Download Flow Meter Calibration - Wright State University

Wright State University
Department of Mechanical and Materials Engineering
ME 495: THERMAL-FLUID SCIENCES LABORATORY
Flow Meter Calibration
Objective:
Learn how to calibrate an electronic flow meter using a data acquisition system and
Labview software.
References:
The manuals for the flow meter and signal conditioner are given below:
FTB-9506 Turbine Flow Meter: http://www.omega.com/manuals/manualpdf/M2728.pdf
or http://www.cs.wright.edu/people/faculty/sthomas/m2728.pdf
FLSC-61 Signal Conditioner: http://www.omega.com/manuals/manualpdf/M2729.pdf
or http://www.cs.wright.edu/people/faculty/sthomas/m2729.pdf
Labview programs for flowmeter calibration:
http://www.cs.wright.edu/people/faculty/sthomas/monitorvoltage.vi
or:
http://www.cs.wright.edu/people/faculty/sthomas/reader02.vi
Method:
1. Calibrate an electronic flow meter using a stop watch, lab scale and beaker.
Analog DC signals from the signal conditioner are to be collected using a data
acquisition system using a Labview virtual instrument. This flow meter will be
used later in the class during an experiment.
Data to be Collected:
1. The average voltage from the signal conditioner over at least 1 minute at each
setting.
2. The time it took to fill the beaker.
3. The mass of the water collected.
Report:
1. Title page
2. A list of the equipment used in the calibration.
3. A detailed description of the procedure. You should be able to hand this to a
technician and they should be able to complete the calibration using only your
description.
4. A copy of the table at the end of this document showing the hand-written raw data
collected for the flow meter.
5. A plot of the mass flow rate (gram/sec) versus the voltage reading (volts) (x-axis
= voltage, y-axis = mass flow rate) for the flow meter. Use a regression analysis
to fit a straight line to the data. Show the equation of the straight line and the R2
term on the plot. The equation must have at least five significant digits for each
coefficient.
6. A plot of the uncertainty of the mass flow rate versus mass flow rate for the flow
meter (x-axis = mass flow rate, y-axis = uncertainty of the mass flow rate).
7. Sample hand calculations showing the uncertainty analysis.
8. A discussion of the results:
 How does a turbine flow meter work? Provide a reference for your discussion.
 How repeatable was the experimental data? Discuss the variability of the mass
flow rate over the tested range.
 What is the mass flow rate and uncertainty when the voltmeter reads 3.23 V
with a standard deviation of 0.15 V over 700 data points with a confidence
level of 95%? Show all calculations.
Discussion
Electronic flow meters are used in many applications where the flow rate within a pipe
must be continuously monitored and the data stored using a data acquisition system.
Attention must be paid to the behavior of the flow meter in order to not make mistakes in
interpreting the data. All flow meters have a stated range of operation. For turbine flow
meters, the DC voltage signal from the signal conditioner is proportional to the flow rate
only in the linear range of the device. If the flow rate approaches the lower flow rate
limit, the propeller in the turbine flow meter can stop intermittently, as shown below.
This will cause the average voltage to be an unreliable measure of the flow rate. A valid
voltage signal is shown in the figure below.
If the y-axis minimum is changed to the automatic setting in Excel, the data looks very
erratic:
The plot above shows that the data is scattered, but it does not have any obvious outliers.
Data sets should always be checked for outliers, which should be removed from the data.
Also, the data in the above plot does not follow a specific trend, either increasing or
decreasing, so the flow rate for this case was quite steady.
The calibration equation for the flow meter is found by plotting the mass flow rate
readings versus the corresponding mean voltage readings, as shown below. As can be
seen, the flow rate is quite linear (although not exactly) with respect to the voltage
reading.
The calibration uncertainty for the flow meter is equal to the uncertainty in each
measurement plus the difference between the actual data point and the prediction by the
calibration curve. The uncertainty in each measurement can be found using the root-sumsquare method:
 m
  m

m  
 m   
 t 
 m
  t

2
2
where the mass flow rate is given by
m 
m
t
The uncertainty of the mass measurement can be estimated to be the resolution of the lab
scale, which is the smallest quantity that is readable on the digital readout. The
uncertainty of the time measurement is related to the speed at which a person can
start/stop the watch.
Once the flow meter is calibrated, it is ready for use. The uncertainty of any mass flow
rate measurement can be estimated to be the sum of the calibration uncertainty discussed
above and the confidence interval of the voltage data collected. To be conservative, the
maximum uncertainty shown in the plot in #6 above would be appropriate.
The effect of the scatter in the voltage data collected during use of the flow meter can be
related to the uncertainty of the mass flow rate as follows. For a given mean voltage
reading, the confidence interval in the voltage data is calculated by knowing the standard
deviation, the number of data points and the confidence level. The confidence interval is
then added and subtracted to the mean of the voltage reading. This provides an upper and
lower limit on the voltage. These values can then be substituted into the linear equation
for the mass flow rate. This will provide an upper and lower limit on the mass flow rate.
The uncertainty of the mass flow rate is half of this range, which is due to the scatter in
the voltage data. This uncertainty would then be added to the calibration uncertainty to
determine the total uncertainty of the mass flow rate reading.
FTB-9506 Turbine Flow Meter with the FLSC-61 Signal Conditioner
Trial
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Mean
Voltage
Time to Fill
Beaker (s)
Mass of
Water
(g)
Mass Flow
Rate (g/s)