Answer / tarique r

dear friends i have very simple answer just use conductivity
type level tansmitter so can measure water level as rest of
you can see as oil level because of non conductivity

Answer / sam

In a case like this “how to measure a interface level?” is
not a straight forward answer since I cannot know what the
vessel looks like, know what type of tap-off points is
available and so on so I will give you a generic rule of
thumb explanation on interface levels and tell you what is
the perfect solution to all interface level problems. I will
also tell you what you must not do.

Since this is a very confusing subject to a lot of
technicians and engineers, although very few will admit it,
so it might be worth the effort to do a detail explanation
on the subject.

First of all regardless of what anyone tells you, you NEVER
use a differential pressure transmitter for a oil/water
interface level application. Neither a piped nor a capillary
type DPT is suitable to measure interface level. Believe me
I have tried as well, and have done the calculations front
to back and back to front and saw that it is theoretically
possible to do, but believe me in practice it just doesn’t work.
The only application where it might have a small chance of
success is if you work on a vessel with a very stable and
constant top product overflow. In other words your top
product is always at exactly the same level and you only
measure the variance of the bottom product. I don’t thing a
application like this exist but anyway this is the theory of it.
The moment the top product level changes, even by a couple
of mm, your whole calibration is invalid and therefore your
level control becomes unstable. So if you have a application
like this you can try it but other than, that stay away from
the DPT to measure interface levels.
Further more this is whole installation is dependent on
product density so you can image for yourself what will
happen if the top or bottom product density changes so this
is just not the way to do it, it’s to unstable. It is like
standing on a knife edge. Yes you might be able to stand
straight and upright for a couple of seconds, but not for long.

a Lot of people will tell you the capacitance probe it the
answer, it’s not. The capacitance probe can only measure one
product. There is a special interface capacitance probe
available on the market but most people are not even aware
that the probe they are working with is not a interface
measuring probe and that it is just a single measuring probe.
100% of the bottom product is 0% of the top product and then
100% of the top product is 0% of the bottom product they
would say is the way to do it. In theory that makes sense
but in practice it is not so easy to do.
Image you are on a live plant and you now want the
production to fill up the vessel to 100% with only the top
product and then ask them to drain that and fill the vessel
up with the bottom product again. They will most probably
start laughing at you, thinking you are joking. I have tried
this the one time since the cap probes I was working on was
installed in a separate stand pipe on the side of the vessel
so I thought if I can fill this standpipe I will not
interfere with operations but eventually this didn’t work
either since production will not allow you to open a
pressurized vessel that is online with single isolation
only. So in theory something might sound easy to do but in
practice it is not always so easy. The normal capacitance
probe calculations are also just for measuring a single
product in a vessel under perfect conditions so they are
useless as well.

Don’t trust your sight classes either since with interface
levels most sight glasses do not work accurately all the
time. These sight glasses were designed to measure a single
product and not the variance of two products in a vessel.
Draw yourself a vessel and vary the levels of the two
products and see for yourself how it will reflect on the
sight glasses. You will find that at various points the
sight glass cannot reflect the levels accurately due to the
sight glass tap-off points. Yes I know about the overlapping
type of sight glasses but even they do not reflect the
product levels accurately all the time.

But even if they do, you still sit with a problem of
blockage when working with crude and other high viscous
products and big vessels where the level changes very
slowly. Is this now a accurate level indication or is the
sight glass blocked again?

So in theory, if you can trust your sight glass and your
sight glass is installed in a stand pipe attached to your
vessel and you can open this stand pipe up to fill and drain
it as you please, you can set these probes up like that, but
this is a lot of if’s.

The best result I eventually got with these Cap probes was
to setup my TDR radars (radars and cap probes installed on
same vessel for control and ESD) perfectly according to the
design specs and then calibrate the capacitance probes to
the same zero and span positions as the radars. This
eventually resolved the whole problem. If I had my way I
would have thrown them out and installed a TDR in their
place as well.

THE TDR RADARS ARE THE BEST INTERFACE MEASURING INSTRUMENT
ON THE MARKET TODAY.

You can accurately and reliably (up to mm) measure the top
and bottom product continuously and give two separate 4 to
20mA outputs to the CCR, one for the level of the top
product and one for just the interface level in the vessel.
The CCR is normally interested in both these readings. These
radars are not influenced by density changes, temperature
changes, pressure changes or condensation or vapor changes.
They even still work perfectly after the product have
attached itself and started building up on the probes after
long periods of time.. Most other instruments will stop
working in a case like this or start to become inaccurate
even cap probes don't like it.

The only thing that will influence them, but only slightly
is changes in the dielectric constants of the products.
The chances of these DC changes is very remote and will
hardly ever occur, so it is not a major concern. Even if
they do occur it takes two minutes to make a adjustment on
one of the parameters and it will be accurate again.
The negative side of these radars is that most technicians
and engineers find them very difficult and confusing to work
with and I know about instances where the people struggled
for three years and still could not get them working
properly and reliably. This gives a negative name and
reputation to the TDR radar, but the truth is the same as
with anything else, unless you calibrate them correctly you
cannot expect them to work correctly.
TDR is new technology and you cannot use your previous
experiences to help you understand them. You need to study
and learn them from scratch, there is no easy way. They were
specially designed to resolve the decades of problems of
measuring interface levels and they work like a charm if you
set them up properly. I would recommend you go this way as
well.

There are other devices as well like a magnetic float that
will float only on the bottom product and not on the top
product and work by magnetically closing reed switches in
series with resistors inside a guide pipe but again they
will only measure only one product per instrument.
To install one for the top and one for the bottom product
might be a solution if you need both readings but they tend
to get stuck on the guides from time to time due to product
build up, but this might be possibility if you have a clean
product. Definitely not suitable for crude. Keep in mind
these are also density dependent instruments but they will
not be as unstable as a DPT. If the products have a lot of
turbulence, you can also install them inside a round damping
standpipe opened to the product, this will make the readings
a bit more readable and stable. I would also not consider
them for critical applications only for more or less low
priority applications and just for indication.

Below is a previous write up I have done for another
question from someone struggling to understand the TDR. If
you read it the first time it will be very confusing but is
you study it for a while you will see that it is not that
difficult, and once you have actually done it in the field,
you will find it is actually quite easy to do. The main
thing is to do it the way I have described below. The
manuals is sometimes a bit confusing so I have developed my
own way to set them up and this is much easier to understand
than the procedures in the books. The ones I have worked on
is the Khrone BM100A (2x S/S rods probe type) as well as the
BM100C (coaxial probe type)
Good luck


Re: ON RADAR INTERFACE LEVEL TRANSMITTER IF DI-ELECRIC IS
WRONG WITH CONTINIUS PROCESS THAN HOW CAN INDENTIFY OR HOW
CAN I PUT NEW DI-ELECTRIC VALUE?(ROSEMOUNT-TDR-3300-COXIAL
PROBE TYPE) Answer
# 1
You said interface level so I must assume you are measuring
oil and water. My experience is on the Khrone BM100 A but
your radar might be similar since the both use TDR technology.
The dielectric constant of crude is about 2 to 4 and water
is 80. The variance in dielectric constant will have a small
effect, so in order to find the right valve one quick way is
to use your sight glass to set the dielectric constants so
that the radar reads the same as the sight glass on the
water and oil. a Good average is normally 2,5 and 80.
Unfortunately this will not work unless you have setup your
Z/S parameters correctly.
If you are still having problems you need to do a complete
setup from scratch. In order to do this you need to get hold
of the design engineer's internal vessel drawings and look
what the calibrated span should be. What you are interested
in is the exact mm measurements from vessel bottom to Z/S
points or positions. From there it is just a matter of
taking exact measurements in the field of your vessel and
your radar installation and make yourself a neat, accurate
detailed drawing to indicate the design spec positions and
the actual position of your probe in relation to the vessel,
and put these measured values in the output 1 and output 2
parameters, keeping in mind zero position is measured from
the probe bottom up and 100% is also from the probe bottom
up and not from zero position up. So if you can see where
the design engineer have said zero should be and you can see
in exactly what position your probe is in relation to those
points it is a matter of calculating how high you need to
measure up from probe bottom to get to those Z/S points
marked by the design engineer. It takes a bit of
trigonometry to do but is easy enough.

Typically these parameters should look something similar to
this. Output 1 (Top product level) 4mA = 150mm, 20mA =
2500mm, Output 2 (Bottom product) 4mA = 150mm, 20mA = 2500mm.
Look strange I know but we have found it is better to set
them both the same instead of trying to set each one to it's
individual span. Both Spans are setup in reference to actual
vessel level %. Interface is also a actual level measurement
in relation to the whole vessel and not to just half the
vessel where for instance to where your weir plate is. If
you do this it will have the effect that you have a very
sensitive interface measurement to a slow level measurement
making your control very difficult. We have done it at one
point and it worked eventually, but it was very difficult to
optimize and get stable control, and even the smallest upset
will cause everything to go crazy again.

In this example the 150mm might be the mm you need to
measure from the probe bottom up to get to the Zero position
of the actual vessel as indicated by the design drawing and
the same with the 2500mm. Obviously just examples. This is
where your exact measurements in the field comes in.
NB!!
Also make sure you have the right probe length in the "tank
Height" parameter and not the real vessel height.
This probe length is normally stamped on the little spec
plate on the head by the supplier.
Good luck!

Answer / jack

For sure its displacer level transmitter. just note that
this is interface, meaning the top liquid is always full.
for example to measure boot level of an oil vessel to
prevent water carryover.

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