quantity I of this type and the output quantity L of the pneumatic valve can be obtained as shown in equation (3):

3.3 Simulation of valve body

The flow characteristic curve of the valve body is divided into four types: linear, quick opening, parabolic, and equal percentage. The flow characteristics of valves are mainly related to the shape of the valve core and the manufacturing process of the manufacturer [2], so the referenced function is obtained by interpolating the flow characteristic curve provided by the manufacturer after taking points.  

Method of joint simulation between actuator and valve body

Connect the simulation of the actuator and valve body of the regulating valve together to obtain the overall simulation function, as shown in Figure 6. Since the (l, Q) curve is provided by the manufacturer, l and Q are known values, while Ii is the input value. Therefore, by taking a certain step size from l=f (Ii), l can be obtained from Ii, and then the value of Q can be found through the (l, Q) curve, thus obtaining the point set (Ii, Q). The final input-output curve is shown in Figure 7 (taking the 48-41000 series of Shanghai Automation Instrument Co., Ltd. as an example).

Simulation of Control Valve Malfunctions

In order to enable users to have a more accurate understanding of the principles and phenomena of faults in actual industrial and mining situations, and to achieve the goal of preventing problems from escalating, this article has added a fault simulation section. On the basis of simulating the input and output relationship of the regulating valve, perform fault simulation on the regulating valve. The faults in this system are mainly caused by changes in simulation parameters. When a component in the regulating valve is damaged or worn, its corresponding constant will inevitably change, which will lead to changes in the transfer function of the regulating valve, ultimately reflected in the input-output curve, forming the corresponding faults.

The relationship (partially) between variables and faults of various regulating valves studied by this software under constant other parameters is shown in Table 1. For example, when the fault is set as damage to the bellows, the parameters become smaller, and the fault is manifested as a decrease in the slope of the input-output curve on the curve.

In the process of selecting regulating valves, this system has achieved: (1) Users can learn regulating valve selection or conduct self testing with or without assistance. (2) Users can conduct tests on the selected regulating valve under different media and form a relationship curve between input current, voltage, or pressure and output flow rate. (3) The user sets the fault and observes the fault phenomenon curve. This selection system can play a good teaching role, with advantages such as economy, speed, and safety, and is closely related to actual production, serving as a warning for faults.