Application of the latest intelligent valve positi

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Application of new intelligent valve positioner in regulating valve

control valve is mainly divided into electric regulating valve and pneumatic regulating valve according to the driving mode, so as to adapt to different working conditions and process requirements. Electric regulating valve generally drives the valve directly by the angular stroke electric actuator, and controls the opening of the valve through 4 ~ 20mA or 0 ~ 10V analog signal, so as to achieve the purpose of control. The valves used in angular stroke control mainly include ball valve, butterfly valve, etc. The electric control valve is simple to operate and does not need compressed air, but its response speed is slow and its control accuracy and regulation performance are poor. It is only used in some workplaces with low requirements for control accuracy and low action frequency. Comparatively speaking, pneumatic control valve is widely used in the field of process control in all walks of life because of its high control accuracy, fast response speed, good working stability and wide range of applications

as the brain of the regulating valve, the valve positioner plays a decisive role in the control performance and field function of the whole control valve. Compared with the traditional electro pneumatic conversion valve positioner, the intelligent valve positioner has a wider application and market prospect in the control accuracy, response speed, function expansion, improvement of valve automation control level and so on. Therefore, intelligent valve positioner is regarded as the development direction of valve positioner in the future

new intelligent valve positioner

different intelligent valve positioners not only have similarities in structure and function, but also have their own characteristics

common points:

■ as a standard valve positioner (function of electric pneumatic converter), it can be widely used in the position control of various process control valves with pneumatic actuators

■ as a process controller (with PID function), it forms an intelligent regulating valve with the valve with pneumatic actuator. It can directly receive the real-time process value signal of the sensor and form a relatively independent complete process control loop with the sensor to realize the closed-loop control function

■ it can be combined with the valves of the straight stroke pneumatic actuator, such as angle seat valve, stop valve, diaphragm valve, etc., and the valve positioning control system is composed of external line position sensors; It can also be combined with the valves of angular stroke pneumatic actuators, such as ball valves, butterfly valves, and diaphragm pneumatic control valves, and the valve positioning control system is composed of built-in angular stroke sensors

■ it can be used not only for single acting actuator valves, such as normally open or normally closed valves, but also for the control of valves or cylinders of double acting actuators

■ with analog position feedback output and two binary output signals. The position feedback signal can feed back the actual position or actual process value of the valve to the PLC or controller, which is convenient for system information collection and monitoring. The binary output signal can expand the control function of the regulating valve and improve the automation of the system

■ good man-machine interface, easy to operate; Large screen digital liquid crystal display, real-time display of set and actual values, and display of valve ambient temperature; The three key menu indicates the operation, which is convenient for on-site debugging and maintenance

feature introduction:

1067 intelligent positioner (Figure 1):

Figure 1 1067 intelligent positioner

■ three wire controller, 24VDC working power supply and additional external setting signals

■ standard configuration with integrated process controller function (PID)

■ quick exhaust valve can be selected for valve control of larger actuators

■ standard Namur and din IEC connection interface, suitable for valve control of third-party companies

■ acceptable external setting signal (position value/process value): 0/4 ~ 20mA, 0/5 ~ 10VDC

■ acceptable sensor signal (actual process value): 4 ~ 20mA, which can realize split installation and control

8630 intelligent positioner (Figure 2):

■ three wire controller, optional fieldbus control: PROFIBUS DP or DeviceNet

■ optional process controller function (PID), including process self-tuning function

■ acceptable external setting signal (position value/process value): 0/4 ~ 20mA, 0/5 ~ 10VDC

■ can accept a variety of sensor signals (actual process value): 4 ~ 20mA/PT100/frequency

■ optional explosion-proof standard: II 3g/d Eex T4

8635 intelligent positioner (Figure 3):

■ standard two-wire controller, working power from 4 ~ 20mA or PROFIBUS Pa

■ low power design (12.5 MA)

■ optional intrinsically safe explosion-proof standard: Eex ia IIC t4/t5/t6 (intrinsically safe) version with the variety of plastic building materials, it is gradually serialized, matched and standardized on, ATEX, FM

