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from the SSGCL department...
Level Transmitter Calibration
Continuous process industries, DCS questions. topic
Posted by jkh on 3 July, 2010 - 3:16 pm
TOP URGENT
I have a displacer level transmitter which must work at 4-20ma for 0-400mm level changes.

when I change level from 400mm(at the top of displacer) to 300mm, current will reduce from 20ma to 16ma. when we reduce level more, the current not only reduce but also increase! so we haven't range from 0-300mm.

how can we solve this problem? we have a HART COMMUNICATOR as a calibrator tools.

thank you.


Posted by Sam on 4 July, 2010 - 5:50 am
Hi there,

> when we reduce level more, the current not only reduce but also increase! <

Please elaborate, what do you mean the current decrease and increase at the same time?

Did the instrument worked before or is this a first time installation? If the instrument worked before did it just stopped working by itself or did it stop working after maintenance was done on it?

What have you done so far to rectify the problem?
Can you isolate the chamber and remove the displacer to test the mechanical operation? Have you done this already?

Do you have a instruction manual on the instrument? Have you already done a calibration according to the procedure in the manual? If not, why not? Have you looked at the trouble shooting guide lines in the manual already? If not why not?

Send us more info on exactly what is your problem and what you have tried so far and why you need more help than what the vendor's manual can give you.

To me it sound like either a mechanical problem with the float or the spring that is stuck or the calibration that got screwed up by someone incompetent to work on a instrument like this.

Obviously if this is a first time calibration and installation different things apply that needs to be looked up.

If you really are stuck, let us know why and we will see what we can do to help but you need to let us know what you have done so far and as much detail on the application as possible.


Posted by jkh on 4 July, 2010 - 4:17 pm
sam

when we reduce level, get reverse current mean current will increase when level fall.
cc distance is 420 mm, please let me know how we can change factory setpoint if it calibrated on span value???

our media is phosphorus with sp.gr 1.745 as lower liquid, upper liquid is sp.gr 1.5

we got 20 ma in 400 mm while our span value is 420 mm and in this level current is 23 ma and over

we test this in laboratory with h2so4 (same sp.gr)

but when installed in site could get proper reply

do you think problem is with displacer and it designed incorrect


Posted by Sam on 5 July, 2010 - 10:26 am
Hi again,

Ok thanks for trying again, but I still cannot figure out what you are trying to say or what your problem is.

Since we keep on having some communication problem I will give you a general procedure to setup a displacer interface level transmitter and will try and incorporate various options that you might have available on your system.

Some times when I get to a point where I am stuck and completely unsure how to proceed I would wipe everything I have done so far and start from scratch. I think let's do that.

If possible write down all the critical parameters and do a factory reset on the instrument and start from scratch. Make sure you know how to change the various parameters with the HART and also try and get hold of the factory calibration sheet that was supplied with the instrument originally before you start the following procedures, it might be useful to see what the original parameters were for zero and span compared to what you are going to set it to now.

I have managed to understand that you want to measure interface so we will only concentrate on that since a normal one liquid measurement is as easy as letting the float hang free in a single liquid and set the 4mA and then fill up the chamber to 100% mark and set the 20mA.

Ok back to the interface setup. Fist you need to confirm if everything works, so remove the head and float from the chamber and let it hang free in air. Move the float up and down and see what the response is. Once you have confirmed that the instrument respond properly you can fill the chamber with the bottom liquid to the point where zero and 4 mA should be on the vessel. In this case mark this point a 0mm or 0%.

Now insert the float and head in the normal operating position in the chamber. If I am right in my assumptions, the float had been designed for interface so should hang completely free in the bottom liquid and should not exert any upward movement at all. Now drain some of the liquid so that the liquid level, now with the float in it, is in line with your 0% mark. Now start to fill the chamber with top product to the top of the chamber and the float should still be in the free hanging zero position and not float upwards at all since it was designed only to float in the denser bottom product. If not due to the top liquid filling, make adjustments to the float chain to move the float deeper or lower into the bottom liquid until it is hanging completely free in the bottom liquid with the chamber filled to the top with top liquid.

So the bottom liquid is now at the desired zero point of the vessel and the float is hanging free in the bottom liquid and the chamber is filled to the top with top liquid. That is all you are trying to accomplish for now. Make adjustments to the float chain until the float is to the point where it is hanging free but will start to float the moment you increase the level of the bottom liquid. Test this by disconnecting the float from the head and inset it into the liquid and see where this point is and where it will start to float in the bottom liquid and extend or shorten the chain to get to that point. Once this is done set the 4 mA to the measure mm as your zero point. In this case set 4mA to 0mm. The LVDT will now remember this position as zero and 4 mA.

Measure 400mm up from the zero position and mark it as 400mm or 100%. Now fill the chamber up with bottom liquid and at the same time drain or remove the top liquid to the point on the chamber where 100%(400mm) must be. So the float will now be about 80% of it's length be suspended in the bottom liquid and have moved upwards to the point where the chamber is just about completely filled with bottom liquid and only a small amount of top liquid at the top of the chamber which is where your 100% is marked. Now set the mm for 20 mA. In this case 20mA will be set to 400mm.

This is the way we use to do it in the old days with pneumatic interface measuring displacers as well.

You are obviously are using a SMART Transmitter but there is no other way to do it when you want to measure interface with the displacer. The SMART transmitter will allow you to do some fine tuning afterwords when you have closed and pressurized everything. You can then fill and drain the chamber with the process and do some fine tuning by making use of the sight glass if you have one on the vessel or chamber.

