Ultrasonic Flow Meters Working Principle

Ultrasonic flow meters calculate the flow rate by utilizing the speed of sound through a fluid created by transducers mounted to the pipe wall. There are two types of ultrasonic meters: Doppler and Time-of-Flight. The Doppler ultrasonic meter requires particles in the fluid to reflect sound waves back to the pipe wall transducers. The difference in frequency between the sent and reflected wave is proportional to fluid velocity. The Time-of-Flight ultrasonic meter requires a clean fluid and works by using opposing transducers mounted to transmit/receive sound waves at an angle across the pipe. The difference in the time required to send a pulse along the path between transducers in the direction of flow vs. against the flow is proportional to the fluid velocity. Some models use multiple pairs of transducers to fully cover the pipe cross-section, which provides a more accurate flow rate than a single-path meter.

There are two principle

• Transit time principle
• Doppler effect principle

Transit time principle

Ultrasonic flow meters measure the difference of the transit time of ultrasonic pulses propagating in a flowing fluid. This time difference is a measure for the average velocity of the fluid along the path of the ultrasonic beam. By using the absolute transit times both the averaged fluid velocity and the speed of sound can be calculated. This measurement principle is only possibly for large bore tubes, for higher flow ranges.

Doppler effect principle

Another method in ultrasonic flow metering, also not suited for very low flowrates, is the use of the Doppler shift that results from the reflection of an ultrasonic beam off sonically reflective materials, such as solid particles or entrained air bubbles in a flowing fluid, or the turbulence of the fluid itself, if the liquid is clean.

Applications

Transit time principle:-

Clean liquids with little or no solids or bubbles; gases

Doppler effect principle

Slurries with solids (0.2 to 60% concentration, depending on particle size), liquids that are aerated or contain bubbles, gases with sound-reflecting particles, single-phase turbulent clean liquid.

Process Temperature :-

− 300 to 500 ° F ( − 184 to 260 ° C); higher or lower with special sound-transmitting wedges.

Materials of Construction :-

Spools or transducer probes: steel, stainless steel, or alloys.

Sizes :-

0.125 to 120 in. (3 mm to 3 m) diameter ( Transit time )

0.5 to 72 in. (13 mm to 1.8 m) diameter (Doppler effect )

Price :-

Spool designs in steel, not including options or special features and of the single-path design: \$5000 for 4 in. (100 mm), \$8000 for 10 in. (250 mm), \$14,000 for 24 in.

• Non-contact measurement can be done.
• There is no pressure loss for flow free obstruction measurement.
• Non conductive liquid can be measured, which is a supplement to electromagnetic flowmeter without obstruction.
• Ultrasonic flowmeter is a kind of non-contact measuring instrument, which can be used to measure the flow rate of fluid and large pipe diameter which are not easy to contact and observe.
• Ultrasonic flowmeter will not change the flow state of the fluid, will not produce pressure loss, and easy to install.
• The flow rate of strong corrosive medium and non conductive medium can be measured.
• The range of the ultrasonic flowmeter is large, and the pipe diameter ranges from 20mm to 5m.
• Ultrasonic flowmeter can measure the flow of various liquids and sewage.
• The volume flow measured by ultrasonic flowmeter is not affected by the thermophysical parameters such as temperature, pressure, viscosity and density of the fluid under test. It can be made into two forms: fixed and portable.

Limitations :-

• Ultrasound flowmeter temperature measurement range is not high, generally can only measure the temperature of fluids below 200 degrees Celsius.
• Propagation time method can only be used to clean liquids and gases, while Doppler method can only be used to measure liquids containing a certain amount of suspended particles and bubbles.
• The accuracy of Doppler method is not high.
• Poor anti-interference ability. Ultrasonic noise interference, which is easily affected by bubbles, scales, pumps and other sound sources, affects the accuracy of measurement.
• The straight line section is strict, for the former 20D and after 5D. Otherwise the discreteness is poor and the measurement accuracy is low.
• The uncertainty of installation will bring greater error to flow measurement.
• Scaling of measuring pipeline will seriously affect the accuracy of measurement, bring about significant measurement error, and even in serious cases, no flow meter display.
• The reliability and accuracy level is not high (generally 1.5 to 2.5 levels), and the repeatability is poor.
• The service life is short (the general accuracy can only be guaranteed for one year.
• The ultrasonic flowmeter determines the volume flow rate by measuring the velocity of the fluid. The mass flow rate of the liquid should be measured. The mass flow rate of the instrument is obtained by multiplying the volume flow rate by the artificial density. When the temperature of the fluid changes, the density of the fluid changes. The artificial density value can not guarantee the quality. The accuracy of volume flow. Only when the velocity of the fluid is measured and the density of the fluid is measured, can the true mass flow value be obtained by calculation.

