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Interface Level Measurement

07/14/2017 1:11 AM

I have a query about interface level measurement.

Interface level measurement is required in boot of a vessel and we are considering a standpipe for installing GWR type level transmitter.

As boots gets filled up with two immiscible fluids, will there is same situation in standpipe? Will the upper fluid with lower density will get filled u in standpipe?

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#1

Re: Interface level measurement

07/14/2017 1:52 AM

What bets and odds are available?

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#2

Re: Interface Level Measurement

07/14/2017 7:37 AM

A1) No.

A2) No.

<...GWR...>?

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#4
In reply to #2

Re: Interface Level Measurement

07/14/2017 8:47 AM

If I had to guess, Guided Wave Radar is what I think he is talking about.

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#33
In reply to #4

Re: Interface Level Measurement

07/20/2017 5:54 AM

Reasonable. There is an opportunity for an update to www.acronymfinder.com.

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#3

Re: Interface Level Measurement

07/14/2017 8:18 AM

What is your transmitter?

The ECLIPSE® 705 seems capable to detect both levels.

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#5
In reply to #3

Re: Interface Level Measurement

07/14/2017 11:28 AM

That is possible, but what the OP is describing with the tank boot, and the standpipe, I suspect that there is no way to establish a representative layering outside the bulk portion of the tank.

This idea is destined to epic fail from the get go. Get rid of attempting to measure layers in the boot and standpipe? Why are they needed at all?

Explain please, Mr. MSN.

Do you have a physical sketch or representation line diagram of the physical layout, that paints a clear picture of the boot's purpose?

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#6

Re: Interface Level Measurement

07/14/2017 12:21 PM

Well, any difference in level/interface between the vessel and a bridle/bypass is probably due to the temperature differences beteween the bridle, the instrument column and the vessel itself, because the pressure is the same in all.

Whatever the differences are seems to be acceptable as a process phenomenon because level/interface measurement has been done with bridle/bypass instrumentation for decades, since the 1940's.

See the graphic on this thread showing bridle/bypass

http://cr4.globalspec.com/thread/85309/Level-Measurement-Briddle-Strongback

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#7
In reply to #6

Re: Interface Level Measurement

07/14/2017 12:40 PM

We are talking about two levels from two immiscible fluids. It can only be done in the bulk tank and not in a side arm, for obvious reasons.

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#10
In reply to #7

Re: Interface Level Measurement

07/15/2017 1:08 AM

It is indeed obvious to you and it is to me as well, but not necessarily to everyone!

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#18
In reply to #10

Re: Interface Level Measurement

07/18/2017 5:06 AM

Then the others should think about it a bit more ��

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#20
In reply to #18

Re: Interface Level Measurement

07/18/2017 9:26 AM

This is really an interesting and challenging topic. I suppose it might be addressed a number of ways, one of which would be a side-strap gauge with a vertical slit interface to the bulk tank, so that the "Golden Rule" of strapping is obeyed at any combination of levels, and with the slit being the only communication with the tank, the levels must have a heavily damped response to changes in the interface levels, but still maintain fidelity to the actual levels in the tank.

As to the electronic means, I think we need to discuss and elaborate on those details a great deal more, and develop a profile of how each technique "stacks up". Sorry for the pun.

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#21
In reply to #20

Re: Interface Level Measurement

07/18/2017 10:11 AM

Yes, I suppose it might be possible to design some sort of standpipe which maintains the same interface level as the main tank. But I get the impression OP was thinking about a standard standpipe connected at the bottom.

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#24
In reply to #21

Re: Interface Level Measurement

07/18/2017 4:16 PM

In that case, any measurement is completely worthless and hopeless.

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#22
In reply to #18

Re: Interface Level Measurement

07/18/2017 10:28 AM

That, of course, is why some others don't understand; they don't take the time to think about it!

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#25
In reply to #22

Re: Interface Level Measurement

07/18/2017 5:17 PM

Measure pressure at the bottom and total depth. The total pressure will be a function of the ratio of the two densities.

Question is, can pressure be measured with enough resolution if the two densities are very similar.

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#27
In reply to #25

Re: Interface Level Measurement

07/19/2017 8:58 AM

You are aware that many times the level transmitter on a water tank is just a pressure transmitter? How are you proposing to measure total depth of the two layers when all you apparently have is bottom pressure thus far? Come on, don't leave us in the lurch, tell the whole story.

