EPA Protocol Calibration T400 Ozone Analyzer Operator’s Manual
212
ZERO CAL M RANGE = 500.0 PPB O3 =XXX.X
< TST TST > ZERO SPAN CONC EXIT
WAIT 10
MINUTES
Or until the
reading
stabilizes and
the SPAN button
is displayed
SAMPLE RANGE = 500.0 PPB O3 =XXX.X
< TST TST > CAL CALZ CALS SETUP
Record the O
3
reading as
displayed on the
instrument’s front
panel
Press
EXIT
to
Return to the
Main SAMPLE
Display
CTION:
Allow Calibration Gas diluted to
proper concentration for Midpoint N
ACTION:
Allow Calibration Gas diluted to
proper concentration for
Midpoint N+1
Plot the analyzer responses versus the corresponding calculated concentrations to obtain
the calibration relationships. Determine the straight line of best fit (y = mx + b);
determined by the method of least squares (e.g., see Appendix J of Volume I of the Q.A.
Handbook
6
).
After the best-fit line has been drawn, determine whether the analyzer response is linear.
To be considered linear, no calibration point should differ from the best-fit line by more
than 2% of full scale.
10.3.3. DYNAMIC MULTIPOINT CALIBRATION CHECK
The EPA-prescribed calibration procedure is based on photometric assays of O
3
concentrations in a dynamic flow system. It is based on the same principles that the
T400 uses to measure ozone. The theory is covered in Section 13 of this manual.
Since the acc
uracy of the calibration standards obtained by this calibration procedure
depends entirely on the accuracy of the photometer, it is very important that the
photometer is operating properly and accurately. The fact that the photometer makes a
ratio measurement (I/I
o
) rather than an absolute measurement eases this task.
The checks described in this section, if carried out carefully, will provide reasonable
confidence that a photometer which has the required inherent capability is operating
properly. Checks should be carried out frequently on a new calibrator, and a
chronological record of the results should be kept. If the record of the photometer
performance shows continued adequacy and reliability, the frequency of the checks can
be reduced with no loss of confidence in the photometer. (The record, however, may
indicate the need for continued frequent verification of the system condition.) Even
where the record shows excellent stability, the checks should still be carried out
monthly, as the possibility of malfunction is always present.
