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 20milli amps is converted to 3 to 15 PSI by I/P. this 3 to 15 psi is the control signal for positioner, Iwould like to know the exact working as I am into projects.

By Abhijit Goswami, Haldia on 11 March, 2007 - 6:32 pm2 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 thecontrol 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 whichis its input signal. I/P converter output is its setpoint input. The difference between these two is theerror signal based on which the positioner positions the valve to correct position to reduce error tozero. Hence positioner is nothing but a pneumatic feedback controller. Controlled external supplyair to positioner provides power to positioner to position a valve. Also positioner is used in a valvewhen 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 requireI/P converter and has many features like advanced valve diagnostics, partial stroke testing, remote

communication etc.

By Anonymous on 13 March, 2007 - 1:07 am0 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 pm4 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, theneverybody 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 calibratenow i know the detail thankyou please do share your knowledge and problem you face duringcalibration i will love to read it.

By Chandru on 1 October, 2008 - 9:16 am2 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 a1.2 psi change has been given in the signal to the valve diaphragm (without a positioner), there'sno 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) isachieved.

In short, a valve with positioner means a closed loop control (with feedback) and without it meansan 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 completeand assembled on valve" that's mean valve + positioner worked as control valve

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

Thanks, Well Explained

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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 signalfrom 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, thegreater 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 wouldlike 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 strokelength for the given v/v.The safest way to do this is to disable the positioner's ability to control the valve, by removing itssupply 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 statedmax working pressure for the diaphragm!)

Next , check the data plate on the valve for its stroke length. This figure will be used whensetting 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 asyou can judge it to be, and engage the drive pin in the feeback arm slot , setting it at the requiredfigure derived from the data plate.


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Tighten the stem coupling arm, (use a suitably sized spanner to counter the movement of thestem 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 calibrationFinally, calibrate the positioner to your requirements, (assuming full range linear application, a 4to 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 moreaccurate 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 tothe travel mark of the arm when the valve is fully open or close. Plastic alignment pin has to beinserted 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

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Not necessarily, although most analog input/output positioners now have HARTcommunications. 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 TechnologistLife Fellow, International Society of AutomationEditor in Chief, Control and [email protected]

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 a positioner?..

Whether actuator can completely replace positioner?

By rishi on 19 October, 2013 - 3:05 am

Valve Body with plug is installed in the process line. That plug is operated up/down or inangular position by actuator. Actuator may be diaphragm type or cylinder type.

The actuator moves from 0-100% position in according to minimum and maximum pressuresupply. This pressure is supplied by positioner.

If we see the flow path then DCS to IP convertor to positioner to Actuator to valve. In casethe valve malfunctions due to positioner and you do not have spare positioner then you canalso connect the output of IP convertor to the actuator of the actuator spring range is 3-15PSI. One more point i want to discuss here is that if the calibration of IP is out then its better

to change the IP rather than calibrate it.

By V1 on 15 February, 2013 - 2:05 am

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

It May be called as smart positioner...

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By semsem on 14 August, 2008 - 1:13 am1 out of 1 members thought this post was helpful...

The positioner is designed for controlling control valves by producing analog pneumatic signal tocontrol the percentage of opening or closing operation for valve.

Example:

Inputs to positioner Air supply (feeding of positioner)Control pneumatic signal: it comes from I/P equipment

Output: pneumatic signal

Numerical example:Air supply: 35 psiControl signal: 3-15 psiOutput : 6-30 psi

By CPPguy on 16 March, 2009 - 12:43 am

Mr. AnonymousScientist Newton was debarred from school as he used to remain mentally absent, But during your studies you learnt lot from his inventions and you know why freshers are not appointed as Generalmanager? Because they do not have practical experience. It not possible to know every thing inthe world, and no Man is PERFECT in the world. And this is right time for him he can ask sillyquestion (silly for Me & You). But this is the way he is marching towards PERFECTION.Thank you

CPPguy

By YKL on 8 September, 2009 - 11:49 pm

Dear CPPguy,

very much agreed with you. It is never a shame to ask if you don't know.

