Here are some thoughts from Harold Skinner, an old steam and boiler guy ... "The standard Foxboro Vortex sensor is a piezio crystal (like in a telephone mouthpiece). The sensor is rated for 400 deg. F (233 psig saturated steam). It has two problems. It rolls-over and dies at 410 deg., and deteriorates quickly above 400. I also suspect, after having replaced several, that never operated over 400 deg., that the sensor deteriorates at high (allowed) temperatures, and looses performance over time. This may be caused by deterioration of the fill-fluid (silicone) which causes out gassing and bubbles to form within the capsule (a problem capillary seal d/p level transmitters have.) The fill fluid passes the pressure pulses from the shed vortices to the piezio crystal to produce an electrical signal. The solution, was to develop the un-filled capsule (high-temperature, 700 deg. F). Any transmitter can be retrofitted, but they require a pre-amplifier and can not measure quite as low a flow rate as the standard sensor. More theory in Foxboro TI 27-65b. (They also re-designed the standard capsule, going to grounding one side of the crystal, to minimize signal noise; and they switched manufacturers.) Also, the old sensor had a problem with high velocity flows (as steam can be) in that it's ability to measure above a certain frequency was the limiting factor in sizing full-scale flows, not the vortex principle itself. Don't know if this has ever been fixed (the new model 84 was supposed to address this with a new sensor technology) but it is not yet out. Foxboro eventually modified their computer sizing programs in recognition of this limitation. (I think it was at about 200 Hz. I have seen it happen even on air flow. The signal just drops-out, or can be very erratic - yet returns to good readings as the flow decreases.) Another problem I am tracking with another brand of vortex meters, on natural gas flow at a power-generating plant, is the effect of changing turbulence on the accuracy, as the flow changes. Could this be a problem on steam? Coriolis mass flow. A vibrating (or oscillating) tube measures density from the frequency of oscillation. From this additional signal they can also calculate volume flow. It is not a new technique, as density meters were on the market using this approach, even before the mass meters. Rosemount had a good video illustration on their web site The problem with two-phase flows is: how do you set up a flow lab to calibrate the meter (no manufacturer has a good answerer to this one) and how does the meter tell the difference between a change in flow rate vs. a change in the ratio? Foxboro touted their original design as being more tolerant of entrained air (to a higher percentage that the competition) then came out with the CFT50 which was supposed to be even better. E+H, whose meter doesn't seem to do well with entrained air and inhomogeneous mixtures, had derogatory comments about Foxboro's limitations. The perfect technology may not exist." Best Regards, Ken Heywood Process Control Services, Inc. -----Original Message----- From: Balmer, Robert D. [mailto:robert_balmer@xxxxxxx] Sent: Wednesday, August 08, 2007 9:08 AM To: Foxboro DCS Mail List Subject: [foxboro] General Instrument Question Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable I am involved on a project in China and there is a control engineer over there saying they can use a mass flow meter to measure density. I have never heard of such a thing, has anyone out there in control world seen such an application. If so could you point me to some literature on how it is accomplished? Regards, =20 Robert Balmer =20 Senior Applications Analyst/Programmer ISA CCST 319 463 2206 Robert_Balmer@xxxxxxx =20 -- No attachments (even text) are allowed -- -- Type: image/jpeg -- File: image001.jpg -- Desc: image001.jpg _______________________________________________________________________ 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 -------------------------------------------------------- This message (and any associated files) is intended only for the use of the individual or entity to which it is addressed and may contain information that is CONFIDENTIAL, subject to copyright or constitutes a trade secret. 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