Ultrasonic flow meter is a non-contact flow measurement device designed to measure the velocity of liquid within a closed conduit. Ultrasonic flow meter usually uses clamp-on type flow transducers which don't block flow, thus no pressure drop and almost free maintenance.And they are also easy to install and operate. Meanwhile, in order to meet different request of ultrasonic flowmeter, we also develop inline type and insertion (hot-tap) type flow transducers.
1.Principle of Ultrasonic Flow Meter?
Ultrasonic flow meters mainly have three kinds of principle: transit-time (time of flight), doppler and cross-correlation.
Transit-time principle flowmeter is mainly for measuring clean and average fluid, the typical is water.
Doppler principle flow meter is mainly for measuring un-average fluid, the typical is dirty water with a larger bubble and particle.
Another not so popular ultrasonic flowmeter is based on cross-correlation principle.Cross-correlation flow meter can works better for suspension flow or turbulent gas flow.
2.Classification of Ultrasonic Flow Meter?
1)As principle, mainly transit time ultrasonic flow meter and Doppler ultrasonic flow meter
The Doppler ultrasonic flowmeter is based on the Doppler effect. It works well with suspension flow where particle concentration is above 100ppm and particle size is larger than 100um, but less than 10% in concentration. Doppler flow meter is easier to make and less accurate (±3-5%), thus, it is cheaper than transit-time ultrasonic flowmeter.
The transit-time ultrasonic flow meter is based on the time difference between upstream and downstream sound propagation intervals. It usually provides very good accuracy (±1%). The former works well for clean flow or flow with minor particles. Applications include pure water, sea water, wash water, sewage, process liquids, oils, chemicals, and any homogeneous liquids which are capable of ultrasonic wave propagation.
2)As transducers type, there are clamp-on flow meter and wetted flow meter (inclduing inline full bore type and insertion wetted type)
Wetted ultrasonic flow meter comes with two varieties, insertion and flow cell. Insertion flow meter requires to dill holes on the pipe wall to install the transducers. Flow cell flow meter, also called spool piece ultrasonic flowmeter, needs to be installed in line with the pipe, thus needs pipe fitting, etc. The transducers are pre-installed on the flow cell, thus, installation error has been reduced to minimum. In general, wetted transducer has better accuracy and better long-term stability than clamp-on type, but it might be more expensive. Comparing with conventional flowmeters, wetted type does not have moving parts, no interference to flow profile, no pressure drop and needs very little maintenance.
Flow cell type ultrasonic flow transducer (also called spool meter,full bore or inline meter) is easy to install with flange or thread connection.
Insertion wetted type ultrasonic flowmeter has a higher ratio in price,especially in big size pipe.
Clamp-on ultrasonic flow transducer is non-contact, non-intrusive, easy to install and easy to maintain. The transducers are mounted out side of a pipe, thus, no need to cut the pipe or to drill holes on the pipe, and there is no direct contact thus no pollution to the liquid, no pressure drop, etc.
3)As portability type, the main are handheld (portable) ultrasonic flow meter and fixed installing ultrasonic flow meter
Wall-mount fixed type ultrasonic flowmeter is more suitable for applications such as process control and long-term continuous flow monitoring. The instrument enclosure is normally weather-resistant or explosive-proof. Wall-mount flow meter is normally cheaper than handheld flow meter.For low cost and large quantity, we also develop low cost unit ultrasonic flowmeter.
Handheld or portable ultrasonic flowmeter is very good for flow survey, HVAC and many applications where mobility is a concern. Another trend of using handheld ultrasonic flow meter instead of wall-mount flowmeter is to save cost, since some handheld flowmeters (e.g. TDS-100H) can also be deployed as long-term measurement device if the environment is accommodating.
3.Installation Method of Ultrasonic Flow Meter
With several years of development, ultrasonic flow meters have different transducers(sensors) to meet different requirement. But mainly there are three type as below:
1)clamp-on ultrasonic flow meter transducers(sensors) installing.
Abest's ultrasonic flowmeters have 3 sizes of clamp-on transducers for max pipe of 6000mm. After inputting necessary application parameters, ultrasonic flowmeters will give installing space between two pcs of transducers(sensors).
Clamp-on ultrasonic flow transducers have four installing method: V method,Z method,N method and W method.
V installing method is for pipe size 15-400mm.
