Greetings, Invensys sells a very good flow compensation package if you need very = accurate calculated flows. You can also use it to update C' type values = in the equations already discussed. ...regards Robert Brennen Shell Canada Limited This email, any attachment and/or series of responses, is intended for = the use of the recipient to which it is addressed, and may contain = confidential, personal and/or privileged information. If you are not the = intended recipient, telephone or email the sender and delete this = message and any attachment immediately. Do not copy, distribute, or take = action relying on it. Electronic communications over a public network = are not secure and therefore Shell does not accept any legal = responsibility for the contents of this message, including any damage = caused by any virus transmitted by this e-mail. > -----Original Message----- > From: foxboro-bounce@xxxxxxxxxxxxx > [mailto:foxboro-bounce@xxxxxxxxxxxxx]On Behalf Of Gregory A Hurwitt > Sent: January 26, 2006 7:44 AM > To: foxboro@xxxxxxxxxxxxx > Subject: Re: [foxboro] Typical Orifice Flowmeter Compensation > Calculations >=20 >=20 > Bernoulli's equation underlies the original orifice sizing=20 > calculation. > The equation given below is based on the ideal gas law, and is used to > calculate the approximate mass flow at conditions other than=20 > the design > temperature/pressure. The closer the gas is to ideal, the better the > approximation. Small molecules that don't tend to interact=20 > with each other > (e.g., methane, nitrogen) are excellent candidates for this method. >=20 > One very common gas behaves in a non-ideal manner: steam. =20 > (The polarity > of the water molecule causes interactions between the=20 > molecules that are > not accounted for in the ideal gas model.) We have done some=20 > calculations > and determined that ideal-gas compensation is in many cases=20 > virtually no > better than no correction at all for steam. The further away=20 > you are from > design conditions. the worse the error. >=20 > For steam you need a steam table. There are ways to=20 > approximate one using > CHARC blocks. Does Invensys sell a "physical properties" package that > includes a steam table? Can this package be accessed by a CP? >=20 > Greg Hurwitt > BASF Corporation > Freeport, Texas >=20 >=20 >=20 > =20 > =20 > "Jim =20 > =20 > Mowrey" =20 > =20 > <jmowrey =20 > To=20 > @bellsou =20 > <foxboro@xxxxxxxxxxxxx> =20 > th.net> =20 > cc=20 > Sent by: =20 > =20 > foxboro- =20 > Subject=20 > bounce@f Re: [foxboro]=20 > Typical Orifice =20 > reelists Flowmeter=20 > Compensation =20 > .org Calculations =20 > =20 > =20 > =20 > =20 > =20 > 01/24/06 =20 > =20 > 10:26 PM =20 > =20 > =20 > =20 > =20 > =20 > Please =20 > =20 > respond =20 > =20 > to =20 > =20 > foxboro@ =20 > =20 > freelist =20 > =20 > s.org =20 > =20 > =20 > =20 > =20 > =20 >=20 >=20 >=20 >=20 > I haven't looked this up or derived it, but isn't this=20 > applicable for a gas > only? I think this comes out of Bernoulli's equation and=20 > the ideal gas > law, assuming an adiabatic expansion across the orifice. >=20 > The equation would be different for a liquid, correct? >=20 > Jim >=20 > -----Original Message----- > From: foxboro-bounce@xxxxxxxxxxxxx=20 > [mailto:foxboro-bounce@xxxxxxxxxxxxx] On > Behalf Of Pablo Lioi > Sent: Monday, January 23, 2006 5:13 AM > To: foxboro@xxxxxxxxxxxxx > Subject: Re: [foxboro] Typical Orifice Flowmeter Compensation=20 > Calculations >=20 > Kirk, > Hope this helps: >=20 > CALCA BLOCK >=20 > RI01 FIxxxx.PNT > RI02 PIxxxx.PNT > RI03 TIxxxx.PNT >=20 > M01 1.013 (Base Pressure, Bar) > M02 273.15 (Base Temp, Kelvin) > M03 298.15 (Reference Temp, in Kelvin) > M04 18.103 (Reference Pressure, Bara) > M05 350 ( max differential pressure, mBar) > M06 6.39 (Flow @ max dif pressure, Ref. Pressure and Ref. Temp) >=20 > ADD RI02 M01 > ADD RI03 M02 > DIV > MUL M03 > DIV M04 > MUL RI01 > DIV M05 > SQRT > MUL M06 > OUT RO01 > END >=20 >=20 > The formula is >=20 > Qcomp =3D Qref Sqrt[( FI/FImax) ((PI+1.013)/(Pref + 1.013)) * > ((Tref+273.15)/(TI+273.15))] >=20 > Pref+1.013 is stored in M04 > Tref+273.15 is stored in M03 > FImax is stored in M05 > Qref is stored in M06 >=20 > Determine Qref with a flow calculation program, using FI =3D=20 > max differential > pressure, P =3D work pressure T =3D work temperature >=20 > Pref is the work pressure and Tref the work temperature >=20 > Note in the above formula that if (FI=3DFImax, PI =3D Pref and TI=20 > =3D Tref) then > Qcomp =3D Qref, so the formula compensates for the deviations from the > reference pressure and temperature. >=20 > You can put this formula in Excel and make a table of Qcomp=20 > vs. P and Qcomp > vs. T and compare results against your flow calculation=20 > program to see how > it works >=20 > I am using SI units. If you need otherwise, just change the values in > M01-M06 > As you see, the transmitter is not calculating the square=20 > root of the diff > pressure. >=20 > If you have square root at the transmitter then the MUL RI01=20 > line has to be > moved after the SQRT, leaving the rest unchanged (you still=20 > need the SQRT > for the FI range, pressure and temp). >=20 > Good luck > Pablo Lioi > System Engineer > TOTAL AUSTRAL > ARGENTINA >=20 > >From: kirk.d.carver@xxxxxxxxxxxxxx > >Reply-To: foxboro@xxxxxxxxxxxxx > >To: foxboro@xxxxxxxxxxxxx > >Subject: [foxboro] Typical Orifice Flowmeter Compensation=20 > Calculations > >Date: Sun, 22 Jan 2006 16:32:17 -0600 > > > >I am comparing some different configurations on our project=20 > and wanted to > >get a quick survey of how others perform flowmeter=20 > compensation in I/A. > > > >Assuming two flavors of 4-20mA flowmeter signal: > >a) in H2O (or psi) differential > >b) volumetric flow (square root in the transmitter) > >How do you compensate the flow for pressure and temperature? > > > >Calc block steps would be appreciated. > > > > > >Hook 'Em, > >Kirk > > > >Kirk Carver, PE > >ExxonMobil Development Company > >Facilities - Instrumentation and Controls > >12450 Greenspoint Drive > >GP6-315 > >Houston, TX 77060 > >(281) 654-4881 (Greenspoint Office) > >(713) 350-1158 (Worley Parsons) > >(713) 962-2549 (mobile) > >kirk.d.carver@xxxxxxxxxxxxxx (best chance of contacting me) > > > > >=20 >=20 >=20 >=20 > ______________________________________________________________ > _________ >=20 >=20 >=20 > =20 > =20 > ______________________________________________________________ > _________ > This mailing list is neither sponsored nor endorsed by=20 > Invensys Process > Systems (formerly The Foxboro Company). Use the info you=20 > obtain here at > your own risks. Read=20 > http://www.thecassandraproject.org/disclaimer.html > =20 > foxboro mailing list: =20 > //www.freelists.org/list/foxboro > to subscribe: =20 > mailto:foxboro-request@xxxxxxxxxxxxx?subject=3Djoin > to unsubscribe: =20 > mailto:foxboro-request@xxxxxxxxxxxxx?subject=3Dleave > =20 >=20 >=20 _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: //www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave