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Calibration
Equipment Required
Equipment Required
Calibration Standard
(Span Gas)
CO Free Dilution Air
(Required for multi-
point calibration only)
4-2
Model 48i Trace Level-Enhanced Instruction Manual
concentration and the instrument's analog signal can then be generated and
used to interpret data taken during normal operation.
Although the Model 48i Trace Level-Enhanced will provide high quality
data without using an external multi-point calibration, it is a regulatory
requirement in many cases. In addition, the external calibration does
provide an opportunity to verify the analyzer's accuracy over the entire
measurement range. Moreover, if an instrument were to display a non-
linearity in response, the external calibration could be used to correct for
that error. Some further discussion of multi-point calibration is included in
the following procedures. However, the operator should consult the Quality
Assurance Handbook for Air Pollution Measurement Systems
earlier for a more detailed explanation of the procedure.
The following sections discuss the required apparatus and procedure for
calibrating the instrument.
The following equipment is required to calibrate the instrument:
A cylinder of CO in air containing an appropriate concentration of CO
suitable for the selected operating range of the analyzer under calibration is
necessary. For most applications, the span concentration should be about
80% of the full-scale range that will be used during normal operation. For
example, if the instrument will be operated with the analog output set on a
full-scale range of zero to 50 ppm, the span gas concentration should be
about 40 ppm. Selection of the analog output's full-scale range will depend
on the application, and in some cases the choice may be subject to
regulatory considerations.
For legal reasons, the assay of the span cylinder must be traceable either to a
National Institute of Standards and Technology (NIST) CO in Air
Standard Reference Material (SRM), or a NIST/EPA approved gas
manufacturer's Certified Reference Material (CRM).
A recommended protocol for certifying CO gas cylinders against an SRM
or CRM is given in the Quality Assurance Handbook
should be recertified on a regular basis determined by the local quality
control program.
Because the enhanced trace level instrument is equipped with an internal
CO scrubber, a separate source of zero air is not required for routine single
point calibration. However, a high quality CO-free air source may be
needed to supply dilution air that can be used to generate span gas from a
higher concentration cylinder, or to generate test gases containing varying
concentrations of CO.
1
referenced
1
. The CO gas cylinder
Thermo Fisher Scientific
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