Advantages:
- Can be used with very small nominal diameters (DN 15 to 4,000 / from 1 / 2 to 160 ").
- Allow measure highly corrosive fluids without any direct contact.
- No load losses experienced
- High life expectancy.
- Minimum time constant: 1 to 20 ms for high-flow meters.
- Ultrasonic sensors can be mounted afterwards, both external fixation and soldiers to the pipe.
- The principle of measurement is independent of the physical properties of the fluid, if it is homogeneous.
Disadvantages:
- The measurement results are highly dependent on the flow velocity profile because the fluid velocity is measured along a narrow road noise, or small area where the measurement takes place.
- Degree of accuracy intermediate to low. The accuracy is strongly dependent on the properties of propagation of sound waves in the fluid.
- The deposits on the sensor pipe or equipment failure and cause errors
measurement.
- The method of measuring the Doppler effect is used only for certain types of applications,
for example, flow control.
Limitations:
- Large amounts of intrusive material in the fluid.
- Golf fluid temperature values.
- Profiles of flow over disturbed
Applications
Ultrasonic flowmeters are versatile. To measure gas, steam and liquids. The restrictions involved with these flowmeters are mainly from his own "physical integrity", ie the constraints related to, for example, heat resistance, or, at a much less significant, other factors such as low acoustic propagation in the fluid. Although only a few have a fluid sound propagation so poor that they can not function with this type flowmeters. However, other external influences such as two-phase fluids or fluids containing suspended solid particles can become too high significantly attenuate the ultrasonic waves. The two real examples below illustrate the variety of possible applications for flowmeters of external fixation.
Example # 1 - Mounting post without service interruption
A water supply system for an estimated 18 million consumers would be divided between two operators. To be properly localized consumption of users, it was necessary to provide pipes with flow meters. The network load was 30,000 liters per second (7,900 U.S. gal / s), so it was discarded the option of cutting off the supply for operation. Then it was understood that the ultrasonic measurement systems were the best option and that there was no serious alternative to it. Flowmeters were mounted on the exterior of steel pipes (concrete coatings, DN from 1.000/40 "to 3.000/120") unmodified (Fig. below). There was no need for structural work and water supply remained uninterrupted.
The same advantages were evident in a car factory. Again, the production did not have to be interrupted to install ultrasonic flowmeters.
Furthermore, the same type of sensors are mounted on all pipes with nominal diameters from DN 80 (3 ") to above DN 300 (12").
Figure: Mounting of ultrasonic sensors post external fixation in a network of water pipes (DN 1.400/55 ").
Example 2 - Substitution of defective flowmeter
Ultrasonic flowmeters are common substitutes for conventional equipment faulty. A power plant used river water both as sea water for cooling. To avoid too sudden increases in temperature in the return flows, the velocity of the fluid is controlled and regulated at two points, the inlet and discharge, with electromagnetic flowmeters.
During a routine maintenance check, workers discovered that a coil of one of the flowmeters was broken, and decided to replace the two. This would have required cutting off the supply in general. Another problem was the difficulty of obtaining new magnetic flow meter of appropriate size (700 to 900 DN / 28 to 36 ") in a reasonable time.
There were some reservations as to whether ultrasound systems would be a viable solution, because the material of manufacture of the pipe, fiberglass reinforced, it was practically impervious to sound. A simple walk around solved this problem: measuring systems were coupled ultrasonic flow over the tubes simply measuring the original magnetic flowmeters (Fig. 76). The measuring tubes were removed, the covers and coils of electromagnetic flowmeters removed and the original siding was changed by a soft rubber. It took three days of work to complete the operation.
