CN105605289A - Three-breaker protection circuit of industrial pneumatic control valve actuating mechanism - Google Patents

Abstract

The invention provides a three-break protection circuit for an actuator of an industrial pneumatic control valve, which includes a control circuit composed of a displacement locator, a valve position feedback device, a filter pressure reducing valve, a signal comparator, a three-way solenoid valve, a pressure switch and an air lock valve. , the upper level of the signal comparator is connected to the DCS control center, and then sends out two electrical signals, one of which is a command signal of 4-20mA is sent to the intelligent positioner, and the other is sent to the three-way solenoid valve, and the three-way solenoid valve is sent to the upper level Connect the control air source from the filter pressure reducing valve, the lower level is connected to the pressure switch, the lower level connection device of the pressure switch is an air lock valve, the upper level of the air lock valve is connected to the displacement positioner, and the lower level is connected to the air intake chamber of the pneumatic actuator, and the pneumatic actuator Drive the valve stem to adjust up and down. The beneficial effect of the present invention is that: when the control valve subsystem loses input power, input signal and gas source, it can safely realize self-protection, that is, "valve position retention", so as to prevent the process control system from being damaged.

Description

A three-break protection circuit for an industrial pneumatic control valve actuator

technical field

The invention relates to an executive mechanism of an automatic control intelligent digital pneumatic control valve in an important occasion in the application of industrial process control, which implements self-maintenance when the system fails, so as to prevent the control system from being damaged.

Background technique

Control valves are an increasingly important component of modern manufacturing around the world. Correctly sized and maintained control valves contribute to increased efficiency, safety, profitability and ecological protection. A process plant is composed of hundreds or even thousands of control loops, all of which are connected into a network and operated through a central console to produce salable products, including chemicals, oil refining, electricity and food, etc. Wait.

Each control loop is designed to ensure that important parameter variables such as pressure, flow, liquid level and temperature do not exceed the required operating range, so as to ensure the quality of the final product, each loop will accept and generate disturbances from within, These perturbations can have a deterministic effect on the process variable, and interactions between other loops in the network can also produce perturbations that affect the process variable.

To reduce the effects of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to the desired set point. The controller then processes this information and decides what must be done to bring the process variable under load. Returns to its normal range after the disturbance. The control valve assembly is the terminal element to realize the recovery process, and the control valve assembly includes: a valve body, an actuator and a control accessory, and the present invention is aimed at the control accessory.

Contents of the invention

The purpose of the present invention is to provide an actuator for automatic control of intelligent digital pneumatic control valves in important occasions, in the application of industrial process control, which is different from the control valve in ordinary occasions being set to open or close when air is lost. When the control valve subsystem fails, the valve position is implemented to avoid extreme situations such as explosion of the control system, overflow of dangerous liquid, or rotor flying.

To achieve its purpose, the present invention provides a control circuit comprising a displacement positioner, a valve position feedback device, a filter pressure reducing valve, a signal comparator, a three-way solenoid valve, a pressure switch, and an air lock valve. The upper level of the comparator is connected to the DCS control center, and the signal is re-adjusted inside it, and the signal distortion caused by various interferences on the filtered communication line is sent out, and then two electrical signals are sent out, and the command signal of 4-20mA is sent to the smart computer. The positioner is used to control its action, and the other is sent to the three-way solenoid valve to control its action. The upper level of the three-way solenoid valve is connected to the control air source from the filter pressure reducing valve, and the lower level is connected to the pressure switch. The lower level of the pressure switch is connected to The device is an air lock valve. The upper level of the air lock valve is connected to the displacement locator, and the lower level is connected to the air intake chamber of the pneumatic actuator. The pneumatic actuator drives the valve stem to adjust up and down. The control center sends back 4~20mA electrical signals, and forms a closed-loop system with the DCS control center.

