Calibration
Zero and Span Check
Thermo Fisher Scientific
Model 42
i
Trace Level Instruction Manual
4-21
You should have a quality control plan where the frequency and the
number of points required for calibration can be modified on the basis of
calibration and zero and span check data collected over a period of time.
Note however, that the EPA requires a minimum of one multipoint
calibration per calendar quarter. Such a quality control program is essential
to ascertain the accuracy and reliability of the air quality data collected and
to alert the user if the accuracy or reliability of the data should become
unacceptable. A compilation of this kind might include items such as dates
of calibration, atmospheric conditions, calibration factors, and other
pertinent data.
Use the following procedure to perform a zero and span check.
1.
Connect the zero gas to the SAMPLE bulkhead in a standard
instrument or to the ZERO bulkhead in a Model 42
i
Trace Level
equipped with the zero/span and sample solenoid valve option.
2.
Allow the instrument to sample zero gas until a stable reading is
obtained on the NO, NO
2
, and NO
x
channels then record the zero
readings. Unless the zero has changed by more than ±0.010 ppm, it is
recommended that the zero not be adjusted. If an adjustment larger
than this is indicated due to a change in zero reading, a new multipoint
calibration curve should be generated.
3.
Attach a supply of known concentration of NO and NO
2
(usually
generated via an NIST traceable NO working standard and a GPT
system) to the SAMPLE bulkhead (or SPAN bulkhead for instruments
equipped with the zero/span and sample solenoid valve option) on the
rear panel.
4.
Allow the instrument to sample the calibration gas until a stable
reading is obtained on the NO, NO
2
, and NO
x
channels. If the
calibration has changed by more than ±10%, a new multipoint
calibration curve should be generated.
5.
When the calibration check has been completed, record the NO, NO
2
,
and NO
x
values.
6.
Reconnect the analyzer sample line to the SAMPLE bulkhead.
