INTRODUCTION Intelligent valve positioner is a new generation of products, its working principle, structural characteristics, compared with conventional electrical valve positioner is very different, and therefore encountered some new problems in use This paper combines me unit installed more than 100 FISHER company and Successful applications and typical malfunctions of more than 20 intelligent valve positioners manufactured by NELES, discuss the following issues of intelligent (analog signal overlay digital signal) valve positioners. 1. Structure Principle A new generation of intelligent valve positioner is based on the microprocessor reads the input signal (mA), the position sensor position signal, and the pressure sensor output pressure signal is processed to generate a drive signal, the actuator action. Now choose the more representative meaning slider type DVC5000 and rotating type ND800 to be described in detail. 2.DVC5000 digital valve controller has a separate module base, which can be easily replaced in the field without having to demolish the scene of the wire or catheter. The module base includes sub-modules: I / P converter; PWB (printed circuit board) assembly; pneumatic relay; indicator. The module base can be reassembled by changing modules. The FIELDVUE family of digital valve controllers accepts both input and electrical power by entering a pair of twisted pairs in the terminal box and simultaneously feeds the signal to the PWB component submodule where it is appended with many parameters such as node coordinates in multi-section linearisation, Limits and other values. The PWB component submodule then sends a signal to the I / P converter submodule. I / P converter to change the input signal into a pressure signal. The pneumatic signal is sent to the pneumatic relay, amplified and sent to the actuator as an output signal. This output signal can also be sensed by pressure-sensitive components mounted on the PWB subassembly. Diagnostic information for valve actuators. Valve and actuator stem position as the input signal into the PWB sub-module, used as a digital valve controller feedback signal, and the input signal value comparison, if there is deviation, the microprocessor through the operation to generate a new current value To correct the deviation, until the valve position valve signal and the input signal is consistent, the deviation is zero. (ÎœC) for the ND800 By changing the control current of the pre-stage (PR) coil, the pre-stage valve reduces the control pressure at the SV terminal. The spool moves in the low pressure direction and opens to the top of the actuator cylinder And opens the flow of air from the other side of the piston, increasing the differential pressure on the piston to move the piston. The microprocessor uses control to calculate a new control current until the actuator's new position signal coincides with the input signal. The spool valve (SV) is in its steady state and the PR valve is closed. 2. Performance Due to the intelligent valve positioner, a new generation of microprocessor-based products with high accuracy of the valve position signal sensor output pressure sensor, which has a high control accuracy of (0.5-1%), (conventional Electrical valve positioner accuracy of only 2-5%), and has long-distance configuration, commissioning, diagnosis, data management and other operations. After more than a year of operation, compared with ordinary valve positioner performance, usage, cost performance and other aspects were compared. 3. Rich software features Intelligent valve positioner has a wealth of software features, such as automatic adjustment of zero and full scale; configuration required valve characteristics, coupled with special software such as FISHE intelligent positioner VAVLELINK software; NELE intelligent locator VAVLEMANAGE TM software nine advanced dynamic diagnostic features, the valve mechanical properties and control system indicators combined to determine the valve damage. 4. Intelligent Valve Positioner and DCS Connection Matching Impedance Conventional electrical positioner general input impedance of 250 ohms, and intelligent positioner input impedance greater than 250 ohms, different brands, different models, different impedances, the expression is different. The greater the impedance, the greater the DCS load capacity, the system operation is affected. When the mechatronic circuit of our plant is linked and adjusted, the DCS output card can only drive the NELES ND8221 / S1 positioner control valve to operate only 28% Stroke, specific solutions, replacement drive greater security (less internal resistance) to reduce the safety of Shan in the regulation circuit to increase the partial pressure on the intelligent positioner output power. The following is a list of the input impedance of some well-known smart valve positioners. 5. Device and transmission of intelligent valve positioner valve position detection Accurate valve position signal is an important parameter of the control system is an important parameter to form advanced dynamic diagnostic function. Therefore, the valve position detection of high-precision measurement and transmission. Various brands, different models of valve position detection device, the feedback signal transmission is different. 