Thermo Electron 48C, Instruction Manual

Page: 108 / 204

Chapter 4 Calibration
4-6
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 Model 48C's total
flow demand. For each concentration generated, calculate the exact CO concentration
using Equation (1). Record the concentration and the Model 48C's response for each
concentration.
Calibration Curve
Plot the Model 48C'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.
Frequency of Calibration
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, or any time the zero or span checks give results outside the
limits described in “Periodic Zero and Span Checks” below.
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 Model 48C with zero air. The output of the zero air
supply should be greater than the flow demand of the Model 48C. 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 48C's response in
percent of scale as A
O
. Compute the zero drift from the following equation:
= % Drift Zero
A
O
- Z
where Z is the recorder response obtained at the last calibration for zero air, % scale.