Ultrasonic flowmeters
ULTRASONIC RUNTIME DIFFERENTIAL FLOW METER
Sound that is sent along with a flowing medium arrives at the other side faster than sound that is sent against the flow. This difference in transit time is proportional to the speed of the medium (this can be a liquid or a gas). The main advantages of an ultrasonic flowmeter are:
- No moving parts
- Free flow, no obstructions, no pressure drop.
- Can measure zero flow.
- Can measure bi-directional flow.
- Measurement principle independent of pressure, temperature and viscosity.
- Quite to extremely good accuracy (depending on the application)
Each ultrasonic flow meter has two transducers controlled by a flow computer. One of the transducers is a transmitter (it sends an ultrasonic sound at a certain frequency), the other is a receiver. The time it takes to go with the flow minus the time it takes to go against the flow creates a measure of the speed of the liquid or gas. The run time difference is proportional to the velocity of the medium. A great advantage is that this type of flow meter can be used for many applications:
- Liquids and gases
- With an enormous temperature range of the medium (cryogenic, but also very hot)
- The medium may be electrically conductive, but does not have to be.
Disadvantages of the ultrasonic flowmeter
There are also disadvantages and limitations:
- Sensitive to bubbles in the medium
- Sensitive to solids in the medium (everything on which the sound can reflect, called scattering)
- Sensitive to the flow profile, because only a few points in the flow are measured. This type of flowmeter is therefore critical when it comes to straight flow lengths (just like differential pressure flowmeters).
Measuring mass flow and molecular weight
Although it is not necessary for flow measurement, this type of instrument also measures the speed of sound in the medium. Possibly in combination with pressure and especially the temperature, this measurement value can be used to get an indication of the density and the average molecular weight.
This gives the ultrasonic flowmeter various diagnostic possibilities. Thus, with wet gas measurements the composition of the gas can be determined to a certain extent.
Ultrasonic flowmeter types
This measuring technique can be used in clampable instruments, but we do not often use it. Generally speaking, in-line flow meters are preferred to clamp-on instruments. The clampable measuring technique offers the advantage that no cuts need to be made in an existing pipeline and the process can simply continue. Although there is a single exception, a clampable ultrasonic flowmeter is a 1-channel instrument. There is one sound path between 2 transducers.
In-line flowmeters can sometimes be 1-channel, but the standard is multi-channel : 2 and 3 channels for process flow measurements. Ultasone flowmeters with more than 3 channels are often calibration grade flowmeters and will have 4 to 18 channels. The more channels, the more information about product speeds and flow profiles, so more channels generally means higher accuracy.
Doppler measurement technique
The Doppler measuring technique has become obsolete and is no longer used by us.
Downloads
More information?
More information about our products or looking for a custom solution?
Please contact our Sales Engineers.
NL: +31 70 413 07 00
CN: +86-(0)10-60576210
USA: +(1) 973 383 0691
TW: +886-(0)3-5600560
Already know who you're dealing with? Contact your salesperson directly:
Look up salesperson
WE MAKE YOUR TECHNOLOGY WORK
NL - Tel. +31 70 413 07 50
USA - Tel. +(1) 973 383 0691
CN - Tel. +86 (10) 56865822/56865835
TW - Tel. +886-(0)3-5600560