6 intelligent positioner intelligent features 1.2.1 real-time information control, improve safety and reduce expenses 1) to improve control: the two-way digital communication to the valve current information to you, you can rely on the valve work information base for process control Manage decisions and ensure timely control. 2) Increased safety: You can use your terminal, PC or system workstations to select information from field junction boxes, terminal strips or in a safe area such as a control room to minimize your chances of facing a hazardous environment without having to visit on site. 3) Protection of the environment: Valve leakage detector or limit switch can be connected to the intelligent digital valve controller auxiliary terminals, so as not to increase the field wiring, the instrument will alarm if the limit occurs. 4) Save Hardware Costs: When the FIELDVUE Series Digital Valve Positioner is used in an integrated system, hardware and installation costs can be saved by replacing the regulator with a FIELDVUE digital valve controller. The FIELDVUE family of digital valve controllers saves investment in wiring investment, terminal and I / O requirements by 50%. While FIELDVUE meter with two-wire power supply, does not require separate and costly power supply wire. They replace existing analog valves fitted to the valve, saving the high cost of laying separate power cords and signal cables. 7. Intelligent valve positioner common fault and on-site processing (1) control signal changes, the control valve does not move (excluding valve body factor) is intelligent locator DVC5000 common faults in the process of operation, approach, focusing on checking the valve position sensor is running Free, electrical continuity, etc. (2) valve position is difficult to control, small signal does not move, the signal is not fully open or not fully closed, after many adjustments are still not normal, the replacement of the new locator is still not normal, replace the new Of the locator is still not normal, and finally found ND800 intelligent locator feedback lever and locator internal signal conversion part of the non-contact induction connection. The feedback lever can be rotated by 360 degrees, resulting in a difference of 180 degrees between the feedback lever and the stem, and the re-installation and adjustment work is normal (3) Small opening oscillation. Regulating valve work in a small opening easily lead to oscillation. The solution is to avoid the small opening work, flow closed type to open the flow, more trouble. The smart locator to solve such problems seem more relaxed simply set the parameters, the oscillation has been greatly improved. DVC5000 is used as an example to illustrate the use of HART275 terminal adjustment DVC5000 positioner, online, select STABILIZE / OPTIMIZE by shortcut key, select DECREASE RESPONSE (lower response sensitivity 0, select the lower set of tuning parameters to be improved (4) Intelligent valve positioner can not communicate with HART275 normally Common reasons Check the effective voltage in the field is greater than 12V, the output impedance is less than 250 ohms, the wire capacitance is too high, the input signal is less than 4mA, etc. 8. Application And maintenance DVC5000 intelligent valve positioner installed in April 2002 for use in our company melamine plant used in more than 100. Using a handheld device to configure and verify it, the linearity of up to 99%, zero and range And hysteresis can be controlled within the accuracy requirements of the extremely stable control and anti-interference ability is also very strong, fully meet the process control requirements. FIELDVUE locator maintenance is minimal, essentially maintenance-free. Its on-site adaptability But in order to ensure long-term, stable operation, instrumentation staff should do the following aspects of the work. In order to ensure a good working environment, to prevent accidental damage, you should check around the locator work environment on a regular basis. At the same time, it ensures the stability and cleanness of the working air source and reduces the fluctuation and malfunction of the instrument caused by external factors. 2) The instrumentation staff should check the leakage and working condition of the valve and locator weekly to eliminate the hidden danger in time. Every month, use the hand terminal to check the characteristic curve of the positioner, check parameters such as zero point, span, linearity and hysteresis, and optimize and adjust them to ensure the quality of their work. 3) regular maintenance and maintenance of the control valve to ensure the quality of the valve work. At the same time, the DCS control loop parameters are optimized to ensure the coordination and stability of the positioner working with each other. 4) Due to DCS and other reasons, the fieldbus and software functions we have not fully developed and utilized, can not be fully used for intelligent maintenance and diagnostic functions, but still greatly reduce the daily maintenance. Through the past two years in the use of melamine plant results point of view, intelligent valve controller stable performance, easy adjustment.
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