Are you saying d(aq.) and d(x) are known from process knowledge, and that you have the following:

P= d(aq.)gh(aq.) + d(x)gh(x) and from that I have one equation with two independent variables, h(aq.) and h(x).

There needs to be a second observable, in order to solve the independent variables explicitly.

Why not just use other transmitter that reads the two levels of the immiscible liquids such as transit delay reflectometry (TDR). In such instrument, the delay times of the primary reflected signals tells all the information about the depth of each layer.

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#31
In reply to #27

Re: Interface Level Measurement

07/19/2017 11:08 AM

You have the total height if you use an ultrasonic or TDR to get the top surface of the liquid.

Yes, these technologies could be used to get the level of the interface, as well, but if there is any significant turbulence, as you mentioned, that interface will be confused with bubbles of both liquids above and below the average interface level.

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#32
In reply to #31

Re: Interface Level Measurement

07/19/2017 12:35 PM

Ok, now show us the closed form solution for that.

In the meantime, LERTX industries (not a real company, yet), is introducing its new line of flange slits, and flange slit side-arms (strapping tube), with transparent window for every combination of immiscible liquids. A scanner robot from an undisclosed toy robot vendor will scale the strapping tube and take readings in search of minuscule menisci, and report back to OHQ with the results of each traverse. NOT.

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#34
In reply to #32

Re: Interface Level Measurement

07/21/2017 12:39 AM

Cute.

You get the height from the ultrasonic or TDR. h= total tank height minus distance from top of tank to top of liquid.

Calculate pressure if h were all water. Subtract from that the actual pressure. Now, calculate the h of the second liquid necessary to give you that pressure.

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#35
In reply to #34

Re: Interface Level Measurement

07/21/2017 1:00 AM

Hi DavidSMullins:

Every interface generates separate time delayed reflection signal. You read them separately.

For ultrasonic, interfaces are, metal, air, fluid 2 and fluid 1 and metal if mounted from top. If mounted from bottom then interfaces are metal, fluid 1, fluid 2, air. Up to 10m depth range can be used.

For TDR, interfaces as dielectric media for RF > 100MHz are, air, fluid 2 and fluid 1. There is continuous signal in time from depth of the dielectric other than interfaces. 6mm dia stainless steel rod for about 2m in length can be used as antenna in fluids. Do not use this technology for greater depths.

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#37
In reply to #35

Re: Interface Level Measurement

07/21/2017 9:08 AM

TDR can only deal with 2 meter depth? Really? I am somewhat disappointed.

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#38
In reply to #37

Re: Interface Level Measurement

07/21/2017 11:26 AM

Same equation you provided.

p = ρ g h

where

p = pressure, ρ = density of fluid, g = acceleration due to gravity (9.81 m/s2, 32.17 ft/s2), h = height (or depth) of fluid at which the pressure is measured.

And, just so I don't get the dreaded gong, first solve the equation above for pressure using density of water and the total depth of both fluids for h. Subtract that from actual pressure at the bottom of the tank. Then, solve for h of the second fluid using h = p/(ρ g), using the pressure difference for p and the density of the lighter fluid for ρ.

This all assumes water and a less dense fluid like oil are involved. Please adjust this process if your fluids are different.

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#39
In reply to #38

Re: Interface Level Measurement

07/21/2017 11:44 AM

Yeah, what I thought, go rethink your math, sorry.

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#40
In reply to #39

Re: Interface Level Measurement

07/21/2017 12:55 PM

Same equations you used. If you have an accusation to make that I did something wrong, state it. I don't have to defend myself against vague accusations.

Or maybe just stop being a troll.

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#41
In reply to #40

Re: Interface Level Measurement

07/21/2017 1:40 PM

P = ρ1gh1 + ρ2gh2 This is the statics equation.

H = h1 +h2, by definition for a static two immiscible component system.

Some systems can be designed such that H is a constant of the design (fluid is tapped off, etc.) Or there is some other type of level gauge (take your pick), that reads the top level of fluid only.

