Thermo Scientific HB-S200, User Manual

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Sarasota 200 Ultrasonic Multipath
Flowmeter
Section 1 INTRODUCTION Page 1-7 Thermo Fisher Scientific
INTRODUCTION
1.2.9 Performance estimates
ISO 6416 describes how to estimate the uncertainty of measurement in any particular
installation. Please consult Thermo Fisher Scientific for advice on this.
1.3 Implementation of the principles of operation in the Sarasota 200
The principles described in Section 1.2 are used by the Sarasota 200 subject to certain rules
as listed below. See also Appendix 1: GAFA Screens that describe in detail how the
flowmeter is programmed via a PC.
Flow
•
There is a choice of mean or mid section method of flow calculation.
•
The channel cross section shape is entered as a height/width table independent from the
path lengths and angles. (For rectangular or trapezoidal channels it is only necessary to
enter 2 points to define the channel.) The separate table allows the path velocities to be
applied to more accurate slice areas since the defined shape is used rather than a fixed
width for each slice as specified in the Standard.
•
Where no path velocity is available, for example at low water height, flow may be inferred
from water level. This is done via a flow estimation table, which may be derived
empirically or by calculation.
Velocity
•
The upstream velocity transducers are connected as shown in section 2.
•
Path numbering is from the bottom.
•
Paths are automatically brought into operation according to the water level and the
programmed minimum water cover.
•
Paths entered as being at the same height are taken as crossed, otherwise they are
separate.
•
Separate paths may be “normal” with transducers on each side or “reflected” with
transducers on one side only. The latter method saves cable but is not recommended
because of the increased path lengths and sensitivity to alignment.
•
The velocities calculated by a pair of paths comprising a crossed path are averaged and
the average velocity used for the slice. The velocity calculated by a separate path is used
alone for the slice.
•
When a velocity path fails, the slice boundaries automatically adjust to use only the
working paths.
•
A failed path will show on the status indicated. The path status is a percentage of the
“instantaneous” transducer firings which result in successful reception. If this figure drops
below 12% the path is considered to have failed during the corresponding instantaneous
cycle time and is discarded for that cycle. This could be the result of a fault, misalignment
or obstruction.
•
Only valid velocity paths which are in the water and covered by sufficient water to be
operating are used for the status indication.
•
Each path may have a multiplying factor (“X Factor”) assigned to it. This will normally be 1
but may be different in exceptional circumstances for calibration purposes. An example of
when this might be is when the transducers are not exactly at the channel edges.
•
Transducers in each velocity path may be set to operate simultaneously (the norm) or
sequentially. Simultaneous operation allows more measurements in a given time but
there is a small possibility of confusing a signal reflected back to the firing transducer with
one received from the opposite transducer.