Method Of Flow Calculation - Siemens SITRANS LUT400 Operating Instructions Manual

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Method of Flow Calculation

The SITRANS LUT400 can be programmed to use either of two methods for calculating flow
from the head measurement: absolute or ratiometric. The result is the same regardless of the
method used. The main difference is the information that must be entered in order for the
device to carry out the calculation. Refer to
2. 1 5.4.PMD Dimensions
For the ratiometric method, it is usually sufficient that the user know the flow rate (Q
occurs at maximum head (h
On the other hand, absolute calculations require that the user enter information such as: the
physical dimensions of the PMD and the constant relating to units of measure for both linear
dimensions and flow rates.
Example:
the general formula for flow through a single exponent PMD is:
x
Q = KH
the specific formula for flow through a 45 ° V-notch weir is:
2.5
cfs = 1.03H
thus: Q = flow in cubic feet per second
K = constant of 1.03
H = head in feet
The absolute method is not applicable to the following:
Palmer Bowlus Flume
H-Flume
Page 268
SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS
2. 1 5. 1 .Primary Measuring Device (PMD)
for list of information required.
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A5E33329501

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