Ultrasonic Flow Meters

The Ultrasonic Flow Meters operate in the ultrasonic frequency range, from which they also take their name. The wave frequency changes depending on the flow velocity of the material inside the pipe. By measuring acoustic phenomena, the device determines the volume and flow of specific materials (water, oil, gas, and other fluids). The measurement is carried out both in the direction of flow and in the opposite direction (upstream), with the aim of determining the rate and volumetric flow. When there is no flow, the difference in the measurements is minimal. However, as the flow increases, the wave has more difficulty moving against the flow than downstream. Thus, the higher the flow velocity, the greater the difference in transit time between the downstream and upstream measurements.

The use of a probe that responds to the density of the medium provides the capability to measure even mass flow. Much depends on the liquid whose flow must be measured. If the material is clean, high frequencies are applied and a very reliable and accurate measurement is ensured. If there are solid particles in the liquid that are distributed unevenly or the material is not sufficiently clean, the frequencies must be lowered to avoid their scattering and the absorption of oscillations.

An ultrasonic flow meter is easy to use and operate; it is a fixed instrument with no moving parts and is sufficiently robust with a long service life. However, before its application, it is necessary to check the flowing liquid in order to avoid uncertainties and failures during the measurement process. When using flow meters, it should be taken into account that if certain materials/fluids are highly resistant to ultrasonic waves and reflect them instead of allowing them to pass through, the measurement will be very inaccurate and errors may occur. Particles that may be present in the material have their own velocity, different from the overall flow in which they are located, and theoretically this can also cause large variations and errors in flow rate measurements. Despite the possible difficulties, it is fair to say that modern ultrasonic devices have reached a level where they can handle even obstacles such as very dark and non-homogeneous liquids.

The range of application possibilities of an ultrasonic flow meter is broad: almost all types of industry where material flows in pipes, with most applications in water/wastewater, food and beverage production industries, pharmaceutical, chemical, and others.

Ultrasonic flow meters have clear advantages that are very valuable and make them an indispensable tool for maintenance and service inspections, as well as for measurements that should preferably be performed without intrusion into the pipes. Depending on the material and the type of facility where the measurement is carried out, intrusion into the pipes may be quite undesirable (power plant or chemical plant), which is why the use of a non-contact meter that measures the flow of a sometimes hazardous substance is very convenient. A flow meter with clamp-on probes can be installed on the pipe and carry out the measurement externally, from the outside, but there are some things to pay attention to: it must be positioned and applied correctly on the pipe to avoid weakening or loss of the ultrasonic signal so that it can fully reach the liquid. The use of clamp-on probes makes it possible to apply the device at any time, without depending on the types of liquid and its properties, as the device remains dry and is not damaged. The measurement is carried out continuously and the results can be obtained in real time.

A mobile/portable ultrasonic flow meter facilitates measurements to such an extent that the operator does not require additional instruments to carry out immediate checks where necessary (from water to oils and chemicals). It is ideal for cases where a quick measurement is needed to detect a problem or simply to check the general condition of the ongoing process. Due to the rechargeable battery, the portable device provides several hours of operation, and the internal data logger stores the measurements for further analysis and processing. Mobile flow meters can always be used as a reference for fixed installed flow meters, since, despite their compact form, they provide good measurement results.

One of the newer fields of application is the use of a flow meter for HVAC monitoring. Since nowadays there are strict requirements and regulations regarding heating, air conditioning, and ventilation, especially in enclosed spaces, rooms, offices, and similar areas, the need for accurate air flow measurement is quite high. For this type of measurement, temperature becomes an important parameter and the measurement is performed taking into account the thermal flow principle. The best solution, when it comes to measurements in heaters, heating systems, and fire extinguishing systems, is a clamp-on heat meter. Without additional intrusion into the pipe with hot/cold substance inside, the meter is fixed to the pipe (pipe size does not matter) and allows monitoring to be carried out in the most hard-to-reach and hazardous locations.

The application of the flow meter helps not only in identifying problems and troubleshooting in pipes, but also provides monitoring and quality control capabilities (for example, in beverage production or in the analysis of equipment and heating installations). If the device has a dual or multi-channel option, it enables simultaneous measurements not only at a few points on one pipe, but also on a few pipes, thus providing better accuracy and the ability to compare values. Either clamp-on probes or probes with clamps can be used to make the measurement process more convenient, and they are suitable for both low and high operating temperatures, which ensures application for cooling monitoring as well as for heating systems.