By Ultima on 10 September, 2009 - 4:24 am

well, that was a harsh comment, if you want to learn more specific for the use of an valve positioner, check fisher website at emerson.com find brand fisher. because as far as i knowthey have an good explanation for the use of that thing. and as an addition an pneumatic

positioner who not use I/P converter (or not installed) are have other use as amplifier signal(pneumatic) for the actuator. since some of the actuator are actually doesn't use exact 3-15 psifor moving the diaphragm or piston (for some valve actuator they even installed an pressureaccumulator tank), because the needs for higher pressure to actuated it and some hascharacterizable function such as for valve that have quick opening, equal precentage or linier.

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well i forgot the definiton of the characteristic above but the point is the positioner are havemore usable function than just an feedback control for the control valve. same as the pneumaticthe "modern" positioner also have some other function who already mention by othersgentlemen at this topics.

plus the HART and Fieldbuses Protocols who made it easier (and looks very cool if you areconfiguring an control valve from remote desktop or laptop) to monitor, configuring,troubleshooting, even calibrates the position of the valve. to make it sure, you still need to go

on sites or do it bench test. so go find details about the positioner, and don't shame if you"unfamiliar" with that thing (to be honest, until now I cannot even understand what is"Facebook")

By Ronald Deepak on 24 October, 2009 - 12:38 pm1 out of 1 members thought this post was helpful...

Dear All,

I work in the Fisher control valves division of Emerson.

I would like to explain few things about the working of a positioner.

The positioner is a device mounted on a control valve that receives control signal from a DCSor any host system. The signal can be a 4-20mA/HART/Fieldbus, etc. The positioner receivesthe signal and understands the desired (target) position of the valve.

E.g.,A positioner working on a 4-20mA signal range receives a 12mA means the valve has to be positioned at 50% open. Without a positioner, the valve might not be positioned at 50%due to several factors such as fluid forces, friction, etc. The positioner sends pressure to the

actuator in order to position the valve at 50%. The positioner is also physically connectedwith the valve stem, so it recieves feedback about the current position of the valve. Based onthe feedback, the positioner adjusts the output to the actuator if required. In short, the ultimatefunction of the positioner is to ensure that the Desired opening of the valve is achieved inresponse to the control signal received from the host system.

Advanced positioners which are often referred to as SMART positioners have several other useful features that improve the performance. They have the abiliity to transmit diagnosticdata about the valve back to the host system.

Positioners also have tuning features that allow users to set gain values based on the required

performance criteria like stroking time, over-shoot, etc.

Positioners used in special applications like Compressor anti-surge control , Emergency shut-down valves, etc. have added features which are essential to meet the performancespecifications in those applications.

I hope this helps. If you would have any specific questions regarding a control valvePositioner, please contact me.

Ronald Deepak jronalddeepak [at] gmail.com

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


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By NIK on 26 October, 2009 - 6:44 am

Is it a proportional controller or a PI controller. Somewhere I read that it is a P onlycontroller. This would mean that there will be an offset associated with it like every other Ponly controller. So how the Offset is being removed.

Another question:

For spring diaphragm actuators: whether the positioner output is proportional to 0.2 to 1 kgsignal when the spring range is different for example 1-4 kg output. For example 0.2 signalcorresponds to 1 and 1 kg signal corresponds to 4 kg output.

By George Buckbee on 26 October, 2009 - 9:37 am

Most positioners are P-only controllers, usually with a fairly large gain. This provides enoughkick to the actuator to overcome valve restriction.

Keep in mind that the positioner is effectively the inner/slave loop in a cascade controlscheme. The integral action comes from the outer control loop, which will keep adjusting thedesired valve position to overcome any offset with the process variable (i.e. temperature).

For good control with a cascade system, you must ensure that the inner and outer (slave andmaster) control loops have different response times. This has 2 major implications:

1. Do not apply positioners on very fast control loops (i.e. most flow loops).

2. Ensure that the outer loop tuning is not overly aggressive, as this could result in interaction

(cycling) of the controls.

