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The DIVA flowmeter operates
on the well established spring loaded variable area (SLVA)
principle, where the area of an annular orifice is
continuously varied by a precision shaped moving cone. This
cone is free to move axially against the resistance of a
spring.
However, unlike other SLVA
flowmeters, the DIVA does not rely on the measurement of
differential pressure drop across the flowmeter to calculate
flow, measuring instead the force caused by the deflection
of the cone via a series of extremely high quality strain
gauges. The higher the flow of steam the greater the force.
This strain is then converted into density compensated mass
flowrate and is transmitted via a single loop powered 4 -20
mA and pulsed output. This removes the need for expensive
differential pressure transmitters, reducing installation
costs and potential problems.
The DIVA has an internal
temperature sensor, which provides full density compensation
for saturated steam applications.
The DIVA steam flowmeter has a system uncertainty in
accordance with EN ISO/IEC 17025, of:
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± 2% of actual flow to a
confidence of 95% (2 standard deviations) over a range
of 10% to 100% of maximum rated flow.
-
± 0.2% FSD to a
confidence of 95% (2 standard deviations) from 2% to 10%
of the maximum rated flow.
As the DIVA is a
self-contained unit the uncertainty quoted is for the
complete system. Many flowmeters claim a pipeline unit
uncertainty but, for the whole system, the individual
uncertainty values of any associated equipment, such as DP
cells, need to be taken into account.
The turndown of a flowmeter
is the ratio of the maximum to minimum flowrate over which
it will meet its specified performance, or its operational
range. The DIVA flowmeter has a high turndown ratio of up to
50:1, giving an operational range of up to 98% of its
maximum flow. |
