control valve positioner

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    Control valve positioner  I would like to know the operation of positioner.

    By Hemanth on 8 March, 2007 - 10:56 pm

    Hi, I am a fresher and just joined Essar, would like to know the operation of positioner. Like 4 to 20 milli amps is converted to 3 to 15 PSI by I/P. this 3 to 15 psi is the control signal for positioner, I would like to know the exact working as I am into projects.

    By Abhijit Goswami, Haldia on 11 March, 2007 - 6:32 pm 2 out of 2 members thought this post was helpful...

    A positioner is a device put into a valve to ensure that it is at a correct position of opening as per the control signal. An I/P converter only sends the opening/closing request to valve but can not confirm

    its position.

    Positioner senses the valve opening through a position feedback link connected to valve stem which is its input signal. I/P converter output is its setpoint input. The difference between these two is the error signal based on which the positioner positions the valve to correct position to reduce error to zero. Hence positioner is nothing but a pneumatic feedback controller. Controlled external supply air to positioner provides power to positioner to position a valve. Also positioner is used in a valve when valve operating signal range is different from I/P converter output range.

    In recent days software configurable digital positioner are being used in valves which do not require I/P converter and has many features like advanced valve diagnostics, partial stroke testing, remote

    communication etc.

    By Anonymous on 13 March, 2007 - 1:07 am 0 out of 6 members thought this post was helpful...

    Dear Hemanth,

    Without you knowing the concept of Postioner, who selected you in ESSAR? Pls return to your  college and study once again and join... I think it would be better for you. MR 

    Bye.

    By Ashwanth Narain on 24 March, 2007 - 2:45 pm 4 out of 4 members thought this post was helpful...

    Dear Mr.Anonymous person,

     Nobody knows everything (even if it is basics)

    http://control.com/thread/1026232438

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    If some body needs to go back to college, if he/she does not know a basic concept, then everybody will be sitting in college

    What is really required, is only the attitude, to learn and keep learning

    By anonymous on 8 December, 2007 - 3:09 pm

    0 out of 1 members thought this post was helpful...

    Dear Mr.Anonymous person, you are right with your question i learn detail about the positioner usally i use to only calibrate now i know the detail thankyou please do share your knowledge and problem you face during calibration i will love to read it.

    By Chandru   on 1 October, 2008 - 9:16 am 2 out of 2 members thought this post was helpful...

    A valve positioner is a device which exactly positions a control valve to the required position as  per the signal given to it.

    For example, if a process change requires the valve to open/close a further 10%, and accordingly a 1.2 psi change has been given in the signal to the valve diaphragm (without a positioner), there's no guarantee that the command is obliged. Due to factors like valve friction, static pressure, etc., stem may assume only a 7% or 8% change in its position and thereby, an error in control.

    Whereas in case of a valve with a positioner, the signal from the controller is given to the  positioner. The positioner then compares it with current valve position and gives an output

    suitable to the valve diaphragm until the desired position is achieved. The output from the  positioner stabilizes when the desired position (signal matches feedback from valve stem) is achieved.

    In short, a valve with positioner means a closed loop control (with feedback) and without it means an open loop control.

    By OMID on 25 June, 2012 - 2:17 am

    Thanks for info

    could you please inform me in this case "we don't need any actuator and positioner is complete and assembled on valve" that's mean valve + positioner worked as control valve

    By shameerrahman   on 26 November, 2014 - 3:45 am

    Thanks, Well Explained

    http://control.com/member.php?m=shameerrahman http://control.com/member.php?m=rk.chandru

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    Thanks Again

    By translator on 12 March, 2009 - 6:34 pm

    I stumbled upon this website in search of some knowledge, and I just want to thank you for your  explanation. It helped to find the equivalent in my language.