I will be hosting two webinars on Cascade control tomorrow, Oct. 27. These are free 60-minute webinars, and all are welcome to register at:

http://www.expertune.com/r2.asp?f=AList&l=webinarcascade.asp

-George


Yes, you are right. The positioner in fact has an integral gain component. However, there isan dead zone within which the valve travel is allowed to vary. The dead zone can typically be1%. Only if the travel varies outside of this zone, the error is integrated. This is done in order to avoid travel oscillation.

To answer your second question, the span of air pressure for which the valve moves from 0%to 100% open is referred to as "BENCHSET". The benchset defines the range of pressure tomove the actuator spring between 0 and 100% valve travel (without considering valve

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forces). The benchset is arrived at, when actuator sizing is performed. When the positioner ismounted on to the valve/actuator assembly and calibrated, the positioner understands the end-

points of valve travel by moving the valve from 0 to 100% and measuring the pressures sentto the actuator corresponding to the end points (0 & 100).

In short, the pressure output from the positioner to a Spring & Diaphragm actuator is notfixed, but rather depends on the spring being used.

A simple equation relating the pressure span and spring rate is as follows :

(Pu - Pl)*A = K*T

where (Pu-Pl) - pressure span (psig)Pu - Upper benchset pressure (psig)Pl - Lower benchset pressure (psig)A - Actuator diaphragm area (in2)K - Actuator spring rate (lb/in)T - Travel (in)

Hope this helps.

Please let me know if you have questions.


By Mik on 26 October, 2009 - 3:35 pm

Hello,now, I am confused. One reply stated that positioner is a P-controller only, while other replystated that it has only integral gain.Which one is true?

I think that it must have an integral component to ensure that set point from outer loop isachieved.

By nik on 27 October, 2009 - 12:15 am

Deepak

since you are from the CV industry some more questions for U.

What is the effect of DP across the valve on CV/ Actuator sizing.Whether DP and DP-shut off of the valve are different. In my opinion DP across the valve isat the normal flow and DP -shut off obviously at valve fully closed position. But why thenthese 02 things are normally included in CV data sheets. I also hope that these 2 values areused only for actuator sizing and not the valve part.

Regards


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NIK


What George said earlier is true. The positioner is in fact working in a cascade (inner) loopwhile the DCS is controlling the process variable (flow/pressure/level,etc.) From what Iknow, the positioners in fact have integral gains, so the error in the main process variable isnot accumulated. However, like I mentioned earlier, there is an integral dead-zone for thevalve travel, so the integral action is disabled when travel varies within this zone outside theset-point. So practically, the integral gain is almost non-existent in most positioners becausethe dead-zone is set high enough so that the valve position does not oscillate.

However, I do not quite agree to the comment about the usage of positioners in fast loops. At present, positioners are used in all kinds of loops and I don't see any problem with using acorrectly sized valve and optimally tuned positioner in any kind of flow loop.

To answer your question about pressure drop :

The flowing pressure drop is used for Cv calculation. You might be aware that

Cv (approx.) = Q * Sqrt(SG/dP)

Where, Q is the vol. flow rate, SG is fluid specific gravity and dP is the pressure drop. In caseof gases/vapors, the equation is different -dP is replaced by (dP/P1).

The shut-off pressure drop is used in actuator sizing. Like you said, the shut-off pressure dropoccurs when the valve is fully closed. So this value is used in calculating the total actuator thrust required to keep the valve closed, because the actuator has to keep the valve closedopposing this pressure drop, in addition to providing the desired leakage class andovercoming friction.

In short, flowing pressure drop is used for Cv calculation and subsequently for sizing thevalve. Shut-off pressure drop is used for sizing the actuator.

Hope this helps. If you still have questions, please let me know.


By NIK on 28 October, 2009 - 2:51 am

This is excellent reply.

Regards NIK

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


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By mani on 16 September, 2013 - 10:10 am

> Yes, you are right. it is helpful for me. thanks.

I have other question?

1. how to change DVC positioner online with Double acting Control valve (also valve hashand wheel)? is it possible to change positioner or isolate the control valve and then

change(offline)?

2. please explain how to do calibration.

By Alun James on 17 March, 2014 - 5:31 pm

Hi,

was there an answer to this question? I have recently installed a Fisher 6205 / 6215 set on a plant critical system where we do not have the luxury of stroking the valve post installation.