Substitution: P = ρ1gh1 + ρ2g(H-h1), thus we also have

h1 = (P/g - ρ2H ) / (ρ1 - ρ2)

Example: heptane-water system, ρ1 = 0.9922 at 40 °C, ρ2 = 0.6665 at 40 °C

IF the P value is 25 kPa, and H = 3.048 m

h1 = 1.589 m, and h2 = 1.458 m

Can we now agree on that? Note, this has to be an open vessel, since the vapor pressures of each liquid at that temperature is not insignificant.

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#42
In reply to #37

Re: Interface Level Measurement

07/21/2017 10:23 PM

"TDR can only deal with 2 meter depth? Really? I am somewhat disappointed."

RF absorption is dielectric perhaps is the reason for short range. Sometime one has to use shield metal tube of about 1" to 2" diameter which works like a coaxial cable and it reduces the quantity of dielectric in between. This way one can increase the range up to 20m.

There is one great advantage that it has propagation time signal which makes it fluid type independent. However, signal processing is to be done at very high speed due to 100MHz to 1GHz transmit and receive signal range.

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#43
In reply to #42

Re: Interface Level Measurement

07/22/2017 12:41 AM

Can that metal tube have lengthwise slits, or possibly be a rolled sheet that does not quite close, so there is a slit the full length of the "tube". Obviously there would have to be some form of dielectric "spiders" to keep the sensor wire centered in the tube, yet allow fluid to enter and exit. If the tube is mounted vertically, it should be possible to use these spiders only at the ends, to avoid intermediate signal reflection.

That slit would surely change the impedance of the coaxial unit, but presumably the sizes of center wire and outer tube could be chosen th get the desired impedance

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#44
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Re: Interface Level Measurement

07/22/2017 12:14 PM

Metal tube that encloses center electrode / antenna, can have holes or wire mesh. It is essential to maintain the position of the center electrode / antenna in position preferably in the center of the shield tube. It can be a metal wire or rod. One end connected to BNC having shield connected to BNC shield and other end open like wire antenna.

Only short pulse of rise time < 3ns is applied with pulse width limited to <100ns. Just 1V pulse will do. Measurement of the reflected pulses is to be done using RF amplifier and Fast ADC / Comparator etc. as electronics.

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#45
In reply to #44

Re: Interface Level Measurement

07/22/2017 2:15 PM

Wire mesh sounds perfect! Thanks.

Now it's up to the OP to take this and run with it...

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#46
In reply to #42

Re: Interface Level Measurement

07/24/2017 9:56 AM

Thank you sir, for the timely information on that aspect.

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#36
In reply to #34

Re: Interface Level Measurement

07/21/2017 9:06 AM

You were supposed to put down both of the two equations with two independent variables, GONG - -warning stage hook approaching.

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#8

Re: Interface Level Measurement

07/14/2017 1:15 PM

Is the bridle/bypass designed for interface?

See pages 9 - 11

http://www.chemicalprocessing.com/assets/wp_downloads/pdf/level-management-ehandbook.pdf

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#9
In reply to #8

Re: Interface Level Measurement

07/14/2017 1:53 PM

And one of the key statements I found in that document: In any set-up, it may be impossible to satisfy The Golden Rule for all liquids and headspace. (transliterated by me.)

Bottom line: It is better have a tank top transmitter sensor that can "see" all interfaces, and read the bounce height to them.

Cheap way: Bridle the tank with a gauge glass with numerous ports, such that nearly all levels and combinations of levels will reach fluid hydraulic equilibrium with their respective phases. Good luck with that, especially if the wrong indication could result in a catastrophe.

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#11

Re: Interface Level Measurement

07/15/2017 5:32 AM

The problem with GWR is that it gives false readings if the interface level is sloping about. The introduction of a standpipe is an attempt to prevent this from happening. All the fluid trapped in the standpipe cannot escape unless the tank is emptied below the bottom of the standpipe. If the tank is partially emptied some or all the dense fluid will be expelled but only some of the less dense fluid. As the tank is refilled the new batch separates out and the correct proportions for the new batch will be added to the lower density residue in the standpipe. There will be a progressive build up of the lower density fluid in the standpipe giving an incorrect reading. Rather than a conventional standpipe you need a stilling tube which has a series of overlapping vertical slots cut in around the circumference all the way up. If the liquids are very low density some slop can pass through the slots so a second outer concentric tube is added and aligned so it's slots offset horizontally (usually 180o) from the inner tube. This effectively creates a labyrinth for the slop levels to negotiate. The width of slots and the distance between the inner and outer tubes (the damping effect created by the labyrinth) are selected achieve the required accuracy for the given liquid density.

