The result is that Coriolis flowmeters have become somewhat of an industry standard, and are regarded by many as the top-of-the-tree in terms of specification. After all, they have proven their capabilities in many applications for both fluids and gases as well as mass flow measurements. However, they are not perfect. For example, the initial cost is high and they do have some other constraints that need to be considered.
The design of the Coriolis flowmeter means they are susceptible to ‘pressure drops’, and this can affect the upper limit of their measurable range. Pressure drops also increase with fluid viscosity as well as flowrate, and the corresponding velocity through the meter.
Additionally, the bulky size and weight of the Coriolis flowmeter means packaging it within the necessary pipework can be tricky, as it also requires careful support. It also means installation time is generally higher than for many other sensors within a plant.
Overall though, the Coriolis flowmeter offers exceptional levels of accuracy (0.1%) which can be improved to 0.05% with special calibration. The design is also capable of bidirectional measurement without the need for inlet or outlet sections in the installation.
However, it is often not a straight-through device and this can have some major drawbacks when it comes to the type of media that can be passed through it including product wastage and additional Clean-In-Place (CIP) requirements for heat and volume of cleaning process fluid.
Furthermore, in many cases, the mass flow measurement may not be required for the application but a Coriolis flowmeter will have been specified purely on the need for accuracy. In such cases, the increased investment in the traditional equipment is wasted on features that are not required.
Surface Acoustic Wave
Now, there is an alternative flow measurement sensing technology that seems to tackle many of the shortcomings of Coriolis flowmeters.
In terms of liquid flow measurement then, there is an obvious opening for a device that can deliver a compact, accurate and non-contact measurement, irrespective of media characteristics, flow direction and flow conditions.
Leading manufacturer of measurement and control systems for liquids and gases, Bürkert Fluid Control Systems, is using Surface Acoustic Wave (SAW) technology to develop a flow meter that is contactless with the fluid, meaning no disturbance to the flow of the fluid being measured.
Furthermore, the internal surface of the tube can be manufactured to the same surface finish as the rest of the pipeline, meaning that in terms of hygiene, cleaning and flow conditions, there is no difference to any other piece of straight pipe within the process.
The main principle for measurement is based on wave propagation forms, similar to seismic waves, which start from an initial point of excitation before spreading along the surface of a solid material.
The sensor known as FLOWave uses at least four interdigital transducers that are located on the outside of the measuring tube, allowing contactless fluid measurement. Each transducer acts both as a transmitter and as a receiver, with the signals processed by onboard electronics and software.
The analysis of all the signals and comparisons based on different criteria such as amplitude, frequency and runtimes, allows evaluation of the quality of the measurement, the existence of gas bubbles as well as identifying the liquid type. The result is a flowmeter with an accuracy of up to ±0.4% and a repeatability of ±0.2% of measured value with fluid temperatures up to 140°C.
Primarily, the fact that the internal surface of the FLOWave can be manufactured to the same specification as the rest of the production pipeline means that hygienic cleaning processes, including CIP and Steam-in-Place (SIP), can be maintained to the highest standard and at lower costs. Furthermore, there is no risk of contamination from any components being in contact with the fluid and there is no flow restriction.
In terms of installation, the process is significantly less complicated when using a FLOWave device as it can be mounted in any orientation and it requires a great deal less space than similar devices using more traditional measurement techniques. The FLOWave can also be specified with or without a display module that can be positioned to suit the final orientation in the process pipework.
Once installed, the FLOWave range offers ongoing benefits including a device status indicator that provides diagnostic status information to the operator. In addition, this technology requires considerably less energy to operate; approximately one third of that required by a standard Coriolis flowmeter, which can have a significant impact on running costs and overall total cost of ownership (TCO).
The equipment used to deliver such accurate flow readings at the top end of the market relies on software to provide the necessary algorithms and calculations to provide the final data. As such, this software is under constant review and Bürkert employs a policy of continuous improvement that also implements additional features suggested in customer feedback.
Since its launch, customers in a variety of industries have provided important information and suggestions that have led to a number of improvements. These have included the ability to detect liquid changes using a density factor, the detection of gas bubbles and solids in liquids as well as the ability to set the refresh times for the values being measured.
The principles behind this design enable the flowmeter to work with a stagnant liquid, meaning even the most reliable flow figures are available even for the smallest flow volumes. The technology also enables it to recognise quick flow changes reliably, which makes it suitable for fast filling processes.
This is just the beginning of the FLOWave story, with so many suitable applications and so many advantages, it is predicted the range will grow to provide additional solutions for a much wider audience, enabling more processes and industry sectors to benefit from SAW flow measurement technology.