We understood that it was possible to copy the entire config over from one positioner to thenext - particularly as the feedback device is a remote hall-effect and therefore the positioner has no physical connection to the process.

> 1. how to change DVC positioner online with Double acting Control valve (also> valve has hand wheel)? is it possible to change positioner or isolate the control> valve and then change(offline)?

> 2. please explain how to do calibration.

By Harold Wade on 27 October, 2009 - 10:38 am

Ronald,

Your reply is excellent, but I suggest one slight change in wording. I think you should not usethe terms "valve opening" and "stem position" interchangeably. A signal from the controller of 50% is a request for a 50% stem position, not 50% valve opening, since the valve openingmust also take into account the valve characteristics, which is not the subject of this thread,

but may be a good subject for another thread.

Harold Wadehlwade [at] aol.com

By M. Hopkins on 30 October, 2009 - 8:16 am

The problem I have is in understanding what I call, the resolution of the unit. How much of achange in current does it take to create actual movement for the positioner, and what is thespecification that defines this? Every vendor defines their product by what appears to bewhatever spec puts it in the best light. Yes, they do, for the most part, use common

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terminology, and maybe I'm just stupid, but none of the spec's clearly identifies the 'number of step changes' available for a given 4-20mA signal.

mshopkins [at] dow.com

By Angony Kirsh on 18 June, 2012 - 1:33 pm

Ronald,

Thanks for your explanation. As a follow up, please confirm if a control valve equipped witha HART positioner DVC6200 function properly with a HART-to-Fieldbus Converter connected to a Delta V DCS where a DVC6200f is not readily avalaible?

By Akash on 4 September, 2013 - 8:41 am

Hi Ronald,

Thank you so much for the explanation.This really helps me up in understanding positioner better. I do keep in touch for further queries.

Thanks,Akash

By Dilip on 26 October, 2009 - 2:07 pm

There is nothing wrong in asking a basic question if you that, you do not know much about it. Sinceyou are in project, you must understand basic question, otherwise it may cost your company a lot inlater stage. So keep asking questions, don't keep mum.

By Noth Sea Tiffy on 2 November, 2011 - 6:24 pm

Quite correct Dilip...as we say in the North Sea,"There is no such thing as a daft question...there is only the daftie (fool), who doesn't ask it !"

By arunachalam on 27 October, 2009 - 8:25 am

hi hemanth,

i am also a fresher now joined in a power plant. your questions help me to understand the basics.thanks for every one who appreciates freshers like me and hemanth.

and Mr.Ananymous, guide us if you like. otherwise don't demotivate us..

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By Ronald Deepak on 28 October, 2009 - 10:22 am1 out of 1 members thought this post was helpful...

Harold,

Thanks a lot for pointing it out. I used the term %opening because it is frequently used these days by valve vendors and end-users to refer to % travel. In fact, the more appropriate term is % travel(this is the term that is used in ISA specification sheets for control valve).

However, I didn't refer to the actual flowing area or the effective opening inside the valve that isavailable for flow. Only the total effective flow area depends on the valve characteristic.

Ronald Deepak [email protected]

By Ronald Deepak on 7 November, 2009 - 11:25 am

Mr.Hopkins,

I would like to answer your questions. First of all, when it comes to the issue of resolution, it ismore appropriate to talk about the resolution of the entire control valve assembly (valve,actuator & positioner)than that of just the positioner alone. With the advent of smart digital positioners,the valve&actuator assembly is the one that limits the resolution of the entire unit, not the

positioner.

Like you mentioned, the actual movement of a valve in response to a control signal will not be asmooth ramp, but in 'steps'. The question is what is the minimum step change a valve exhibits(this defines the resolution)? Friction inside the valve tends to 'hold' the valve or make the valve

stem "stick". Stem packing, seal rings, Actuator O-rings - all of these account for friction andsubsequently contribute to dead-band. When there is a significant difference in static & dynamicfriction values, the valve tends to exhibit "stick-slip" motion and this affects resolution. In thecase of large size valves, the valve & actuator internal components like valve plug/stem, actuator

piston (in the case of piston actuators)themselves are very heavy and the sheer forces involved inmoving them, in addition to the friction components already mentioned play a significant role indetermining the response of the valve.