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#12

Re: Interface Level Measurement

07/15/2017 8:33 AM

Hi,

Try TDR and Ultrasound sensors from standard manufacturers for fluid level and interface distance sensing. Both types of sensors can sense media properties and can give +/-1% accurate details of interface distance from signal transmission point. Sensors may be in the price range of US$300-500.

Shyam, India

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#13

Re: Interface Level Measurement

07/15/2017 10:14 AM

As liquid levels rise and fall, fluid can only enter a standpipe through its bottom opening (assuming it's not slotted, as some have mentioned). Therefore, only the fluid that is present at the bottom of the standpipe can enter. But, if the level drops low enough all fluid will eventually exit. This means that it will only contain a quantity of the lighter fluid that can enter before the tank level raises the interface above the bottom opening. You will not get a representative sample in the standpipe.

What are the fluids? Is either one conductive? Are they optically clear? Knowing the physical properties is key in determining a detection method.

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#14
In reply to #13

Re: Interface Level Measurement

07/17/2017 9:15 AM

Try again, sir. As Iris pointed out, and as I mistakenly tried to put down, a tank side bridled with a multiple port tube (as many as are necessary to allow full communication of the separate layers at most levels of the tank), will indeed allow the lighter and denser portions to achieve equilibrium with the bulk layer depth, as long as three ports minimum are in communication with the liquids. There are situations where this system can be "fooled", however if one layer is thinner than the distance between legs/ports.

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#15
In reply to #14

Re: Interface Level Measurement

07/17/2017 10:52 AM

Yes, I mentioned that, "(assuming it's not slotted, as some have mentioned)." And, as you mention, the distance between slots has to be less than the required resolution of the measurement. We are now approaching a side tube with a continuous slot. So why use the side tube, at all? Any sensor that will work in the side tube will work in the main tank.

We really need to know what the two liquids are. They may have some specific properties we can take advantage of.

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#16
In reply to #15

Re: Interface Level Measurement

07/17/2017 10:56 AM

Did you miss the part about the tank levels surging, sloshing about? The side strapping is for oscillation damping as one of its primary functions.

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#17
In reply to #16

Re: Interface Level Measurement

07/17/2017 10:02 PM

James Stewart: Good point here that side strapping sure will have damped averaged output for the fluid level. However it will have serious problem about fluids of different densities and with separate interface to find the replica of what is inside the primary tank. I think for multiple interface fluids side tubes just won't give interface information.

Ultrasound waves reflect from interfaces and such sensor can be mounted from bottom or top.

TDR sensor has time domain reflective signal for the entire length of the sensor and sure to give much more information. I have seen these being used in Oil Water emulsion cooling tanks and they are also used for soil moisture measurement over a range of depth of soil.

Perhaps a capacitance sensor will also do some good if it is designed for segmented measurement.

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#19
In reply to #17

Re: Interface Level Measurement

07/18/2017 9:22 AM

Very interesting about the TDR, I rate that as a great answer!

In the meantime, I found this article:

DIY time domain reflectometry

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#23
In reply to #19

Re: Interface Level Measurement

07/18/2017 10:40 AM

GA. Excellent link. I read all three parts.

I have no idea how a slit along the length of the outer cylinder would affect the impedance of the sensor; I'm pretty sure multiple overlapping slits would produce multiple reflections of signal, so it would have to be a single continuous slit, to allow the different layers of fluid to enter.

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#26

Re: Interface Level Measurement

07/19/2017 4:55 AM

Sorry, I couldn't reply to the query.

We have considering installation as shown in the diagram.

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#28
In reply to #26

Re: Interface Level Measurement

07/19/2017 8:59 AM

Yeah, that will never work. Good luck.

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#29
In reply to #28

Re: Interface Level Measurement

07/19/2017 9:21 AM

Yes even I think so after reading replies from all of you.

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#30
In reply to #29

Re: Interface Level Measurement

07/19/2017 9:30 AM

GA from me for honesty

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