Ultrasonic Flow meter Inspection Plan :-

This content provides with a example ultrasonic flow meter inspection and test plan. This is a draft ultrasonic flow meter ITP and must be edited and meet your purchase order specification.

Ultrasonic Flow Meter Inspection and Test Plan TaskVendorTPI InspectionClient
Ultrasonic Flow Meter mill test reportHRR
Ultrasonic Flow Meter Performance test including hystersisHHR
Ultrasonic Flow Meter Insulation resistance testHWR
Ultrasonic Flow Meter Final visual / Dimension InspectionHHR
Ultrasonic Flow Meter Documentation review prior to release(Final activity of Technical Inspection)HHR
Ultrasonic Flow Meter Pre-shipment InspectionHHR

H: Hold Point implies that relevant production activities shall not proceed until the continuation of work is permitted by Purchaser. (Notification req’d)

W: Witness point implies that Purchaser intends to witness the designated inspection feature. If Purchaser decides not to witness the relevant feature, production can proceed without permission of Purchaser. (Notification req’d)

S: Witness, but spot check basis. Initial operation will be witness point and subsequent operation will be witnessed at discretion of Purchaser considering the results of previous inspection. (Notification not req’d : Randam Inspection)

R: Review inspection & test records (Notification not req’d)

General Note:

1) Ultrasonic Flow Meter Witness/hold point by Code Inspector, when applied by Code /Local Regulation, is to comply with its requirements and to specify in Vendor’s ITP.

2) Type of Inspection by Ultrasonic Flow Meter Purchaser may be changed according to equipment criticality and vendor QC evaluation at job stage.

3) When requested in the requisition, detailed Ultrasonic Flow Meter ITP shall be submitted by Vendor.

4) Monitoring/Observation of Ultrasonic Flow Meter Vendor shop daily routine works (i.e. Storage of materials ,Adherence to approved procedures, Testing tool calibration check, workmanship, cleanliness and etc.) shall be done by Purchaser during inspection visit.

5) Ultrasonic Flow Meter 100% inspection which is covered by the combination of witness / spot check / record review inspection & tests listed above and vendor’s original QC activity shall be confirmed by Purchaser’s inspector prior to shipment.

6) Unless otherwise specified in REQ., the Ultrasonic Flow Meter sampling Q’ty of ” S (Spot Witness Check) ” shall be as follows:

3 to 20→3Pcs(all if total 2 and less) , 21 to 50→5Pcs, 51 to 100→10Pcs,101 to 200→20Pcs, 201 to 300→30Pcs, 301 to 500→50Pcs

Minimum 25 pcs or more of the commodity shall be arranged for H/W/S inspection and test at one time inspector’s visit as much as practical.

7) Final Ultrasonic Flow Meter Visual Inspection/Documentation Review / Pre-Shipment Inspection may be combined within one time visit.

Ultrasonic Flow Meters Installation Guidelines for Liquids

1. Introduction To give the best performance, KROHNE flowmeters must be installed in a correct way. Important instructions should be taken into consideration, like the inlet and outlet length, pipe to be completely filled, direction of the flow, etc. Depending on the measuring principle of each device, the guidelines will differ. In this article we will explain the installation instructions for inline Ultrasonic flow meters for liquid measurements (OPTISONIC 3400 and OPTISONIC 4400). 2. Recommended installation positions
• Ensure that the pipe is completely filled, partially filled pipelines are not allowed, as they can give fluctuating or inexact readings.
• Avoid installations where gas can be present; therefore, install in the lower pipe bend in an a vertical or slightly uphill pipe.
• Installation in front of an open discharge must be avoided since a completely filed pipe may not be guaranteed.
• Upstream of an ultrasonic flowmeter in case of OPTISONIC 3400 using bends in 2 dimensions: ≥ 5 DN; when having bends in 3 dimensions: ≥ 10 DN  (the diameter of the measuring tube) must be left as the inlet run. While the outlet runs must be at least 3DN (The distances are always measured from the flange).
• In case of OPTISONIC 4400 the outlets will be (for 2 path using bends in 2 dimensions: ≥ 10 DN; when having bends in 3 dimensions: ≥ 15 DN for 1 path using bends in 2 dimensions: ≥ 20 DN; when having bends in 3 dimensions: ≥ 25 DN)
•  After a T-piece that is when two pipes intersect, a 5 DN inlet run must be used for OPTISONIC 3400 and for OPTISONIC 4400 10 DN for two paths or 20 for one path.
• It is recommended to install the measuring device upstream of a control valve not downstream.
• If a shut-off device is installed downstream of the flowmeter, an outlet run of at least 40 DN should be used.
• A pump should be installed upstream, of the flowmeter with distance of greater than or equal to 15 DN for Optisonic 3400 and 30 DN for Optisonic 4400.
• All vibrations in the process should be avoided. If vibrations should occur, a compact device must preferably not be used, instead install a remote version.
•  Always make sure that the converter is no more than 90° relative to the sensor.
Note: Shortening the inlet and outlet runs can, however, affect the measuring accuracy. For example, if a straight inlet run is shortened by 2 DN, so it is 8 DN long, we must expect an additional measuring inaccuracy of 0.2%; in other words, if sensor standard inaccuracy was 0.3% then total measuring inaccuracy in this case would be 0.5%.