Having said all this, today's positioners are tuned to handle such large valve constructions tomeet typical resolution requirements. Yes, there is no universal specification that specifies anacceptable resolution for a control valve assembly. But several End-Users and Engineering

contractors specify the resolution for valve response. Some applications like compressor anti-surge control require precise response to control signals and accordingly the resolution isspecified. Most valve assemblies offered these days have the ability to respond to control signalchanges as small as 1%.

When highly precise control is required, for ex., in applications like pulp flow control to the paper machine in the pulp & paper industry, basis weight control valves with Electric actuatorsare used. These valve/actuator assemblies have very high resolutions (somewhere in the range of 10,000 steps for a 0-100% control signal span i.e, a resolution of 0.01%).

However, the resolutions offered by standard globe valves with pneumatic actuators are good

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enough to handle most other applications encountered across process industries.

Hope this helps.


By red on 27 April, 2010 - 9:26 pm

How do one calculate the actual air consumption of the positioner?I know that the amount of air used in general for sizing is approx 0.6 scfm to 1 scfm.

But the actual consumption varies for different manufacturer. What data do one need in order to calculate the actual air consumption of a valve positioner? and how to calculate it.

Thanks in advance

By GJA on 24 October, 2010 - 3:32 pm

Yes, there is a big difference in air consumption between manufacturers because there are anumber of designs, most of which I think got installed in our power plant. We've got 'em all.

The Siemens and ABB digital positioners move the control valve using fast acting valves,similar to fuel injectors. You can hear them rapidly fire their valves when they're maintaininga control valve in a position if the control signal varies or if the valve's pneumatic actuator isleaking.

The advantage of this design is that air consumption goes to zero in an air-tight system,unlike the old nozzle and flapper types that use far more air, particularly when they'reapplying zero pressure to the actuator. It doesn't shut off the air supply to the actuator--itvents it off.

We've gotten years of reliable service out of the ABB's in indoor applications on small valvesthat aren't subjected to vibration or water hammer. The Siemens PS2's weren't so fortunateand we've had to replace them in harsh applications. They do offer an upgrade for harsh duty,

but we I&C types tend to cull out the weak in favor of the reliable.

We've gotten good, reliable performance out of Masoneilan SVII's on single acting actuators.

They use pneumatic relays which use more air and are less precise than the ABB's or Siemens but they make a lot of mounting brackets for a variety of control valves, and that means a lotfor the techs who have to install and calibrate them.

One of our plants had problems with double acting SVIIs on drum level control which werenever resolved. They were replaced with Flowserves' Logix positioners that are easy toconfigure, reliable and reasonably priced. They're a definite favorite.

We're impressed with all the gee-wiz firmware and software available that gives youadvanced diagnostics and a zillion configurable parameters but for all of its 50 plus

parameters on board the PSII's, we prefer the simplicity of the Logix and we haven't got time


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to play with all the bells and whistles. If a positioner is causing process problems and can'tquickly be corrected, it gets replaced, not studied.

PMV's are primitve by todays standards but the only thing that's gone out in 10 years of reliable service on several of them is their position feedback to the DCS which isn't critical.

Fisher DVC 5000's are one of the few that are accepted in nukes because they're rock solid,too, but overpriced and are designed to fit their valves. When applied to non-Fisher products,

they tend to require a lot of levers to translate stem travel to rotary motion which creates a lotof linkage slop. We've replaced those with Logix.

Unfortunately, we've got other manufacturer's positioners such as STI on CCI DRAG valves(very robust but difficult to callibrate) to Siemens nozzel/flapper whatever. They all havetheir pros and cons, but do us maintenance guys a favor: standardize when possible and don'tlet the gee-wiz factor sway you unless you have lots of play time.

By Sam on 26 October, 2010 - 10:50 am

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

Hi there,

Thanks for the effort, very interesting read.

When you mentioned Siemens PS2 I all off a sudden felt sick. Biggest crap the world haveever seen.

