Chapter 1 Flowmeter Description - Accusonic 8510+ series Reference Manual

C H A P T E R 1
Flowmeter Description
The Accusonic Model 8510+ Flowmeter is designed for use in pipes, channels and sewers, ranging from 8
inches to 300 feet (0.2m to 90m) in width, and of cross section which may be circular, rectangular,
trapezoidal, "horseshoe" or other defined shape.
The depth of water above the invert or bottom of the conduit may vary from zero to surcharged. The flow
may be in either direction, and generally there is no assumed relation between depth and flow. Under
certain conditions of low water level, a Manning type of relation between level and flow may exist. To
cope with all these three possible flow conditions, and the possible temporary loss of velocity
measurements, "Compound" flowmeter logic is required.
The water may range in quality from clean to raw sewage, from natural or industrial sources, having a pH
in the range 3.5 to 10, temperature between 32F and 105F (0C and 40C), and a solids loading from
near zero to 2000 parts per million. It is assumed that the conduit does not contain vapors of ketones or
esters which might eventually reduce the integrity of the plastic housing of the transducers. In addition, the
water may contain floating weed, rag, paper and plastic debris, and may deposit grease on the walls and any
devices attached to the walls, especially in the region around the dry weather flow level.
Sewers may be classified as "confined spaces" as regards access: they may also contain potentially
explosive atmospheres. If this is the case, the Hazardous Area Classification in USA and Canada, is
typically Class I, Division 1, Gas groups C & D; elsewhere it is usually classified according to IEC codes
as Zone 0 or Zone 1, Gas groups IIA & IIB.
For these applications, all transducers, cabling and other electrical equipment in the sewer and associated
with it, should be installed in accordance with the appropriate National codes.
In USA installation should follow NEC Articles 500 & 501 for Explosion proof protection, or NEC Article
504 for Intrinsically Safe protection.
Elsewhere IEC 79-14, or EN 50014 & EN 50018 should be consulted.
For those conduits which are always surcharged the flowmeter may be configured in the "Pipe" mode. In
this mode the level inputs are ignored, and in some cases the flowmeter may be supplied from the factory
without level input circuits. For the flow computation, either the "Gaussian" (Gauss-Legendre) or
"Chebyshev" (Jacobi-Gauss) multi-path integration methods can be implemented by setting the parameters
describing path lengths, angles and weighting coefficients in accordance with ASME or IEC codes.
For all other conduits the "Compound" mode should be used. The flowmeter is based on the "velocity-
area" method for flow determination, generally described in ISO 6416 1992, and more specifically in
Appendix A of this manual.
The water velocity is determined using the multi-path ultrasonic time-of-flight method. The elevation of
the water surface above the site datum is called the "Level," and the variable component of this value is
input to the flow computer in analog form from one or two sensors, (typically downlooker ultrasonic units
or pressure transmitters). A single arbitrated value for Level is obtained from the two inputs. The wetted
cross section area is computed from the Level and parameters stored in the computer defining the shape of
the conduit. The integration technique for computing the flow from the velocity data is determined
automatically from the water level and from the quality of the velocity data.
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