Before specifying a low flow meter, it is also advisable to find out whether the flow information will be more useful if presented in volumetric or mass units. When measuring the flow of compressible materials, volumetric flow is not very meaningful unless density – and at times, also viscosity – is steady.
When the velocity – volumetric flow – of incompressible liquids is measured, the presence of suspended bubbles will cause error, as a result, gas and air must be taken away before the fluid reaches the meter. In other velocity sensors, pipe liners can cause issues – ultrasonic – or the meter may stop execution if the Reynolds number is very low – in vortex shedding meters, RD > 20,000 is required.
Precision Versus Repeatability
If acceptable metering performance can be obtained from two different flow meter categories and one has no moving components, choose the one without moving components. Moving components of a hydrogen pressure transmitter are a potential source of issues, with multi channel data logger, not just the obvious reasons of sensitivity, lubrication, and wear to coating, but even for the reason that moving components have need of clearance spaces that, at times, introduce “slippage” into the flow being measured.
Even with the meters that are calibrated and maintained properly, this unmeasured flow is different with modifications in temperature and viscosity of fluid. Amendments in temperature even alter the internal dimensions of the meter and have need of compensation.
In addition, if one can obtain the same performance from both a point sensor and a full flow meter, it is generally advisable to make use of the flow meter. For the reason that point sensors do not look at the full flow, they ready precisely only if they are inserted to the deepness where the flow rate is the average of the speed outline across the pipe. Even if the point is carefully decided at the time of calibration, it is not likely to remain unchanged, in view of the fact that velocity profiles amend with temperature, viscosity, flow rate, and other factors.
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