Made me think about how some people went on in another thread about Siemens and their very advanced technological knowledge and better than most PLC's(S7).Might be true butthen they should stick to PLC's and stay away from trying to design SMART positioners.

In contrast the Fisher DVC 6000 series from Fisher is the best I ever worked on. We mountedthem on Valtech valves as well without any problems.

By Staffan Buhr on 6 November, 2010 - 5:48 am

Hi there,I suggest you look at Quick Stepper valve positioner at www.processcomponent.se.

It has ZERO consumption and manual mechanical override! Free diagnostic software etc.

Best regardsStaffan Buhr [email protected]

By Rob on 12 November, 2010 - 11:07 pm

I have used the PS1 and PS2 positioners. I recently went through a process of standardizing

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basic service positioners across a site. Had 6 different types of positioners due to varioussections of plant being package supplied. Siemens won as e PS2 was comparable to theDVC5000 on cost and ease of set up - doesn't require a 375. Diagnostics is still new to us butwe looking to start utilizing existing diagnostic packages to aid in determining maintenancestrategy for valves.

By Nasr on 25 December, 2010 - 5:06 pm

Great contribution DEEPAK.God bless you.......

By Chris on 9 April, 2012 - 3:02 pm

Hi guys,

I'm doing a research project on 4 positioners.,two smart which are the Fisher DVC6200 and

the Masoneilan SVI IIAP. I'm also doing Fisher 3610J and MAsoneilan 4700P for pneumatic positioners. I was wondering if anyone could give me any insight on what applications pneumatic positioners would be best for. Also i would like to know out of four positionerswhat one would you recommend for tight shut off applications and throttling.

Thanks,chris

By Dick Caro on 9 April, 2012 - 6:51 pm

Both smart valve positioners are available with either HART or Foundation Fieldbus inputand are the most adaptable choices. Pure pneumatic positioners with 3-15psi air pressureinput can be used with DCS or electronic controllers if a I-to-P (I/P) converter is used toconvert the electronic 4-20ma signal from the controller to the requisite 3-15psi air pressure.The only reason I can think of where I would use a pneumatic positioner is where there is anexplosive gas mixture present at all times such as in chemical plants making ether or acetylene. Otherwise, smart positioners are always preferred unless their higher cost is a

problem. The purpose of all control valves is to throttle the process flow over a narrow rangeof flow rates.

Tight shutoff cannot be expected with any control valve; the valve itself determines if tightshutoff can be achieved not the positioner; and globe valves used for control are not designedfor tight shutoff. If you need tight shutoff, you should use solenoid operated quarter-turn ballvalves that are unsuitable for control purposes.

Dick Caro

By Fieldbus query on 10 April, 2012 - 11:20 am

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


17/19

Hi Chris,

Tight shutoff for conventional pneumatic positioners with 4-20 mA is a functionality driven by the control system it is connected. For eg: if tight shutoff needs to be done the controlsystem will deliver 3.6 mA or sightly less and for full open the current will be 21mA

if you take the case of foundation fieldbus positioners this functionality resides in the positioner and is tuned by appropriately making changes in the parameters of TB01

(tranducer01 block) Not sure I thinks it can be done by changing

- final cutoff value_HI =110- final cutoff value_LO =-10

OR- Stop value_HI =110- Stop value_LO =-10

Coming back to throttle / Stroke

you can throttle conventional positioner, if you feed mA from 4to20(4mA=0%,8=25%,12=50%....)

Foundation fieldbus positioners - its done by digital communication and needs a host toexecute the commands

By Chris on 10 April, 2012 - 9:39 pm

Hey guys,

Thank you for the insight for what applications would best be suited for pneumatic positioners as it is helping me with my report. With this report i am basically trying to decideand convince my college faculty which positioner is for best for use out in the field and why.This is between the DVC6200 by Fisher and the Masoneilan SVI II Ap. If there is anyopinion or features that will help defend my argument that the Masoneilan SVI II AP is better it would help greatly.