Just keep in mind the retention times during the setup when working with interfaces, meaning that once you add or removed some of the top or bottom liquids you need to wait until the two liquids have separated and stabilized again and formed a definite interface again before you take readings or make adjustments. This retention times will vary from product to product so you need to figure out yourself how long to wait.

If you want the instrument to work in the reverse all you need to do is set 4mA to 400 mm when you have the float at the zero point and 20mA to 0 mm when you have the float in the 100% position but I suggest you first do the calibration in the direct mode and then just modify/reverse the zero and span values afterwords.

There could be various other possible problems that you need to check before you do this setup. Check the original calibration sheet to see if the float was correctly sized to float only in the density of the bottom product. If not you will not get the instrument to work properly and need to get hold of the supplier to send you the correct float. You can still try and do the calibration by just making adjustment to the length of the float chain or to shorten the chain and see if you can get it to float at the correct zero level in the bottom liquid when the chamber is filled with top liquid. Might be worth a try if this is actually a problem.

Bottom line is that if you can get the instrument to respond properly and the float to start to move upward as soon as you start to increase the bottom liquid level you will get it working, so concentrate on those two points. The rest is just bubbles.


Posted by jkh on 5 July, 2010 - 3:10 pm
thank u,
give me your mail as i want to send drawings. i got manual from emerson site model MLT1OO

all tests has be done, just answer to my below question

i submerged displacer into liquid with density 1.745 but sensor did not float on liquid and totally fall into liquid,supplier designed sensor with sp.gr between 1.745 (lower) and 1.5 (upper)

i removed sensor (displacer) from spring rod and test it manually but did not work

say to me reason

regards


Posted by W.L. Mostia on 5 July, 2010 - 3:04 pm
I find the below calibration description a bit complicated and hard to follow at times. Also, referral to a displacer as a float is a misnomer (though common usage). Interface displacers are typically purchased for the specific application (nominally 400mm and for the range of specific gravities involved in this case) and as always follow the manufacturer's instructions. The basic calibration of a displacer for interface service is simple though the field logistics can be somewhat difficult at times, i.e.

1. Set the zero with the displacer fully immersed in the top fluid (1.5 SG) - 4 mA.

2. Set the span with the displacer full immersed in the bottom fluid (1.745 SG) - 20 mA.

3. Modern digital displacer transmitters may allow electronic range changes within the displacer's range (length and specific gravities)

If you follow the above and it still does not work properly, get the manufacturer involved.

William (Bill) L. Mostia, Jr. PE
Sr. Consultant
SIS-TECH Solutions, LP

Any information is provided on Caveat Emptor basis.


Posted by Juan Pinzon on 5 July, 2010 - 5:19 pm
Jkh,

*What is the make and model of your level transmitter?*
Fisher, Magnetrol, Masoneilan

Which one?

The Hart is not a calibrator tool, it is used for get a way of communication with your instrument in order to make changes regarding the tag, range, mA output (direct or reverse) and more.

The best way for me depending of the transmitter and the process is decrease the level and increase the level with the transmitter directly installed in its process in order to do the adjust the range, I mean the current output, by the way you need your mA direct or reverse, this is: mA output direct = when the level increase the mA increase, and reverse = when the level increase the mA decrease.

Before to increase or decrease the level in your process please consider if it is permuted, Other important consideration is that both liquids must be present all the time

Regards
J.Pinzon


Posted by Jonas Berge on 15 July, 2010 - 11:56 am
True, a HART communicator is not a calibrator. However, a HART/Fieldbus communicator is important for calibration of smart transmitters. Learn more about calibration of intelligent devices here:

http://www.eddl.org/DeviceManagement/Pages/Calibration.aspx

Cheers,
Jonas


Posted by Juan Pinzon on 4 July, 2010 - 1:47 pm
Jkh,

What kind of transmitter is it? I mean brand, Masoneilan, Magnetrol, Fisher?

interface? or one liquid?
Regards


Posted by jkh on 6 July, 2010 - 8:21 am
brand is mobery mlt100.

support 2 phase and sp.gr for ea. mentioned in my mail


Posted by Juan Pinzon on 7 July, 2010 - 6:49 am
jkh,

5 years ago I had the same experience as you with a displacer of a fisher level transmitter, and many people even guys with a lot experienced in instrumentation said the displacer is bad because donīt float on water.

The displacer is not design to float, because is not a float, it is based in the Archimedes principles right, then don't worry about if you displacer is not floating on the liquid. If you supply the correct process condition to the mobry people the transmitter must work good.

Take a look in the manual from the emerson web page and you will get operate the instrument.

Regards
J.Pinzon


Posted by Luciano Silva on 27 October, 2012 - 4:38 pm
You didn't identify level model, but if a 12300/400 from Masoneilan, try this:

Using HHT HART 375 or 475;

Change operation mode from automatic to manual

Choose calibration zero,keep the tube empty and procedure 4mA as zero (0 mm).

Go to span adjustment and filling the tube until desirable level (400 mm), procedure span 20mA adjust.

Some differences can occurs but,in outlines this is the that you will do.


Posted by me on 20 November, 2012 - 2:36 am
I got problem with masonailand displacer transmitter. the reading fluctuated sometime spike from 0 to 7 %, actually the level zero. try re-calibrated but same result. event both insulation valve blocked.

Please please urgent urgent.........

Thanks All
Ridwan

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