Flow Control and Measurement

Electromagnetic and Coriolis meters have no obstruction and no moving parts in the stream, so grit and fibre pass through instead of wearing down a turbine or blocking an orifice plate. An electromagnetic meter needs a conductive liquid and a full pipe, which sludge lines and return flows normally give you. Most of the field experience with this sits in wastewater processing, where meters run for years between calibrations.

Volumetric meters read a different number every time pressure or temperature moves, so hydrogen is normally measured as mass. Coriolis and thermal mass meters give mass flow directly, and the small molecule size makes sealing and material choice as important as the meter itself. Hydrogen processing plants specify on mass for exactly this reason.

It has to survive caustic and hot water cycles, drain fully, and leave no crevice where product can sit, which rules out most insertion meters. Hygienic electromagnetic and Coriolis meters with 3-A or EHEDG approval are the usual answer, welded or clamped into the line. The same requirement drives equipment choice across food, beverage and pharmaceutical plants.

A differential pressure or turbine meter reads a distorted profile as a different flow rate, so the rule of thumb is ten to twenty diameters upstream and five downstream, and more after two bends out of plane. Coriolis and electromagnetic meters are far less sensitive, which is why they win where the pipework is cramped. Retrofits in power generation often come down to exactly this trade-off.

The meter tells you what is happening; the control valve, the pump drive or the controller decides what happens next, and the loop is only as good as its slowest element. A fast meter behind a sluggish valve still gives you overshoot, so the two are specified together. Batching and dosing lines in chemical plants show how tight that pairing has to be.

That depends on the service and on what a wrong reading costs, not on a fixed rule. A Coriolis or electromagnetic meter in clean service can hold its calibration for years and is often only verified in place; a turbine or differential pressure meter in dirty or abrasive service drifts and deserves a yearly check. Custody transfer follows its own legal intervals. Built-in verification catches most faults in between.

Yes. Clamp-on ultrasonic meters sit on the outside of the pipe and measure through the wall, which makes them the standard choice for temporary surveys, for lines that cannot be shut down, and for checking an existing meter. Accuracy is lower than a wetted meter, typically 1 to 3 %, and it depends on knowing the wall thickness, the liner and the pipe material. For permanent custody-grade measurement a wetted meter still wins.

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