Furthermore, the three-break protection circuit also includes an open-loop control system composed of a signal comparator, a three-way solenoid valve, a pressure switch, and corresponding pipelines and circuits, so that when the control valve subsystem loses power, loses When the input signal and the displacement locator lose the gas source, the self-protection can be safely realized, and the pressure switch has a danger alarm function.

After testing, it is found that the best control curve of the control valve is: equal percentage characteristic curve, and the other two characteristic curves: linear curve and quick opening curve are not the best control curve. The optimal ideal opening of the control valve is: 40%-60%. In practice, the set point is often in the range of 25%-75%. Too large or too small opening is not conducive to achieving good control of the system.

The present invention takes the control valve with equal percentage characteristic valve cage as the object, and designs a set of control loop on the premise that the control valve realizes the optimal opening degree, that is, the optimal control through the positioner and the valve position feedback device. The feature is different from the ordinary control loop, compared with the ordinary control loop, the signal comparator, three-way solenoid valve, pressure switch and corresponding pipelines and circuits are added.

g On the basis of the open-loop control system composed of ordinary loops, the present invention adds another open-loop control system composed of signal comparators, three-way solenoid valves and pressure switches, as well as corresponding pipelines and circuits, and is integrated with the DCS control center A closed-loop system is formed to make the accessory system of the control valve more perfect. The pressure switch in the system composition has a danger alarm function, which can send the alarm signal to the DCS control center, and the center will respond to the failure of the control valve subsystem caused by power failure, signal failure and loss of gas source according to the control strategy set by the system. After the calculation is completed, the DCS control center sends a new command signal or repair signal to the failed control valve subsystem.

Description of drawings

Figure 1. Control valve inherent flow characteristic curve;

Figure 2. Schematic diagram of the three-break protection of the control circuit of the intelligent pneumatic actuator;

Figure 3. Schematic diagram of the ordinary control circuit of the intelligent pneumatic actuator;

1, 2, and 3 in the figure represent Line 1, Line 2, and Line 3, respectively.

detailed description

The principle of the present invention will be further elaborated below in conjunction with the accompanying drawings and embodiments.

Example 1

As shown in Figure 2, a control circuit comprising a displacement positioner, a valve position feedback device, a filter pressure reducing valve, a signal comparator, a three-way solenoid valve, a pressure switch, and an air lock valve, the signal comparator The upper level is connected to the DCS control center, and the signal is re-adjusted inside it, and the signal distortion caused by various interferences on the filtered communication line is sent out, and then two electrical signals are sent, and the command signal of 4-20mA is sent to the intelligent positioner. , to control its action, and the other is sent to the three-way solenoid valve to control its action. The upper level of the three-way solenoid valve is connected to the control air source sent from the filter pressure reducing valve, and the lower level is connected to the pressure switch. The lower level connection device of the pressure switch is Air lock valve, the upper level of the air lock valve is connected to the displacement locator, and the lower level is connected to the air intake chamber of the pneumatic actuator. The pneumatic actuator drives the valve stem to adjust up and down. Send back 4 ~ 20mA electrical signal, and form a closed-loop system with the DCS control center.

In the case of failure of line 1: when the whole system is running normally, the DCS control center sends a 4~20mA command signal to the signal comparator in this subsystem, and the signal comparator is sent to the positioner after the signal comparator is set. The positioner passes this signal through the internal electrical/pneumatic replacement components to open the intake air source, and the air source enters the inner cavity of the actuator through the air lock valve, and the diaphragm in the inner cavity is squeezed by the gas, and starts to drive the valve stem to move , the valve starts to adjust the flow, the fluid pressure decreases from the inlet pressure P1 to the outlet pressure P2, and the system starts to work normally. When the No. 1 line fails and the power is cut off, the signal comparator detects that the solenoid valve group has no feedback signal, and immediately sends out a message of "loss of input power signal", and the solenoid valve performs a deflation action after power failure (preset ), which causes the air lock valve to start and lock, and realize the valve position retention. At the same time, after the pressure switch detects the pressure change of the gas circuit, it sends an alarm signal to the control center, and the valve position retention is completed.

