37
Throughout these example problems you may find that your answers vary some from those arrived at
here. This is probably due to different calculators carrying numbers to different decimal points. The
variations are usually slight and should not be a point of concern. Also, with a good calibration there
should be at least three Qa numbers in the range of 1.02 to 1.24 m3/min (36 to 44 CFM). From the
data sheet there is 4 out of 5 numbers in the range for PM10 thus a good calibration.
With the Qa determined, the corrected chart reading (IC) for this run point needs to be calculated using
the following equation:
10. IC = I[Sqrt(Ta/Pa)]
where: IC = continuous flow recorder readings corrected to current Ta and Pa
I = continuous flow recorder readings during calibration
Pa = ambient barometric pressure during calibration, mm Hg.
Ta = ambient temperature during calibration, K ( K = 273 + C)
Inserting the data from run point one on the calibration worksheet we get:
11. IC = 56 [Sqrt(294/753)]
12. IC = 56 [Sqrt(.390)]
13. IC = 56 [.6244997]
14. IC = 34.97
This procedure should be completed for all five run points. EPA guidelines state that at least three of the
five Qa flow rates during the calibration be within or nearly within the acceptable operating limits of 1.02
to 1.24 m3/min (36 to 44 CFM). If this condition is not met, the instrument should be recalibrated.
Using Qa as our x-axis, and IC as our y-axis, a slope, intercept, and correlation coefficient can be
determined using the least squares regression method.
The equations for determining the slope (m) and intercept (b) are as follows:
15. m =
 
( x)( y)
xy - n
x ; b = y - mx
x - n
2
2
 
where: n = number of observations
_ _
y = y/n; x = x/n = sum of.