Thermo 42i, Instruction Manual

Page: 145 / 314

Calibration
Zero and Span Check
Thermo Electron Corporation Model 42
i
Low Source Instruction Manual 4-17
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
Low Source
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.