Example 2

As shown in Figure 2, in the case of a failure on line 2: when the entire system is running normally, the DCS control center sends a 4-20mA command signal to the signal comparator in this subsystem, and the signal comparator is set and then turned on. This signal is sent to the positioner, and the positioner passes the signal through the internal electrical/pneumatic replacement components to open the intake air source, and the air source enters the inner cavity of the actuator through the air lock valve, and the diaphragm in the inner cavity is squeezed by the gas. Pressure starts to drive the valve stem to move, the valve starts to adjust the flow, the fluid pressure decreases from the inlet pressure P1 to the outlet pressure P2, and the system starts to work normally. When there is a failure signal on line 2, the signal comparator detects that the positioner has no feedback signal, and immediately sends a message of "lost input control signal", and at the same time directs the solenoid valve to perform a deflation action (preset), so that The air lock valve is activated and locked to realize the position retention of the valve. At the same time, after the pressure switch detects the pressure change of the air circuit, it sends an alarm signal to the control center, and the position retention of the valve is completed.

Example 3

As shown in Figure 2, when line 3 fails:

When the whole system starts normally, the DCS control center sends a 4-20mA command signal to the signal comparator in this subsystem, and the signal comparator sends this signal to the positioner after the signal comparator is set, and the positioner passes the signal through the internal electric circuit /Pneumatic replacement of components, open the intake air source, the air source enters the inner cavity of the actuator through the air lock valve, the diaphragm in the inner cavity is squeezed by the gas, and starts to drive the valve stem to move, the valve starts to adjust the flow rate, and the fluid pressure is controlled by The inlet pressure P1 is reduced to the outlet pressure P2, and the system starts to work normally. When the No. 3 line fails and the gas source is cut off, it will directly cause the air lock valve to start and lock to realize the position of the valve. At the same time, after the pressure switch detects the pressure change of the gas circuit, it will send an alarm signal to the control center, and the valve will Position is complete.

It should be noted that the preferred embodiments of the invention include the best mode known to the inventors for carrying out the invention. Variations of the preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled practitioners to employ such modifications appropriately, and the inventors believe that the invention may be practiced otherwise than as expressly described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims as permitted under applicable law. Moreover, any combination of all possible variations of the above-described elements is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims (2)

1. A three-break protection circuit for the actuator of an industrial pneumatic control valve, including a control circuit composed of a displacement positioner, a valve position feedback device, a filter pressure reducing valve, a signal comparator, a three-way solenoid valve, a pressure switch, and an air lock valve. It is characterized in that: the upper level of the signal comparator is connected to the DCS control center, and the signal is re-adjusted inside it, and the signal distortion caused by various interferences on the filtered communication line is sent out two circuits of electrical signals, one of which is 4~ The 20mA command signal is sent to the intelligent positioner to control its action, and the other is sent to the three-way solenoid valve to control its action. The upper level of the three-way solenoid valve is connected to the control air source from the filter pressure reducing valve, and the lower level is connected to Pressure switch, the lower-level connection device of the pressure switch is the air lock valve, the upper level of the air lock valve is connected to the displacement locator, and the lower level is connected to the air intake chamber of the pneumatic actuator, the pneumatic actuator drives the valve stem to adjust up and down, and the valve position feedback device detects After the movement of the valve stem, a 4-20mA electric signal is sent back to the DCS control center to form a closed-loop system with the DCS control center. 2. A three-break protection circuit for an actuator of an industrial pneumatic control valve according to claim 1, characterized in that: the three-break protection circuit also includes a signal comparator, a three-way solenoid valve and a pressure switch with corresponding pipelines The open-loop control system composed of the control valve subsystem and the circuit can safely realize self-protection when the control valve subsystem loses the power supply, the input signal and the displacement positioner lose the air source, and the pressure switch has a danger alarm function .