Z installing method is for pipe size 200-6000mm. If pipe size over 200mm, Z method is recommended.
N is for small pipe size, and not often used.
W is for small pipe size below 50mm, and not often used.
2) Insertion wetted (also called hot-tap) ultrasonic flow transducers(sensors)installing.
Abest insertion transducers are used for pipe size range of DN80mm-DN6000mm.
The installing method is only Z installing method.
Abest have two types insertion ultrasonic flow transducer, one is standard type for most of pipes, the other is longer insertion transducer for cement/concrete pipes. If pipe material can't be welded directly, please tell us because it will need special fixing band.
3)Inline wetted (also called full bore,flow cell,tube type,spool piece) ultrasonic flow transducers(sensors)installing
For DN15-DN40mm, the connection is thread screw way.
For DN50-DN1000mm, the connection is flanges way.
The flange or thread screw standard can be specially manufactured as request by Abest Technology. Customers need to send the standard to us while placing an order.
We suggest to use insertion or clamp-on transducers when pipe is over DN200mm which has a high ratio on price.
Ultrasonic flowmeters like electromagnetic flowmeters are velocity flowmeters, so it must have long enough installing straight section. It is at least 15D (here D is diameter of pipe).
And installing point is at least 30D far from pump outlet.
4.Selection Guide of Ultrasonic Flow Meter
- Is fluid full of pipe?
- What pipe size range?
- What pipe material,especially note cement or concreter pipe or lining material?
- What fluid? Fluid type can depend doppler or transit-time ultrasonic flowmeters needed?
- What temperature of fluid? Must confirm the flow fluid temperature range falls into tempeature range of ultrasonic flow transducers.
- For insertion and inline ultrasonic flowmeters, what flow pressure?
- What output and input and data logger is needed?
- Permanent installing or portable type?
- What power supply is available, DC, AC,solar or battery powered needed?
- Flow rate or flow velocity range?
- Is there enough long installing straight pipe section?
- Is there any strong signal interference at spot?
- Ambient humidity and temperature
5.Calibration of Ultrasonic Flow Meter
With clamp-on or insertion transducers, ultrasonic flowmeters can reach a feature of wide pipe size range and wide flow range measurement.. And this usually need 1-3 pairs of transducers only, so ultrasonic flowmeters are very easy for stock purpose. But the feature of wide pipe size range makes it very difficult to calibrate on the requested pipe size. That's why clamp-on can't get a very high accuracy like electromagnetic flowmeters because good accuracy electramagnetic flowmeters are full bore inline type, and thus insertion magnetic flowmeters have a lower accuracy too.
6. Comparison with Other Main Selling Flow Meters
According to incomplete statistics,there are over one hundred of types of flowmeters for different request, and here will simply introduce main-selling flowmeters for liquid and gas.
Gas flow meters(including steam flow meter,air flowmeter,oxygen flow meter):
Vortex Flowmeter,Turbine Flowmeter,Orifice Plate Flowmeter,Rotameter,Venturi Flowmeter,Thermal Mass Flowmeter,ultrasonic gas flowmeter,etc.
Liquid flow meters(including water flow meter, fuel flow meter,hydraulic flow meter): Ultrasonic flowmeters, electromagnetic flowmeters,turbine flowmeters, coriolis mass flowmeters, wheel(gear) flowmeters, variable area flowmeter(rotameter),Positive Displacement (PD) Flowmeters,etc.
Here will mainly make the comparision between liquid ultrasonic,magnetic, turbine,coriolis mass flowmeters.
Electromagnetic flow meters are used to measure electric conduction liquid and can't measure gas. It needs 7D installing straight pipe section. It has no moving parts, less intrusive.Can measure wide pipe size range. Main type is inline type, insertion type is available. But should note potable water and pure water may not use electromagnetic flowmeters.
Turbine flow meters can measure liquid and gas. It is velocity flowmeters, and need 15-20D straight installing pipe section. It has moving parts, so need more maintaining cost. Thus, for liquid flow measurement, it has replaced by other type flowmeters. And now mainly for gas measurement.
Coriolis flow meters are very advanced device for flow measurement.It don't need special straight installing pipe section, and can measure mass, flow rate, density,velocity,etc. But its cost is very expensive. When pipe is over DN200mm, it is difficult to make. It can't get a good accuracy in small flow rate, and can't bear much vibration.