Page 268 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS A5E33329501
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App. A - Technical Ref.
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
2.15.1.Primary Measuring Device (PMD)
, and
2.15.4.PMD Dimensions
for list of information required.
For the ratiometric method, it is usually sufficient that the user know the flow rate (Q
cal
) which
occurs at maximum head (h
cal
).
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:
Q = KH
x
the specific formula for flow through a 45 ° V-notch weir is:
cfs = 1.03H
2.5
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
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