    By ajay on 23 October, 2010 - 9:55 am

    Dear Sir thanks a lot for your valuable explanation. my doubts are cleared

    By suman on 17 March, 2011 - 12:28 pm

    Sir, I have a doubt. Suppose a control valve with a pneumatic positioner receives instrument signal from an IP. If the I to P is disturbed.. Then which is the better way

    (1) To Calibrate the I/P with a master gauge separately and then calibrate the positioner 

    Or (2) calibrate the positioner first and then calibrate the I to P with respect to the positioner..

    Please give me a reply..

    By North Sea Tiffy on 2 November, 2011 - 4:13 pm

    Consider this, please.....the more error factors that exist within the system components, the greater the overall error will be within the complete system.

    I see much very informed advice in this thread, but if you will indulge me a moment, I would like to take you back to some more basic elements of setting up a valve positioner.

    First of all, set up the basic v/v and positioner alignment (mechanical alignment) and stroke length for the given v/v. The safest way to do this is to disable the positioner's ability to control the valve, by removing its supply air and output tubing.

    Connect a regulated air supply directly to the diaphragm of the valve. Slowly increase the air  feed until the v/v is at 50% of its travel, and maintain it at this position.(Do not exceed the stated max working pressure for the diaphragm!)

     Next , check the data plate on the valve for its stroke length. This figure will be used when setting up the Stem coupling drive pin on the positioner's feedback arm graduated scale(for  example, it is typically given on a Kent P3300 positioner as being X mm, in multiples of 10mm).

    With the v/v still in mid-position, carefully align the positioner feedback arm as horizontal as you can judge it to be, and engage the drive pin in the feeback arm slot , setting it at the required figure derived from the data plate.

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    Tighten the stem coupling arm, (use a suitably sized spanner to counter the movement of the stem coupling arm as you finally tighten up).

    Finally, check the following: a) that the v/v stem is still at mid-position,

     b) that the positioner feedback arm is horizontal

    c) that the drive pin is still located in the feedback arm drive slot at the required length as above.

    Basic alignment is now complete, and you may remove the regulator and tubing which you used, and re-instate the positioner air supply and output tubing to its original set-up

     Next, check and adjust I to P calibration Finally, calibrate the positioner to your requirements, (assuming full range linear application, a 4 to 20mA input producing 0 to 100% travel)

    Check performance/linearity and repeatability in 25% increments upscale and downscale.

    Bingo...job done,with all sources of error having been eliminated.(assuming correct cam profileetc are set)

    The short of it is , that the more accurately you set up the individual components, then the more accurate will be the overall result

    Hope this is of help to you !

    By A2 on 14 February, 2013 - 6:07 pm

     Nice explanation, except that for some positioners like Fisher, the feedback arm is line up to the travel mark of the arm when the valve is fully open or close. Plastic alignment pin has to be inserted fist; if you are doing it as per the book.

    By rishi   on 12 May, 2012 - 2:10 am

    You must calibrate the I/P converter so that there is 1 to 1 relationship between input and output. If I/P is disturbed and you calibrate the control valve, you may solve the problem temporarily,

     but your colleagues & successor may not know what you have done and he may have to re

    calibrate the valve again if he go for change of I/P converter.

    By A.Roy on 24 May, 2012 - 4:11 am

    A positioner without I/P converter is known as HART? Please give me some idea how it works.

    By Walt Boyes on 24 May, 2012 - 11:39 am

    http://control.com/member.php?m=cheers73

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     Not necessarily, although most analog input/output positioners now have HART communications. Unless they have Profibus, or Foundation fieldbus.

    Look up HART, Profibus and Foundation fieldbus on Google for more information. It's all there, in copious quantity.

    You might also look up the manufacturer and model number of the positioned in question. Their  websites usually have more information on their products than you can possibly absorb.

    Best, Walt

    Walt Boyes, FInstMC, Chartered Measurement and Control Technologist Life Fellow, International Society of Automation Editor in Chief, Control and ControlGlobal.com wboyes@putman.net

    By sandeep   on 16 January, 2013 - 11:47 pm

    Sir,

    can you please explain me the difference between positioner and actuator.... And when to go for an actuator and when to go far

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