News - The control valve positioner Selection Guide

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Home > News > The control valve positioner Selection Guide

The control valve positioner Selection Guide - 2013-12-13 10:26:20

Positioner ( also known as : pneumatic valve positioner ) is the main regulator valve attachment , usually associated with supporting the use of pneumatic control valve , which accepts the output signal of the regulator , then its output signal to control the pneumatic control valve, when the control valve after the action , the displacement of the valve stem and feedback by mechanical means to the valve positioner , valve position status to the host system via electrical signals .

In many control applications , the valve control valve positioner is one of the most important accessories. Especially for a particular application , if you want to choose the most suitable valve positioner, then consideration should be given to the following factors :

1 ) The positioner can achieve "Split (Split_ranging)" achieve " Split" is easy and convenient with the "Split " function means that the valve positioner only a certain range of the input signal ( eg : ? 4 ~ 12mA or 0.02 ~ 0.06MPaG) responding. Therefore, if we can , " Split" , then it can be based on actual needs , achieve only one input signal has two or more control valve .

2 ) locator zero and span adjustment is easy and convenient is not without opening the lid to complete the zero and span adjustment but it is worth noting: ? Sometimes in order to avoid incorrect ( or illegal ) operation, this adjustment can be carried way above needs to be disabled .

3 ) How stable positioner zero and span ? If the zero and span easy to change with temperature, vibration, pressure and time, or enter drift , then the valve positioner often need to be recalibrated to action to ensure the accuracy of the control valve stroke .

4 ) precision positioner in ideal conditions, corresponding to a given input signal, adjusting the valve assembly (TrimParts, including ball / spool , stem, seat , etc. ) should be accurately positioned in each required position , regardless of the direction of travel of the valve member or the inner bear much load.

5 ) How positioner on air quality requirements since only a handful of gas supply device can provide to meet the ISA standard ( relevant instrument air quality standards :? ISA standard F7.3) required by air , therefore, for pneumatic ( or electric - gas ) valve positioner , if you want to stand the test of reality , we must be able to withstand a certain amount of dust , moisture and oil.

6 ) zero and span calibration of both influence each other or independently of each other ? If mutual influence, the zero and span adjustment will need to spend more time , this is because these two parameters adjustment must be repeated adjustments in order to gradually achieve accurate settings.

7 ) whether the positioner with "bypass" that allows input signals direct role in regulating valve this " bypass" or sometimes eliminating the need to simplify the setting of the actuator assembly verification , such as: ? Implementing agencies ' support seat assembly set "and" spring load settings " - this is because in many cases , some of the pneumatic actuator pneumatic actuator output signal " carriage assembly set a "perfect match to match , do not need them then set ( in fact , in this case , the positioner completely dispensed with , of course , if selected , then the positioner can also use the " bypass" pneumatic actuator pneumatic output signal of the direct effect in valve ) . In addition , with the "bypass" is sometimes permissible line valve positioner limited adjustment or repair and maintenance ( ie, the use of the valve positioner " bypass" valve to maintain normal operation , no need to force the valve offline ) .

8 ) valve positioner is fast ? Air flow (Airflow) larger ( positioner continuously compares the input signal and valve position , and according to the deviation between them, adjust its own output if this positioner misalignments fast response , then the flow of air per unit of time on the big ) , response regulator system set point and load changes , the faster - which means that the system error ( lag ) smaller , better quality control .

9 )Frequency characteristic 9 ) valve positioner (or frequency response , FrequencyResponse - namely G (jω), the steady-state response to sinusoidal input ) What is the general, the higher the frequency characteristics ( ie, frequency response sensitivity ? higher ) , the control performance is better. It must be noted : a stable frequency characteristics of the experimental method should be used instead of the theoretical method to determine and assess the determination of the frequency characteristics should positioner and actuator combined consideration.

10 ) The maximum rated supply pressure valve positioner is the number for example : ? Some positioner maximum rated supply pressure is only calibrated to 501b/in2 ( ie : 50psi, lpsi = 0.070kgf/cm2 ≈ 6.865kPa), if executed higher than the rated operating pressure mechanism 501b/in2, then the positioner on the actuator output constraints become the driving force .

11 ) When the valve assembly in combination with a positioner , their positioning resolution (PositioningResolution) How ? This quality control system for regulating a very significant role, because the higher the resolution , the more control valve positioned close to the ideal value , because the control valve fluctuations caused by overshoot curb can be obtained , and eventually reaches the limit amount is adjusted periodically varying purposes.

12 ) positive and negative effects positioner conversion is feasible ? Conversion is easy ? Sometimes this feature is necessary. For example, to a " signal increases - the valve off " approach to " signal increases - the valve open " approach , you can use the positive and negative effects positioner conversion function .

13 ) How positioner operation and maintenance of the internal complexity of ? As we all know , the more parts, the more complex the structure of the internal operations of maintenance ( repair ) , the more the valve technical training of personnel , and the more spare parts inventory .

14 ) valve positioner parameters for the steady-state air consumption of this device is very critical of certain plants , and may be a limiting factor.

15 ) Of course , in the evaluation and selection of valve positioners, other factors should also be considered . For example : valve positioner feedback linkage (FeedbackLinkage) true position to be able to react spool ; addition , the positioner must be durable, with environmental protection and anti- corrosion ability, and easy installation and connection convenience . Our Water Pumping Station and abrasion status quo.

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