Calibration
Periodic Zero and Span Checks
4-6 Model 48i Instruction Manual Thermo Electron Corporation
5. Record the CO concentration and the instrument’s response.
Additional Concentration
Standards
Generate several additional concentrations (at least five others are suggested)
by decreasing F
CO
or increasing F
D
. Be sure the total flow exceeds the
instrument’s total flow demand. For each concentration generated, calculate
the exact CO concentration using Equation (1). Record the concentration
and the instrument’s response for each concentration.
Calibration Curve Plot the instrument’s response versus the corresponding CO concentrations.
Connect the experimental points using a straight line, preferably determined
by linear regression techniques. The calibration curve is used to reduce
subsequent ambient data.
Calibration Frequency In order to generate data of the highest confidence, it is recommended that a
multipoint calibration be performed:
• every three months
• any time any major disassembly of components is performed
• any time the zero or span checks give results outside the limits described
in the “Periodic Zero and Span Checks” that follows
Periodic Zero and
Span Checks
In order to achieve data of the highest confidence, it is suggest that periodic
zero and air span checks be performed. These checks can be performed by:
1. Periodically challenging the instrument with zero air. The output of the
zero air supply should be greater than the flow demand of the
instrument. In addition, an atmospheric dump bypass should be utilized
to ensure that the zero air gas flow is being delivered at atmospheric
pressure.
Record the Model 48i's response in percent of scale as A
O
. Compute the
zero drift from the following equation:
Where:
Z is the recorder response obtained at the last calibration for zero air,% scale.
= %Drift Zero
A
O
- Z
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