Also when looking at the calibration of the DVC6200 i noticed there are two modes of calibration which are travel calibration which consists of manual and auto and sensor calibration. The DVC6200 uses a HART communicator for these modes of calibration. The

SVI II AP by Masoneilan uses push buttons and a LCD display for calibration and also canincorporate the HART communicator like the DVC6200. Does this feature give the positioner an advantage over the DVC6200

Also if there are any other advantage or comparisons between the SVI II AP and theDVC6200 that i should be aware of it would help out very much.

Thanks.Chris


18/19

By Safar on 2 March, 2014 - 9:57 pm

One problem i'm facing calibrating with DVC6200 is when the valve is set to fully closed,there are often small pressure in the actuator left that i can't get fully shut off of the valve. thecertain pressure that left in actuator at 0% will let the CV didn't achieve better seat leakageresult. did anyone encounter this problem?

By BC on 11 May, 2012 - 11:59 am1 out of 1 members thought this post was helpful...

Hello to all!

First off: there has been some great discussion with some very qualified individuals in this thread.

I currently work in the nuclear field with the title Field Service Engineer on AOVs. The mainadvice I can offer to newbies is to tinker with all types of positioners on a bench. Have a qualifiedindividual nearby to assist you if you need it and to also check your work.

In my line of work, we have realized that on a 3-15 positioner, setting the values to 3.2 and 14.8 Psiends up being the optimal setpoints for an AOV.

3.2psi meaning the diaphragm is completely bled off at this point and valve travel has ceased.

14.8 means the the diaphragm is saturating with air and the valve travel has reached its peak andcannot move anymore.

Also, if you are working with Fisher positioners (3582) and they are straight out of the box, morethan likely a beam alignment will need to be performed before calibrating the ZERO and SPANsetpoints. Also, Adjust your span before adjusting the zero. A 3582 positioner is different than mostinstrumentation and adjusting the span before the zero will eliminate excess time spent calibratingthe positioner.

As to Chris's question: the nuclear field in the states uses mostly Fisher and ABB brand positioners.DVCs are making there way but only on the secondary side.

I presume the Fisher 3582 over just about any other positioner, except when I'm dealing with dualacting actuators (Piston actuators). Then an ABB Baileys is a great instrument for the configurationat hand.

By Ben on 17 May, 2012 - 10:40 am

Hello to all!

I got very intrested in this forum when i saw the rich replies on positioners. Pls my question is this"ARE POSITIONERS PRIMARY SENSING ELEMENTS"? i am trying to group them in my"technical object type." i am a cmms engineer and we do build data base for asset maintenance.


19/19

By jmnyoung on 5 October, 2013 - 2:59 pm1 out of 1 members thought this post was helpful...

Question in reply to BC on 11 May, 2012 - 11:59 am??

Would you happen to have any written procedure for #1 below? This manual is hard to understandfor #1 below.

1. The specific procedure I am looking is setting the range +(fwd/rev) , zero, span, flapper/nozzle.

2. D-RING procedure would be helpful too, but the manual seems to be decent on D-RINGalignment.

I am pretty sure I have been instructed wrong for #1 above.

jmnyoung

By vaseem on 15 February, 2013 - 12:27 am

The Positioner is a force-balance instrument that provides a control valve position proportional to a pneumatic input signal. The balance of opposing forces in the positioner occurs at the summing beam. One force applied to the summing beam is developed from the input signal pressure on thediaphragm. The other force is from the feedback spring and is proportional to the position of thefeedback lever. When the input pressure is increased to the diaphragm of the input module, thediaphragm strokes down, increasing the effective force from the input module and compressing thefeedback spring. The summing beam moves the spool down in the spool body, opening output portB to supply air to the left side of the actuator. At the same time, output port A of the spool valveopens, allowing the right side of the actuator to vent to atmosphere.

The piston in the actuator moves to the right, rotating the feedback shaft and cam counterclockwise.This rotation causes the feedback lever to rotate clockwise, increasing the compression on thefeedback spring. These rotations continue until the additional force from the spring balances withthe input module force on the summing beam. When the forces are equal, the summing beamreturns to its steady state or neutral position and the actuator is held at a new position. U can havelot of information from the below URL

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d200437x012.pd

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