Ultrasonic Flow Meters Installation Guidelines for Gases:-

1. Introduction To give the best performance, KROHNE flowmeters must be installed in a correct way. Important instructions should be taken into consideration, like the inlet and outlet length, pipe to be completely filled, direction of the flow, etc. Depending on the measuring principle of each device, the guidelines will differ. In this article we will explain the installation instructions for Inline Ultrasonic flow meters for gas measurements. The article cover the following topics:
• Recommended installation positions for OPTISONIC 7300
• Recommended installation positions for OPTISONIC 8300

2. OPTISONIC 7300

• The OPTISONIC 7300 is designed for the measurement of dry gas flow. Excess of liquids may disturb the acoustic signals and should thus be avoided.
• Install the flow sensor in a horizontal position in a slightly descending line and make sure to orientate the flow sensor such that the path of the acoustic signal is in the horizontal plane.
• Keep a free space of 1 m / 39″ around the transducer in case of exchanging the transducers.
• Upstream of the flowmeter at least 20 DN (the diameter of the measuring tube) must be left in case of 1 path and 10 DN only in case of 2 path.
• The outlet runs must be at least 3 DN.
•  After a T-piece that is when two pipes intersect, a 10 DN inlet run must be used.
• To avoid distorted flow profiles and interference caused by valve noise in the sensor, control valves or pressure reducers should not be installed in the same pipeline as the flowmeter. In case this is required, please contact the manufacturer.
• Make sure to mount the device vertically or horizontally with the acoustic path in horizontal plane.
• Avoid vibrations on the line.
3. OPTISONIC 8300:
• Install the flow sensor in a horizontal position in a slightly descending line.
• Do not install the flow sensor in a lowered pipe section to avoid that water can collect in the measuring tube.
• Orientate the flow sensor such that the path of the acoustic signal is in the horizontal plane.
• Keep a free space of 0.3 m / 11.81″ around the transducer in case of exchanging the transducers.
• Upstream of the flowmeter at least 20 DN (the diameter of the measuring tube) must be left as the inlet run and 3 DN atleast as outlet run.
•  After a T-piece that is when two pipes intersect.  A 20 DN inlet run must be used.
• Make sure to mount the device horizontally with the acoustic path in horizontal plane.
• To avoid distorted flow profiles and interference caused by valve noise in the sensor, control valves or pressure reducers should not be installed in the same pipeline as the flowmeter. In case this is required, please contact the manufacturer.

Ultrasonic Flow meter Manufacturer

Ultrasonic Flow meter Manufacturers / VendorsCountryWebsitePhone No.
ABB AGGERMANYwww.abb.de+49 62143810
ABB LIMITEDUKwww.abb.com+44 1925741111
FMCGERMANYwww.general-overnight.com+49 8501914083
DANIELUKwww.daniel.com+44 1786433400
EMERSONUKwww.frco.com+44 1162822822
ENDRESS & HAUSERGERMANYwww.endress.com+49 71562090
FUJI ELECTRIC CO LTD.JAPAN +81 425856201
KAM CONTROLS,INCFRANCEwww.kam.com+33 491031000
KROHNE MESSTECHNIK GMBH & Co. KGGERMANYwww.krohne.de+49 2033010
OIL & GAS SYSTEM LIMITEDUKwww.ogsl.com+44 1353666640
PANAMETRICS(THE KANOO GROUP)U.A.E. +971 26954301
SIEMENSGERMANYwww.powergeneration.siemens.com+49 9131180