Teledyne Deltaflow DF180, Operation And Maintenance Manual, Page: 30 / 42

January, 2018
Page 30
5.2 Interference Check
An interference check attempts to determine if the data collected is inaccurate due to probe or sample
line cloggage. An interference check consists of taking an average DP sample over a length of time
defined by the user, performing a blowback, then taking another average DP sample. The pre and post
blowback samples should agree to some extent depending on how steady the process is. The extent at
which they should agree will take some time to determine through trial and error. A good starting point
is to conduct three consecutive interference checks with a new probe that is known to be free of
cloggage. Determine the average result of these three checks, and multiply it by 1.25. Enter the result
into the
Daily Interference Check Tolerance field in the Configuration: Calibrations: Evaluations screen.
See section 4.3.4.2.
5.3 Creating a Correction Curve
The DeltaFlow can be programmed with a correction curve to achieve better accuracy based on a
reference measurement. This is sometimes necessary because the Deltaflow takes only a point
measurement. A reference method like EPA Method 2 takes an average of many sample points to get a
more accurate measurement of the overall average velocity in the stack. Creating a correction curve is
done using the following procedure.
First Deltaflow Raw Velocity data is collected along with a reference method velocity measurement,
such as EPA Method 2. It is important to synchronize the Deltaflow and the reference measurements to
ensure an accurate correction curve is produced. This can be done by synchronizing the time keeping
device used to track the reference measurement start and stop times with the clock of the data
acquisition system logging the Deltaflow data. Typically a reference method measurement takes about
10 to 15 minutes to get all the point samples recorded, after which the test personnel will average the
points to come up with a single velocity measurement for the 10 to 15 minute period. The DeltaFlow
data collected for this period should also be collect and averaged into a single value. If possible parallel
Deltaflow and reference measurements should be taken at multiple loads.
Once the data is collected, plot the reference method data (y-axis) verse the Deltaflow Raw Velocity
data (x-axis) as shown in figure 5-1.