Meriam Laminar Flow Elements - Manual (Page 9)

9
Determining Flow from your Laminar Flow Element
Calibration Curve/Table
The curve/table of each LFE is normalized to standard conditions listed by multiplying the calibration
data points by the ratio of:
୴୧ୱୡ୭ୱ୧୲୷ ୭୤ ୥ୟୱ ୟ୲ ୡୟ୪୧ୠ୰ୟ୲୧୭୬ ୲ୣ୫୮ୣ୰ୟ୲୳୰ୣ
୴୧ୱୡ୭ୱ୧୲୷ ୭୤ ୥ୟୱ ୟ୲ ଻଴°୊ (ୱ୲ୟ୬ୢୟ୰ୢ ୲ୣ୫୮ୣ୰ୟ୲୳୰ୣ)
Therefore, you should NOT read the flow rate directly from the curve/table unless your flow
temperature and pressure are identical to the standard conditions. The following steps must be taken to
determine flow rate at flowing conditions other than standard.
1. Measure and correct to 4ºC and if necessary, the DP across the LFE.
2. Measure and record the inlet temperature (always) and absolute line pressure (for
s tandard or mass flow rates). Convert both values to absolute units.
3. Follow the AIR FLOW or GAS OTHER THAN AIR guidelines below
Model 50MK10 All Other Models
Air Flow
Select the proper flow curve/table for the LFE being used.
Standard Volumetric Flow Rate
1) To obtain standard volumetric flow rate if inlet pressure and temperature are other than 29.92"
Hg absolute and 70ºF, respectively, find the flow rate (Q) that corresponds to the corrected DP.
Multiply Q by temperature/viscosity and pressure corrections shown on charts A-32422 and
A-31031, respectively, to bring flow to standard conditions of 29.92" Hg and 70ºF.
2) At flowing conditions of 70'F and 29.92" Hg, read curve directly in standard volumetric
flow rate.
F
lo
w
,
Q
F
lo
w
,
Q
0 1 2 3 4
Differential Pressure,
Inch of Water @ 4ºC
F
lo
w
, Q
0 1 2 3 4
Differential Pressure,
Inch of Water @ 4ºC
4 5 6 7 8