■ safe structural design, all aluminum shell, internal display, which can work stably in harsh field environment

■ standard Namur and din IEC connection interface, suitable for valve control of third-party companies

■ it can accept a variety of sensor signals (actual process value): 4 ~ 20mA/PT100/frequency

additional functions:

in addition to meeting some conventional functions and control of the regulating valve, the above intelligent positioners can also realize some special additional functions through software under the control of a powerful microprocessor, so as to improve the control accuracy and automation of the whole regulating valve. It has good controllability and powerful system functions in some complex process control systems and control systems with special process requirements

■ flow characteristic curve

this additional function allows the user to select a conversion characteristic curve (linear/proportional characteristic curve) of the relationship between the valve setting value and the valve stroke, or it can be defined by the user (freely programmable characteristic curve)

the flow characteristic curve of the valve reflects the relationship between the valve flow (Kv value) and the valve stroke, which is determined by the shape of the valve body and valve core. There are generally two kinds: linear and equal ratio. In the linear characteristic curve, equal valve stroke changes produce equal flow changes. Some companies have planned to realize the commercial production of 2,3-bdo in the next 2 (3) years; In the equal percentage characteristic curve, the change of valve stroke corresponds to the equal percentage change of flow value

therefore, in order to meet the requirements of some special processes, such as sterilization, temperature control system of heat exchanger, titration system of acid-base neutralization, etc., higher requirements are usually put forward for the flow characteristic curve of the valve. The intelligent positioner can set a linear curve and a variety of equal percentage characteristics, and the adjustment ratio is 1: 25/1: 50/25: 1/50: 1. In addition, the intelligent positioner also has a freely programmable characteristic curve. According to the specific valve and application, the user divides the setting signal into 21 set points with an interval of 5% according to 0~100%. The stroke of the valve can be redefined at each set point, but the stroke difference between two adjacent set points cannot exceed 20%

■ valve close function

this function can keep the control valve closed or stable outside the control signal range. The variation range of the control signal of the regulating valve is 0 ~ 100%, but generally, the control signal of a regulating valve is rarely used to the limit position (0 and 100%). Moreover, under the limit state, some weak interference signals may cause the valve to malfunction or fail to close, resulting in leakage. Therefore, using this function can ensure that the valve remains closed or stable when the control signal does not exceed the set tight closing range

■ valve stroke limit

this function can set the upper and lower limits of the physical stroke of the valve, corresponding to the range of the input signal. Generally, the stroke of a regulating valve (0 ~ 100%) corresponds to the change of control signal (0 ~ 100%). However, in some system transformation or design selection, we will encounter the embarrassing situation of large pipeline and small flow. When the pipeline has been installed and the valve has been finalized, in order to realize the precise control of small flow without changing the valve and pipeline, this function can be used to set the travel range of the valve between 0 ~ 50%, while the control signal range remains unchanged. In this way, the requirements of small flow control are guaranteed without losing the resolution of valve control

■ safety position setting

this function can set the safety position of a regulating valve in the system emergency state or valve failure state. Using this function, the valve can be controlled by a binary input signal with the highest priority, and the valve can be controlled at the preset position of 0 ~ 100%, which does not depend on the external control signal of the valve. This enables the valve to ensure the normal operation of the system in some specific application environments, such as the uninterruptible oil supply system of the kiln combustion system, the cooling and lubrication system of large generators, etc., even in the case of failure or emergency

■ password protection function

this function can set a password for the intelligent positioner, but it does not affect the normal operation display of the positioner and the conversion of manual/automatic working state. It only protects the parameter setting interface to avoid screening the stone chips in the sample. Ordinary operators mistakenly modify the working parameters of the valve in the process of use, resulting in unnecessary system failures and production losses. Only authorized technicians can enter the parameter setting state through password, and adjust the parameters of the valve according to the process requirements

with the help of corresponding additional functions, combined with the requirements of on-site production process and the control process of the system itself, the control accuracy and control performance of the regulating valve can reach the best state, and the process control level of the whole system can reach a new height. (end)

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