A guide to flow monitoring
14 February 2013
James Roper, Industrial brand manager at Durapipe UK, discusses the options that are available to meet a variety of different flow monitoring needs.
Many manufacturing and process applications rely on the accurate measuring and monitoring of flow rates. Choosing the most appropriate product, however, can be a difficult task. There are a wide variety of options available, making it important for specifiers and contractors to carefully consider the needs of the application – ‘over-engineered’ products will result a costly outlay for the end-user.
The performance requirements demanded of the flow monitoring equipment and the level of accuracy needed should be given careful consideration to ensure that the most appropriate product is selected for a specific application. The main considerations when choosing a flowmeter should be the measurement range, installation requirements, pipe size and material, chemicals to be monitored, type of fluid, velocity of fluid and temperature and pressure of the system.
With a view to aiding specification, the following list details the main types of flowmeters available and the applications best suited to each.
Variable area flowmeter – This is the simplest form of flowmeter and should be used when only a basic level of information is required. The flow rate is indicated by the position of the top of the float against the scale on the tube; the flow speed is displayed, but if exact levels of accuracy are required other technology may be more appropriate. To work correctly, the flow sensor must be mounted with the flow tube axis vertical and the media flowing upwards.
A variable area flowmeter is best suited to use within a system that purely needs to maintain a flow rather than measure it, such as a caustic wash which needs to be continuously circulated around a system. Other equipment can be added to this product to increase its performance, for example, an alarm can be fitted to alert operators to extreme changes in flow.
Paddle wheel flowmeter – The digital paddlewheel technology provides a greater level of accuracy and calibration so that flow can be controlled to a higher degree. The mechanical process is simple but effective and the technology guarantees good performance – the flow of the fluid moves the wheel and this speed is converted into the flow rate. Providing a highly accurate reading, the sensor can measure flow from 0.15 m/sec.
This type of flowmeter is suited to use with clean solutions and fluids. In dirty water or fluids which may contain solids, the wheel can become contaminated and will not move freely, resulting in inaccurate readings before the meter fails, leading to costly repairs a
Insertion magmeter flowmeter – The insertion magmeter is suitable for the measurement of measure flow rate in both metal and thermoplastic pipelines. This technology puts an electro-magnetic charge onto the particles in the solution which measures the speed of flow.
This sensor cannot be used with ultra-pure water as it needs the ions found in contaminated substances to carry the charge making it well suited for use with use with dirty solutions, slurries and solids. The product has no moving parts so cannot disrupt the flow, ensuring a precise reading is always generated.
Flow monitor and transmitter – In addition to the range of flowmeters available, flow monitors and transmitters are also available to convert the signal from a flowmeter into a display indication and a 4-20mA signal for long distance transmission. Simple calibration menus will allow a customised setup of all measuring parameters while a state-of-the-art electric design will ensure stable signal and long-term reliability.
Such products are suited to use in situations where remote access to flowrate readings are required; typical in larger plants that operate multiple processes and demand instant access to system performance data.
It is crucial to select the most appropriate flowmeter for an application in order to maintain an efficient, cost-effective operation. In addition to ensuring that the correct flowmeter is selected for an application, it is also important to consider the pipework system into which it is being installed, and the other equipment with which it will need to work, such as valves and batch control or chemical dosing technology. If all of these products can be specified from a single manufacturer, end-users can be confident that a fully matched system will be installed, increasing the system performance.
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