Orifice Plate Flow Meters - Measurable Range
Orifice Plate Flow Meters - Measurable Range
(OP)
All,
I have an orifice plate flow meter installed to track N2 usage throughout my plant. The issue is that the meter (the transmitter) goes full scale when a downstream solenoid gets stuck open. Obviously I need to rescale the transmitter.
My question is, how do I know what the true measurable range is for my orifice plate; over what range are the orifice plate calculations valid? Theoretically, zero pressure loss = zero flow, and 100% pressure loss = infinite flow. Clearly, that isn't actually the case. Based on pipe size and orifice size, how do I know what the "range" of the actual orifice plate is?
-SK
I have an orifice plate flow meter installed to track N2 usage throughout my plant. The issue is that the meter (the transmitter) goes full scale when a downstream solenoid gets stuck open. Obviously I need to rescale the transmitter.
My question is, how do I know what the true measurable range is for my orifice plate; over what range are the orifice plate calculations valid? Theoretically, zero pressure loss = zero flow, and 100% pressure loss = infinite flow. Clearly, that isn't actually the case. Based on pipe size and orifice size, how do I know what the "range" of the actual orifice plate is?
-SK





RE: Orifice Plate Flow Meters - Measurable Range
as reported here,
http://en.wikipedia.org/wiki/Turndown_ratio
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Orifice Plate Flow Meters - Measurable Range
Thanks, exactly what I wanted to know.
-SK
RE: Orifice Plate Flow Meters - Measurable Range
The range is associated with the bore of the plate, the pipe inside diamter and the transmitter range. Without changing the plate, the maximum flow rate is normally extended by extending the differential pressure at 100% flow. You need orifice sizing software to calculate the bore. However, if the bore is set associated with a given differential pressure an maximum flow range, you can use a square root relationship to determine the maximum range obtained by increasing the pressure differential.
Volumetric Flow (Q = A • v)
Square root relationship between the output and flow rate for head type Flowmeter
10 % dp output= 31.6 % flow rate
25 % dp output= 50 % flow rate
50 % dp output= 70.7 % flow rate
100 % dp output= 100 % flow rate
ΔP = constant x ρ x Q2
Fluid density affects the measurement. Not needed to recalibrate if the density used did not change.
Pressure drop is proportional to the square of the flow rate.
Double the flow... quadruple (four times) the differential
Q = constant • (ΔP/ρ)½
Flow rate is proportional to the square root of the differential pressure
...
RE: Orifice Plate Flow Meters - Measurable Range
At 100% of "maximum pressure drop" the flow rate will be what is called "meter maximum".
The "maximum pressure drop" is your dP cell range (often 100 inH2O). So, by using the orifice equations you can calculate the "meter max" flow based on a dP=100 inH2O and the orifice size.
If you cannot find the equations, let us know.
RE: Orifice Plate Flow Meters - Measurable Range
My transmitter is scalable from 150"H2O-1000"H20 or so. What I was getting at with my orignial question is that that at some point the sqrt method for calculating flow falls apart (ceases to correlate accurately). So, I can easily go rescale my transmitter and control software to read within range, but I want to make sure that the reading is accurate for the given orifice, or if I need to install a new plate.
RE: Orifice Plate Flow Meters - Measurable Range
RE: Orifice Plate Flow Meters - Measurable Range
RE: Orifice Plate Flow Meters - Measurable Range
If you use a single 0 to 1000 transmitter, at 15% flow (6 to 1), your DP is 28 inches +/1 1.5 inches, so your measurement is +/-2.5% or so.
Remember, your transmitter is +/-.15% of span!
RE: Orifice Plate Flow Meters - Measurable Range
rangeability is or can be more than just the square root transformation esp when you go to high ranges
RE: Orifice Plate Flow Meters - Measurable Range