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When using coriolis mass flow meters to measure liquids flow with entrained air (especially viscous liquids), the meter reports inaccurate readings. The problem is reportedly related to the meter drive coil running out of energy. Entrained air requires additional energy to drive the meter tube, as the entrained air absorbs some of the energy. The energy is limited by intrinsic safety requirements and therefore cannot be increased. This appears to be a bigger issue with larger size meters (1.5 inch to 3 inch), where the reserve energy is lower than in smaller size meters (0.25 to 1 inch).

Anyone else see similar problems?

Hi Jim,
To avoid such gas that causes the coriolis fail to work, it is recommended to physically install it at the lower level from the process piping. For
instances our vessel setup piping, the coriolis is installed in a pit underneath the vessel. This would minimize the gas ingress into the coriolis.
Hope this helps.
Cheers,
Jose Chong

I understand that Coriolis mass flow meter is not meant for two phase service (liquid with air).

Regards,

P. Karuppasami

We have had similar problems we had with a 3" meter on a viscous fluid. Nitrogen was used to help push the viscous material out of the tanker. The nitrogen was readily absorbed into this fluid and transmitted as gas bubbles in the process. This was not as much slug flow, but a viscous bubbly flow that acted like a compressible fluid. This messed up the flow readings in the Micro Motion Elite meters. Once the gas absorption problem was understood and resolved, meter readings did improve somewhat.

D. Brooks Wells
Dow Corning Corporation
Corporate Facilities Engineering
Process Information and Control Engineer
brooks.wells@dowcorning.com

We ran into a similar problem some time ago as the product we measure is quite viscous. The drive to the tube was maxed out and gave erroneous
readings. Air slugs didnt help the matter. We found that on our unit, the interface module that supplies the voltage to the tube was for certified for intrinsically safe installations which was not necessary for our situation. This module therefore limited the output. The manufacturer was able to supply us with an interface module which was not certified for intrinsic installations BUT was able to give us about twice the drive to the tube. That solved our problems. Check with the manufacturer of your meter to see if this could be possible with your
installation. Good luck.

Gerald Beaudoin
Leahy Orchards Inc.
gerald@applesnax.com

Best method to remove the entrapped air is to provide a filter with automatic air vent on the top. This greatly eliminates the entrapped air in the highly viscous liquids. Brooks Instruments (Fisher Flow products) have similar type of air vents to be installed before the meter. I very well understand it is difficult to eliminate the trapped air from the highly viscous liquids. But the Brooks has products to eliminate the air.
REgards,
K.V.Kumar

Jim, Micro Motion offers a transmitter modification for the RFT9739 transmitter which is the same of as a feature that is standard in the Series 3000 transmitter that could help you determine when the gas entrainment is significant enough to start to cause flow errors. This may be of some assistance to you. The "coil energy" or drive gain can be set to one of the 4-20 mA outputs. Under normal operating conditions the drive gain should be steady. Just before the meter starts to read flow erradically the drive gain will begin to rise. You may be able to use this information to help you obtain better flow readings. You may also be able to use the density output to in a similar way but drive gain is much more sensitive.

If you can, try increasing the pressure on the liquid, which will decrease the bubble size.

I am using coriolis mass flow meter for measurement of LDO flow in volume mode, but I am not getting the correct reading in that I have checked all parameter of my flow meter they all are same. Sir kindly suggest me what to do and after how much time mass flow meter should be calibrate. I am waiting for your prompt reply.