Re: [foxboro] Compensated Level Indication
- From: "Brazell, Troy L" <TLBrazell@xxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Wed, 1 Sep 2010 16:29:38 -0400
Question: But there could still be design and/or installation issues which is
why I also asked a 2nd question; why is it suspect?
Answer: I think that he is grasping at straws, the 20% level swing from cool of
night to heat of day is causing him some heartburn. Once I have the
measurements I asked for I think I can help him understand what is going on.
Question: Is your installation based on a dry or wet reference leg, could
there be condensate in the dry reference leg, where is the condensate pot
located, etc.?
Answer: It is a dry leg installation.
They have experience some issues with this, but think that the local instrument
tech has now resolved this or at least is making an attempt to. I suggested
that he introduce a loop above the top of the tank. This has worked well for me
in the past.
Trending the last 24 hours we had a 3 DegF temp swing and a 7 psig deviation.
Thanks
Troy
**************************
Troy Brazell
DCP Midstream
ISA CCST
Sr. Process Control Analyst
Office 405-605-3877
Cell 405-301-2994
tlbrazell@xxxxxxxxxxxxxxxx
**************************
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Joseph M. Riccardi
Sent: Wednesday, September 01, 2010 2:10 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
Troy,
The point we need to make with your plant manager is that you are already
doing pressure compensation with the way you have piped the transmitter. It
is inherent with the design. But there could still be design and/or
installation issues which is why I also asked a 2nd question; why is it
suspect? Is your installation based on a dry or wet reference leg, could
there be condensate in the dry reference leg, where is the condensate pot
located, etc.? A lot of work without a good reason to suspect the existing
installation and measurement accuracy.
If the installation is clean, then temperature compensation could be easily
added if necessary. I would perform a simple hand calculation based on your
typical temperature swings to estimate the potential error as a result of no
temperature compensation.
The final question to your plant manager would be "What is an acceptable
error (.0008 per degree change)?"
Next...
Joseph M. Riccardi
DCS Services - Industrial Process Control
North-Central Office (OH, PA, MI, IN, WV area)
South-East Office (FL, GA, AL, SC, NC area)
"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A. Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Brazell, Troy L
Sent: Wednesday, September 01, 2010 2:46 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
Thanks Joseph.
The transmitter is tubed just as you described. I have done the Boiler
applications that the list has been talking about, but with propane,
from the research that I have done, I really don't know why this plant
manager thinks that he need any compensation. I took the GPA physical
properties for propane and interpolated the density and unless my
calculations are totally wrong the density only changes about .0008 per
degree. Not enough to worry about.
I guess what I was really looking for is there a real need for doing
compensation on most level applications and if so how would one do this
outside of using a MV transmitter?
A little history on this case;
Twice in the last year they had a loss of their refrigerant propane do
to operator error. As usual they want something to "monkey proof" the
system. I can do rate of change alarming or something similar which
should do what they are asking. The normal swing in this surge tank is
about 20% from the heat of day until the cool of night (demand) and the
level is not maintained at a constant level. When the level gets low
enough they will order a transport load and shove it into the surge
tank, so it can be all over the place.
I am still waiting for the local folks to send the tap location
dimensions so that I can run some calculations. It could be that 20% is
only a few hundred gallons.
Thanks
**************************
Troy Brazell
DCP Midstream
ISA CCST
Sr. Process Control Analyst
Office 405-605-3877
Cell 405-301-2994
tlbrazell@xxxxxxxxxxxxxxxx
**************************
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Joseph M. Riccardi
Sent: Wednesday, September 01, 2010 12:54 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
Folks,
In reading some of the responses and suggestions to Troy's inquiry, I
have
now been waiting for some of the old boiler control experts to chime in
before possibly embarrassing myself by making another bid. Old boiler
control experts; another dying breed? Where is Fred Devore when I need
him?
Hope he is still enjoying his retirement in Raccoon Lake, IN.
IMHO, and with all due respect, I would not get side tracked with the
drum
level comparisons. Yes, it also has its unique characteristics (as many
of
them were listed in the responses) but they are different from the
propane
level application Troy is looking at. As for the reference to the steam
tables, I suspect they were required for the mass steam flow
calculation,
not for the drum level measurement. The steam table properties are
needed
because of the different properties associated with saturated steam
(there
is a relationship between the saturation temperature and the pressure)
vs.
superheated steam (no direct relationship between temperature and
pressure)
et al.
If I can back up 1 step, I would get answers to the following questions:
* How is the existing propane level transmitter piped?
o Is it piped the way I suggested below (low pressure side of the
dP
level transmitter connected to the top of the tank)?
* If yes, why is there a request for the pressure compensation
(why is
it suspect?)?
* If no, how is it piped?
Once we address the pressure compensation issues, the temperature side
of
the equation is easy.
Joseph M. Riccardi
DCS Services - Industrial Process Control
North-Central Office (OH, PA, MI, IN, WV area)
South-East Office (FL, GA, AL, SC, NC area)
Joe@xxxxxxxxxxxxx
"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A.
Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On
Behalf Of Joseph M. Riccardi
Sent: Tuesday, August 31, 2010 8:33 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
Troy,
I have been waiting for all of the measurement experts to chime in
before
possibly embarrassing myself but it seems they are few and far between.
Another dying breed? I am certainly no expert but I'll throw my 2 cents
on
the table to start the bidding process.
In a closed tank pressurized system, the only pressure compensation
required
on the level measurement is from the pressure in the vapor space above
the
liquid; no? Isn't the low pressure side of the dP level transmitter
connected to the top of the tank; this is called the reference leg?
This
reference leg can be dry or wet depending on the application and/or
installation. Changes to the vapor pressure are automatically
compensated
for in the same way as the effect of barometric pressure changes are
canceled out in open tanks (low pressure side of the dP level
transmitter is
open to atmosphere).
Temperature changes affect the Specific Gravity but I think this is a
straight forward calculation that must be included.
Any help so far or should I fold them...
Joseph M. Riccardi
DCS Services - Industrial Process Control
North-Central Office (OH, PA, MI, IN, WV Area)
South-East Office (FL, GA, AL, SC, NC Area)
"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A.
Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On
Behalf Of Brazell, Troy L
Sent: Tuesday, August 31, 2010 12:12 PM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Compensated Level Indication
All knowing list,
I have had a request thrown at me that I have never had before.
This plant is asking for pressure and temperature compensated level
indication on a propane refrigerant surge tank.
I have the dP level, head pressure and vapor temperature. Has anyone
done
this?
Thanks
Troy
**************************
Troy Brazell
DCP Midstream
ISA CCST
Sr. Process Control Analyst
Office 405-605-3877
Cell 405-301-2994
tlbrazell@xxxxxxxxxxxxxxxx
**************************
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Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
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