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Danfoss Flow Meter User Manual


Basic Elements

Just like other flowmeters, differential pressure flowmeters consist of two elements. They are:
A primary element: This element causes a change in kinetic energy which results in the differential pressure in the pipe. The unit must be suitably matched to the

Flow
  • pipe size,
  • flow conditions, and
  • the liquid’s properties

Danfoss Flow Meter User Manual Transfer Switch

Local Danfoss partner. The T7 (525-690 V) frequency converters are not certified for UL. The frequency converter complies with UL508C thermal memory retention requirements. For more information refer to the section Motor Thermal Protection in the Design Guide. Danfoss only vouches for the correctness of the English version of this declaration. In the event of the declaration being translated into any other language, the translator concerned shall be liable for the correctness of the translation. ID No: DPD01856 Revision No: A Page 1of 1 Danfoss A/S DK-6430 Nordborg Denmark CVR nr.: 20 16 57 15. The conditions require meters with a robust construction and fulfilling high demand requirements on e.g. Temperature and pressure. These meters cover sizes from DN15 up to DN100 with flow rates from 0.6 up to 60 m3/h and are available in pressure range PN16 and PN25.

Besides, the measurement accuracy of the element must be fine over a practical range.
A secondary element: The secondary element measures the differential pressure created by primary element and gives the signal or read-out which is in turn transformed to the actual flow value.

Types of Differential Pressure Flowmeters

Most widely used differential pressure flowmeters are:

  • Orifice Plates
  • Flow Nozzles
  • Venturi Tubes
  • Variable Area flowmeters, i.e. Rotameters


Accuracy & Rangeability

MeterDanfoss

Performance of a head-type flowmeter installation is a function of the

  • precision of the flow element and
  • the accuracy of the d/p cell

On average, flow element precision is expressed in percentage of actual reading terms, whereas d/p cell accuracy is stated as a percentage of calibrated span. A d/p cell typically provides accuracy of ±0.2% of the calibrated span. With no detrimental effect on accuracy, rangeability of a flowmeter can be extra enhanced by employing several d/p flowmeters in parallel runs.


Errors and Noise

In case of compressible fluids, the ratio of differential pressure divided by upstream pressure should not exceed 0.25 for reduction of error and correction of density. Metering errors caused due to wrong installation of the primary element can become considerable i.e. up to 10%. Following are the possible causes of these errors:

  • the condition of the mating pipe sections
  • insufficient straight pipe runs
  • pressure tap and lead line design errors

In turbulent flow conditions, not more than 10% of the d/p signal could possibly be noise produced by disturbances from valves and fittings. These disturbances can be both up- and downstream of the element, and by the element itself. To sort out this noise, a damping is provided in d/p cells which prove to be adequate for majority of the applications. Rigorous noise can be diminished by applying two or more pressure taps connected in parallel on both sides of the d/p cell.

Danfoss Flow Meter User Manual Download

Sources

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Danfoss Flow Meter User Manual Instructions

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