Article: Grappling with the complexities of flow and level measurement
Flow and level measurement may be treated as one subject, but it comes in thousands or even millions of different implementations across the entire spectrum of industry. The process sector may constitute the lion’s share, but flow and level measurement will have a bearing on almost any business, argues David Almond, head of sales and marketing at PVL Ltd.
A mathematician, a physicist, and an engineer were all given a red rubber ball and told to find its volume. The mathematician carefully measured the diameter and evaluated a triple integral. The physicist filled a beaker with water, put the ball in the water, and measured the total displacement. The engineer looked up the model and serial numbers in his red-rubber-ball table.
Engineers often work under time pressure and have little time to formulate solutions to problems from first principles like mathematicians and physicists do, particularly if solutions already exist. With respect to flow and level measurement, engineers are spoilt for choice.
Nevertheless, the application of flow and level measurement can be riddled with complexities, like the type of liquid, whether it is slow or fast flowing, losses in the system, and so on. PVL looks for the best solutions for engineers from among a large number of suppliers. For example, how do you measure the flow of a liquid - such as seawater, brine, and solutions with high (or low) pH - so corrosive that it destroys flow switches?
The answer is to use a switch with no metal parts that contact the process fluid. PVL’s Kelco flow switches use only plastics that are inert to corrosive fluids, and so enable flow measurement with no unwanted reactions between process fluid and the switch, and no switch failures because of corrosion.
The Kelco F25 is extensively used for flow status signalling in water treatment plants, for control of effluent and fluid neutralising systems and for corrosive and saline ground water applications. The F25 also has extensive applications in safety and control signalling for chemical handling, control of flow in ultra pure water systems and irrigation control.
Flow speed is another problem; for example where there is a need to detect flow of less than 5ml per minute. The chemistry of water treatment, and of wastewater recycling, has changed in a big way during the past decade or so, and the increased dosing precision required makes intelligent dosing using flexible intelligent electronic control essential.
Much greater concentrations of dosing chemicals, which reduce chemicals cost, also make it essential that operators are able to measure and control precisely how much chemical is being dispensed, to eliminate wastage and the environmental risks of over-dosing.
The Kelco CR20 microflow switch is a compact in-line flow sensor designed to detect extremely small flows. It’s capable of monitoring flows – or the lack of them - of less than 5ml per minute. That makes the Kelco CR20 suitable for verifying the efficient function of modern micro-dosing systems. Like all other Kelco products, the CR20 microflow switch has no metal parts in contact with the process fluid, so are unaffected by aggressive or corrosive chemicals or extremes of pH. Easily able to deal with pulsed or continuous flows of up to four litres per minute, the CR20 handles pressures to 18 bars and can be fitted to pipes from 6mm to 20mm.
If the flow is almost non-existent, the FLEX-FIN flow and temperature sensor is suitable for extremely low rates of flow down to 0.001litres per minute. It has no moving parts and the medium is in contact with only one material. The FLEX-FIN is linearised and temperature compensated, and delivers very fast reaction times for a calorimetric system.
Where there is a need for super-sensitive control of back-up dosing, the Kelco MF20 micro flow switch is a super sensitive in line mechanical flow switch that can detect extremely low flows, either continuous or pulsed. Typical applications include monitoring chemical metering pumps to ensure they are delivering flow in water treatment or cooling towers or a multitude of industrial processes. There are no metal parts in contact with liquids within the switch, so the MF20 is ideal for use in aggressive media such as acids and alkalis and many chemical solutions.
So, although engineers probably make the best programmers, they want to spend their time solving engineering problems – not programming systems. As a result, they want systems with easy programming and high security. The Honsberg Omni range of transducers is easy to programme and protects against tampering.
Turning the programming ring enables engineers to set switch points, hysteresis and delay, to change units and to select an output. Removing the ring prevents anyone changing the settings. In the Omni range, there are piston-type flow meters, vortex-type flow meters, flow sensors with switching capability, a flow meter with a dynamic flap, turbine-type flow meters and gear-type flow meters. There is even a piston-type flow meter for viscous fluids.
So, next time you are faced with a metaphorical red rubber ball and a volume quandary, referring to this article might be the initial step back to first principles. Equally, it might be the useful flow and level chart you need to answer your question.
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